PTC Therapeutics (PTCT) 10-K 29 Feb 16 2015 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2015	Feb. 24, 2016	Jun. 30, 2015
Document and Entity Information
Entity Registrant Name	PTC THERAPEUTICS, INC.
Entity Central Index Key	1,070,081
Document Type	10-K
Document Period End Date	Dec. 31, 2015
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Public Float			$ 1,351,807,253
Entity Common Stock, Shares Outstanding		34,272,019
Document Fiscal Year Focus	2,015
Document Fiscal Period Focus	FY

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Current assets:
Cash and cash equivalents	$ 58,022	$ 49,748
Marketable securities	280,903	265,493
Prepaid expenses and other current assets	5,930	3,885
Trade receivables, net	11,094	4,445
Total current assets	355,949	323,571
Fixed assets, net	8,974	9,159
Deposits and other assets	3,118	489
Total assets	368,041	333,219
Current liabilities:
Accounts payable and accrued expenses	45,247	29,121
Deferred revenue	139	3,354
Total current liabilities	45,386	32,475
Long-term debt	94,608
Other long-term liabilities	2,046	2,277
Total liabilities	142,040	34,752
Stockholders' equity:
Common stock, $0.001 par value. Authorized 125,000,000 shares; issued and outstanding 33,916,559 shares at December 31, 2015. Authorized 125,000,000 shares; issued and outstanding 32,898,392 shares at December 31, 2014	34	33
Additional paid-in capital	820,165	721,722
Accumulated other comprehensive loss	(1,200)	(737)
Accumulated deficit	(592,998)	(422,551)
Total stockholders' equity	226,001	298,467
Total liabilities and stockholders' equity	$ 368,041	$ 333,219

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2015	Dec. 31, 2014
Consolidated Balance Sheets
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, authorized shares	125,000,000	125,000,000
Common stock, issued shares	33,916,559	32,898,392
Common stock, outstanding shares	33,916,559	32,898,392

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Revenues:
Net product revenue	$ 33,696	$ 717
Collaboration and grant revenue	3,070	24,528	$ 34,696
Total revenues	36,766	25,245	34,696
Operating expenses:
Research and development	121,816	79,838	54,875
Selling, general and administrative	82,080	44,820	25,219
Total operating expenses	203,896	124,658	80,094
Loss from operations	(167,130)	(99,413)	(45,398)
Interest (expense) income, net	(2,367)	1,180	(6,084)
Loss on extinguishment of debt			(130)
Other (expense) income, net	(465)	(213)	38
Loss from operations before tax (expense) benefit	(169,962)	(98,446)	(51,574)
Income tax (expense) benefit	(485)	4,693
Net loss	(170,447)	(93,753)	(51,574)
Deemed dividend			(18,249)
Gain on exchange of convertible preferred stock in connection with recapitalization			3,391
Net loss attributable to common stockholders	$ (170,447)	$ (93,753)	$ (66,432)
Weighted-average shares outstanding:
Basic and diluted (in shares)	33,626,248	31,565,310	12,829,411
Net loss per share-basic and diluted (in dollars per share)
Net loss per share-basic and diluted (in dollars per share)	$ (5.07)	$ (2.97)	$ (5.18)

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Consolidated Statements of Comprehensive Loss
Net loss	$ (170,447)	$ (93,753)	$ (51,574)
Other comprehensive loss:
Unrealized (loss)/gain on marketable securities	(202)	(457)	70
Foreign currency translation loss	(261)	(350)
Comprehensive loss	$ (170,910)	$ (94,560)	$ (51,504)

Consolidated Statements of Conv

Consolidated Statements of Convertible Preferred Stock and Changes in Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Series One-Three convertible preferred stock	Series Four convertible preferred stock	Series Five convertible preferred stock	Common stock	Additional paid-in capital	Accumulated other comprehensive income (loss)	Accumulated deficit	Total
Balance, beginning of period at Dec. 31, 2012	$ 80,824
Balance, beginning of period (in shares) at Dec. 31, 2012	15,038,259
Increase (decrease) in temporary equity
Issuance and exchange of series of convertible preferred stock for series of convertible preferred stock	$ (80,824)	$ 60,785	$ 101,682
Issuance and exchange of series of convertible preferred stock for series of convertible preferred stock (in shares)	(15,038,259)	5,374,954	8,796,002
Conversion of series of convertible preferred stock to common stock		$ (60,785)	$ (101,682)
Conversion of series of convertible preferred stock to common stock (in shares)		(5,374,954)	(8,796,002)
Balance at Dec. 31, 2012					$ 177,584		$ (277,224)	$ (99,640)
Balance (in shares) at Dec. 31, 2012				545,345
Increase (Decrease) in Stockholders' Equity
Reverse stock split				(540,819)
Issuance and exchange of series of convertible preferred stock for series of convertible preferred stock					(14,858)			(14,858)
Issuance of common stock from IPO and exercise of over allotment exercise, net of offering costs				$ 10	131,640			131,650
Issuance of common stock from IPO and exercise of over allotment exercise, net of offering costs (in shares)				9,627,800
Conversion of series of convertible preferred stock to common stock				$ 14	162,453			162,467
Conversion of series of convertible preferred stock to common stock (in shares)				14,170,956
Share-based compensation expense					8,427			8,427
Net loss							(51,574)	(51,574)
Comprehensive income (loss)						$ 70		70
Balance at Dec. 31, 2013				$ 24	465,246	70	(328,798)	136,542
Balance (in shares) at Dec. 31, 2013				23,803,282
Increase (Decrease) in Stockholders' Equity
Issuance of common stock from public offerings and exercise of over allotment exercise, net of offering costs				$ 9	235,971			235,980
Issuance of common stock from public offerings and exercise of over allotment exercise, net of offering costs (in shares)				8,613,265
Exercise of stock options					1,195			1,195
Exercise of stock options (in shares)				108,645
Restricted stock vesting (in shares)				373,200
Share-based compensation expense					19,310			19,310
Net loss							(93,753)	(93,753)
Comprehensive income (loss)						(807)		(807)
Balance at Dec. 31, 2014				$ 33	721,722	(737)	(422,551)	298,467
Balance (in shares) at Dec. 31, 2014				32,898,392
Increase (Decrease) in Stockholders' Equity
Equity component of the convertible notes issuance, net					57,538			57,538
Debt Issuance Cost					(1,784)			(1,784)
Exercise of stock options				$ 1	8,710			8,711
Exercise of stock options (in shares)				656,248
Restricted stock vesting (in shares)				361,919
Share-based compensation expense					33,979			33,979
Net loss							(170,447)	(170,447)
Comprehensive income (loss)						(463)		(463)
Balance at Dec. 31, 2015				$ 34	$ 820,165	$ (1,200)	$ (592,998)	$ 226,001
Balance (in shares) at Dec. 31, 2015				33,916,559

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Cash flows from operating activities
Net loss	$ (170,447)	$ (93,753)	$ (51,574)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	2,876	2,235	2,396
Change in valuation of warrant liability	(140)	130	(38)
Amortization of premiums on investments	2,480	1,607
Amortization of debt issuance costs	107
Share-based compensation expense	33,979	19,310	8,427
Non-cash interest expense	2,146		6,049
Loss on extinguishment of debt			130
Disposal of asset	(37)
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(2,107)	(2,286)	(760)
Trade receivables, net	(6,907)	(3,487)	56
Deposits and other assets	131	(340)	48
Accounts payable and accrued expenses	16,981	16,914	5,183
Other long-term liabilities	(92)	(80)	(285)
Deferred revenue	(3,307)	2,476	(16,554)
Net cash used in operating activities	(124,337)	(57,274)	(46,922)
Cash flows from investing activities
Purchases of fixed assets	(2,720)	(4,664)	(846)
Purchases of marketable securities	(223,762)	(247,804)	(156,045)
Sale & redemptions of marketable securities	205,671	107,300	29,062
Net cash used in investing activities	(20,811)	(145,168)	(127,829)
Cash flows from financing activities
Payments on long-term debt		(49)	(4,996)
Net proceeds from sale of Series Four preferred stock			60,785
Proceeds from exercise of options	8,711	1,196
Net proceeds from public offerings		235,979	131,650
Debt issuance costs related to convertible notes	(4,650)
Proceeds from issuance of convertible notes	150,000
Net cash provided by financing activities	154,061	237,126	187,439
Effect of exchange rate changes on cash	(639)	(350)
Net increase in cash and cash equivalents	8,274	34,334	12,688
Cash and cash equivalents, beginning of period	49,748	15,414	2,726
Cash and cash equivalents, end of period	58,022	49,748	15,414
Supplemental disclosure of cash information
Cash paid for interest		1	367
Cash paid for income taxes	111		2
Supplemental disclosures of non-cash information related to investing and financing activities
Change in unrealized (loss) gain on marketable securities	$ (202)	$ (457)	70
Change in carry value of preferred securities resulting from recapitalization			$ 3,391

The Company

The Company	12 Months Ended
	Dec. 31, 2015
The Company
The Company	1. The Company PTC Therapeutics, Inc. (the Company or PTC) was incorporated as a Delaware corporation on March 31, 1998. PTC is a global biopharmaceutical company focused on the discovery, development and commercialization of orally administered, small molecule therapeutics targeting an area of RNA biology referred to as post-transcriptional control. The letters "PTC" in the corporate name are an acronym for post-transcriptional control processes, which are the regulatory events that occur in cells during and after a messenger RNA is copied from DNA through the transcription process. The Company has discovered all of its compounds currently under development using its proprietary technologies. The Company plans to continue to develop these compounds both on its own and through selective collaboration arrangements with leading pharmaceutical and biotechnology companies. The Company believes that systematically targeting post-transcriptional control processes represents an unexploited approach to drug discovery and development. The Company's internally discovered pipeline addresses multiple therapeutic areas, including rare disorders and oncology. On the evening of February 22, 2016, the Company received a Refuse to File letter from the United States Food and Drug Administration, or FDA, regarding its New Drug Application, or NDA, for its lead product, Translarna™ (ataluren), for the treatment of nonsense mutation Duchenne muscular dystrophy, or nmDMD. The FDA stated in the Refuse to File letter that the NDA was not sufficiently complete to permit a substantive review. Specifically, the Company was notified in the letter that, in the view of the FDA, both the Phase 2b and Phase 3 ACT DMD trials were negative and do not provide substantial evidence of effectiveness. Additionally, the FDA stated that the Company had proposed a post-hoc adjustment of ACT DMD that eliminates data from a majority of enrolled patients. In addition, the FDA noted that the NDA does not contain adequate information regarding the abuse potential of Translarna. While other comments and requests are noted in the letter, as items to be addressed if the NDA is resubmitted the FDA specified that they were not related to its refusal to file the NDA. Translarna received marketing authorization from the European Commission, or EC, in August 2014 for the treatment of nmDMD in ambulatory patients age 5 years and over in the 31 member states of the European Economic Area, or EEA. nmDMD is a rare, life threatening disorder. The marketing authorization was primarily based upon the safety and efficacy results of our 48-week, 174-patient Phase 2b double-blind, placebo controlled clinical trial evaluating the long-term safety and efficacy of Translarna in patients with nmDMD completed in 2009, or the Phase 2b trial. The Company's authorization in the EEA is subject to annual review and renewal by the EC following reassessment by the European Medicines Agency, or EMA, of the risk benefit balance of the authorization, which we refer to as the annual EMA reassessment. This marketing authorization was further conditioned on the Company's ability to complete its global, confirmatory Phase 3 clinical trial in nmDMD, which the Company refers to as ACT DMD, and submit the final report, including additional efficacy and safety data from the trial. The Company submitted this final report to the EMA in January 2016 and requested that the condition to our marketing authorization be removed. The Company expects that the EMA's Committee for Medicinal Products for Human Use, or CHMP, will issue a recommendation regarding this request in mid-2016. In June 2014, the Company initiated a reimbursed expanded access program, or EAP program, for Translarna for nmDMD patients in selected territories in the EEA and recorded its first sales of Translarna in the third quarter of 2014 pursuant to the EAP program. In December 2014, the Company recorded its first commercial sales in Germany. As of December 31, 2015, Translarna was available in 17 countries on a commercial basis or pursuant to the EAP program. The Company expects to expand its launch activities across the EEA pursuant to the marketing authorization granted by the EMA throughout 2016 and future years, subject to continued renewal of its marketing authorization following annual EMA reassessments and successful completion of pricing and reimbursement negotiations. Concurrently, the Company plans to continue to pursue EAP programs in select countries where those mechanisms exist, both within the EEA and in other countries. In October 2015, the Company announced results from ACT DMD, including that the trial did not meet the primary efficacy endpoint of change from baseline at week 48 in distance walked in the 6-minute walk test, or 6MWT, which the Company also refers to as six-minute walk distance, or 6MWD, in the overall intent-to-treat, or ITT, study population, as it showed a 15 meter benefit (p=0.213) in favor of Translarna compared to placebo, which was not statistically significant. Analyses of data from pre-specified subgroups, including patients with baseline 6MWD of 300 - 400 meters, was also conducted. A pre-specified meta-analysis was also performed of combined data from the ACT DMD and ambulatory decline phase patients from the Company's randomized, double-blind, placebo controlled, Phase 2b clinical trial evaluating the long-term safety and efficacy of Translarna in patients with nmDMD, or the Phase 2b trial. During 2015, the Company's revenues have been and are expected to be primarily generated from sales of Translarna in counties in the EEA where pricing and reimbursement approval is obtained at acceptable levels and in other territories where the Company is permitted to distribute Translarna under reimbursed early access programs, or EAPs. The Company is subject to a number of risks similar to those of other early stage companies, including dependence on key individuals, the difficulties inherent in the development of commercially usable products, the potential need to obtain additional capital necessary to fund the development of its products, and competition from other companies. As of December 31, 2015, the Company had an accumulated deficit of approximately $593.0 million. The Company has financed its operations to date primarily through the private offering in August 2015 of 3.00% convertible senior notes due 2022 (see Note 6), public offerings of common stock in February 2014 and October 2014, its initial public offering of common stock in June 2013, private placements of its convertible preferred stock, collaborations, bank debt, convertible debt financings, grant funding and clinical trial support from governmental and philanthropic organizations and patient advocacy groups in the disease area addressed by the Company's product candidates.

