Avexis (AVXS) 10-Q 4 May 18 2018 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2018	May 03, 2018
Document and Entity Information [Abstract]
Entity Registrant Name	AveXis, Inc.
Entity Central Index Key	1,652,923
Document Type	10-Q
Document Period End Date	Mar. 31, 2018
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		36,816,476
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q1

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 586,808	$ 324,117
Prepaid expenses and other current assets	11,636	8,321
Total current assets	598,444	332,438
Property and equipment, net	62,864	56,174
Restricted cash	2,830
Other long-term assets	3,115	2,966
Total assets	667,253	391,578
Current liabilities:
Accounts payable	14,118	10,587
Accrued expenses and other current liabilities	29,566	44,938
Short-term licensing fees payable	27,508
Accrued indemnification obligation	1,635	2,788
Total current liabilities	72,827	58,313
Long-term liabilities	25,100	525
Total liabilities	97,927	58,838
Preferred stock, par value $0.0001 per share, 10,000 shares authorized, none issued
Common stock; par value $0.0001 per share, 100,000 shares authorized, 36,810 shares issued and outstanding at March 31, 2018; 32,090 shares issued and outstanding at December 31, 2017	4	3
Additional paid-in capital	1,151,037	692,350
Accumulated deficit	(581,715)	(359,613)
Total stockholders’ equity	569,326	332,740
Total liabilities and stockholders’ equity	$ 667,253	$ 391,578

Condensed Consolidated Balance3

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares shares in Thousands	Mar. 31, 2018	Dec. 31, 2017
Preferred stock
Preferred stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Preferred stock, shares authorized (in shares)	10,000	10,000
Common stock
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized (in shares)	100,000	100,000
Common stock, shares issued (in shares)	36,810	32,090
Common stock, shares outstanding (in shares)	36,810	32,090

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Operating expenses:
General and administrative	$ 22,747	$ 9,638
Research and development expenses	199,709	20,327
Total operating expenses	222,456	29,965
Loss from operations	(222,456)	(29,965)
Interest income, net	354	246
Net loss and comprehensive loss	$ (222,102)	$ (29,719)
Basic and diluted net loss per common share (in dollars per share)	$ (6.20)	$ (1.07)
Weighted-average basic and diluted common shares outstanding (in shares)	35,842	27,734

Condensed Consolidated Stateme5

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Cash flows from operating activities
Net loss	$ (222,102)	$ (29,719)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,267	244
Stock-based compensation	12,988	5,084
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(3,391)	(2,533)
Other long-term assets	(149)	(642)
Accounts payable	1,706	6,526
Accrued expenses and other current liabilities	(1,884)	(7,154)
Accrued indemnification obligation	(1,153)	67
Accrued licensing fees payable	52,107
Net cash used in operating activities	(160,611)	(28,127)
Cash flows from investing activities
Capital expenditures	(7,921)	(8,064)
Net cash used in investing activities	(7,921)	(8,064)
Cash flows from financing activities
Proceeds from issuance of common stock	431,857
Proceeds from exercise of stock options	5,029	215
Taxes paid on stock-based compensation vesting and exercise	(2,833)
Net cash provided by financing activities	434,053	215
Net increase (decrease) in cash and cash equivalents and restricted cash	265,521	(35,976)
Cash and cash equivalents and restricted cash, Beginning of Period	324,117	240,430
Cash and cash equivalents and restricted cash, End of Period	589,638	204,454
Supplemental Disclosure of Non-cash Investing and Financing Activities
Capital expenditures in accounts payable and accrued liabilities	7,009	$ 5,842
Shares issued in settlement with stockholder (See Note 9)	$ 11,647

Background

Background	3 Months Ended
	Mar. 31, 2018
Background
Background	1. Avexis, Inc., (“the Company”) is a clinical‑stage gene therapy company dedicated to developing and commercializing novel treatments for patients suffering from rare and life‑threatening neurological genetic diseases. The Company’s initial product candidate, AVXS‑101, is its proprietary gene therapy product candidate for the treatment of spinal muscular atrophy, (“SMA”). SMA is a severe neuromuscular disease characterized by the loss of motor neurons, leading to progressive muscle weakness and paralysis. SMA is generally divided into sub‑categories termed SMA Type 1, 2, 3 and 4. On April 6, 2018, the Company entered into an Agreement and Plan of Merger (the “Merger Agreement”) with Novartis AG, a company organized under the laws of Switzerland (“Parent”), and Novartis AM Merger Corporation, a Delaware corporation and a wholly owned subsidiary of Parent (“Purchaser”), pursuant to which, and upon the terms and subject to the conditions described therein, on April 17, 2018, Purchaser commenced a cash tender offer (the “Offer”) to acquire all of the outstanding shares of the Company’s common stock at a purchase price of $218.00 per share, net to the seller in cash, without interest, subject to any required withholding of taxes. As of the date of this filing, the Offer and the merger contemplated by the Merger Agreement have not been completed (see Note 11). January 2018 Underwritten Public Offering On January 22, 2018, the Company completed an underwritten public offering of 4,509,840 shares of its common stock, including the exercise in full by the underwriters of their option to purchase 588,240 shares from the Company, at a public offering price of $102.00 per share. After deducting the underwriting discounts and commissions, the net proceeds to the Company were approximately $431.9 million.

Summary of Significant Accounti

Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2018
Summary of Significant Accounting Policies
Summary of Significant Accounting Policies	2. Basis of Presentation The condensed consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”) for interim financial reporting and the rules and regulations of the U.S. Securities and Exchange Commission (“SEC”) and, therefore, do not include all information and footnote disclosures normally included in the annual consolidated financial statements. In the opinion of management, the unaudited condensed consolidated financial statements reflect all adjustments of a normal recurring nature that are necessary for a fair statement of the results for the interim periods presented. Interim results are not necessarily indicative of results for a full year. The December 31, 2017 condensed consolidated balance sheet data contained within this Form 10-Q was derived from audited consolidated financial statements included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2017 (“Annual Report on Form 10-K”), but does not include all disclosures required by GAAP. Significant Accounting Policies There have been no material changes in the Company’s significant accounting policies as of and for the three months ended March 31, 2018, as compared with the significant accounting policies described in the Company’s Annual Report on Form 10-K. Use of Estimates The preparation of the condensed consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and reported amounts of revenues, if any, and expenses during the reporting period. Actual results could differ from those estimates. Recently Issued Accounting Pronouncements In February 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2016-02, Leases (“ASC 842”). The guidance requires lessees to recognize almost all leases on their balance sheet as a right-of-use asset and a lease liability. For income statement purposes, the FASB retained a dual model, requiring leases to be classified as either operating or finance. Lessor accounting is similar to the current model, but updated to align with certain changes to the lessee model and the new revenue recognition standard. Existing sale-leaseback guidance, including guidance for real estate, is replaced with a new model applicable to both lessees and lessors. ASC 842 is effective for fiscal years beginning after December 15, 2018. The Company is evaluating the adoption of ASC 842, but has not determined the effects it may have on the Company’s consolidated financial statements. Recently Adopted Accounting Pronouncements In August 2016, the FASB issued ASU No. 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash . This update is intended to reduce diversity in the presentation of restricted cash and restricted cash equivalents in the statement of cash flows. The updated standard was effective for the Company in the quarterly period ending March 31, 2018. The adoption of this updated standard resulted in restricted cash being combined with cash and cash equivalents on the cash flow statement.

Restricted Cash

Restricted Cash	3 Months Ended
	Mar. 31, 2018
Restricted Cash
Restricted Cash	3. As of March 31, 2018, restricted cash was $2.8 million and related to a letter of credit signed by the Company in the three months ended March 31, 2018. The letter of credit was signed in conjunction with an amendment to the lease at the Libertyville, Illinois manufacturing facility. There was no restricted cash as of December 31, 2017. The following table provides a reconciliation of cash and cash equivalents and restricted cash as reported within the condensed consolidated balance sheet to the same items as reported in the condensed consolidated statement of cash flows: Three Months Ended March 31, 2018 2017 Cash and cash equivalents $ 586,808 $ 204,454 Restricted cash 2,830 — Cash and cash equivalents and restricted cash $ 589,638 $ 204,454

Property and Equipment, Net

Property and Equipment, Net	3 Months Ended
	Mar. 31, 2018
Property and Equipment, Net
Property and Equipment, Net	4. Property and equipment, net, consists of the following (in thousands): March 31, December 31, 2018 2017 Equipment $ 41,733 $ 34,777 Leasehold improvements 12,513 7,123 Construction in progress 11,208 15,656 Furniture 978 919 Property and equipment, gross 66,432 58,475 Less: accumulated depreciation (3,568) (2,301) Property and equipment, net $ 62,864 $ 56,174 Depreciation expense was $1.3 million and $0.2 million for the three months ended March 31, 2018 and 2017, respectively . Advances paid towards the acquisition of property and equipment, and the cost of property and equipment not ready for use before the end of the period, are both classified as construction in progress.

Accrued Expenses and Other Curr

Accrued Expenses and Other Current Liabilities	3 Months Ended
	Mar. 31, 2018
Accrued Expenses and Other Current Liabilities
Accrued Expenses and Other Current Liabilities	5. Accrued expenses and other current liabilities consist of the following (in thousands): March 31, December 31, 2018 2017 Accrued manufacturing development costs $ 8,786 $ 10,356 Accrued construction in progress 5,912 4,156 Accrued payroll, bonus and deferred compensation 4,413 9,589 Accrued clinical trial costs 3,277 864 Accrued professional and consulting fees 3,338 5,406 Accrued loss on settlement — 11,647 Accrued franchise taxes and other 3,840 2,920 Accrued expenses and other current liabilities $ 29,566 $ 44,938

Stock-Based Compensation

Stock-Based Compensation	3 Months Ended
	Mar. 31, 2018
Stock-Based Compensation
Stock-Based Compensation	6. 2014 Stock Plan (the “2014 Plan”) and 2016 Equity Incentive Plan (the “2016 Plan”) The following table summarizes stock option activity under the 2014 Plan and the 2016 Plan (collectively, the “Plans”) for the three months ended March 31, 2018 (in thousands, except per share data): Weighted Weighted Average Average Remaining Aggregate Number of Exercise Contractual Intrinsic Shares Price Life (Years) Value (a) Outstanding at December 31, 2017 3,167 $ 41.30 8.35 $ 219,656 Granted 672 $ 124.57 Exercised (97) $ 26.49 Cancelled or forfeited (62) $ 42.95 Outstanding at March 31, 2018 3,680 $ 56.88 8.45 $ 249,205 Exercisable at March 31, 2018 1,240 $ 22.52 7.55 $ 125,304 Exercisable and expected to vest at March 31, 2018 3,680 $ 56.88 8.45 $ 249,205 (a) The aggregate intrinsic value is calculated as the difference between the exercise price of the underlying options and the estimated fair value of the common stock for the options that were in-the-money at March 31, 2018 and December 31, 2017. The intrinsic value of the outstanding stock options as of March 31, 2018 at the purchase price of $218.00 per share in the Offer is equal to $592.9 million (see Note 11). For the three months ended March 31, 2018 and 2017, the total number of stock options exercised was 97,388 and 43,120, respectively, resulting in total proceeds of $5.0 million and $0.2 million, respectively. As of March 31, 2018 there was $89.8 million of unrecognized stock-based compensation expense related to stock option awards that is expected to be recognized over a weighted-average period of 1.4 years. The Company has recorded total stock-based compensation expense related to the issuance of stock option awards under the Plans in the condensed consolidated statements of operations and comprehensive loss as follows (in thousands): Three Months Ended March 31, 2018 2017 Research and development $ 6,995 $ 1,978 General and administrative 5,274 2,765 $ 12,269 $ 4,743 Stock Options Granted The weighted-average grant date fair value of options granted during the three months ended March 31, 2018 and 2017 was $85.55 and $47.20, respectively on the date of grant using the Black-Scholes option-pricing model with the following weighted-average assumptions: Three Months Ended March 31, March 31, 2018 2017 Expected volatility 77.68 % 86.88 % Risk-free interest rate 2.53 % 1.94 % Expected term (in years) 6.08 6.08 Expected dividend yield 0.00 % % Options generally expire ten years following the date of grant. Options typically vest over a period of four years, but vesting provisions can vary by award based on the discretion of the Board of Directors. Options to purchase common stock carry an exercise price equal to the estimated fair value of the Company’s common stock on the date of grant. Options to purchase shares of the Company’s common stock may be exercised by payment of the exercise price in cash, by the delivery of previously acquired shares of common stock having a fair value equal to the exercise price payable or the withholding of common shares equal to the fair value of the aggregate exercise price. Upon the termination of service of a holder of stock options awarded under the Plans, all unvested options are immediately forfeited and vested options may be exercised within three months of termination. Service-Based Restricted Stock Units The Company grants restricted stock units (“RSUs”) with service-based vesting terms from time to time. The outstanding RSUs vest over a period of three years. For awards that vest subject to the satisfaction of service requirements, compensation expense is measured based on the fair value of the RSUs on the date of grant and is recognized as expense on a straight-line basis over the requisite service period. All RSUs issued vest over time as stipulated in the individual RSU award agreements. A summary of the status of the Company's RSUs at March 31, 2018 and of changes in RSUs outstanding under the 2016 Plan for the three months ended March 31, 2018 is as follows (in thousands, except per share data): Weighted Average Grant Date Number Fair Value of Shares Per Share Outstanding at December 31, 2017 27 $ 38.79 Granted 139 129.85 Vested (10) $ 40.24 Forfeited and cancelled (0) $ 34.90 Outstanding at March 31, 2018 156 $ 119.79 At March 31, 2018, there was $17.7 million of unrecognized compensation cost related to unvested RSUs that will be recognized as expense over a weighted-average period of 1.8 years. The Company has recorded total stock-based compensation expense related to the issuance of service-based RSUs under the Plans in the condensed consolidated statements of operations and comprehensive loss as follows (in thousands): Three Months Ended March 31, 2018 2017 Research and development $ 399 $ 302 General and administrative 320 39 $ 719 $ 341 Performance-Based Restricted Stock Units On March 20, 2017, the Company granted to certain employees a total of 49,332 performance-based restricted stock units (“PSUs)”. These PSUs vest upon the achievement of certain regulatory and manufacturing milestones. If the milestones do not occur on or before the three-year anniversary of the grant date, all unvested PSUs will be cancelled. As of March 31, 2018, all 49,332 of these PSUs were outstanding, none had vested and the weighted-average grant date fair value of all shares was $79.75 per share. The Company has not yet recognized any PSU-related stock-based compensation expense as regulatory and manufacturing milestones have not yet been met; however, in the event the performance conditions are met, $3.9 million of research and development compensation expense will be recognized by the Company. There were no PSUs granted during the three months ended March 31, 2018. Warrants Granted to Non-Employees During the three months ended March 31, 2018 and 2017, there were no warrants exercised and as a result no proceeds received by the Company. As of March 31, 2018, there were 305,775 common stock warrants vested and outstanding issued to non-employees with a weighted-average exercise price of $2.57.