Summary of significant accounti

Summary of significant accounting policies	12 Months Ended
	Dec. 31, 2015
Summary of significant accounting policies
Summary of significant accounting policies	2. Summary of significant accounting policies Basis of presentation The accompanying consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (GAAP) and include all adjustments necessary for the fair presentation of the Company's financial position for the periods presented. Use of estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. Significant estimates in these consolidated financial statements have been made in connection with the calculation of net product sales, certain accruals related to the Company's research and development expenses, stock-based compensation, initial valuation procedures for the issuance of convertible notes and the provision for or benefit from income taxes. Actual results could differ from those estimates. Changes in estimates are reflected in reported results in the period in which they become known. Consolidation The consolidated financial statements include the accounts of PTC Therapeutics, Inc. and our wholly owned subsidiaries. All inter-company accounts, transactions, and profits have been eliminated in consolidation. Segment and geographic information Operating segments are defined as components of an enterprise about which separate discrete information is available for evaluation by the chief operating decision maker, or decision making group, in deciding how to allocate resources and in assessing performance. The Company views its operations and manages its business in one operating and reporting segment. Cash equivalents The Company considers all highly liquid investments with a maturity of 90 days or less at the time of purchase to be cash equivalents. Cash equivalents are carried at cost which approximates fair value due to their short-term nature. Marketable securities The Company considers securities with original maturities of greater than 90 days to be available for sale securities. Securities under this classification are recorded at fair value and unrealized gains and losses within accumulated other comprehensive income. The estimated fair value of the available for sale securities is determined based on quoted market prices or rates for similar instruments. In addition, the cost of debt securities in this category is adjusted for amortization of premium and accretion of discount to maturity. The Company evaluates securities with unrealized losses to determine whether such losses, if any, are other than temporary. Fixed assets Fixed assets are stated at cost. Depreciation is computed starting when the asset is placed into service on a straight-line basis over the estimated useful life of the related asset as follows: Leasehold improvements Lesser of useful life or lease term Computer equipment and software 3 years Furniture, fixtures, and lab equipment 3 to 7 years Concentration of credit risk The Company's financial instruments that are exposed to credit risks consist primarily of cash and cash equivalents, available-for-sale marketable securities and accounts receivable. The Company maintains its cash and cash equivalents in bank accounts, which, at times, exceed federally insured limits. The Company has not experienced any credit losses in these accounts and does not believe it is exposed to any significant credit risk on these funds. The Company's investment policy includes guidelines on the quality of the financial institutions and financial instruments the Company is allowed to invest in, which the Company believes minimizes the exposure to concentration of credit risk. The Company is subject to credit risk from its accounts receivable related to its product sales revenue of Translarna. The payment terms are predetermined and the Company evaluates the creditworthiness of each customer or distributor on a regular basis. The Company reserves all uninsured amounts billed directly to a patient until the time of cash receipt as collectability is not reasonably assured at the time the product is received. To date, the Company has not incurred any credit losses. Inventories and cost of product revenue In 2014, the Company was notified that the European Commission, or EC, granted conditional marketing authorization for Translarna for the treatment of nmDMD in ambulatory patients aged five years and older. The conditional marketing authorization allows the Company to market Translarna for the treatment of nmDMD in the 31 member states of the European Economic Area. The launch in these countries is on a country by country basis. This marketing authorization is subject to annual review and renewal by the EC following reassessment by the EMA of the risk benefit balance of the authorization. The authorization was further conditioned on the Company's submission of the final report, including additional efficacy and safety data, from ACT DMD and the Company's ability to implement measures, including pharmacovigilance plans that are detailed in the risk management plan for Translarna that was submitted to EMA. In January 2016, the Company submitted the final ACT DMD report to the EMA. In the third quarter of 2015, the EMA approved the annual renewal of the marketing authorization for Translarna for the treatment of nmDMD. The Company plans to seek to renew the marketing authorization on an annual basis until the Company's obligations have been fulfilled and the approval is converted from a conditional approval into a full approval. If the Company fails to satisfy such requirements, or if it is determined that the balance of risks and benefits of using Translarna changes materially, the European Commission could, at the EMA's recommendation, vary, suspend, withdraw or refuse to renew the marketing authorization for Translarna or require additional clinical trials. The Company does not have sufficient history or experience from which to accurately forecast product sales or demand generation, and there continues to be substantial risk that regulators could suspend or not renew the Company's marketing authorization in the future. As such, as of the date of this filing, the Company has not capitalized inventory. Deferred rent The Company has an operating lease for office space. Rent expense is recorded on a straight-line basis over the initial lease term. The difference between the actual cash paid and the straight-line rent expense is recorded as deferred rent. Leasehold improvements made related to this lease, subsequent to its inception, are amortized over the remaining lease term. Accumulated other comprehensive income (loss) Accumulated other comprehensive income (loss) consists of unrealized gains or losses on marketable securities and foreign currency translation adjustments. Revenue recognition The Company recognizes revenue when amounts are realized or realizable and earned. Revenue is considered realizable and earned when the following criteria are met: (1) persuasive evidence of an arrangement exists; (2) delivery has occurred or services have been rendered; (3) the price is fixed or determinable; and (4) collection of the amounts due are reasonably assured. Net Product Sales The Company's net product sales have consisted solely of sales of Translarna for the treatment of nmDMD in territories outside of the U.S. The Company began recognizing revenue for payments received under the reimbursed EAPs for Translarna in nmDMD patients in select countries in the third quarter of 2014. The Company has now established a pattern of collectability and, since January 2015, the Company recognizes revenue from product sales when there is persuasive evidence that an arrangement exists, title to product and associated risk of loss has passed to the customer, the price is fixed or determinable, collectability is reasonably assured and the Company has no further performance obligations in accordance with Financial Accounting Standards Board ("FASB") Accounting Standards Codification ("ASC") Subtopic 605-15, Revenue Recognition—Products. The Company has recorded revenue on sales where Translarna is available either on a commercial basis or through a reimbursed EAP program. Orders for Translarna are generally received from hospital and retail pharmacies and, in some cases, one of the Company's third-party partner distributors. The Company's third-party distributors act as intermediaries between the Company and end users and do not typically stock significant quantities of Translarna. The ultimate payor for Translarna is typically a government authority or institution or a third-party health insurer. Prior to January 1, 2015, the Company generally recognized revenue for these reimbursed EAP programs once the product was shipped on behalf of the government authority or institution on a cash basis if all other revenue recognition criteria had been met. Beginning in the first quarter of 2015, the Company has recognized revenue for Translarna as product is shipped, as the Company has established a pattern of collectability. The Company records revenue net of estimated third party discounts and rebates. Allowances are recorded as a reduction of revenue at the time revenues from product sales are recognized. Allowances for government and other third-party rebates and discounts are established or estimated at the time of delivery. These allowances are adjusted to reflect known changes in factors and may impact such allowances in the quarter those changes are known. Collaboration and Grant Revenue The terms of these agreements typically include payments to the Company of one or more of the following: nonrefundable, upfront license fees; milestone payments; research funding and royalties on future product sales. In addition, the Company generates service revenue through agreements that generally provide for fees for research and development services and may include additional payments upon achievement of specified events. The Company evaluates all contingent consideration earned, such as a milestone payment, using the criteria as provided by the Financial Accounting Standards Board (FASB), guidance on the milestone method of revenue recognition. At the inception of a collaboration arrangement, the Company evaluates if a milestone payment is substantive. The criteria requires that (1) the Company determines if the milestone is commensurate with either its performance to achieve the milestone or the enhancement of value resulting from our activities to achieve the milestone; (2) the milestone be related to past performance; and (3) the milestone be reasonable relative to all deliverable and payment terms of the collaboration arrangement. If these criteria are met then the contingent milestones can be considered a substantive milestone and will be recognized as revenue in the period that the milestone is achieved. The Company recognizes royalties as earned in accordance with the terms of various research and collaboration agreements. If not substantive, the contingent consideration is allocated to the existing units of accounting based on relative selling price and recognized following the same basis previously established for the associated unit of accounting. The Company recognizes revenue for reimbursements of research and development costs under collaboration agreements as the services are performed. The Company records these reimbursements as revenue and not as a reduction of research and development expenses as the Company has the risks and rewards as the principal in the research and development activities. Research and development costs Research and development expenses include the clinical development costs associated with the Company's product development programs and research and development costs associated with the Company's discovery programs. These expenses include internal research and development costs and the costs of research and development conducted on behalf of the Company by third parties, including sponsored university-based research agreements and clinical study vendors. All research and development costs are expensed as incurred. Costs incurred in obtaining technology licenses are charged immediately to research and development expense if the technology licensed has not reached technological feasibility and has no alternative future uses. Nonrefundable advance payments made for goods and services that will be used in future research and development activities are deferred if the contracted party has not yet performed the related activities. The amount deferred is then recognized as expense when the research and development activities are performed. The deferred research and development advance payments were $0.6 and $0.9 million as of December 31, 2015 and 2014, respectively. Fair value of financial instruments The Company follows the fair value measurement rules, which provides guidance on the use of fair value in accounting and disclosure for assets and liabilities when such accounting and disclosure is called for by other accounting literature. These rules establish a fair value hierarchy for inputs to be used to measure fair value of financial assets and liabilities. This hierarchy prioritizes the inputs to valuation techniques used to measure fair value into three levels: Level 1 (highest priority), Level 2, and Level 3 (lowest priority). · Level 1—Unadjusted quoted prices in active markets for identical assets or liabilities that the Company has the ability to access at the balance sheet date. · Level 2—Inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly. Level 2 inputs include quoted prices for similar assets and liabilities in active markets, quoted prices for identical or similar assets or liabilities in markets that are not active, inputs other than quoted prices that are observable for the asset or liability (i.e., interest rates, yield curves, etc.), and inputs that are derived principally from or corroborated by observable market data by correlation or other means (market corroborated inputs). · Level 3—Inputs are unobservable and reflect the Company's assumptions as to what market participants would use in pricing the asset or liability. The Company develops these inputs based on the best information available. Cash equivalents and investments are reflected in the accompanying financial statements at fair value. The carrying amount of receivables and accounts payable and accrued expenses approximates fair value due to the short-term nature of those instruments. Beneficial conversion When the Company issues a debt or an equity security that is convertible into common stock at a discount from the fair value of the common stock at the date the debt or equity security counterparty is legally committed to purchase such a security (Commitment Date), a beneficial conversion charge is measured and recorded on the Commitment Date for the difference between the fair value of the Company's common stock and the effective conversion price of the convertible debt or equity security. If the intrinsic value of the beneficial conversion feature is greater than the proceeds allocated to the convertible debt or equity security, the amount of the discount assigned to the beneficial conversion feature is limited to the amount of the proceeds allocated to the convertible debt or equity security. The amount allocated to the beneficial conversion feature is presented as a discount or reduction to the related debt security or as an immediate charge to earnings available to common shareholders for convertible preferred stock instruments that are convertible by the shareholders at any time. Warrant liability Warrants to purchase the Company's common stock with nonstandard antidilution provisions, regardless of the probability or likelihood that may conditionally obligate the issuer to ultimately transfer assets, are classified as liabilities and are recorded at their estimated fair value at each reporting period. Any change in fair value of these warrants is recorded as gain/(loss) on warrant valuation each reporting period in Other income/(expense) on the Company's statement of operations. Impairment of long-lived assets The Company monitors its long-lived assets for indicators of impairment. If such indicators are present, the Company assesses the recoverability of affected assets by determining whether the carrying value of such assets is less than the sum of the undiscounted future cash flows of the assets. If such assets are found not to be recoverable, the Company measures the amount of such impairment by comparing the carrying value of the assets to the fair value of the assets, with the fair value generally determined based on the present value of the expected future cash flows associated with the assets. Although current and historical negative cash flows are indicators of impairment, management believes the future cash flows to be received from the long-lived assets and the potential success of the Company's research programs will exceed the assets' carrying value, and accordingly, the Company believes that no impairment of long-lived assets exists as of December 31, 2015. Share-based compensation The Company measures the cost of employee services received in exchange for an award of equity instruments based on the grant date fair value of the award. Restricted stock awards are measured based on the fair market values of the underlying stock on the dates of grant. For service type awards, share-based compensation expense is recognized on a straight-line basis over the period during which the employee is required to provide service in exchange for the entire award. For awards that vest or begin vesting upon achievement of a performance condition, the Company estimates the likelihood of satisfaction of the performance condition and recognizes compensation expense when achievement of the performance condition is deemed probable using an accelerated attribution model. The fair value of options is calculated using the Black-Scholes option pricing model to determine the fair value of stock options on the date of grant based on key assumptions such as expected volatility and expected term. As a new public company, the Company does not have sufficient history to estimate the volatility of its common stock price or the expected life of the options. The Company calculates expected volatility based on reported data for similar publicly traded companies for which historical information is available and will continue to do so until the historical volatility of its common stock is sufficient to measure expected volatility for future option grants. Income taxes Deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases and net operating loss and credit carryforwards. Deferred tax assets and liabilities are measured at rates expected to apply to taxable income in the years in which those temporary differences and carryforwards are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in the statement of operations in the period that includes the enactment date. A valuation allowance is recorded when it is not more likely than not that all or a portion of the net deferred tax assets will be realized. The Company recognized a tax benefit of $4.9 million related to the sale of net operating losses in the New Jersey Technology Business Tax Certificate Transfer Program for the year ended December 31, 2014. The Company did not participate in this program during the years ended December 31, 2015 and 2013. Net (loss) income per share Basic net income per share is calculated by dividing the net income attributable to common stockholders by the weighted average number of common shares outstanding for the period, without consideration for common stock equivalents. Diluted net income per share is calculated by dividing the net income attributable to common stockholders by the weighted-average number of common share equivalents outstanding for the period determined using the treasury-stock method and the if-converted method. During periods in which the Company incurs net losses, both basic and diluted loss per share is calculated by dividing the net loss by the weighted average shares outstanding—potentially dilutive securities are excluded from the calculation because their effect would be anti-dilutive. Dilutive common stock equivalents are comprised of convertible preferred stock and options outstanding under the Company's stock option plans. Recent accounting pronouncements In May 2014, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2014-09, Revenue from Contracts with Customers. ASU 2014-09 will eliminate transaction- and industry-specific revenue recognition guidance under current GAAP and replace it with a principle-based approach for determining revenue recognition. ASU 2014-09 will require that companies recognize revenue based on the value of transferred goods or services as they occur in the contract. The ASU also will require additional disclosure about the nature, amount, timing and uncertainty of revenue and cash flows arising from customer contracts, including significant judgments and changes in judgments and assets recognized from costs incurred to obtain or fulfill a contract. ASU 2014-09 is effective for annual reporting periods beginning after December 15, 201 7 . Early application is not permitted. Entities can transition to the standard either retrospectively or as a cumulative-effect adjustment as of the date of adoption. Presently, the Company is assessing what effect the adoption of ASU 2014-09 will have on its financial statements and accompanying notes. In April 2015, the FASB issued ASU 2015-03, Interest—Imputation of Interest, Simplifying the Presentation of Debt Issuance Costs topic of the Codification. This standard provides a simplified presentation of debt issuance costs and requires that debt issuance costs related to a recognized debt liability to be presented on the balance sheet as a direct deduction from the carrying amount of that debt liability, consistent with debt discounts. The standard is effective for public companies for annual periods beginning after December 15, 2015. The Company's unamortized debt issuance cost at December 31, 2015 was $2.8 million which is included within "Deposits and other assets" on the consolidated balance sheet. Upon adoption, the Company expects that the carrying value of its debt liability will decrease by the value associated with the unamortized debt cost. In November 2015, the FASB issued ASU 2015-17, Income Taxes, Balance Sheet Classification of Deferred Taxes topic of the Codification. This standard requires all deferred tax assets and liabilities to be classified as non-current on the balance sheet instead of separating deferred taxes into current and non-current amounts. In addition, valuation allowance allocations between current and non-current deferred tax assets are no longer required because those allowances also will be classified as non-current. This standard is effective for public companies for annual periods beginning after December 15, 2016. The Company's deferred tax assets is provided with full valuation allowance as of December 31, 2015. As such, the Company does not expect that this standard will have a significant impact upon adoption.

Fair value of financial instrum

Fair value of financial instruments and investments	12 Months Ended
	Dec. 31, 2015
Fair value of financial instruments and investments
Fair value of financial instruments and investments	3. Fair value of financial instruments and investments Fair value of certain investments is based upon market prices using quoted prices in active markets for identical assets quoted on the last day of the year. In establishing the estimated fair value of the remaining investments, the Company used the fair value as determined by its investment advisors using observable inputs other than quoted prices. The Company reviews its investments on a periodic basis for other-than-temporary impairments. This review is subjective, as it requires management to evaluate whether an event or change in circumstances has occurred in that period that may have a significant adverse effect on the fair value of the investment. The following represents the fair value using the hierarchy described in Note 2 for the Company's financial assets and liabilities that are required to be measured at fair value on a recurring basis as of December 31, 2015 and 2014: December 31, 2015 Total Quoted prices in active markets for identical assets (level 1) Significant other observable inputs (level 2) Significant unobservable inputs (level 3) Marketable securities $ $ — $ $ — Warrant liability — — December 31, 2014 Total Quoted prices in active markets for identical assets (level 1) Significant other observable inputs (level 2) Significant unobservable inputs (level 3) Marketable securities $ $ — $ $ — Warrant Liability — — The Company uses the market approach to measure fair value for its financial assets. The market approach uses prices and other relevant information generated by market transactions involving identical or comparable assets. The Company's marketable securities investments classified as Level 2 primarily utilize broker to value these securities. No transfers of assets between Level 1 and Level 2 of the fair value measurement hierarchy occurred during the year ended December 31, 2015. The following is a summary of marketable securities accounted for as available-for-sale securities at December 31, 2015 and 2014: December 31, 2015 Gross Unrealized Amortized Cost Fair Value Gains Losses Commercial paper $ $ $ — $ Corporate debt securities — ) Government obligations ) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ $ $ $ ) $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2014 Gross Unrealized Amortized Cost Fair Value Gains Losses Corporate debt securities $ $ $ ) $ Government obligations ) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ $ $ $ ) $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Unrealized gains and losses are reported as a component of accumulated other comprehensive (loss) income in stockholders' equity. During the year ended December 31, 2015, the Company did not have any realized gains/losses from the sale of marketable securities. The cost of securities sold is based on the specific identification method. The Company evaluates investments with unrealized losses to determine if the losses are other than temporary. At December 31, 2015, the Company held securities with an unrealized loss position that were not considered to be other-than-temporarily impaired as the Company has the ability to hold such investments until recovery of their fair value. In addition, the Company considered the financial condition, credit ratings and near-term prospects of the issuers, and the magnitude of the losses as compared to the cost and the length of time the investments have been in an unrealized loss position when determining if the losses are other than temporary. Marketable securities on the balance sheet at December 31, 2015 and 2014 mature as follows: December 31, 2015 Less Than 12 Months More Than 12 Months Commercial paper $ $ — Corporate debt securities Government obligations ​ ​ ​ ​ ​ ​ ​ ​ Total Marketable securities $ $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2014 Less Than 12 Months More Than 12 Months Corporate debt securities $ $ Government obligations ​ ​ ​ ​ ​ ​ ​ ​ Total Marketable securities $ $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Convertible 3.0% senior notes In August 2015, the Company issued $150.0 million of 3.0% convertible senior notes due August 15, 2022 (the "Convertible Notes"). Interest is payable semi-annually on February 15 and August 15 of each year, beginning on February 15, 2016. The Company separately accounted for the liability and equity components of the Convertible Notes by allocating the proceeds between the liability component and equity component, as further discussed in Note 6. The fair value of the Convertible Notes, which differs from their carrying values, is influenced by interest rates, the Company's stock price and stock price volatility and is determined by prices for the Convertible Notes observed in market trading which are Level 2 inputs. The estimated fair value of the Convertible Notes at December 31, 2015 was $150.0 million. Level 3 valuation The warrant liability is classified in Other long-term liabilities on the Company's balance sheet. The warrant liability is marked-to-market each reporting period with the change in fair value recorded as a gain or loss within Other income/(expense) on the Company's statement of operations until the warrants are exercised, expire or other facts and circumstances lead the warrant liability to be reclassified as an equity instrument. The fair value of the warrant liability is determined at each reporting period by utilizing the Black-Scholes option pricing model. The table presented below is a summary of changes in the fair value of the Company's Level 3 valuation for warrant liability for the years ended December 31, 2015 and 2014: Level 3 assets Beginning balance as of January 1, 2014 $ Change in fair value of warrant liability ​ ​ ​ ​ ​ Ending balance as of December 31, 2014 $ Change in fair value of warrant liability ) ​ ​ ​ ​ ​ Ending balance as of December 31, 2015 $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair value of the warrant liability is estimated using an option-pricing model, which includes variables such as the expected volatility based on guideline public companies, the preferred stock value, and the estimated time to a liquidity event. The significant assumptions used in preparing the option pricing model for valuing the Company's warrants as of December 31, 2015 include (i) volatility (62%-70%), (ii) risk free interest rate (0.86%-1.54%), (iii) strike price ($128.00-$2,520.00), (iv) fair value of common stock ($32.40) and (v) expected life (1.5-3.7 years). The significant assumptions used in preparing the option pricing model for valuing the Company's warrants as of December 31, 2014 include (i) volatility (68%-70%), (ii) risk free interest rate (0.89%-1.65%), (iii) strike price ($128.00-$2,520.00), (iv) fair value of common stock ($51.77) and (v) expected life (2.5-4.7 years).

Fixed assets

Fixed assets	12 Months Ended
	Dec. 31, 2015
Fixed assets
Fixed assets	4. Fixed assets Fixed assets, net were as follows at December 31, 2015 and 2014: December 31, 2015 2014 Leasehold improvements $ $ Computer equipment and software Furniture, fixtures, and lab equipment Assets in process ​ ​ ​ ​ ​ ​ ​ ​ Less accumulated depreciation and amortization ) ) ​ ​ ​ ​ ​ ​ ​ ​ $ $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Depreciation expense was approximately $2.9 million, $2.2 million, and $2.4 million for the years ended December 31, 2015, 2014 and 2013, respectively.

Accounts payable and accrued ex

Accounts payable and accrued expenses	12 Months Ended
	Dec. 31, 2015
Accounts payable and accrued expenses
Accounts payable and accrued expenses	5. Accounts payable and accrued expenses Accounts payable and accrued expenses at December 31, 2015 and 2014 consist of the following: December 31, 2015 2014 Employee compensation, benefits, and related accruals $ $ Consulting and contracted research Professional fees Accounts payable Other ​ ​ ​ ​ ​ ​ ​ ​ $ $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

Long-term debt

Long-term debt	12 Months Ended
	Dec. 31, 2015
Long-term debt.
Long-term debt	6. Long-term debt 2009 Debt Facility In September 2009, the Company entered into a $25.0 million secured debt facility with a syndicate of two lenders. The Company borrowed $12.5 million under the facility in September 2009 and an additional $10.0 million under the facility in December 2010 and issued the lenders promissory notes. The notes were secured by substantially all of the Company's assets except for intellectual property. In July 2013, the Company paid in full the outstanding principal and interest of $2.6 million due under the promissory notes issued in connection with the secured debt facility. As a result of this transaction, the Company recorded a loss on extinguishment of debt of $0.1 million on the Company's statement of operations for the year ended December 31, 2013. The loss on extinguishment of debt primarily represented the write off of related deferred financing costs, the acceleration of recognition of debt extinguishment fees and the prepayment premium payable. 2015 Convertible Notes In August 2015, the Company issued, at par value, $150.0 million aggregate principal amount of 3.0% convertible senior notes due 2022. The Convertible Notes bear cash interest at a rate of 3.0% per year, payable semi-annually on February 15 and August 15 of each year, beginning on February 15, 2016. The Convertible Notes will mature on August 15, 2022, unless earlier repurchased or converted. The net proceeds to the Company from the offering were $145.4 million after deducting the initial purchasers' discounts and commissions and the offering expenses payable by the Company. The Convertible Notes are governed by an indenture (the Convertible Notes Indenture) with U.S Bank National Association as trustee (the Convertible Notes Trustee). Holders may convert their Convertible Notes at their option at any time prior to the close of business on the business day immediately preceding February 15, 2022 only under the following circumstances: · during any calendar quarter commencing on or after September 30, 2015 (and only during such calendar quarter), if the last reported sale price of the Company's common stock for at least 20 trading days (whether or not consecutive) during a period of 30 consecutive trading days ending on the last trading day of the immediately preceding calendar quarter is greater than or equal to 130% of the conversion price on each applicable trading day; · during the five business day period after any five consecutive trading day period (the "measurement period") in which the trading price (as defined in the Convertible Notes Indenture) per $1,000 principal amount of Convertible Notes for each trading day of the measurement period was less than 98% of the product of the last reported sale price of the Company's common stock and the conversion rate on each such trading day; · during any period after the Company has issued notice of redemption until the close of business on the scheduled trading day immediately preceding the relevant redemption date; or · upon the occurrence of specified corporate events. On or after February 15, 2022, until the close of business on the business day immediately preceding the maturity date, holders may convert their Convertible Notes at any time, regardless of the foregoing circumstances. Upon conversion, the Company will pay cash up to the aggregate principal amount of the Convertible Notes to be converted and deliver shares of its common stock in respect of the remainder, if any, of its conversion obligation in excess of the aggregate principal amount of Convertible Notes being converted. The conversion rate for the Convertible Notes was initially, and remains, 17.7487 shares of the Company's common stock per $1,000 principal amount of the Convertible Notes, which is equivalent to an initial conversion price of approximately $56.34 per share of the Company's common stock. The Company may not redeem the Convertible Notes prior to August 20, 2018. The Company may redeem for cash all or any portion of the Convertible Notes, at its option, on or after August 20, 2018 if the last reported sale price of its common stock has been at least 130% of the conversion price then in effect on the last trading day of, and for at least 19 other trading days (whether or not consecutive) during, any 30 consecutive trading day period ending on, and including, the trading day immediately preceding the date on which the Company provides notice of redemption, at a redemption price equal to 100% of the principal amount of the Convertible Notes to be redeemed, plus accrued and unpaid interest to, but excluding, the redemption date. No sinking fund is provided for the Convertible Notes, which means that the Company is not required to redeem or retire the Convertible Notes periodically. If the Company undergoes a "fundamental change" (as defined in the Indenture governing the Convertible Notes Indenture), subject to certain conditions, holders of the Convertible Notes may require the Company to repurchase for cash all or part of their Convertible Notes at a repurchase price equal to 100% of the principal amount of the Convertible Notes to be repurchased, plus accrued and unpaid interest to, but excluding, the fundamental change repurchase date. The Convertible Notes Indenture contains customary events of default with respect to the Convertible Notes, including that upon certain events of default (including the Company's failure to make any payment of principal or interest on the Convertible Notes when due and payable) occurring and continuing, the Convertible Notes Trustee by notice to the Company, or the holders of at least 25% in principal amount of the outstanding Convertible Notes by notice to the Company and the Convertible Notes Trustee, may, and the Convertible Notes Trustee at the request of such holders (subject to the provisions of the Convertible Notes Indenture) shall, declare 100% of the principal of and accrued and unpaid interest, if any, on all the Convertible Notes to be due and payable. In case of certain events of bankruptcy, insolvency or reorganization, involving the Company or a significant subsidiary, 100% of the principal of and accrued and unpaid interest on the Convertible Notes will automatically become due and payable. Upon such a declaration of acceleration, such principal and accrued and unpaid interest, if any, will be due and payable immediately. The Company accounts for the Convertible Notes as a liability and equity component where the carrying value of the liability component will be valued based on a similar instrument. In accounting for the issuance of the Convertible Notes, the Company separated the Convertible Notes into liability and equity components. The carrying amount of the liability component was calculated by measuring the fair value of a similar liability that does not have an associated convertible feature. The carrying amount of the equity component representing the conversion option was determined by deducting the fair value of the liability component from the par value of the Convertible Notes as a whole. The excess of the principal amount of the liability component over its carrying amount, referred to as the debt discount, is amortized to interest expense over the seven-year term of the Convertible Notes. The equity component is not re-measured as long as it continues to meet the conditions for equity classification. In accounting for the transaction costs related to the issuance of the Convertible Notes, the Company allocated the total costs incurred to the liability and equity components of the Convertible Notes based on their relative values. Transaction costs attributable to the liability component are amortized to interest expense over the seven-year term of the Convertible Notes, and transaction costs attributable to the equity component are netted with the equity components in stockholders' equity. Additionally, the Company initially recorded a net deferred tax liability of $22.3 million in connection with the Notes. The Convertible Notes consist of the following: Year ended December 31 Liability component 2015 2014 Principal $ $ — Less: Debt discount, net (1) ) — ​ ​ ​ ​ ​ ​ ​ ​ Net carrying amount $ $ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (1) Included in the consolidated balance sheets within convertible senior notes (due 2022) and amortized to interest expense over the remaining life of the Convertible Notes using the effective interest rate method. The following table sets forth total interest expense recognized related to the Convertible Notes: Year ended December 31, 2015 2014 Contractual interest expense $ $ — Amortization of debt issuance costs — Amortization of debt discount — ​ ​ ​ ​ ​ ​ ​ ​ Total $ $ — ​ ​ ​ ​ ​ ​ ​ ​ Effective interest rate of the liability component % —

Capital structure

Capital structure	12 Months Ended
	Dec. 31, 2015
Capital structure
Capital structure	7. Capital structure Convertible preferred stock prior to 2013 recapitalization As of December 31, 2012, the Company had authorized for issuance up to 29,500,000 shares of preferred stock, $0.001 par value. The authorized shares as of December 31, 2012 were designated as follows: 2,000,000 shares of Series One convertible preferred stock (Series One), 13,750,000 shares of Series Two convertible preferred stock (Series Two), and 13,750,000 shares of Series Three convertible preferred stock (Series Three). 2013 Recapitalization During January and February of 2013, the Company entered into a "bridge" financing arrangement with certain existing investors providing for the issuance by the Company of an aggregate of $6 million of convertible promissory notes and warrants to purchase 2,527,675 shares of Series One and Series Two convertible preferred stock. The warrants have a per share exercise price of $0.01, and as such, they are referred to as "penny warrants". This bridge financing was closed in anticipation of the March 2013 Series Four financing event, which the Company refers to as the "2013 recapitalization". The Company allocated the proceeds of the convertible promissory notes between debt and warrant liability. Since the value of the warrants exceeded the proceeds from the convertible notes issued to existing investors, the value of the warrant in excess of the proceeds is considered a deemed dividend and reflected as an equity transaction in the financial statements. The Company recorded $6.0 million to interest expense related to the debt discount associated with the convertible debt during the quarter ended March 31, 2013. On March 7, 2013, the Company closed a private placement of a new series of convertible preferred stock that resulted in another recapitalization event (the 2013 recapitalization). In this private placement, the Company issued and sold an aggregate of 4,497,035 shares of its Series Four senior preferred stock (Series Four) for an aggregate purchase price of approximately $54 million. Including the $6.0 million raised with the bridge financing, total gross proceeds raised during the quarter ended March 31, 2013 was approximately $60.0 million. In addition, the Company issued an aggregate of 502,919 shares of Series Four upon the share settlement of the convertible promissory notes described above that were issued in January and February 2013. In connection with this private placement, the Company effected a one- for-120 reverse stock split of its common stock and an exchange of outstanding shares of Series One, Series Two and Series Three convertible preferred stock into an aggregate of 6,700,487 shares of a new series of Series Five junior preferred stock (Series Five). In addition, the Company issued an aggregate of 2,527,675 shares of Series One and Series Two convertible preferred stock upon the exercise of the warrants issued in connection with the bridge loan that were immediately exchanged for 2,095,515 shares of Series Five during the 2013 recapitalization. The Company accounted for the 2013 recapitalization as an extinguishment of its Series One, Series Two and Series Three convertible preferred stock and recorded the Series Five shares at their fair value as of the recapitalization date. In accordance with authoritative accounting guidance, the Company recorded a gain attributable to the common stockholders on the extinguishment of the Series One, Series Two and Series Three convertible preferred stock. The gain of approximately $3.4 million represents the excess of the Series One, Series Two and Series Three convertible preferred stock over the fair value of the shares Series Five issued in connection with the recapitalization. Valuation —The value of the Company was estimated using the PWERM. The PWERM considered the most significant near-term driver of value for the Company as the Company's ability to complete a Phase 3 clinical trial of ataluren for the treatment of Duchenne muscular dystrophy caused by nonsense mutations (nmDMD). The remaining scenarios in the PWERM related to funding the completion of the Phase 3 clinical trial for nmDMD. The path to raising this money made up the remaining nodes in the PWERM. After identifying the various potential liquidity scenarios and their likely timing, a pre-money enterprise value was assigned to each scenario based on a combination of management's guidance and recent trends in the capital markets. The resulting enterprise value for each liquidity event was divided by the total shares that would be outstanding under each scenario to arrive at a price per share for the common and preferred classes of stock. Each scenario was then assigned an outcome probability based on management's estimates. The resulting probability weighted share values were then discounted to present value at a rate that reflects general industry risks (but not Company specific risks). The rights and preferences of the shares of Series Four and Series Five are as follows: Dividends —The holders of Series Four and Series Five, in preference to the holders of common stock, were entitled to noncumulative dividends when and if declared by the Board of Directors. Liquidation —Upon the liquidation, dissolution, reorganization or winding-up of the Company, the holders of Series Four would have been entitled to receive, before any distribution or payment was made to any other class of security, an amount equal to the original issuance price, plus all declared, but unpaid, dividends. To the extent there had been excess assets to distribute, the holders of Series Five would have been entitled to receive, before any distribution or payment was made to the holders of the common stock, an amount equal to the stated liquidation preference, plus all declared, but unpaid, dividends. To the extent there had been remaining assets to distribute, the holders of common stock would have been entitled to receive such remaining assets. Voting —Each holder of Series Four and Series Five was entitled to cast the number of votes into which such holder's shares would have converted. Except as required by law, holders of common stock had limited voting rights. Additionally, except as required by law, and except in certain enumerated circumstances, holders of Series Four and Series Five would have voted together with the holders of common stock as a single class. Conversion —Each share of Series Four and Series Five is convertible at any time at the option of the holder into one share of common stock. These conversion ratios were subject to adjustment for certain dilutive events, including certain types of stock splits or stock dividends or future recapitalizations. In May 2013, the Company issued and sold an additional 375,000 shares of Series Four, at a price per share of $12.00, for an aggregate purchase price of $4.5 million. Common Stock In May 2013, the Company's Board of Directors and stockholders approved an amendment to the Company's certificate of incorporation increasing the number of authorized shares of common stock to 125,000,000. Initial Public Offering In June 2013, the Company closed the initial public offering of its common stock pursuant to a registration statement on Form S-1, as amended. The Company issued and sold an aggregate of 9,627,800 shares of common stock under the registration statement at a public offering price of $15.00 per share, including 1,255,800 shares pursuant to the exercise by the underwriters of an over- allotment option. The Company received net proceeds from the initial public offering of approximately $131.6 million, after deducting underwriting discounts and commissions and other offering expenses payable by the Company. Upon closing the initial public offering, all outstanding shares of the Series Four and Series Five were converted into 14,170,956 shares of common stock. Follow-On Offerings In February 2014, the Company closed a follow-on public offering of its common stock pursuant to a registration statement on Form S-1, as amended. The Company issued and sold an aggregate of 5,163,265 shares of common stock under the registration statement at a public offering price of $24.50 per share, including 673,469 shares pursuant to the exercise by the underwriters of an over-allotment option. The Company received net proceeds from the follow -on public offering of approximately $118.4 million, after deducting underwriting discounts and commissions and other offering expenses payable by the Company. On October 16, 2014, the Company closed an underwritten public offering of its common stock pursuant to a registration statement on Form S-3. The Company issued and sold an aggregate of 3,450,000 shares of common stock under the registration statement at a public offering price of $36.25 per share, including 450,000 shares issued upon exercise by the underwriters of their option to purchase additional shares. The Company received net proceeds of approximately $117.6 million after deducting underwriting discounts and commissions and other offering expenses payable by the Company. Warrants All of the Company's outstanding warrants are classified as liabilities as of December 31, 2015 and 2014 because they contain non-standard antidilution provisions. The following is a summary of the Company's outstanding warrants as of December 31, 2015 and 2014: Warrant shares Exercise price Expiration Common stock $ Common stock $ Common stock $ In connection with the 2013 recapitalization, all of the Series Two outstanding warrants became warrants to purchase Series Five. In connection with the Company's initial public offering all of the Series Five outstanding warrants became warrants to purchase common stock.