Equity and Net Loss Per Common

Equity and Net Loss Per Common Share	3 Months Ended
	Mar. 31, 2018
Equity and Net Loss Per Common Share
Equity and Net Loss Per Common Share	7. Basic net loss per common share is computed using the weighted-average number of common shares outstanding during the period. Diluted net loss per common share is computed using the sum of the weighted-average number of common shares outstanding during the period and, if dilutive, the weighted-average number of potential shares of common stock, including the assumed exercise of stock options, stock warrants and unvested restricted common stock. For the three months ended March 31, 2018 and 2017, the following potentially dilutive securities have been excluded from the computations of diluted weighted-average shares outstanding because the effect would be anti-dilutive (in thousands): Three Months Ended March 31, 2018 2017 Stock options 3,680 2,734 Stock warrants 306 306 Unvested service-based restricted stock units 156 42 Unvested performance-based restricted stock units 49 49 4,191 3,131 Amounts in the table above reflect the common stock equivalents of the noted instruments. The following table summarizes the calculation of the basic and diluted net loss per common share (in thousands, except per share data): Three Months Ended March 31, 2018 2017 Numerator: Net loss and comprehensive loss $ 222,102 $ 29,719 Denominator: Weighted-average basic and diluted common shares 35,842 27,734 Basic and diluted net loss per common share $ 6.20 $ 1.07 On December 29, 2017, the Company entered into a settlement agreement and release with a stockholder

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2018
Commitments and Contingencies
Commitments and Contingencies	8. Operating Leases In March 2018, the Company entered into a lease agreement, which expires in August 2027, for approximately 9,500 square feet adjacent to the Company’s existing space in San Diego, California. The lease agreement provides for annual escalation in rent payments during the lease term. The Company is amortizing the escalation in rental payments on a straight‑line basis over the term of the lease. In March 2018, the Company entered into a lease agreement, which expires in July 2026, for approximately 44,000 square feet of warehouse, office and storage space in Libertyville, Illinois. In March 2018, the Company entered into a lease agreement, which expires in July 2024, for approximately 4,700 square feet adjacent to the Company’s existing facility in Bannockburn, Illinois. The lease agreement provides for annual escalation in rent payments during the lease term. The Company is amortizing the escalation in rental payments on a straight‑line basis over the term of the lease. Guarantees and Indemnifications In the normal course of business, the Company has entered into agreements that contain a variety of representations and provide for general indemnification, including indemnification agreements with the Company’s officers and directors. The Company's exposure under these agreements is unknown because it involves claims that may be made against the Company in the future. To date, the Company has not paid any claims or been required to defend any action related to these indemnification obligations. As of March 31, 2018 and December 31, 2017, the Company did not have any material indemnification claims related to these agreements that were probable or reasonably possible and consequently has not recorded any related liabilities. Litigation On September 8, 2016, Sophia's Cure Foundation (“SCF”), a non-profit 501(c)(3) public charity, filed a complaint in U.S. District Court, Southern District of Ohio, naming as defendants Nationwide Children's Hospital (“NCH”) and other entities affiliated with NCH, the Company and certain of the Company's present and former executives (the “Complaint”). According to the complaint, in 2012, SCF and Nationwide Children’s Hospital Foundation (“NCH Foundation”) entered into a donation agreement under which SCF provided NCH a gift of $550,000 to fund clinical work associated with the study of the product candidate that the Company now refers to as AVXS-101 for SMA Type 1 patients, and NCH Foundation agreed in such donation agreement to reference SCF as the “primary sponsor” of such clinical work in all publications issued by NCH Foundation. The complaint also alleges that NCH breached the donation agreement by not naming SCF as the sponsor of the investigational new drug application (the “IND”) that it filed for AVXS-101. Additionally, the complaint alleges that the Company and the named Company executives (present and former) tortiously interfered with SCF’s rights under the donation agreement by assuming sponsorship of the IND under the NCH License. There is no contractual relationship between the Company and SCF. The complaint seeks, among other relief, monetary damages of $500.0 million and equitable relief, including taking steps to designate SCF as the sponsor of the IND. On October 10, 2017, the Court granted all of the defendants’ motions to dismiss. On October 31, 2017, SCF filed a second amended complaint against all of the defendants except two of the Company’s present executives, who were dropped from the second amended complaint. The Company believes that the second amended complaint is without merit and intends to vigorously defend itself and its present and former executives from the allegations. The Company filed a new motion to dismiss on December 5, 2017. The Company views the possibility of loss in this matter to be remote. Lawsuits may be asserted against the Company in the normal course of business. Based on information currently available, management believes that the disposition of any matters, including the matter involving SCF described above, will not have a material adverse effect on the financial position, results of operations or cash flows of the Company.

Taxes

Taxes	3 Months Ended
	Mar. 31, 2018
Taxes
Taxes	9. Deferred tax assets and liabilities are determined based on the difference between the financial statement and tax bases of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. Valuation allowances are provided if based upon the weight of available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized. The Company has evaluated the positive and negative evidence bearing upon the realizability of its deferred tax assets, including its net operating losses. Based on its history of operating losses, the Company believes that it is more likely than not that the benefit of its deferred tax assets will not be realized. Accordingly, the Company has provided a full valuation allowance for deferred tax assets as of March 31, 2018 and December 31, 2017. On December 22, 2017, the President of the United States signed into law the Tax Cuts and Jobs Act, or TCJA. The TCJA makes significant changes in U.S. tax law including a reduction in the corporate tax rates, changes to net operating loss carryforwards and carrybacks, and a reduction of the amount of the orphan drug credit. As a result of the TCJA, the Company remeasured its ending deferred tax assets and liabilities at December 31, 2017 to the newly enacted U.S. federal corporate tax rate of 21%. The Company recognized the provisional tax impacts related to the remeasurement of the deferred tax assets and liabilities pursuant to SEC Staff Accounting Bulletin No. 118 and included these amounts in its consolidated financial statements for the year ended December 31, 2017. The Company did not record any adjustments to this provisional amount during the three months ended March 31, 2018 and will continue to analyze and refine its calculations related to the remeasurement as the impact of TCJA is finalized.

Collaboration and License Agree

Collaboration and License Agreements	3 Months Ended
	Mar. 31, 2018
Collaboration and License Agreements
Collaboration and License Agreements	10. The Company has entered into three license agreements related to its SMA programs and its planned preclinical programs in Rett syndrome and amyotrophic lateral sclerosis (“ALS”) caused by mutations in the gene that produces the copper zinc superoxide dismutase 1 (“SOD1”) enzyme (“genetic ALS”). REGENXBIO Inc. On January 8, 2018, the Company entered into an amendment (the “Amendment”) to the License Agreement dated March 21, 2014 (as amended, the “REGENXBIO SMA License”) between the Company and REGENXBIO Inc. (“REGENXBIO”). Under the terms of the Amendment, REGENXBIO granted the Company an exclusive, worldwide commercial license, with rights to sublicense, to all recombinant adeno-associated virus vectors in REGENXBIO’s intellectual property portfolio during the term of the license agreement for the treatment of SMA in humans by in vivo gene therapy. Additionally, the Amendment modifies the terms and conditions of the License Agreement relating to assignment. Under the amended assignment provision, the Company is permitted to transfer the License Agreement without REGENXBIO’s consent in connection with a change of control of the Company, subject to the transferee or successor agreeing in writing to be bound by the terms of the License Agreement. The Amendment requires that in a change of control of the Company, the following amounts due under the license agreement, if unpaid at the time of the change in control, become immediately payable: the first and second anniversary payments of $30.0 million each and the first sales-based milestone payment of $40.0 million. As consideration for the Amendment, the Company paid $80.0 million upon entry into the Amendment and is required to pay $30.0 million on the first anniversary of the effective date of the Amendment and $30.0 million on the second anniversary of the effective date of the Amendment. In addition, pursuant to the Amendment, the Company agreed to pay up to $120.0 million in the aggregate of potential future sales-based milestone payments for all REGENXBIO SMA licensed products. The Company also agreed to pay a mid‑single digit to low double-digit royalty percentages on net sales of REGENXBIO SMA licensed products using adeno-associated virus serotype 9 (“AAV9”) and a low-double digit royalty percentage on net sales of any product candidate developed by the Company for the treatment of SMA using an adeno-associated virus vector other than AAV9, in each case subject to a reduction in specified circumstances. During the three months ended March 31, 2018, $130.7 million of expenses were recognized within research and development representing the $80.0 million upfront payment made to REGENXBIO in January 2018 and the net present value of the guaranteed fixed payments due on the first and second anniversaries of the effective date of the Amendment. As of March 31, 2018, the Company has accrued the net present value of the first anniversary payment within short-term licensing fees payable and the second anniversary payment within long-term liabilities on the balance sheet. Additionally, the Company recognized interest expense of $1.4 million associated with the accretion of its discounted guaranteed fixed payments due to REGENXBIO in 2019 and 2020. The REGENXBIO SMA License term continues until the last valid patent claim expires or lapses in all countries of the world. Additionally, the Company may terminate the REGENXBIO SMA License at any time upon a specified notice period and REGENXBIO may terminate the REGENXBIO SMA License upon the breach (after notice and cure periods) or insolvency of the Company, if the Company is greater than a specified number of days late (after notice and cure periods) in paying money due under the REGENXBIO SMA License or if the Company, its affiliates, or sublicensees challenges the REGENXBIO SMA patents subject to the REGENXBIO SMA License. Either party may terminate the REGENXBIO SMA License for material breach if such breach is not cured within a specified number of days. GÉNÉTHON In March 2018, the Company entered into a license agreement with Généthon, acting in its own name and for its own behalf as well as in the name and on behalf of Centre National de la Recherche Scientifique (together “Généthon”), pursuant to which Généthon granted the Company an exclusive, worldwide license to certain patents for in vivo gene replacement therapy delivery of the survival motor neuron protein gene using the AAV9 vector into the central nervous system for the treatment of SMA. Under the Généthon agreement, the Company paid Généthon a one-time upfront license fee of $4.0 million. The Company is also required to pay $0.5 million for the first three years to support Généthon’s ongoing research, ongoing annual management fees of $25 thousand and up to a total of $11.0 million in development and sales-based milestone fees for licensed products. Under the terms of the Généthon agreement, the Company is also required to pay Généthon mid-single digit royalties of net sales on licensed products, subject to reduction in certain circumstances due to royalty stacking provisions and a mid-teens percentage of any sublicense fees that the Company receives from sublicensees for the licensed intellectual property rights. As of March 31, 2018, the Company had recognized $4.5 million of research and development expenses related to the Généthon license and no royalty fees have been recognized.