Earnings per share

Earnings per share	12 Months Ended
	Dec. 31, 2015
Earnings per share
Earnings per share	8. Earnings per share Basic earnings per share is computed by dividing net loss available to common stockholders by the weighted-average number of common shares outstanding. Diluted earnings per share is computed by dividing net loss available to common stockholders by the weighted-average number of common shares plus the effect of dilutive potential common shares outstanding during the period. The following table sets forth the computation of basic and diluted earnings per share for common stockholders: Net loss per share Year ended December 31, 2015 2014 2013 Numerator Net loss $ ) $ ) $ ) Deemed dividend — — ) Gain on exchange of convertible preferred stock in connection with recapitalization — — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net loss attributable to common stockholders $ ) $ ) $ ) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Denominator Denominator for basic and diluted net loss per share ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net loss per share: Basic and diluted $ )* $ )* $ )* ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ * For the years ended December 31, 2015, 2014, and 2013, the Company experienced a net loss and therefore did not report any dilutive share impact. The following table shows historical dilutive common share equivalents outstanding, which are not included in the above historical calculation, as the effect of their inclusion is anti-dilutive during each period. As of December 31, 2015 2014 2013 Stock Options Unvested restricted stock ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Total ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

Stock award plan

Stock award plan	12 Months Ended
	Dec. 31, 2015
Stock award plan
Stock award plan	9. Stock award plan In 2009, the Company's shareholders approved the 2009 Equity and Long-Term Incentive Plan, which provides for the granting of stock option awards, restricted stock awards, and other stock-based and cash-based awards, subject to certain adjustments and annual increases. On March 5, 2013, the Company's Board of Directors approved the 2013 Stock Incentive Plan, which provides for the granting of stock option awards, stock appreciation rights, restricted stock, restricted stock units and other stock-based awards in the aggregate of 739,937 shares of common stock. On March 5, 2013, the Board approved a grant of 735,324 shares of restricted stock and 4,613 stock options. There are no additional shares available for issuance under this plan. In May 2013, the Company's Board of Directors and stockholders increased by 2,500,000 the number of shares authorized under the 2009 Equity and Long Term Incentive Plan, which provides for the granting of stock option awards, restricted stock awards, and other stock-based and cash-based awards. There are no additional shares available for issuance under this plan. In May 2013, the Company's Board of Directors and stockholders approved the 2013 Long Term Incentive Plan, which became effective upon the closing of the Company's IPO. The 2013 Long Term Incentive Plan provides for the grant of incentive stock options, nonstatutory stock options, restricted stock awards and other stock-based awards. The number of shares of common stock reserved for issuance under the 2013 Long Term Incentive Plan is the sum of (1) 122,296 shares of common stock available for issuance under the Company's 2009 Equity and Long Term Incentive Plan and 2013 Stock Incentive Plan, (2) the number of shares (up to 3,040,444 shares) equal to the sum of the number of shares of common stock subject to outstanding awards under the Company's 1998 Employee, Director and Consultant Stock Option Plan, 2009 Equity and Long Term Incentive Plan and 2013 Stock Incentive Plan that expire, terminate or are otherwise surrendered, cancelled, forfeited or repurchased by the Company at their original issuance price pursuant to a contractual repurchase right plus (3) an annual increase, to be added on the first day of each fiscal year until the expiration of the 2013 Long Term Incentive Plan, equal to the lowest of 2,500,000 shares of common stock, 4% of the number of shares of common stock outstanding on the first day of the fiscal year and an amount determined by the Company's Board of Directors. As of December 31, 2015, awards for 266,533 shares of common stock are available for issuance. The Board of Directors has the authority to select the individuals to whom options are granted and determine the terms of each option, including (i) the number of shares of common stock subject to the option; (ii) the date on which the option becomes exercisable; (iii) the option exercise price, which, in the case of incentive stock options, must be at least 100% (110% in the case of incentive stock options granted to a stockholder owning in excess of 10% of the Company's stock) of the fair market value of the common stock as of the date of grant; and (iv) the duration of the option (which, in the case of incentive stock options, may not exceed ten years). Options typically vest over a three- or four-year period. Inducement stock option awards Pursuant to the NASDAQ inducement grant exception, during the year ended December 31, 2015, the Company issued options to purchase an aggregate of 806,600 shares of common stock to certain new hire employees at a weighted-average exercise price of $50.46 per share. An aggregate of 84,150 of these options were forfeited during the year ended December 31, 2015 in connection with employee separations from the Company. A summary of stock option activity is as follows: Number of options Weighted- average exercise price Weighted- average remaining contractual term Aggregate intrinsic value (in thousands) Outstanding at December 31, 2012 $ Granted $ Exercised — $ — Forfeited ) $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Outstanding at December 31, 2013 $ Granted $ Exercised ) $ Forfeited ) $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Outstanding at December 31, 2014 $ Granted $ Exercised ) $ Forfeited ) $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Outstanding at December 31, 2015 $ 8.38 years $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Vested or Expected to vest at December 31, 2015 $ 8.65 years $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Exercisable at December 31, 2015 $ 7.67 years $ The fair values of grants made in the years ended December 31, 2015, 2014 and 2013 were contemporaneously estimated on the date of grant using the following assumptions: 2015 2014 2013 Risk-free interest rate 1.48 - 2.18% 0.11 - 2.04% 0.85 - 1.90% Expected volatility 67 - 69% 70 - 91% 87 - 89% Expected term 5.50 - 9.12 years 5.50 - 6.25 years 6.00 - 6.25 years The Company assumed no expected dividends for all grants. The weighted average grant date fair value of options granted during the years ended December 31, 2015, 2014 and 2013 was $50.81, $22.39, and $8.23 per share, respectively. The Company uses the "simplified method" to determine the expected term of options. Under this method, the expected term represents the average of the vesting period and the contractual term. The expected volatility of share options was estimated based on a historical volatility analysis of peers that were similar to the Company with respect to industry, stage of life cycle, size, and financial leverage. The risk-free rate of the option is based on U.S. Government Securities Treasury Constant Maturities yields at the date of grant for a term similar to the expected term of the option. In December 2013, the Compensation Committee of the Board of Directors modified the terms of stock options granted to executive management. Under the modified terms, the Committee waived all remaining performance conditions associated with the initial vesting of the options such that the options vest with service only conditions. The Company accounted for the modification to the option grants pursuant to ASC Topic 718-20-35 and recognized approximately $0.6 million as additional compensation that was charged to operations during the year ended December 31, 2013. In 2014, the Company modified the terms of stock options granted to a departing member of the executive team. The Company accounted for the modification to the option grants pursuant to ASC Topic 718-20-35 and recognized approximately $1.9 million as additional compensation that was charged to operations during the year ended December 31, 2014. Restricted Stock Awards —Restricted stock awards are granted subject to certain restrictions, including in some cases service conditions (restricted stock). The grant-date fair value of restricted stock awards, which has been determined based upon the market value of the Company's shares on the grant date, is expensed over the vesting period. The following table summarizes information on the Company's restricted stock: Restricted Stock Number of Shares Weighted Average Grant Date Fair Value January 1, 2015 $ Granted — $ — Vested ) $ Forfeited ) $ ​ ​ ​ ​ ​ ​ ​ ​ Unvested at December 31, 2015 $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ The Company recorded share-based compensation expense in the statement of operations as follows: Year ended December 31, 2015 2014 2013 Research and development $ $ $ Selling, general and administrative ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Total $ $ $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, 2015, there was approximately $73.8 million of total unrecognized compensation cost related to unvested share-based compensation arrangements granted under the Company's Plans. This cost is expected to be recognized as compensation expense over the weighted average remaining service period of approximately 2.74 years.

Other comprehensive income (los

Other comprehensive income (loss) and accumulated other comprehensive items	12 Months Ended
	Dec. 31, 2015
Other comprehensive income (loss) and accumulated other comprehensive items
Other comprehensive income (loss) and accumulated other comprehensive items	10. Other comprehensive income (loss) and accumulated other comprehensive items Other comprehensive income (loss) includes changes in equity that are excluded from net loss, such as unrealized gains and losses on marketable securities. The following table summarizes other comprehensive income (loss) and the changes in accumulated other comprehensive items, by component, for the years ended December 31, 2015, 2014, and 2013, respectively. Unrealized Gains/(Losses) On Marketable Securities Foreign Currency Translation Total Accumulated Other Comprehensive Items Balance at December 31, 2012 $ — $ — $ — Other comprehensive income before reclassifications — Amounts reclassified from other comprehensive items — — — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Other comprehensive income — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Balance at December 31, 2013 $ $ — $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Other comprehensive loss before reclassifications ) ) ) Amounts reclassified from other comprehensive items — — — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Other comprehensive loss ) ) ) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Balance at December 31, 2014 $ ) $ ) $ ) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Other comprehensive loss before reclassifications ) ) ) Amounts reclassified from other comprehensive items — — — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Other comprehensive loss ) ) ) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Balance at December 31, 2015 $ ) $ ) $ ) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

Collaborations and grants

Collaborations and grants	12 Months Ended
	Dec. 31, 2015
Collaborations and grants
Collaborations and grants	11. Collaborations and grants The Company has ongoing collaborations with the Spinal Muscular Atrophy Foundation (SMA Foundation) and F. Hoffman-La Roche Ltd and Hoffman- La Roche Inc. (collectively, Roche) and early stage discovery arrangements with other institutions. The following are the key terms to the Company's (i) ongoing collaborations and (ii) early stage discovery and development arrangements. Roche and SMA Foundation In November 2011, the Company and the SMA Foundation entered into a licensing and collaboration agreement with Roche for a spinal muscular atrophy program. Under the terms of the agreement, Roche acquired an exclusive worldwide license to the Company's spinal muscular atrophy program, which includes three compounds currently in preclinical development, as well as potential back-up compounds. The Company received a nonrefundable upfront cash payment of $30.0 million during the research term, which was terminated effective December 31, 2014, Roche provided us with funding, based on an agreed- upon full-time equivalent rate, for an agreed-upon number of full- time equivalent employees that we contributed to the research program. The Company applied the multiple element revenue recognition guidance in evaluating the accounting treatment of this collaboration agreement. The Company identified two possible significant deliverables in the collaboration agreement, the license and the research activities. The Company evaluated whether these significant deliverables have stand-alone value and determined that the license does not have standalone value without the ongoing research and development services given the unique nature of the technology. As such, both of these elements were combined as a single unit for accounting purposes. As a result, the Company deferred the $30.0 million upfront payment which was recognized over the estimated performance period of two years, which was the contracted research period. For the years ended December 31, 2015, 2014 and 2013, the Company recognized approximately $0.6 million, $20.2 million and $26.6 million respectively, in collaboration revenue. The balance of the remaining deferred upfront payment was fully recognized as of December 31, 2013. Under the agreement, the Company is eligible to receive additional payments from Roche if specified events are achieved with respect to each licensed product, including up to $135.0 million in research and development event milestones, up to $325.0 million in sales milestones upon achievement of sales events, and up to double digit royalties on worldwide annual net sales of a commercial product. The Company considers that each of the potential milestone events under the agreement would be substantive because the applicable criteria of its revenue recognition policy (see Note 2) would be satisfied. In January 2014, the Company announced the initiation of a Phase 1 clinical program in its spinal muscular atrophy collaboration with Roche and the SMA Foundation which triggered a $7.5 million milestone payment from Roche. The Company considered this milestone event substantive because the applicable criteria of its revenue recognition policy would be satisfied and recorded it as collaboration revenue for the year ended December 31, 2014. In November 2014, the Company announced the initiation of a Phase 2 study in adult and pediatric patients in its spinal muscular atrophy collaboration with Roche and the SMA Foundation which triggered a $10 million payment from Roche. The Company considered this milestone event substantive because the applicable criteria of its revenue recognition policy would be satisfied and recorded it as collaboration revenue for the year ended December 31, 2014. Early stage collaboration and discovery agreements From time to time, the Company has arrangements with several organizations pursuant to which the Company uses its discovery technologies to help identify potential drug candidates. The Company does not take ownership of the potential compounds, but rather provides research services to the collaborator using its specialized technology platform. Generally, these arrangements are structured such that the collaborator and the Company work together to jointly select targets from which to apply its discovery technologies. The research period for the Company to apply its technology is generally three to four years. The Company will typically receive a nonrefundable, upfront cash payment and the collaborator agrees to provide funding for research activities performed on its behalf. The Company applies multiple element revenue recognition guidance in evaluating the accounting treatment for these arrangements. Generally, the two significant deliverables in these arrangements are the license and the research activities. The Company evaluates whether the deliverables have standalone value. Since the Company's discovery technologies are highly specialized, the Company has generally determined that the license does not have standalone value without the ongoing research and development services and generally accounts for these arrangements as a single unit of accounting. As a result, the Company had deferred revenue of $1.8 million as of December 31, 2014 related to these arrangements. There was no deferred revenue related to these arrangements as of December 31, 2015. For the years ended December 31, 2015 and 2014, the Company recognized approximately $1.8 million and $1.3 million in collaboration revenue, respectively. The Company is eligible to receive additional payments from its early stage discovery research arrangements if the discovery compounds are ultimately developed and commercialized. The aggregate potential payments the Company is eligible for if all products are developed is $143.0 million and up to $252.0 million in sales milestones upon achievement of specified sales events and up to double digit royalties on worldwide annual net sales of the licensed product. The Company considers that each of the potential milestone events under the agreement would be substantive because the applicable criteria of its revenue recognition policy (see Note 2) would be satisfied. Grant revenue The Company receives grant funding from various institutions and governmental bodies. The grants are typically for early discovery research, and typically the grant program lasts from two to five years. The Company records revenue as the research activities are performed. If the granting agency provides for an upfront payment, the amount is deferred and recognized as revenue as the expenditures are incurred.