Subsequent Events

Subsequent Events	3 Months Ended
	Mar. 31, 2018
Subsequent Events
Subsequent Events	11. Subsequent Events On April 6, 2018, the Company entered into the Merger Agreement with Parent and Purchaser, pursuant to which, and upon the terms and subject to the conditions described therein, on April 17, 2018, Purchaser commenced the Offer to acquire all of the outstanding shares of the Company’s common stock at a purchase price of $218.00 per share (such price, as it may be increased as described in the following sentence, the “Offer Price”), net to the seller in cash, without interest, subject to any required withholding of taxes. In the event Parent elects to extend the Outside Date (as defined in the Merger Agreement) in accordance with the terms of the Merger Agreement, the Offer Price will be increased to $225.00 per share, net to the seller in cash, without interest, subject to any required withholding of taxes. The Offer will expire at 12:00 Midnight, New York City time, at the end of the day on Monday, May 14, 2018 (unless the Offer is extended). The obligation of Purchaser to purchase shares of the Company’s common stock tendered in the Offer is subject to customary closing conditions, including (i) shares of the Company’s common stock having been validly tendered and not withdrawn that represent at least a majority of the total number of shares of the Company’s common stock then-outstanding on a fully diluted basis, (ii) the expiration or termination of the waiting period under the Hart-Scott-Rodino Antitrust Improvements Act of 1976, as amended (the “HSR Act”), without the imposition of a Burdensome Condition (as defined in the Merger Agreement), (iii) the absence of injunctions or other legal restraints preventing the consummation of the Offer or the Merger, as defined below, or imposing a Burdensome Condition and (iv) certain other conditions set forth in Exhibit A to the Merger Agreement. The consummation of the Offer is not subject to any financing condition. Following the completion of the Offer, subject to the satisfaction or waiver of certain customary conditions set forth in the Merger Agreement, Purchaser will merge with and into the Company, with the Company surviving as a wholly owned subsidiary of Parent (the “Merger”), pursuant to the procedure provided for under Section 251(h) of the Delaware General Corporation Law (the “DGCL”), without any stockholder approvals. The Merger will be effected as soon as practicable following the time of purchase by Purchaser of shares of the Company’s common stock validly tendered and not withdrawn in the Offer. At the effective time of the Merger (the “Effective Time”), each issued and outstanding share of the Company’s common stock (other than shares owned by (i) the Company, any subsidiary of the Company, Parent, Purchaser and any other subsidiary of Parent and (ii) stockholders of the Company who have validly exercised their statutory rights of appraisal under the DGCL) will be converted into the right to receive the Offer Price, in cash, without interest, subject to any required withholding of taxes. Until the earlier of the termination of the Merger Agreement and the Effective Time, the Company has agreed to operate its business in the ordinary course and has agreed to certain other operating covenants, as set forth more fully in the Merger Agreement. The Merger Agreement includes customary termination provisions for both the Company and Parent and provides that, in connection with the termination of the Merger Agreement under specified circumstances, including termination by the Company to accept a Superior Company Proposal (as defined in the Merger Agreement), the Company will be required to pay a fee equal to $284 million. The Merger Agreement also provides that, in connection with the termination of the Merger Agreement under specified antitrust related circumstances, Parent will be required to pay to the Company a “reverse termination fee” equal to $437 million, which fee increases in the event Parent elects to extend the Outside Date in accordance with the terms of the Merger Agreement. Each of the Company and Parent filed a Premerger Notification and Report Form under the HSR Act with respect to the Offer and the Merger with the Federal Trade Commission and the Antitrust Division of the United States Department of Justice on April 13, 2018. On April 30, 2018, the waiting period under the HSR Act applicable to the Offer and the Merger expired. Accordingly, the condition to the Offer relating to the expiration or termination of the waiting period under the HSR Act has been satisfied

Summary of Significant Accoun17

Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2018
Summary of Significant Accounting Policies
Basis of Presentation	Basis of Presentation The condensed consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”) for interim financial reporting and the rules and regulations of the U.S. Securities and Exchange Commission (“SEC”) and, therefore, do not include all information and footnote disclosures normally included in the annual consolidated financial statements. In the opinion of management, the unaudited condensed consolidated financial statements reflect all adjustments of a normal recurring nature that are necessary for a fair statement of the results for the interim periods presented. Interim results are not necessarily indicative of results for a full year. The December 31, 2017 condensed consolidated balance sheet data contained within this Form 10-Q was derived from audited consolidated financial statements included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2017 (“Annual Report on Form 10-K”), but does not include all disclosures required by GAAP.
Use of Estimates	Use of Estimates The preparation of the condensed consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and reported amounts of revenues, if any, and expenses during the reporting period. Actual results could differ from those estimates.
Recent Accounting Pronouncements	Recently Issued Accounting Pronouncements In February 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2016-02, Leases (“ASC 842”). The guidance requires lessees to recognize almost all leases on their balance sheet as a right-of-use asset and a lease liability. For income statement purposes, the FASB retained a dual model, requiring leases to be classified as either operating or finance. Lessor accounting is similar to the current model, but updated to align with certain changes to the lessee model and the new revenue recognition standard. Existing sale-leaseback guidance, including guidance for real estate, is replaced with a new model applicable to both lessees and lessors. ASC 842 is effective for fiscal years beginning after December 15, 2018. The Company is evaluating the adoption of ASC 842, but has not determined the effects it may have on the Company’s consolidated financial statements. Recently Adopted Accounting Pronouncements In August 2016, the FASB issued ASU No. 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash . This update is intended to reduce diversity in the presentation of restricted cash and restricted cash equivalents in the statement of cash flows. The updated standard was effective for the Company in the quarterly period ending March 31, 2018. The adoption of this updated standard resulted in restricted cash being combined with cash and cash equivalents on the cash flow statement.