Income taxes

Income taxes	12 Months Ended
	Dec. 31, 2015
Income taxes
Income taxes	12. Income taxes For the years ended December 31, 2015 and 2014, the loss from operations before tax (expense) benefit in the United States was $51.0 million and $46.5 million, respectively. For the years ended December 31, 2015 and 2014, the loss from operations before tax (expense) benefit in Non-US was $119.0 million and $52.0 million, respectively. Income Taxes The Income Tax Provision consisted of the following for the years ended December 31, 2015 and 2014: 2015 2014 Current: U.S. Federal $ — $ — U.S. State and Local Foreign ​ ​ ​ ​ ​ ​ ​ ​ $ $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ A reconciliation of the U.S. statutory income tax rate to the Company's effective tax rate is as follows: December 31, 2015 2014 2013 Federal income tax (benefit) at statutory rate % % % State income tax benefit, net of federal benefit ) ) Permanent differences ) ) ) NOL IRC Section 382 Limitations — ) — Research and development Increase to valuation allowance ) ) Foreign tax rate differential ) ) — Other ) — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Effective income tax rate )% % % ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ The significant components of the Company's deferred tax assets and liabilities at December 31, 2015 and 2014 are as follows: 2015 2014 Deferred tax assets: Accrued Expense $ $ Amortization Depreciation Deferred revenue — Federal tax credits State tax credits Federal net operating losses State net operating losses Capitalized research and development costs Other ​ ​ ​ ​ ​ ​ ​ ​ Total gross deferred tax assets Less valuation allowance ) ) ​ ​ ​ ​ ​ ​ ​ ​ Total deferred tax assets, net of valuation allowance $ $ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Deferred tax liabilities: Convertible debt $ ) $ — ​ ​ ​ ​ ​ ​ ​ ​ Total gross deferred tax assets ) — ​ ​ ​ ​ ​ ​ ​ ​ Net deferred tax assets (liabilities) $ — $ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ At December 31, 2015 and 2014, the Company recorded a full valuation allowance against its net deferred tax assets of approximately $139.6 million and $123.3 million, respectively. The change in the valuation allowance during the years ended December 31, 2015 and 2014 was approximately $16.3 million and $9.2 million, respectively. A full valuation allowance has been recorded since, in the judgment of management, these assets are not more likely than not to be realized. The ultimate realization of deferred tax assets is dependent upon the generation of future taxable income during periods in which those temporary differences and carryforwards become deductible or are utilized. As of December 31, 2015, the Company has approximately $270.4 million and $198.1 million of federal and state net operating loss carryforwards, respectively. As a result of realization requirements of the guidance issued by the FASB, certain deferred tax assets that arose directly from tax deductions related to equity compensation in excess of compensation recognized for financial reporting are excluded from the total deferred tax assets. As of December 31, 2015, approximately $49.2 million of the federal net operating loss carryforwards are related to the exercise of employee stock options and vesting of restricted stock, and the Company will record a tax benefit of approximately of $16.7 million through capital in excess of par value if such losses are realized. As of December 31, 2015, research and development credit carryforwards for federal and state purposes are approximately $11.0 million and $4.8 million, respectively. In addition , the Orphan Drug Credit Carryover available as of December 31, 2015 is approximately $39.8 million. The federal net operating loss carryforwards begin to expire in 2021, while the federal credit carryforwards begin to expire in 2019. State net operating loss carryforwards begin to expire in 2030, and the state credit carryforwards begin to expire in 2016. Sections 382 and 383 of the Internal Revenue Code of 1986 subject the future utilization of net operating losses and certain other tax attributes, such as research and development tax credits, to an annual limitation in the event of certain ownership changes, as defined. The Company has undergone an ownership change and has determined that a "change in ownership" as defined by IRC Section 382 of the Internal Revenue Code of 1986, as amended, and the rules and regulations promulgated thereunder, did occur in June of 2013. Accordingly, about $231.5 million of the Company's NOL carryforwards are limited and the Company can only use $16.7 million for the first five years from the ownership change and $5.7 million per year going forward. Therefore, $169.2 million of the NOL's will be freed up over the next 20 years and $62.3 million are expected to expire unused which are not included in the deferred tax assets listed above. In summary, there are $270.4 million of NOLs available, out of which $169.2 million are limited by IRC Section 382. At December 31, 2015, there is $142.9 million available for immediate use and an additional $16.7 million will free up in 2016. The income tax expense and benefit for the years ended December 31, 2015 and 2014 differed from the amounts computed by applying the U.S. federal income tax rate of 34% to loss before tax expense and benefit as a result of foreign taxes, nondeductible expenses, tax credits generated, true up of net operating loss carryforwards, and increases in the Company's valuation allowance. The Company applies the elements of FASB ASC 740-10 regarding accounting for uncertainty in income taxes. This clarifies the accounting for uncertainty in income taxes recognized in financial statements and required impact of a tax position to be recognized in the financial statements if that position is more likely than not of being sustained by the taxing authority. As of December 31, 2015 the company did not have any unrecognized tax benefits and has not accrued any interest or penalties through 2015. The Company does not expect to have any unrecognized tax benefits within the next twelve months. The Company's policy is to recognize interest and penalties related to tax matters within the income tax provision. Tax years beginning in 2012 are generally subject to examination by taxing authorities, although net operating losses from all years are subject to examinations and adjustments for at least three years following the year in which the attributes are used. For all years through December 31, 2015, the Company generated research credits but has not conducted a study to document the qualified activities. This study may result in an adjustment to the Company's research and development credit carryforwards; however, until a study is completed and any adjustment is known, no amounts are being presented as an uncertain tax position. A full valuation allowance has been provided against the Company's research and development credits and, if an adjustment is required, this adjustment would be offset by an adjustment to the deferred tax asset established for the research and development credit carryforwards and the valuation allowance.

Commitments and contingencies

Commitments and contingencies	12 Months Ended
	Dec. 31, 2015
Commitments and contingencies
Commitments and contingencies	13. Commitments and contingencies Operating leases The Company leases office space under a noncancelable operating lease through February 2019. Rent expense was approximately $1.8 million, $0.9 million, and $0.7 million for the years ended December 31, 2015, 2014, and 2013, respectively. The Company also leases certain office equipment under operating leases. Future minimum lease payments as of December 31, 2015 are as follows: 2016 $ 2017 2018 2019 2020 — Thereafter — ​ ​ ​ ​ ​ $ ​ ​ ​ ​ ​ Other contingencies Under various agreements, the Company will be required to pay royalties and milestone payments upon the successful development and commercialization of products. The Company has entered into funding agreements with The Wellcome Trust Limited (Wellcome Trust) for the research and development of small molecule compounds. To the extent that the Company develops and commercializes program intellectual property on a for-profit basis, it may become obligated to pay to Wellcome Trust development and regulatory milestone payments of up to an aggregate of $68.9 million and single-digit royalties on sales of any research program product. The Company's obligation to pay such royalties would continue on a country-by-country basis until the longer of the expiration of the last patent in the program intellectual property in such country covering the research program product and the expiration of market exclusivity of such product in such country. The Company's first such milestone payment of $0.8 million payable to Wellcome Trust is expected to occur in the second quarter of 2016. The Company has also entered into a collaboration agreement with the SMA Foundation. The Company may become obligated to pay the SMA Foundation single- digit royalties on worldwide net product sales of any collaboration product that we successfully develop and subsequently commercialize or, if we outlicense rights to a collaboration product, a specified percentage of certain payments we receive from our licensee. The Company is not obligated to make such payments unless and until annual sales of a collaboration product exceed a designated threshold. The Company's obligation to make such payments would end upon our payment to the SMA Foundation of a specified amount. The Company has employment agreements with certain employees which require the funding of a specific level of payments, if certain events, such as a change in control or termination without cause, occur.

Geographic information

Geographic information	12 Months Ended
	Dec. 31, 2015
Geographic information
Geographic information	14. Geographic information The Company views its operations and manages its business in one operating segment. The following table presents financial information based on the geographic location of the facilities of the Company as of and for the years ended: Year ended December 31, 2015 United States Non-US Total Total assets $ $ $ Property and equipment, net $ $ $ Revenue $ $ $ Year ended December 31, 2014 United States Non-US Total Total assets $ $ $ Property and equipment, net $ $ $ Revenue $ $ — $

401(k) plan

401(k) plan	12 Months Ended
	Dec. 31, 2015
401(k) plan
401(k) plan	15. 401(k) plan The Company maintains a 401(k) plan for its employees. Employee contributions are voluntary. The Company may match employee contributions in amounts to be determined at the Company's sole discretion. The Company provides a 50% matching contribution for up to the first 6% of each contributing employee's base salary contributions. The Company made matching contributions to the 401(k) plan and recorded expense of approximately $0.7 million, $0.3 million and $0.1 million for the years ended December 31, 2015, 2014 and 2013, respectively.

Subsequent events

Subsequent events	12 Months Ended
	Dec. 31, 2015
Subsequent events
Subsequent events	16. Subsequent events On February 22, 2016, the Company received a Refuse to File letter from the United States Food and Drug Administration, or FDA. The letter stated that the New Drug Application, or NDA, submitted by the Company in December 2015 for Translarna for the treatment of nonsense mutation Duchenne muscular dystrophy was not sufficiently complete to permit a substantive review. The Company intends to engage in dialogue with the FDA to discuss and clarify the matters set forth in the letter and determine our best path forward . On February 2 9 , 2016 , the Company announced that the Company expects to delist Translarna from the German pharmacy ordering system.

Selected quarterly financial da

Selected quarterly financial data (Unaudited)	12 Months Ended
	Dec. 31, 2015
Selected quarterly financial data (Unaudited)
Selected quarterly financial data (Unaudited)	17. Selected quarterly financial data (Unaudited) The following financial information reflects all normal recurring adjustments, which are, in the opinion of management, necessary for a fair statement of the results of the interim periods. Summarized quarterly data for 2015 and 2014 are as follows: For the quarters ending March 31 June 30 September 30 December 31 2015: Net product revenue $ $ $ $ Collaboration and grant revenue Operating expenses Loss from operations ) ) ) ) Net loss ) ) ) ) Basic and diluted net loss per common share(1) $ ) $ ) $ ) $ ) 2014: Net product revenue $ — $ — $ $ Collaboration and grant revenue Operating expenses Loss from operations ) ) ) ) Net loss ) ) ) ) Basic and diluted net loss per common share(1) $ ) $ ) $ ) $ ) (1) The amounts were computed independently for each quarter and the sum of the quarters may not total the annual amounts.