Restricted Cash (Tables)

Restricted Cash (Tables)	3 Months Ended
	Mar. 31, 2018
Restricted Cash
Reconciliation of cash and cash equivalents and restricted cash	Three Months Ended March 31, 2018 2017 Cash and cash equivalents $ 586,808 $ 204,454 Restricted cash 2,830 — Cash and cash equivalents and restricted cash $ 589,638 $ 204,454

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	3 Months Ended
	Mar. 31, 2018
Property and Equipment, Net
Summary of property and equipment, net	March 31, December 31, 2018 2017 Equipment $ 41,733 $ 34,777 Leasehold improvements 12,513 7,123 Construction in progress 11,208 15,656 Furniture 978 919 Property and equipment, gross 66,432 58,475 Less: accumulated depreciation (3,568) (2,301) Property and equipment, net $ 62,864 $ 56,174

Accrued Expenses and Other Cu20

Accrued Expenses and Other Current Liabilities (Tables)	3 Months Ended
	Mar. 31, 2018
Accrued Expenses and Other Current Liabilities
Schedule of accrued expenses	March 31, December 31, 2018 2017 Accrued manufacturing development costs $ 8,786 $ 10,356 Accrued construction in progress 5,912 4,156 Accrued payroll, bonus and deferred compensation 4,413 9,589 Accrued clinical trial costs 3,277 864 Accrued professional and consulting fees 3,338 5,406 Accrued loss on settlement — 11,647 Accrued franchise taxes and other 3,840 2,920 Accrued expenses and other current liabilities $ 29,566 $ 44,938

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	3 Months Ended
	Mar. 31, 2018
Summary of stock option activity	The following table summarizes stock option activity under the 2014 Plan and the 2016 Plan (collectively, the “Plans”) for the three months ended March 31, 2018 (in thousands, except per share data): Weighted Weighted Average Average Remaining Aggregate Number of Exercise Contractual Intrinsic Shares Price Life (Years) Value (a) Outstanding at December 31, 2017 3,167 $ 41.30 8.35 $ 219,656 Granted 672 $ 124.57 Exercised (97) $ 26.49 Cancelled or forfeited (62) $ 42.95 Outstanding at March 31, 2018 3,680 $ 56.88 8.45 $ 249,205 Exercisable at March 31, 2018 1,240 $ 22.52 7.55 $ 125,304 Exercisable and expected to vest at March 31, 2018 3,680 $ 56.88 8.45 $ 249,205 (a) The aggregate intrinsic value is calculated as the difference between the exercise price of the underlying options and the estimated fair value of the common stock for the options that were in-the-money at March 31, 2018 and December 31, 2017. The intrinsic value of the outstanding stock options as of March 31, 2018 at the purchase price of $218.00 per share in the Offer is equal to $592.9 million (see Note 11).
Summary of stock-based compensation expense by classification in the Statement of Operations and Comprehensive Loss	The Company has recorded total stock-based compensation expense related to the issuance of stock option awards under the Plans in the condensed consolidated statements of operations and comprehensive loss as follows (in thousands): Three Months Ended March 31, 2018 2017 Research and development $ 6,995 $ 1,978 General and administrative 5,274 2,765 $ 12,269 $ 4,743
Summary of weighted-average assumptions used in determining fair value of stock options	Three Months Ended March 31, March 31, 2018 2017 Expected volatility 77.68 % 86.88 % Risk-free interest rate 2.53 % 1.94 % Expected term (in years) 6.08 6.08 Expected dividend yield 0.00 % %
Summary of service-based restricted stock units activity	A summary of the status of the Company's RSUs at March 31, 2018 and of changes in RSUs outstanding under the 2016 Plan for the three months ended March 31, 2018 is as follows (in thousands, except per share data): Weighted Average Grant Date Number Fair Value of Shares Per Share Outstanding at December 31, 2017 27 $ 38.79 Granted 139 129.85 Vested (10) $ 40.24 Forfeited and cancelled (0) $ 34.90 Outstanding at March 31, 2018 156 $ 119.79
Service Based RSUs
Summary of stock-based compensation expense by classification in the Statement of Operations and Comprehensive Loss	The Company has recorded total stock-based compensation expense related to the issuance of service-based RSUs under the Plans in the condensed consolidated statements of operations and comprehensive loss as follows (in thousands): Three Months Ended March 31, 2018 2017 Research and development $ 399 $ 302 General and administrative 320 39 $ 719 $ 341

Equity and Net Loss Per Commo22

Equity and Net Loss Per Common Share (Tables)	3 Months Ended
	Mar. 31, 2018
Equity and Net Loss Per Common Share
Schedule of potentially dilutive securities excluded from computations of diluted weighted-average shares outstanding	For the three months ended March 31, 2018 and 2017, the following potentially dilutive securities have been excluded from the computations of diluted weighted-average shares outstanding because the effect would be anti-dilutive (in thousands): Three Months Ended March 31, 2018 2017 Stock options 3,680 2,734 Stock warrants 306 306 Unvested service-based restricted stock units 156 42 Unvested performance-based restricted stock units 49 49 4,191 3,131
Summary of the basic and diluted net loss per common share	The following table summarizes the calculation of the basic and diluted net loss per common share (in thousands, except per share data): Three Months Ended March 31, 2018 2017 Numerator: Net loss and comprehensive loss $ 222,102 $ 29,719 Denominator: Weighted-average basic and diluted common shares 35,842 27,734 Basic and diluted net loss per common share $ 6.20 $ 1.07

Background (Details)

Background (Details) - USD ($) $ / shares in Units, $ in Thousands	Jan. 22, 2018	Mar. 31, 2018	Apr. 06, 2018
Liquidity and Risks
Net proceeds from issuance of common stock	$ 431,900	$ 431,857
Merger Agreement
Public Offering
Purchase price per share		$ 218
Subsequent Event | Merger Agreement
Public Offering
Purchase price per share			$ 218
IPO
Public Offering
Shares issued (in shares)	4,509,840
Share price (in dollars per share)	$ 102
Over-Allotment Option
Public Offering
Shares issued (in shares)	588,240

Restricted Cash (Details)

Restricted Cash (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Restricted Cash
Cash and cash equivalents	$ 586,808	$ 324,117	$ 204,454
Restricted cash	2,830
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Total	$ 589,638	$ 324,117	$ 204,454	$ 240,430

Property and Equipment, Net (De

Property and Equipment, Net (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Property and Equipment, Net
Property and equipment, gross	$ 66,432		$ 58,475
Less: accumulated depreciation	(3,568)		(2,301)
Property and equipment, net	62,864		56,174
Depreciation expense
Depreciation and amortization	1,267	$ 244
Equipment
Property and Equipment, Net
Property and equipment, gross	41,733		34,777
Leasehold improvement
Property and Equipment, Net
Property and equipment, gross	12,513		7,123
Construction in progress
Property and Equipment, Net
Property and equipment, gross	11,208		15,656
Furniture
Property and Equipment, Net
Property and equipment, gross	$ 978		$ 919

Accrued Expenses and Other Cu26

Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Accrued Expenses and Other Current Liabilities
Accrued manufacturing development costs	$ 8,786	$ 10,356
Accrued construction in progress	5,912	4,156
Accrued payroll, bonus and deferred compensation	4,413	9,589
Accrued clinical trial costs	3,277	864
Accrued professional fees	3,338	5,406
Accrued loss on settlement		11,647
Accrued franchise taxes and other	3,840	2,920
Accrued expenses and other current liabilities	$ 29,566	$ 44,938

Stock-Based Compensation - Stoc

Stock-Based Compensation - Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Number of Shares
Outstanding at the beginning of the period (in shares)	3,167,000
Granted (in shares)	672,000
Exercised (in shares)	(97,000)
Cancelled or forfeited (in shares)	(62,000)
Outstanding at the end of the period (in shares)	3,680,000		3,167,000
Weighted Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)	$ 41.30
Granted (in dollars per share)	124.57
Exercised (in dollars per share)	26.49
Cancelled or forfeited (in dollars per share)	42.95
Outstanding at the end of the period (in dollars per share)	$ 56.88		$ 41.30
Weighted Average
Remaining Contractual Life (Years)	8 years 5 months 12 days		8 years 4 months 6 days
Aggregate Intrinsic Value (in dollars)	$ 249,205		$ 219,656
Exercisable and Vested and Expected to Vest
Number of Shares - exercisable (in shares)	1,240,000
Weighted Average Exercise Price - exercisable (in dollars per share)	$ 22.52
Remaining Contractual Life (Years) - exercisable	7 years 6 months 18 days
Aggregate Intrinsic Value - exercisable (in dollars)	$ 125,304
Number of Shares - vested and expected to vest (in shares)	3,680,000
Weighted Average Exercise Price - vested and expected to vest (in dollars per share)	$ 56.88
Remaining Contractual Life (Years) - vested and expected to vest	8 years 5 months 12 days
Aggregate Intrinsic Value - vested and expected to vest (in dollars)	$ 249,205
Employee Stock Options
Number of Shares
Exercised (in shares)	(97,388)	(43,120)

Stock-Based Compensation - St28

Stock-Based Compensation - Stock Options Exercised (Details) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Stock Options Granted to Non-Employees
Aggregate Intrinsic Value (in dollars)	$ 249,205,000		$ 219,656,000
Exercised (in shares)	97,000
Proceeds from exercise of stock options	$ 5,029,000	$ 215,000
Employee Stock Options
Stock Options Granted to Non-Employees
Exercised (in shares)	97,388	43,120
Proceeds from exercise of stock options	$ 5	$ 200,000
Unrecognized stock-based compensation expense
Unrecognized stock-based compensation expense	$ 89,800,000
Weighted-average period expected to recognize stock-based compensation expense	1 year 4 months 24 days
Aggregate stock-based compensation expense by category
Aggregate stock-based compensation expense	$ 12,269,000	4,743,000
Research and development expenses | Employee Stock Options
Aggregate stock-based compensation expense by category
Aggregate stock-based compensation expense	6,995,000	1,978,000
General and administrative expenses | Employee Stock Options
Aggregate stock-based compensation expense by category
Aggregate stock-based compensation expense	$ 5,274,000	$ 2,765,000
Merger Agreement
Stock Options Granted to Non-Employees
Purchase price per share	$ 218
Aggregate Intrinsic Value (in dollars)	$ 592,900,000

Stock-Based Compensation - Weig

Stock-Based Compensation - Weighted-average Assumptions (Details) - Employee Stock Options - $ / shares	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Weighted-average grant date fair value
Weighted-average grant date fair value of options granted during the period (in dollars per share)	$ 85.55	$ 47.20
Weighted-average fair value assumptions
Expected volatility (as a percent)	77.68%	86.88%
Risk-free interest rate (as a percent)	2.53%	1.94%
Expected term (in years)	6 years 29 days	6 years 29 days
Expected dividend yield (as a percent)	0.00%	0.00%
2016 Equity Incentive Plan
Vesting and expiration of stock options
Expiration period (in years)	10 years
Period during which vested options may be exercised after termination of service	3 months
2016 Equity Incentive Plan | Maximum
Vesting and expiration of stock options
Vesting period (in years)	4 years

Stock-Based Compensation - Rest

Stock-Based Compensation - Restricted Stock Units - General Information (Details) - Service Based RSUs - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Stock Options Granted to Non-Employees
Vesting period (in years)	3 years
Stock-based compensation expense	$ 719	$ 341
Unrecognized compensation cost	$ 17,700
Weighted-average period expected to recognize stock-based compensation expense	1 year 9 months 18 days
Research and development expenses
Stock Options Granted to Non-Employees
Stock-based compensation expense	$ 399	302
General and administrative expenses
Stock Options Granted to Non-Employees
Stock-based compensation expense	$ 320	$ 39

Stock-Based Compensation - Re31

Stock-Based Compensation - Restricted Stock Units - Activity (Details) - Service Based RSUs - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Number of Shares
Outstanding at the beginning of the period (in shares)	27
Granted (in shares)	139
Vested (in shares)	(10)
Forfeited and cancelled (in shares)	0
Outstanding at the end of the period (in shares)	156
Weighted Average Grant Date Fair Value Per Share
Outstanding at the beginning of the period (in dollars per share)	$ 38.79
Granted (in dollars per share)	129.85
Vested (in dollars per share)	40.24
Forfeited and cancelled (in dollars per share)	34.90
Outstanding at the end of the period (in dollars per share)	$ 119.79
Aggregate stock-based compensation expense	$ 719	$ 341
Research and development expenses
Weighted Average Grant Date Fair Value Per Share
Aggregate stock-based compensation expense	399	302
General and administrative expenses
Weighted Average Grant Date Fair Value Per Share
Aggregate stock-based compensation expense	$ 320	$ 39