Summary of significant accoun25

Summary of significant accounting policies (Policies)	12 Months Ended
	Dec. 31, 2015
Summary of significant accounting policies
Basis of presentation	Basis of presentation The accompanying consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (GAAP) and include all adjustments necessary for the fair presentation of the Company's financial position for the periods presented.
Use of estimates	Use of estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. Significant estimates in these consolidated financial statements have been made in connection with the calculation of net product sales, certain accruals related to the Company's research and development expenses, stock-based compensation, initial valuation procedures for the issuance of convertible notes and the provision for or benefit from income taxes. Actual results could differ from those estimates. Changes in estimates are reflected in reported results in the period in which they become known.
Consolidation	Consolidation The consolidated financial statements include the accounts of PTC Therapeutics, Inc. and our wholly owned subsidiaries. All inter-company accounts, transactions, and profits have been eliminated in consolidation.
Segment and geographic information	Segment and geographic information Operating segments are defined as components of an enterprise about which separate discrete information is available for evaluation by the chief operating decision maker, or decision making group, in deciding how to allocate resources and in assessing performance. The Company views its operations and manages its business in one operating and reporting segment.
Cash equivalents	Cash equivalents The Company considers all highly liquid investments with a maturity of 90 days or less at the time of purchase to be cash equivalents. Cash equivalents are carried at cost which approximates fair value due to their short-term nature.
Marketable securities	Marketable securities The Company considers securities with original maturities of greater than 90 days to be available for sale securities. Securities under this classification are recorded at fair value and unrealized gains and losses within accumulated other comprehensive income. The estimated fair value of the available for sale securities is determined based on quoted market prices or rates for similar instruments. In addition, the cost of debt securities in this category is adjusted for amortization of premium and accretion of discount to maturity. The Company evaluates securities with unrealized losses to determine whether such losses, if any, are other than temporary.
Fixed assets	Fixed assets Fixed assets are stated at cost. Depreciation is computed starting when the asset is placed into service on a straight-line basis over the estimated useful life of the related asset as follows: Leasehold improvements Lesser of useful life or lease term Computer equipment and software 3 years Furniture, fixtures, and lab equipment 3 to 7 years
Concentration of credit risk	Concentration of credit risk The Company's financial instruments that are exposed to credit risks consist primarily of cash and cash equivalents, available-for-sale marketable securities and accounts receivable. The Company maintains its cash and cash equivalents in bank accounts, which, at times, exceed federally insured limits. The Company has not experienced any credit losses in these accounts and does not believe it is exposed to any significant credit risk on these funds. The Company's investment policy includes guidelines on the quality of the financial institutions and financial instruments the Company is allowed to invest in, which the Company believes minimizes the exposure to concentration of credit risk. The Company is subject to credit risk from its accounts receivable related to its product sales revenue of Translarna. The payment terms are predetermined and the Company evaluates the creditworthiness of each customer or distributor on a regular basis. The Company reserves all uninsured amounts billed directly to a patient until the time of cash receipt as collectability is not reasonably assured at the time the product is received. To date, the Company has not incurred any credit losses.
Inventories and cost of product revenue	Inventories and cost of product revenue In 2014, the Company was notified that the European Commission, or EC, granted conditional marketing authorization for Translarna for the treatment of nmDMD in ambulatory patients aged five years and older. The conditional marketing authorization allows the Company to market Translarna for the treatment of nmDMD in the 31 member states of the European Economic Area. The launch in these countries is on a country by country basis. This marketing authorization is subject to annual review and renewal by the EC following reassessment by the EMA of the risk benefit balance of the authorization. The authorization was further conditioned on the Company's submission of the final report, including additional efficacy and safety data, from ACT DMD and the Company's ability to implement measures, including pharmacovigilance plans that are detailed in the risk management plan for Translarna that was submitted to EMA. In January 2016, the Company submitted the final ACT DMD report to the EMA. In the third quarter of 2015, the EMA approved the annual renewal of the marketing authorization for Translarna for the treatment of nmDMD. The Company plans to seek to renew the marketing authorization on an annual basis until the Company's obligations have been fulfilled and the approval is converted from a conditional approval into a full approval. If the Company fails to satisfy such requirements, or if it is determined that the balance of risks and benefits of using Translarna changes materially, the European Commission could, at the EMA's recommendation, vary, suspend, withdraw or refuse to renew the marketing authorization for Translarna or require additional clinical trials. The Company does not have sufficient history or experience from which to accurately forecast product sales or demand generation, and there continues to be substantial risk that regulators could suspend or not renew the Company's marketing authorization in the future. As such, as of the date of this filing, the Company has not capitalized inventory.
Deferred rent	Deferred rent The Company has an operating lease for office space. Rent expense is recorded on a straight-line basis over the initial lease term. The difference between the actual cash paid and the straight-line rent expense is recorded as deferred rent. Leasehold improvements made related to this lease, subsequent to its inception, are amortized over the remaining lease term.
Accumulated other comprehensive income (loss)	Accumulated other comprehensive income (loss) Accumulated other comprehensive income (loss) consists of unrealized gains or losses on marketable securities and foreign currency translation adjustments.
Revenue recognition	Revenue recognition The Company recognizes revenue when amounts are realized or realizable and earned. Revenue is considered realizable and earned when the following criteria are met: (1) persuasive evidence of an arrangement exists; (2) delivery has occurred or services have been rendered; (3) the price is fixed or determinable; and (4) collection of the amounts due are reasonably assured. Net Product Sales The Company's net product sales have consisted solely of sales of Translarna for the treatment of nmDMD in territories outside of the U.S. The Company began recognizing revenue for payments received under the reimbursed EAPs for Translarna in nmDMD patients in select countries in the third quarter of 2014. The Company has now established a pattern of collectability and, since January 2015, the Company recognizes revenue from product sales when there is persuasive evidence that an arrangement exists, title to product and associated risk of loss has passed to the customer, the price is fixed or determinable, collectability is reasonably assured and the Company has no further performance obligations in accordance with Financial Accounting Standards Board ("FASB") Accounting Standards Codification ("ASC") Subtopic 605-15, Revenue Recognition—Products. The Company has recorded revenue on sales where Translarna is available either on a commercial basis or through a reimbursed EAP program. Orders for Translarna are generally received from hospital and retail pharmacies and, in some cases, one of the Company's third-party partner distributors. The Company's third-party distributors act as intermediaries between the Company and end users and do not typically stock significant quantities of Translarna. The ultimate payor for Translarna is typically a government authority or institution or a third-party health insurer. Prior to January 1, 2015, the Company generally recognized revenue for these reimbursed EAP programs once the product was shipped on behalf of the government authority or institution on a cash basis if all other revenue recognition criteria had been met. Beginning in the first quarter of 2015, the Company has recognized revenue for Translarna as product is shipped, as the Company has established a pattern of collectability. The Company records revenue net of estimated third party discounts and rebates. Allowances are recorded as a reduction of revenue at the time revenues from product sales are recognized. Allowances for government and other third-party rebates and discounts are established or estimated at the time of delivery. These allowances are adjusted to reflect known changes in factors and may impact such allowances in the quarter those changes are known. Collaboration and Grant Revenue The terms of these agreements typically include payments to the Company of one or more of the following: nonrefundable, upfront license fees; milestone payments; research funding and royalties on future product sales. In addition, the Company generates service revenue through agreements that generally provide for fees for research and development services and may include additional payments upon achievement of specified events. The Company evaluates all contingent consideration earned, such as a milestone payment, using the criteria as provided by the Financial Accounting Standards Board (FASB), guidance on the milestone method of revenue recognition. At the inception of a collaboration arrangement, the Company evaluates if a milestone payment is substantive. The criteria requires that (1) the Company determines if the milestone is commensurate with either its performance to achieve the milestone or the enhancement of value resulting from our activities to achieve the milestone; (2) the milestone be related to past performance; and (3) the milestone be reasonable relative to all deliverable and payment terms of the collaboration arrangement. If these criteria are met then the contingent milestones can be considered a substantive milestone and will be recognized as revenue in the period that the milestone is achieved. The Company recognizes royalties as earned in accordance with the terms of various research and collaboration agreements. If not substantive, the contingent consideration is allocated to the existing units of accounting based on relative selling price and recognized following the same basis previously established for the associated unit of accounting. The Company recognizes revenue for reimbursements of research and development costs under collaboration agreements as the services are performed. The Company records these reimbursements as revenue and not as a reduction of research and development expenses as the Company has the risks and rewards as the principal in the research and development activities.
Research and development costs	Research and development costs Research and development expenses include the clinical development costs associated with the Company's product development programs and research and development costs associated with the Company's discovery programs. These expenses include internal research and development costs and the costs of research and development conducted on behalf of the Company by third parties, including sponsored university-based research agreements and clinical study vendors. All research and development costs are expensed as incurred. Costs incurred in obtaining technology licenses are charged immediately to research and development expense if the technology licensed has not reached technological feasibility and has no alternative future uses. Nonrefundable advance payments made for goods and services that will be used in future research and development activities are deferred if the contracted party has not yet performed the related activities. The amount deferred is then recognized as expense when the research and development activities are performed. The deferred research and development advance payments were $0.6 and $0.9 million as of December 31, 2015 and 2014, respectively.
Fair value of financial instruments	Fair value of financial instruments The Company follows the fair value measurement rules, which provides guidance on the use of fair value in accounting and disclosure for assets and liabilities when such accounting and disclosure is called for by other accounting literature. These rules establish a fair value hierarchy for inputs to be used to measure fair value of financial assets and liabilities. This hierarchy prioritizes the inputs to valuation techniques used to measure fair value into three levels: Level 1 (highest priority), Level 2, and Level 3 (lowest priority). · Level 1—Unadjusted quoted prices in active markets for identical assets or liabilities that the Company has the ability to access at the balance sheet date. · Level 2—Inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly. Level 2 inputs include quoted prices for similar assets and liabilities in active markets, quoted prices for identical or similar assets or liabilities in markets that are not active, inputs other than quoted prices that are observable for the asset or liability (i.e., interest rates, yield curves, etc.), and inputs that are derived principally from or corroborated by observable market data by correlation or other means (market corroborated inputs). · Level 3—Inputs are unobservable and reflect the Company's assumptions as to what market participants would use in pricing the asset or liability. The Company develops these inputs based on the best information available. Cash equivalents and investments are reflected in the accompanying financial statements at fair value. The carrying amount of receivables and accounts payable and accrued expenses approximates fair value due to the short-term nature of those instruments.
Beneficial conversion	Beneficial conversion When the Company issues a debt or an equity security that is convertible into common stock at a discount from the fair value of the common stock at the date the debt or equity security counterparty is legally committed to purchase such a security (Commitment Date), a beneficial conversion charge is measured and recorded on the Commitment Date for the difference between the fair value of the Company's common stock and the effective conversion price of the convertible debt or equity security. If the intrinsic value of the beneficial conversion feature is greater than the proceeds allocated to the convertible debt or equity security, the amount of the discount assigned to the beneficial conversion feature is limited to the amount of the proceeds allocated to the convertible debt or equity security. The amount allocated to the beneficial conversion feature is presented as a discount or reduction to the related debt security or as an immediate charge to earnings available to common shareholders for convertible preferred stock instruments that are convertible by the shareholders at any time.
Warrant liability	Warrant liability Warrants to purchase the Company's common stock with nonstandard antidilution provisions, regardless of the probability or likelihood that may conditionally obligate the issuer to ultimately transfer assets, are classified as liabilities and are recorded at their estimated fair value at each reporting period. Any change in fair value of these warrants is recorded as gain/(loss) on warrant valuation each reporting period in Other income/(expense) on the Company's statement of operations.
Impairment of long-lived assets	Impairment of long-lived assets The Company monitors its long-lived assets for indicators of impairment. If such indicators are present, the Company assesses the recoverability of affected assets by determining whether the carrying value of such assets is less than the sum of the undiscounted future cash flows of the assets. If such assets are found not to be recoverable, the Company measures the amount of such impairment by comparing the carrying value of the assets to the fair value of the assets, with the fair value generally determined based on the present value of the expected future cash flows associated with the assets. Although current and historical negative cash flows are indicators of impairment, management believes the future cash flows to be received from the long-lived assets and the potential success of the Company's research programs will exceed the assets' carrying value, and accordingly, the Company believes that no impairment of long-lived assets exists as of December 31, 2015.
Share-based compensation	Share-based compensation The Company measures the cost of employee services received in exchange for an award of equity instruments based on the grant date fair value of the award. Restricted stock awards are measured based on the fair market values of the underlying stock on the dates of grant. For service type awards, share-based compensation expense is recognized on a straight-line basis over the period during which the employee is required to provide service in exchange for the entire award. For awards that vest or begin vesting upon achievement of a performance condition, the Company estimates the likelihood of satisfaction of the performance condition and recognizes compensation expense when achievement of the performance condition is deemed probable using an accelerated attribution model. The fair value of options is calculated using the Black-Scholes option pricing model to determine the fair value of stock options on the date of grant based on key assumptions such as expected volatility and expected term. As a new public company, the Company does not have sufficient history to estimate the volatility of its common stock price or the expected life of the options. The Company calculates expected volatility based on reported data for similar publicly traded companies for which historical information is available and will continue to do so until the historical volatility of its common stock is sufficient to measure expected volatility for future option grants.
Income taxes	Income taxes Deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases and net operating loss and credit carryforwards. Deferred tax assets and liabilities are measured at rates expected to apply to taxable income in the years in which those temporary differences and carryforwards are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in the statement of operations in the period that includes the enactment date. A valuation allowance is recorded when it is not more likely than not that all or a portion of the net deferred tax assets will be realized. The Company recognized a tax benefit of $4.9 million related to the sale of net operating losses in the New Jersey Technology Business Tax Certificate Transfer Program for the year ended December 31, 2014. The Company did not participate in this program during the years ended December 31, 2015 and 2013.
Net (loss) income per share	Net (loss) income per share Basic net income per share is calculated by dividing the net income attributable to common stockholders by the weighted average number of common shares outstanding for the period, without consideration for common stock equivalents. Diluted net income per share is calculated by dividing the net income attributable to common stockholders by the weighted-average number of common share equivalents outstanding for the period determined using the treasury-stock method and the if-converted method. During periods in which the Company incurs net losses, both basic and diluted loss per share is calculated by dividing the net loss by the weighted average shares outstanding—potentially dilutive securities are excluded from the calculation because their effect would be anti-dilutive. Dilutive common stock equivalents are comprised of convertible preferred stock and options outstanding under the Company's stock option plans.
Recent accounting pronouncements	Recent accounting pronouncements In May 2014, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2014-09, Revenue from Contracts with Customers. ASU 2014-09 will eliminate transaction- and industry-specific revenue recognition guidance under current GAAP and replace it with a principle-based approach for determining revenue recognition. ASU 2014-09 will require that companies recognize revenue based on the value of transferred goods or services as they occur in the contract. The ASU also will require additional disclosure about the nature, amount, timing and uncertainty of revenue and cash flows arising from customer contracts, including significant judgments and changes in judgments and assets recognized from costs incurred to obtain or fulfill a contract. ASU 2014-09 is effective for annual reporting periods beginning after December 15, 201 7 . Early application is not permitted. Entities can transition to the standard either retrospectively or as a cumulative-effect adjustment as of the date of adoption. Presently, the Company is assessing what effect the adoption of ASU 2014-09 will have on its financial statements and accompanying notes. In April 2015, the FASB issued ASU 2015-03, Interest—Imputation of Interest, Simplifying the Presentation of Debt Issuance Costs topic of the Codification. This standard provides a simplified presentation of debt issuance costs and requires that debt issuance costs related to a recognized debt liability to be presented on the balance sheet as a direct deduction from the carrying amount of that debt liability, consistent with debt discounts. The standard is effective for public companies for annual periods beginning after December 15, 2015. The Company's unamortized debt issuance cost at December 31, 2015 was $2.8 million which is included within "Deposits and other assets" on the consolidated balance sheet. Upon adoption, the Company expects that the carrying value of its debt liability will decrease by the value associated with the unamortized debt cost. In November 2015, the FASB issued ASU 2015-17, Income Taxes, Balance Sheet Classification of Deferred Taxes topic of the Codification. This standard requires all deferred tax assets and liabilities to be classified as non-current on the balance sheet instead of separating deferred taxes into current and non-current amounts. In addition, valuation allowance allocations between current and non-current deferred tax assets are no longer required because those allowances also will be classified as non-current. This standard is effective for public companies for annual periods beginning after December 15, 2016. The Company's deferred tax assets is provided with full valuation allowance as of December 31, 2015. As such, the Company does not expect that this standard will have a significant impact upon adoption.

Summary of significant accoun26

Summary of significant accounting policies (Tables)	12 Months Ended
	Dec. 31, 2015
Summary of significant accounting policies
Schedule of estimated useful life of related assets	Leasehold improvements Lesser of useful life or lease term Computer equipment and software 3 years Furniture, fixtures, and lab equipment 3 to 7 years

Fair value of financial instr27

Fair value of financial instruments and investments (Tables)	12 Months Ended
	Dec. 31, 2015
Fair value of financial instruments and investments
Schedule of financial assets and liabilities that are required to be measured at fair value on a recurring basis	December 31, 2015 Total Quoted prices in active markets for identical assets (level 1) Significant other observable inputs (level 2) Significant unobservable inputs (level 3) Marketable securities $ $ — $ $ — Warrant liability — — December 31, 2014 Total Quoted prices in active markets for identical assets (level 1) Significant other observable inputs (level 2) Significant unobservable inputs (level 3) Marketable securities $ $ — $ $ — Warrant Liability — —
Summary of marketable securities accounted for as available-for-sale securities	December 31, 2015 Gross Unrealized Amortized Cost Fair Value Gains Losses Commercial paper $ $ $ — $ Corporate debt securities — ) Government obligations ) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ $ $ $ ) $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2014 Gross Unrealized Amortized Cost Fair Value Gains Losses Corporate debt securities $ $ $ ) $ Government obligations ) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ $ $ $ ) $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​
Schedule of marketable securities on the balance sheet	December 31, 2015 Less Than 12 Months More Than 12 Months Commercial paper $ $ — Corporate debt securities Government obligations ​ ​ ​ ​ ​ ​ ​ ​ Total Marketable securities $ $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2014 Less Than 12 Months More Than 12 Months Corporate debt securities $ $ Government obligations ​ ​ ​ ​ ​ ​ ​ ​ Total Marketable securities $ $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​
Summary of changes in the fair value of the Company's Level 3 valuation for warrant liability	Level 3 assets Beginning balance as of January 1, 2014 $ Change in fair value of warrant liability ​ ​ ​ ​ ​ Ending balance as of December 31, 2014 $ Change in fair value of warrant liability ) ​ ​ ​ ​ ​ Ending balance as of December 31, 2015 $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

Fixed assets (Tables)

Fixed assets (Tables)	12 Months Ended
	Dec. 31, 2015
Fixed assets
Schedule of fixed assets, net	December 31, 2015 2014 Leasehold improvements $ $ Computer equipment and software Furniture, fixtures, and lab equipment Assets in process ​ ​ ​ ​ ​ ​ ​ ​ Less accumulated depreciation and amortization ) ) ​ ​ ​ ​ ​ ​ ​ ​ $ $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

Accounts payable and accrued 29

Accounts payable and accrued expenses (Tables)	12 Months Ended
	Dec. 31, 2015
Accounts payable and accrued expenses
Schedule of components of accounts payable and accrued expenses	December 31, 2015 2014 Employee compensation, benefits, and related accruals $ $ Consulting and contracted research Professional fees Accounts payable Other ​ ​ ​ ​ ​ ​ ​ ​ $ $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

Long-term Debt (Tables)

Long-term Debt (Tables)	12 Months Ended
	Dec. 31, 2015
Long-term debt.
Summary of convertible notes	Year ended December 31 Liability component 2015 2014 Principal $ $ — Less: Debt discount, net (1) ) — ​ ​ ​ ​ ​ ​ ​ ​ Net carrying amount $ $ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (1) Included in the consolidated balance sheets within convertible senior notes (due 2022) and amortized to interest expense over the remaining life of the Convertible Notes using the effective interest rate method.
Summary of interest expense recognized related to the Convertible Notes	Year ended December 31, 2015 2014 Contractual interest expense $ $ — Amortization of debt issuance costs — Amortization of debt discount — ​ ​ ​ ​ ​ ​ ​ ​ Total $ $ — ​ ​ ​ ​ ​ ​ ​ ​ Effective interest rate of the liability component % —

Capital structure (Tables)

Capital structure (Tables)	12 Months Ended
	Dec. 31, 2015
Capital structure
Summary of the Company's outstanding warrants	The following is a summary of the Company's outstanding warrants as of December 31, 2015 and 2014: Warrant shares Exercise price Expiration Common stock $ Common stock $ Common stock $

Earnings per share (Tables)

Earnings per share (Tables)	12 Months Ended
	Dec. 31, 2015
Earnings per share
Schedule of computation of basic and diluted net loss per share for common stockholders	Year ended December 31, 2015 2014 2013 Numerator Net loss $ ) $ ) $ ) Deemed dividend — — ) Gain on exchange of convertible preferred stock in connection with recapitalization — — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net loss attributable to common stockholders $ ) $ ) $ ) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Denominator Denominator for basic and diluted net loss per share ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net loss per share: Basic and diluted $ )* $ )* $ )* ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ * For the years ended December 31, 2015, 2014, and 2013, the Company experienced a net loss and therefore did not report any dilutive share impact.
Schedule of historical dilutive common share equivalents outstanding	As of December 31, 2015 2014 2013 Stock Options Unvested restricted stock ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Total ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

Stock award plan (Tables)

Stock award plan (Tables)	12 Months Ended
	Dec. 31, 2015
Stock award plan
Summary of stock option activity	Number of options Weighted- average exercise price Weighted- average remaining contractual term Aggregate intrinsic value (in thousands) Outstanding at December 31, 2012 $ Granted $ Exercised — $ — Forfeited ) $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Outstanding at December 31, 2013 $ Granted $ Exercised ) $ Forfeited ) $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Outstanding at December 31, 2014 $ Granted $ Exercised ) $ Forfeited ) $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Outstanding at December 31, 2015 $ 8.38 years $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Vested or Expected to vest at December 31, 2015 $ 8.65 years $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Exercisable at December 31, 2015 $ 7.67 years $
Schedule of assumptions used to estimate fair values of grants made on the date of grant	2015 2014 2013 Risk-free interest rate 1.48 - 2.18% 0.11 - 2.04% 0.85 - 1.90% Expected volatility 67 - 69% 70 - 91% 87 - 89% Expected term 5.50 - 9.12 years 5.50 - 6.25 years 6.00 - 6.25 years
Summary of information on the Company's restricted stock	Restricted Stock Number of Shares Weighted Average Grant Date Fair Value January 1, 2015 $ Granted — $ — Vested ) $ Forfeited ) $ ​ ​ ​ ​ ​ ​ ​ ​ Unvested at December 31, 2015 $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​
Schedule of share-based compensation expense recorded in the statement of operations	Year ended December 31, 2015 2014 2013 Research and development $ $ $ Selling, general and administrative ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Total $ $ $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