Stock-Based Compensation - Perf

Stock-Based Compensation - Performance-Based Restricted Stock Units (Details) - Performance Based RSU - USD ($) $ / shares in Units, $ in Millions	Mar. 20, 2017	Mar. 31, 2018
Stock Options Granted to Non-Employees
Shares granted (in shares)	49,332	0
Period from grant date during which unvested PSUs will be cancelled if milestones do not occur	3 years
Shares outstanding (in shares)		49,332
Shares vested (in shares)		0
Weighted average grant date fair value		$ 79.75
Research and development expenses
Stock Options Granted to Non-Employees
Amount of share based compensation expense to be recognized if performance conditions are met		$ 3.9

Stock-Based Compensation - Warr

Stock-Based Compensation - Warrants Granted to Non-Employees - General Information (Details) - Stock warrants	3 Months Ended
	Mar. 31, 2018USD ($)$ / sharesshares
Warrant information
Stock warrants exercised (in shares)	0
Proceeds from exercise of stock warrants | $	$ 0
Non-Employee
Warrant information
Stock warrants vested ( in shares)	305,775
Stock warrants outstanding (in shares)	305,775
Warrants, exercise price (in dollars per share) | $ / shares	$ 2.57

Equity and Net Loss Per Commo34

Equity and Net Loss Per Common Share - Dilutive Securities (Details) - shares shares in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Antidilutive securities not included:
Antidilutive securities	4,191	3,131
Employee Stock Options
Antidilutive securities not included:
Antidilutive securities	3,680	2,734
Stock warrants
Antidilutive securities not included:
Antidilutive securities	306	306
Service Based RSUs
Antidilutive securities not included:
Antidilutive securities	156	42
Performance Based RSU
Antidilutive securities not included:
Antidilutive securities	49	49

Equity and Net Loss Per Commo35

Equity and Net Loss Per Common Share - Calculation (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Numerator:
Net loss and comprehensive loss	$ 222,102	$ 29,719
Denominator:
Weighted-average basic and diluted common shares (in shares)	35,842	27,734
Basic and diluted net loss per common share (in dollars per share)	$ 6.20	$ 1.07

Equity and Net Loss Per Commo36

Equity and Net Loss Per Common Share - Additional information (Details) - USD ($) $ in Millions	Dec. 29, 2017	Dec. 31, 2017
Public Offering
General and Administrative Expense		$ 11.6
Common Stock
Public Offering
Shares to be issued per settlement agreement	105,237

Commitments and Contingencies -

Commitments and Contingencies - Operating Lease (Details)	Mar. 31, 2018ft²
Research And Development Space In San Diego California [Member]
Operating Leases
Approximate size of leased space (in square feet)	9,500
Office and warehouse space in Libertyville, Illinois
Operating Leases
Approximate size of leased space (in square feet)	44,000
Facility for corporate headquarters Bannockburn, Illinois
Operating Leases
Approximate size of leased space (in square feet)	4,700

Commitments and Contingencies38

Commitments and Contingencies - Guarantees and Indemnifications (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Accrued Indemnification Obligation
Accrued indemnification obligation	$ 1,635	$ 2,788

Commitments and Contingencies39

Commitments and Contingencies - Litigation (Details) - Sophia's Cure Foundation - NCH - Breach of donation agreement - USD ($)	Sep. 08, 2016	Dec. 31, 2012
Litigation
Gift received under donation agreement		$ 550,000
Monetary damages sought	$ 500,000,000

Income Taxes - Tax Cuts and Job

Income Taxes - Tax Cuts and Jobs Act (Details)	Jan. 01, 2018
Effect of Tax Cuts and Jobs Act
Federal statutory rate (as a percent)	21.00%

Collaboration and License Agr41

Collaboration and License Agreements - RegenxBio License (Details) $ in Millions	Jan. 08, 2018USD ($)	Mar. 31, 2018USD ($)item
Collaboration and License Agreements
Number of license agreements | item		3
ReGenX
Collaboration and License Agreements
Interest expense		$ 1.4
License Agreement | ReGenX
Collaboration and License Agreements
Consideration paid or payable per license agreement amendment	$ 80
License Agreement | ReGenX | First Anniversary Of Amendment
Collaboration and License Agreements
Consideration paid or payable per license agreement amendment	30
License Agreement | ReGenX | Second Anniversary Of Amendment
Collaboration and License Agreements
Consideration paid or payable per license agreement amendment	30
License Agreement | ReGenX | Sales-based milestone
Collaboration and License Agreements
Potential milestone payments to be paid	40
License Agreement | ReGenX | Sales-based milestone | Maximum
Collaboration and License Agreements
Potential milestone payments to be paid	$ 120
Research and development expenses | License Agreement | ReGenX
Collaboration and License Agreements
Licensing costs		$ 130.7

Collaboration and License Agr42

Collaboration and License Agreements - Genethon (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2018	Mar. 31, 2017
Collaboration and License Agreements
Research and development expenses		$ 199,709	$ 20,327
License Agreement | GENETHON
Collaboration and License Agreements
Consideration paid or payable per license agreement amendment	$ 4,000
Ongoing research support payments	500
Annual management fees	25
Research and development expenses		4,500
RoyaltyExpense		$ 0
Development and sales-based milestones | License Agreement | GENETHON | Maximum
Collaboration and License Agreements
Potential milestone payments to be paid	$ 11,000

Subsequent Events (Details)

Subsequent Events (Details) - Merger Agreement - USD ($) $ / shares in Units, $ in Millions	Apr. 06, 2018	Mar. 31, 2018
Subsequent Event [Line Items]
Purchase price per share		$ 218
Subsequent Event
Subsequent Event [Line Items]
Purchase price per share	$ 218
Termination fee payable on contract	$ 284
Reverse termination fee receivable from parent	$ 437
Subsequent Event | Maximum
Subsequent Event [Line Items]
Purchase price per share	$ 225