Other comprehensive income (l34

Other comprehensive income (loss) and accumulated other comprehensive items (Tables)	12 Months Ended
	Dec. 31, 2015
Other comprehensive income (loss) and accumulated other comprehensive items
Summary of other comprehensive income (loss) and the changes in accumulated other comprehensive items	Unrealized Gains/(Losses) On Marketable Securities Foreign Currency Translation Total Accumulated Other Comprehensive Items Balance at December 31, 2012 $ — $ — $ — Other comprehensive income before reclassifications — Amounts reclassified from other comprehensive items — — — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Other comprehensive income — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Balance at December 31, 2013 $ $ — $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Other comprehensive loss before reclassifications ) ) ) Amounts reclassified from other comprehensive items — — — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Other comprehensive loss ) ) ) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Balance at December 31, 2014 $ ) $ ) $ ) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Other comprehensive loss before reclassifications ) ) ) Amounts reclassified from other comprehensive items — — — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Other comprehensive loss ) ) ) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Balance at December 31, 2015 $ ) $ ) $ ) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

Income taxes (Tables)

Income taxes (Tables)	12 Months Ended
	Dec. 31, 2015
Income taxes
Components of Income Tax Provision	2015 2014 Current: U.S. Federal $ — $ — U.S. State and Local Foreign ​ ​ ​ ​ ​ ​ ​ ​ $ $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​
Schedule of reconciliation of the U.S. statutory income tax rate to the Company's effective tax rate	December 31, 2015 2014 2013 Federal income tax (benefit) at statutory rate % % % State income tax benefit, net of federal benefit ) ) Permanent differences ) ) ) NOL IRC Section 382 Limitations — ) — Research and development Increase to valuation allowance ) ) Foreign tax rate differential ) ) — Other ) — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Effective income tax rate )% % % ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​
Schedule of significant components of the Company's deferred tax assets and liabilities	2015 2014 Deferred tax assets: Accrued Expense $ $ Amortization Depreciation Deferred revenue — Federal tax credits State tax credits Federal net operating losses State net operating losses Capitalized research and development costs Other ​ ​ ​ ​ ​ ​ ​ ​ Total gross deferred tax assets Less valuation allowance ) ) ​ ​ ​ ​ ​ ​ ​ ​ Total deferred tax assets, net of valuation allowance $ $ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Deferred tax liabilities: Convertible debt $ ) $ — ​ ​ ​ ​ ​ ​ ​ ​ Total gross deferred tax assets ) — ​ ​ ​ ​ ​ ​ ​ ​ Net deferred tax assets (liabilities) $ — $ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

Commitments and contingencies (

Commitments and contingencies (Tables)	12 Months Ended
	Dec. 31, 2015
Commitments and contingencies
Schedule of future minimum lease payments	Future minimum lease payments as of December 31, 2015 are as follows: 2016 $ 2017 2018 2019 2020 — Thereafter — ​ ​ ​ ​ ​ $ ​ ​ ​ ​ ​

Geographic information (Tables)

Geographic information (Tables)	12 Months Ended
	Dec. 31, 2015
Geographic information
Summary of financial information based on geographical location	Year ended December 31, 2015 United States Non-US Total Total assets $ $ $ Property and equipment, net $ $ $ Revenue $ $ $ Year ended December 31, 2014 United States Non-US Total Total assets $ $ $ Property and equipment, net $ $ $ Revenue $ $ — $

Selected quarterly financial 38

Selected quarterly financial data (Tables)	12 Months Ended
	Dec. 31, 2015
Selected quarterly financial data (Unaudited)
Summary of quarterly data	For the quarters ending March 31 June 30 September 30 December 31 2015: Net product revenue $ $ $ $ Collaboration and grant revenue Operating expenses Loss from operations ) ) ) ) Net loss ) ) ) ) Basic and diluted net loss per common share(1) $ ) $ ) $ ) $ ) 2014: Net product revenue $ — $ — $ $ Collaboration and grant revenue Operating expenses Loss from operations ) ) ) ) Net loss ) ) ) ) Basic and diluted net loss per common share(1) $ ) $ ) $ ) $ ) (1) The amounts were computed independently for each quarter and the sum of the quarters may not total the annual amounts.

The Company (Detail)

The Company (Detail) $ in Thousands	Aug. 04, 2014	Aug. 31, 2014stateitem	Dec. 31, 2015USD ($)country	Aug. 31, 2015	Dec. 31, 2014USD ($)
Minimum age of ambulatory patient	5 years	5 years
Number of States In European Economic Area | state		31
Period of placebo controlled clinical trail		336 days
Number of patients tested in placebo controlled clinical trail | item		174
Number of countries made availability of Translama on a commercial basis | country			17
Accumulated deficit. | $			$ (592,998)		$ (422,551)
3.00% Convertible senior notes due 2022 | Convertible debt
Interest rate				3.00%

Summary of significant accoun40

Summary of significant accounting policies (Detail)	12 Months Ended
	Dec. 31, 2015item
Segment and geographic information
Number of operating segments	1
Computer equipment and software
Fixed assets
Estimated useful life	3 years
Furniture, fixtures, and lab equipment | Minimum
Fixed assets
Estimated useful life	3 years
Furniture, fixtures, and lab equipment | Maximum
Fixed assets
Estimated useful life	7 years

Summary of significant accoun41

Summary of significant accounting policies (Details 2) $ in Thousands	Aug. 04, 2014state	Aug. 31, 2014	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)
Research and development costs
Minimum age of Ambulatory Patient	5 years	5 years
Number of States | state	31
Deferred research and development advance payments			$ 600	$ 900
Impairment of long-lived assets
Impairment of long-lived assets			0
Income Tax Expense (Benefit), Continuing Operations
Income tax (expense) benefit			(485)	4,693
Recent accounting pronouncements
Unamortized debt issuance cost			$ 2,800
New Jersey
Income Tax Expense (Benefit), Continuing Operations
Income tax (expense) benefit				$ 4,900

Fair value of financial instr42

Fair value of financial instruments and marketable securities (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Financial assets and liabilities measured at fair value on recurring basis
Marketable securities	$ 280,903	$ 265,493
Recurring basis | Total
Financial assets and liabilities measured at fair value on recurring basis
Marketable securities	280,903	265,493
Warrant liability	48	188
Recurring basis | Significant other observable inputs (level 2)
Financial assets and liabilities measured at fair value on recurring basis
Marketable securities	280,903	265,493
Recurring basis | Significant unobservable inputs (level 3)
Financial assets and liabilities measured at fair value on recurring basis
Warrant liability	$ 48	$ 188

Fair value of financial instr43

Fair value of financial instruments and marketable securities (Details 2) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Marketable securities accounted for as available-for-sale securities
Amortized Cost	$ 281,492	$ 265,880
Gross Unrealized Gains	83	87
Gross Unrealized Losses	(672)	(474)
Marketable securities	280,903	265,493
Transfers of assets between Level 1 and Level 2 of the fair value measurement hierarchy	0
Commercial paper
Marketable securities accounted for as available-for-sale securities
Amortized Cost	26,877
Gross Unrealized Gains	80
Marketable securities	26,957
Corporate debt securities
Marketable securities accounted for as available-for-sale securities
Amortized Cost	226,959	230,379
Gross Unrealized Gains		80
Gross Unrealized Losses	(640)	(428)
Marketable securities	226,319	230,031
Government obligations
Marketable securities accounted for as available-for-sale securities
Amortized Cost	27,656	35,501
Gross Unrealized Gains	3	7
Gross Unrealized Losses	(32)	(46)
Marketable securities	$ 27,627	$ 35,462

Fair value of financial instr44

Fair value of financial instruments and marketable securities (Details 3) - USD ($) $ in Thousands	Dec. 31, 2015	Aug. 31, 2015	Dec. 31, 2014
Marketable securities on the balance sheet
Total Marketable securities, Less Than 12 Months	$ 186,782		$ 163,761
Total Marketable securities, More Than 12 Months	94,121		101,732
Commercial paper
Marketable securities on the balance sheet
Total Marketable securities, Less Than 12 Months	26,957
Corporate debt securities
Marketable securities on the balance sheet
Total Marketable securities, Less Than 12 Months	140,831		157,758
Total Marketable securities, More Than 12 Months	85,488		72,273
Government obligations
Marketable securities on the balance sheet
Total Marketable securities, Less Than 12 Months	18,994		6,003
Total Marketable securities, More Than 12 Months	8,633		$ 29,459
3.00% Convertible senior notes due 2022 | Convertible debt
Marketable securities on the balance sheet
Principal amount of Notes	$ 150,000	$ 150,000
Interest rate		3.00%

Fair value of financial instr45

Fair value of financial instruments and marketable securities (Details 4) - Warrants - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Changes in the fair value of warrant liability
Beginning balance	$ 188	$ 58
Change in fair value of warrant liability	(140)	130
Ending balance	$ 48	$ 188
Minimum
Assumption used to estimate the fair value of warrant liability by utilizing the Black-Scholes option-pricing model
Volatility (as a percent)	62.00%	68.00%
Risk-free interest rate (as a percent)	0.86%	0.89%
Strike price (in dollars per share)	$ 128	$ 128
Expected life	1 year 6 months	2 years 6 months
Maximum
Assumption used to estimate the fair value of warrant liability by utilizing the Black-Scholes option-pricing model
Volatility (as a percent)	70.00%	70.00%
Risk-free interest rate (as a percent)	1.54%	1.65%
Strike price (in dollars per share)	$ 2,520	$ 2,520
Expected life	3 years 8 months 12 days	4 years 8 months 12 days
Common stock
Assumption used to estimate the fair value of warrant liability by utilizing the Black-Scholes option-pricing model
Fair value of shares (in dollars per share)	$ 32.40	$ 51.77

Fixed assets (Details)

Fixed assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Fixed assets
Gross fixed assets	$ 36,676	$ 34,076
Less accumulated depreciation and amortization	(27,702)	(24,917)
Net fixed assets	8,974	9,159
Depreciation expense	2,876	2,235	$ 2,396
Leasehold improvements
Fixed assets
Gross fixed assets	14,029	13,051
Computer equipment and software
Fixed assets
Gross fixed assets	4,102	2,472
Furniture, fixtures, and lab equipment
Fixed assets
Gross fixed assets	17,443	15,070
Assets in process
Fixed assets
Gross fixed assets	$ 1,102	$ 3,483

Accounts payable and accrued 47

Accounts payable and accrued expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Accounts payable and accrued expenses
Employee compensation, benefits, and related accruals	$ 11,187	$ 9,312
Consulting and contracted research	13,753	9,349
Professional fees	2,523	3,334
Accounts payable	11,940	4,128
Other	5,844	2,998
Accounts payable and accrued expenses	$ 45,247	$ 29,121

Long-term debt (Details)

Long-term debt (Details) $ in Thousands	1 Months Ended			12 Months Ended
	Jul. 31, 2013USD ($)	Dec. 31, 2010USD ($)	Sep. 30, 2009USD ($)item	Dec. 31, 2013USD ($)
Long-term debt
Gains (Losses) on Extinguishment of Debt				$ (130)
Secured debt facility
Long-term debt
Maximum borrowing capacity			$ 25,000
Number of lenders | item			2
Amount borrowed		$ 10,000	$ 12,500
Paid outstanding principal and interest, due under promissory notes issued	$ 2,600

Long-term debt, 2015 Convertibl

Long-term debt, 2015 Convertible Notes (Details 2)	1 Months Ended	12 Months Ended
	Aug. 31, 2015USD ($)item$ / shares	Dec. 31, 2015USD ($)
Long-term debt
Amortization of debt issuance costs		$ 107,000
3.00% Convertible senior notes due 2022 | Convertible debt
Long-term debt
Principal amount of Notes	$ 150,000,000	150,000,000
Less: Debt discount, net		(55,392,000)
Net carrying amount		94,608,000
Interest rate	3.00%
Net proceeds from issuance of convertible notes	$ 145,400,000
Trading days, number | item	20
Consecutive trading days, period	30 days
Stock price trigger (as a percent)	130.00%
Business days, period	5 days
Consecutive trading-day period	5 days
Common stock per principal amount	$ 1,000
Maximum product of the closing sale price of shares of the Company's common stock and the applicable conversion rate for such trading day (as a percent)	98.00%
Conversion ratio	17.7487
Conversion price per share | $ / shares	$ 56.34
Minimum percentage of principal held by convertible debt instrument holders required to issue notice for declaration of principal and unpaid interest payable upon events of default (as a percent)	25.00%
Convertible Instruments Principal And Unpaid Interest Payable Upon Events Of Default	100.00%
Term of the convertible notes	7 years
Net deferred tax liability in connection with convertible notes	$ 22,300,000
Contractual interest expense		1,702,000
Amortization of debt issuance costs		107,000
Debt discount recorded to interest expense		2,146,000
Total		$ 3,955,000
Effective interest rate of the liability component (as a percent)		11.00%
3.00% Convertible senior notes due 2022 | Convertible debt | Redemption on or after August 20, 2018
Long-term debt
Trading days, number | item	19
Consecutive trading days, period	30 days
Stock price trigger (as a percent)	130.00%
Redemption price (as a percent)	100.00%

Capital structure (Details)

Capital structure (Details)	Dec. 31, 2012$ / sharesshares
Capital structure
Par value (in dollars per share) | $ / shares	$ 0.001
Maximum
Capital structure
Shares authorized	29,500,000
Series One convertible preferred stock
Capital structure
Shares authorized	2,000,000
Series Two convertible preferred stock
Capital structure
Shares authorized	13,750,000
Series Three convertible preferred stock
Capital structure
Shares authorized	13,750,000

Capital structure (Details 2)

Capital structure (Details 2) $ / shares in Units, $ in Thousands	Oct. 16, 2014USD ($)$ / sharesshares	Mar. 07, 2013USD ($)shares	Feb. 28, 2014USD ($)$ / sharesshares	Jun. 30, 2013USD ($)$ / sharesshares	May. 31, 2013USD ($)$ / sharesshares	Mar. 31, 2013USD ($)	Dec. 31, 2013USD ($)	Dec. 31, 2015shares	Dec. 31, 2014shares	Feb. 28, 2013USD ($)$ / sharesshares
Capital structure
Gross proceeds raised | $						$ 60,000
Gain on extinguishment of shares of Series One, Two and Three stock | $							$ 3,391
Aggregate purchase price | $							$ 131,650
Common stock
Common stock, authorized shares								125,000,000	125,000,000
Series One and Series Two | Warrants
Capital structure
Warrants issued to purchase shares										2,527,675
Exercise price (in dollars per share) | $ / shares										$ 0.01
Shares issued and sold		2,527,675
Series Four convertible preferred stock
Capital structure
Shares issued and sold		4,497,035			375,000
Aggregate gross proceeds | $		$ 54,000
Share price (in dollars per share) | $ / shares					$ 12
Aggregate purchase price | $					$ 4,500
Series Five convertible preferred stock
Capital structure
Number of shares issued upon conversion		6,700,487
Common stock
Number of shares issued upon conversion		6,700,487
Series Five convertible preferred stock | Warrants
Capital structure
Number of shares issued upon conversion		2,095,515
Common stock
Number of shares issued upon conversion		2,095,515
Common stock
Capital structure
Shares issued and sold	3,450,000		5,163,265	9,627,800
Reverse stock split ratio		0.0083
Public offering price (in dollars per share) | $ / shares	$ 36.25		$ 24.50	$ 15
Common stock
Common stock, authorized shares					125,000,000
Common stock shares issuable pursuant to the exercise by the underwriters of an over-allotment option	450,000		673,469	1,255,800
Net proceeds from public offerings | $	$ 117,600		$ 118,400
Net proceeds from initial public offering | $				$ 131,600
Series Four and Series Five Convertible Preferred Stock
Capital structure
Number of shares issuable upon conversion of each stock				1
Number of shares issued upon conversion				14,170,956
Common stock
Number of shares issued upon conversion				14,170,956
Convertible promissory notes
Capital structure
Principal amount of Notes | $										$ 6,000
Debt discount recorded to interest expense | $						6,000
Amount raised in bridge financing | $						$ 6,000
Convertible promissory notes | Series Four convertible preferred stock
Capital structure
Shares issued upon conversion of convertible promissory notes		502,919

Capital structure (Details 3)

Capital structure (Details 3) - Common stock - $ / shares	Dec. 31, 2015	Dec. 31, 2014
2,017
Class of Warrant or Right [Table]
Warrant shares	6,250	6,250
Exercise price (in dollars per share)	$ 128	$ 128
2,019
Class of Warrant or Right [Table]
Warrant shares	7,030	7,030
Exercise price (in dollars per share)	$ 128	$ 128
2,019
Class of Warrant or Right [Table]
Warrant shares	130	130
Exercise price (in dollars per share)	$ 2,520	$ 2,520

Earnings per share (Details)

Earnings per share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Net loss per share
Total shares excluded from calculation									5,170,812	4,151,372	3,205,818
Numerator
Net loss	$ (50,948)	$ (43,223)	$ (38,361)	$ (37,915)	$ (27,269)	$ (27,282)	$ (25,104)	$ (14,098)	$ (170,447)	$ (93,753)	$ (51,574)
Deemed dividend											(18,249)
Gain on exchange of convertible preferred stock in connection with recapitalization											3,391
Net loss attributable to common stockholders									$ (170,447)	$ (93,753)	$ (66,432)
Denominator
Denominator for basic and diluted net loss per share (in shares)									33,626,248	31,565,310	12,829,411
Net loss per share:
Basic and diluted (in dollars per share)	$ (1.50)	$ (1.27)	$ (1.14)	$ (1.15)	$ (0.84)	$ (0.93)	$ (0.86)	$ (0.58)	$ (5.07)	$ (2.97)	$ (5.18)
Stock options
Net loss per share
Total shares excluded from calculation									4,826,477	3,432,972	2,095,592
Restricted stock
Net loss per share
Total shares excluded from calculation									344,335	718,400	1,110,226

Stock award plan (Details)

Stock award plan (Details) - USD ($) $ / shares in Units, $ in Thousands	Mar. 05, 2013	May. 31, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Stock option plan
Additional compensation recognized due to modifications to the options granted				$ 1,900	$ 600
Stock option
Number of options
Outstanding at the beginning of the period (in shares)			3,432,972	2,095,592	42,394
Granted (in shares)			2,201,800	1,639,996	2,117,113
Exercised (in shares)			(656,248)	(108,645)
Forfeited (in shares)			(152,047)	(193,971)	(63,915)
Outstanding at the end of the period (in shares)			4,826,477	3,432,972	2,095,592
Vested or expected to vest at the end of the period (in shares)			3,266,769
Exercisable at the end of the period (in shares)			1,357,478
Weighted-average exercise price
Outstanding at the beginning of the period (in dollars per share)			$ 25	$ 20.24	$ 474
Granted (in dollars per share)			50.81	31.09	11.29
Exercised (in dollars per share)			13.27	11
Forfeited (in dollars per share)			49.58	32.91	12.57
Outstanding at the end of the period (in dollars per share)			37.20	$ 25	$ 20.24
Vested or expected to vest at the end of the period (in dollars per share)			40.14
Exercisable at the end of the period (in dollars per share)			$ 29.38
Weighted-average remaining contractual term
Outstanding at the end of the period			8 years 4 months 17 days
Vested or expected to vest at the end of the period			8 years 7 months 24 days
Exercisable at the end of the period			7 years 8 months 1 day
Aggregate intrinsic value
Outstanding at the end of the period (in dollars)			$ 32,391
Vested or expected to vest at the end of the period (in dollars)			13,590
Exercisable at the end of the period (in dollars)			$ 18,242
Valuation assumptions
Expected dividend yield (as a percent)			0.00%	0.00%	0.00%
Weighted average grant date fair value (in dollars per share)			$ 50.81	$ 22.39	$ 8.23
Stock option | Minimum
Stock option plan
Vesting period			3 years
Valuation assumptions
Risk-free interest rate (as a percent)			1.48%	0.11%	0.85%
Expected volatility (as a percent)			67.00%	70.00%	87.00%
Expected term			5 years 6 months	5 years 6 months	6 years
Stock option | Maximum
Stock option plan
Vesting period			4 years
Valuation assumptions
Risk-free interest rate (as a percent)			2.18%	2.04%	1.90%
Expected volatility (as a percent)			69.00%	91.00%	89.00%
Expected term			9 years 1 month 13 days	6 years 3 months	6 years 3 months
2009 Equity and Long Term Incentive Plan
Stock option plan
Number of shares available for issuance		0
Number of additional shares authorized		2,500,000
2009 Equity and Long Term Incentive Plan | Stock option | Minimum
Stock option plan
Stock options granted, exercise price as percentage of the fair market value of common stock at grant date			100.00%
Stock options granted to stockholder with specified ownership percentage, exercise price as percentage of the fair market value of common stock at grant date			110.00%
Stockholder's specified ownership percentage			10.00%
2009 Equity and Long Term Incentive Plan | Stock option | Maximum
Stock option plan
Expiration period			10 years
2013 Stock Incentive Plan
Stock option plan
Number of shares available for issuance	0
2013 Stock Incentive Plan | Restricted stock
Stock option plan
Options granted (in shares)	735,324
2013 Stock Incentive Plan | Stock option
Number of options
Granted (in shares)	4,613
2013 Stock Incentive Plan | Common stock
Stock option plan
Number of shares authorized	739,937
2009 Equity and Long Term Incentive Plan and 2013 Stock Incentive Plan | Common stock
Stock option plan
Number of shares available for issuance		122,296
2013 Long Term Incentive Plan | Common stock
Stock option plan
Number of shares available for issuance			266,533
Annual increase in the number of shares outstanding on the first day of the fiscal year (as a percent)		4.00%
2013 Long Term Incentive Plan | Common stock | Minimum
Stock option plan
Annual increase in the number of shares on the first day of the fiscal year		2,500,000
2013 Long Term Incentive Plan | Common stock | Maximum
Stock option plan
Number of shares subject to outstanding awards		3,040,444
Inducement grant plan | Stock option
Number of options
Granted (in shares)			806,600
Forfeited (in shares)			(84,150)
Exercise price
Granted (in dollars per share)			$ 50.46

Stock option plan (Details 2)

Stock option plan (Details 2) - Restricted stock	12 Months Ended
	Dec. 31, 2015$ / sharesshares
Number of Shares
Balance at the beginning of the period (in shares) | shares	718,400
Vested (in shares) | shares	(361,919)
Forfeited (in shares) | shares	(12,146)
Balance at the end of the period (in shares) | shares	344,335
Weighted Average Grant Date Fair Value
Balance at the beginning of the period (in dollars per share) | $ / shares	$ 10.72
Vested (in dollars per share) | $ / shares	10.60
Forfeited (in dollars per share) | $ / shares	10.84
Balance at the end of the period (in dollars per share) | $ / shares	$ 10.85

Stock award plan (Details 3)

Stock award plan (Details 3) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based compensation expense recorded in the statement of operations
Share-based compensation expense	$ 33,979	$ 19,310	$ 8,427
Unrecognized compensation cost	$ 73,800
Weighted average remaining service period for recognition of unrecognized compensation cost	2 years 8 months 27 days
Research and development
Share-based compensation expense recorded in the statement of operations
Share-based compensation expense	$ 16,138	9,739	4,312
Selling, general and administrative
Share-based compensation expense recorded in the statement of operations
Share-based compensation expense	$ 17,841	$ 9,571	$ 4,115

Other comprehensive income (l57

Other comprehensive income (loss) and accumulated other comprehensive items (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Other comprehensive income (loss) and accumulated other comprehensive items
Balance at the beginning of the period	$ (737)	$ 70
Other comprehensive income/(loss) before reclassifications	(463)	(807)	$ 70
Other comprehensive income/(loss)	(463)	(807)	70
Balance at the end of the period	(1,200)	(737)	70
Unrealized Gains/(Losses) On Marketable Securities
Other comprehensive income (loss) and accumulated other comprehensive items
Balance at the beginning of the period	(387)	70
Other comprehensive income/(loss) before reclassifications	(202)	(457)	70
Other comprehensive income/(loss)	(202)	(457)	70
Balance at the end of the period	(589)	(387)	$ 70
Foreign Currency Translation
Other comprehensive income (loss) and accumulated other comprehensive items
Balance at the beginning of the period	(350)
Other comprehensive income/(loss) before reclassifications	(261)	(350)
Other comprehensive income/(loss)	(261)	(350)
Balance at the end of the period	$ (611)	$ (350)

Collaborations and grants (Deta

Collaborations and grants (Details) $ in Millions	Jan. 02, 2011item	Nov. 30, 2014USD ($)	Jan. 31, 2014USD ($)	Nov. 30, 2011USD ($)item	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)
Minimum
Grant revenue
Term of grant program					2 years
Maximum
Grant revenue
Term of grant program					5 years
Collaboration agreement | Development event milestones
Collaborations and grants
Collaboration revenue recognized		$ 10	$ 7.5
Collaboration agreement | Roche and SMA Foundation [Member]
Collaborations and grants
Number of compounds in preclinical development | item				3
Deferred revenue				$ 30
Number of significant deliverables | item				2
Research period for applying technology				2 years
Collaboration revenue recognized					$ 0.6	$ 20.2	$ 26.6
Collaboration agreement | Roche and SMA Foundation [Member] | Development event milestones | Maximum
Collaborations and grants
Additional consideration receivable upon achievement of specified events					135
Collaboration agreement | Roche and SMA Foundation [Member] | Sales milestones | Maximum
Collaborations and grants
Additional consideration receivable upon achievement of specified events					325
Early stage collaboration and discovery agreements
Collaborations and grants
Deferred revenue					0	1.8
Number of significant deliverables | item	2
Collaboration revenue recognized					$ 1.8	$ 1.3
Early stage collaboration and discovery agreements | Minimum
Collaborations and grants
Research period for applying technology					3 years
Early stage collaboration and discovery agreements | Maximum
Collaborations and grants
Research period for applying technology					4 years
Early stage collaboration and discovery agreements | Development event milestones
Collaborations and grants
Additional consideration receivable upon achievement of specified events					$ 143
Early stage collaboration and discovery agreements | Sales milestones | Maximum
Collaborations and grants
Additional consideration receivable upon achievement of specified events					$ 252

Income taxes (Details)

Income taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Current:
Loss before income tax expense	$ (169,962)	$ (98,446)	$ (51,574)
U.S. State and local	(2)	4,890
Foreign	(483)	(197)
Current Income Tax Expense (Benefit), Total	$ (485)	$ 4,693
Reconciliation of the U.S. statutory income tax rate to the entity's effective tax rate
Federal income tax (benefit) at statutory rate (as a percent)	34.00%	34.00%	34.00%
State income tax benefit, net of federal benefit (as a percent)	(0.43%)	(1.60%)	5.65%
Permanent differences (as a percent)	(6.61%)	(0.93%)	(5.90%)
NOL IRC Section 382 Limitations (as a percent)		(21.53%)
Research and development (as a percent)	19.50%	3.78%	15.88%
Increase to valuation allowance (as a percent)	(20.87%)	9.17%	(49.63%)
Foreign tax rate differential	(24.06%)	(18.14%)
Other (as a percent)	(1.82%)	0.01%
Effective income tax rate (as a percent)	(0.29%)	4.76%	0.00%
Deferred tax assets:
Accrued expense	$ 848	$ 611
Amortization	57	69
Depreciation	2,631	2,268
Deferred revenue		699
Federal tax credits	50,850	17,807
State tax credits	3,356	1,274
Federal net operating losses	75,200	76,933
State net operating losses	8,848	9,185
Capitalized research and development costs	8,917	10,585
Other	10,345	3,852
Total gross deferred tax assets	161,052	123,283
Less valuation allowance	(139,584)	(123,283)
Total deferred tax assets, net of valuation allowance	21,468
Deferred tax liabilities:
Convertible debt	(21,468)
Total gross deferred tax liabilities	(21,468)
Non US
Current:
Loss before income tax expense	119,000	52,000
US
Current:
Loss before income tax expense	$ 51,000	$ 46,500

Income taxes (Details 2)

Income taxes (Details 2) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Income taxes
Change in valuation allowance	$ 16.3	$ 9.2
Federal
Operating loss carryforwards
Net operating loss carryforwards	270.4
Operating loss carryforwards associated to exercise of stock options and vesting of restricted stock	49.2
Tax benefit related to operating loss carryforwards	16.7
State
Operating loss carryforwards
Net operating loss carryforwards	$ 198.1

Income taxes (Details 3)

Income taxes (Details 3) $ in Millions	12 Months Ended
	Dec. 31, 2015USD ($)
Credit carryforwards
Orphan drug credit carryover	$ 39.8
Limited NOL carryforwards	231.5
Operating loss carryforwards, not subject to expiration	$ 169.2
NOL carryforward period	20 years
Operating loss carryforwards, subject to expiration	$ 62.3
Operating loss carryforwards for immediate use	142.9
Operating loss carryforwards in next twelve months	16.7
Federal
Credit carryforwards
Research and development credit carryforwards	11
Net operating loss carryforwards	270.4
State
Credit carryforwards
Research and development credit carryforwards	4.8
Net operating loss carryforwards	198.1
First five years from ownership change
Credit carryforwards
Net operating loss carryforwards	16.7
After five years
Credit carryforwards
Net operating loss carryforwards	$ 5.7

Income taxes (Details 4)

Income taxes (Details 4) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income taxes
U.S. federal income tax rate (as a percent)	34.00%	34.00%	34.00%
Uncertain tax position	$ 0

Commitments and contingencies63

Commitments and contingencies (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Commitments and contingencies
Operating Leases, Rent Expense, Net	$ 1,800	$ 900	$ 700
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity
2,016	1,529
2,017	966
2,018	1,035
2,019	176
Total future minimum lease payments	3,706
Funding agreement | Wellcome trust | Expected in second quarter 2016
Other contingencies
Development and regulatory milestone payments which the entity may be obligated to pay	800
Funding agreement | Wellcome trust | Maximum
Other contingencies
Development and regulatory milestone payments which the entity may be obligated to pay	$ 68,900

Geographic information (Details

Geographic information (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2015USD ($)item	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)
Revenues from External Customers and Long-Lived Assets
Number of Operating Segments | item	1
Total assets	$ 368,041	$ 333,219
Property and equipment, net	8,974	9,159
Revenue, Net	36,766	25,245	$ 34,696
Operating segments
Revenues from External Customers and Long-Lived Assets
Total assets	368,041	333,219
Property and equipment, net	8,974	9,159
Revenue, Net	36,766	25,245
US
Revenues from External Customers and Long-Lived Assets
Total assets	343,515	330,663
Property and equipment, net	8,206	8,555
Revenue, Net	5,218	25,245
Non US
Revenues from External Customers and Long-Lived Assets
Total assets	24,526	2,556
Property and equipment, net	768	$ 604
Revenue, Net	$ 31,548

401(k) plan (Details)

401(k) plan (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
401(k) plan
Matching contribution up to the first 6% of employee's base salary (as a percent)	50.00%
Percentage of employee's base salary, matched by employer	6.00%
Expense recorded	$ 0.7	$ 0.3	$ 0.1

Selected quarterly financial 66

Selected quarterly financial data (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Selected quarterly financial data (Unaudited)
Net product revenue	$ 12,694	$ 9,772	$ 6,161	$ 5,069	$ 636	$ 81			$ 33,696	$ 717
Collaboration and grant revenue	40	4	613	2,413	12,022	1,613	$ 1,677	$ 9,217	3,070	24,528	$ 34,696
Operating expenses	60,935	52,008	45,400	45,553	44,888	29,295	27,046	23,429	203,896	124,658	80,094
Loss from operations	(48,201)	(42,232)	(38,626)	(38,071)	(32,230)	(27,601)	(25,369)	(14,212)	(167,130)	(99,413)	(45,398)
Net loss	$ (50,948)	$ (43,223)	$ (38,361)	$ (37,915)	$ (27,269)	$ (27,282)	$ (25,104)	$ (14,098)	(170,447)	(93,753)	(51,574)
Deemed dividend											18,249
Gain on exchange of convertible preferred stock in connection with recapitalization											3,391
Net loss attributable to common stockholders									$ (170,447)	$ (93,753)	$ (66,432)
Net loss per share-basic and diluted (in dollars per share)	$ (1.50)	$ (1.27)	$ (1.14)	$ (1.15)	$ (0.84)	$ (0.93)	$ (0.86)	$ (0.58)	$ (5.07)	$ (2.97)	$ (5.18)