Viridian Therapeutics (VRDN) 10-Q 9 Nov 17 2017 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2017	Nov. 02, 2017
Document And Entity Information [Abstract]
Entity Registrant Name	MIRAGEN THERAPEUTICS, INC.
Entity Central Index Key	1,590,750
Document Type	10-Q
Document Period End Date	Sep. 30, 2017
Amendment Flag	false
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	Q3
Current Fiscal Year End Date	--12-31
Entity Filer Category	Smaller Reporting Company
Entity Common Stock, Shares Outstanding		22,309,419

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 42,805	$ 22,104
Accounts receivable	635	20
Prepaid expenses and other current assets	2,981	1,753
Total current assets	46,421	23,877
Property and equipment, net	610	625
Other assets	50	258
Total assets	47,081	24,760
Current liabilities:
Accounts payable	409	1,007
Accrued liabilities	4,142	3,909
Current portion of notes payable	1,983	1,969
Total current liabilities	6,534	6,885
Notes payable, less current portion	1,391	2,820
Other liabilities	171	0
Total liabilities	8,096	9,705
Commitments and contingencies
Stockholders’ equity (deficit):
Common stock, $0.01 par value; 100,000,000 shares authorized; 21,886,568 and 833,744 shares issued and outstanding at September 30, 2017 and December 31, 2016, respectively	219	8
Additional paid-in capital	125,973	5,147
Accumulated deficit	(87,207)	(67,076)
Total stockholders’ equity (deficit)	38,985	(61,921)
Total liabilities, preferred stock, and stockholders’ equity (deficit)	47,081	24,760
Series A
Current liabilities:
Redeemable convertible preferred stock	0	23,124
Series B
Current liabilities:
Redeemable convertible preferred stock	0	12,975
Series C
Current liabilities:
Redeemable convertible preferred stock	$ 0	$ 40,877

Condensed Consolidated Balance3

Condensed Consolidated Balance Sheets (Parenthetical) - USD ($)	Sep. 30, 2017	Dec. 31, 2016
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	100,000,000	100,000,000
Common stock, shares issued (in shares)	21,886,568	833,744
Common stock, shares outstanding (in shares)	21,886,568	833,744
Series A
Redeemable convertible preferred stock, par value (in dollars per share)		$ 0.001
Redeemable convertible preferred stock, shares authorized (in shares)		7,169,176
Redeemable convertible preferred stock, shares issued (in shares)		7,149,176
Redeemable convertible preferred stock, shares outstanding (in shares)		7,149,176
Redeemable convertible preferred stock, liquidation preference		$ 21,448
Series B
Redeemable convertible preferred stock, par value (in dollars per share)		$ 0.001
Redeemable convertible preferred stock, shares authorized (in shares)		2,183,318
Redeemable convertible preferred stock, shares issued (in shares)		2,166,651
Redeemable convertible preferred stock, shares outstanding (in shares)		2,166,651
Redeemable convertible preferred stock, liquidation preference		$ 13,000
Series C
Redeemable convertible preferred stock, par value (in dollars per share)		$ 0.001
Redeemable convertible preferred stock, shares authorized (in shares)		9,303,000
Redeemable convertible preferred stock, shares issued (in shares)		9,268,563
Redeemable convertible preferred stock, shares outstanding (in shares)		9,268,563
Redeemable convertible preferred stock, liquidation preference		$ 41,060

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Revenue:
Collaboration revenue	$ 1,493	$ 715	$ 1,991	$ 2,479
Grant revenue	138	221	820	489
Total revenue	1,631	936	2,811	2,968
Operating expenses:
Research and development	5,018	2,965	14,625	9,786
General and administrative	2,502	2,053	8,364	4,255
Total operating expenses	7,520	5,018	22,989	14,041
Loss from operations	(5,889)	(4,082)	(20,178)	(11,073)
Other income (expense):
Interest and other income	113	7	245	23
Interest and other related expense	(58)	(78)	(193)	(250)
Net loss	(5,834)	(4,153)	(20,126)	(11,300)
Accretion of redeemable convertible preferred stock to redemption value	0	(13)	(5)	(37)
Net loss available to common stockholders	$ (5,834)	$ (4,166)	$ (20,131)	$ (11,337)
Net loss per share, basic and diluted (in dollars per share)	$ (0.27)	$ (6.92)	$ (1.11)	$ (18.84)
Weighted-average shares used to compute basic and diluted net loss per share (in shares)	21,572,498	601,667	18,215,857	601,667

Condensed Consolidated Stateme5

Condensed Consolidated Statements of Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Common stock	Additional paid-in capital	Accumulated deficit	Redeemable Convertible Preferred Stock	Private Financing	Private FinancingCommon stock	Private FinancingAdditional paid-in capital	At-the-Market Offering	At-the-Market OfferingCommon stock	At-the-Market OfferingAdditional paid-in capital
Beginning balance (in shares) at Dec. 31, 2016					18,584,390
Beginning balance at Dec. 31, 2016					$ 76,976
Redeemable Convertible Preferred Stock
Accretion of redeemable convertible preferred stock to redemption value					$ 5
Conversion of preferred stock to common stock (in shares)					(18,584,390)
Conversion of preferred stock to common stock					$ (76,981)
Ending balance (in shares) at Feb. 13, 2017					0
Ending balance at Feb. 13, 2017					$ 0
Beginning balance (in shares) at Dec. 31, 2016	833,744	833,744
Beginning balance at Dec. 31, 2016	$ (61,921)	$ 8	$ 5,147	$ (67,076)
Stockholders’ deficit
Conversion of preferred stock to common stock (in shares)					(18,584,390)
Conversion of preferred stock to common stock					$ (76,981)
Beginning balance (in shares) at Dec. 31, 2016					18,584,390
Beginning balance at Dec. 31, 2016					$ 76,976
Redeemable Convertible Preferred Stock
Accretion of redeemable convertible preferred stock to redemption value					$ 5
Conversion of preferred stock to common stock (in shares)		13,066,666			(18,584,390)
Conversion of preferred stock to common stock	$ 76,981	$ 131	76,850		$ (76,981)
Ending balance (in shares) at Sep. 30, 2017					0
Ending balance at Sep. 30, 2017					$ 0
Beginning balance (in shares) at Dec. 31, 2016	833,744	833,744
Beginning balance at Dec. 31, 2016	$ (61,921)	$ 8	5,147	(67,076)
Stockholders’ deficit
Issuance of common stock to investors, net of issuance cost (in shares)							6,359,628			297,653
Issuance of common stock to investors, net of issuance cost						$ 39,156	$ 64	$ 39,092	$ 2,622	$ 3	$ 2,619
Accretion of preferred stock to current redemption value	(5)			(5)
Conversion of preferred stock to common stock (in shares)		13,066,666			(18,584,390)
Conversion of preferred stock to common stock	76,981	$ 131	76,850		$ (76,981)
Issuance of common stock upon reverse merger (in shares)		1,024,960
Issuance of common stock upon reverse merger	204	$ 10	194
Reclassification of preferred stock warrant to common stock warrant	51		51
Issuance of common stock upon exercise of warrant (in shares)		16,387
Exercises of stock options and issuance of restricted stock awards (in shares)		274,337
Exercises of stock options and issuance of restricted stock awards	220	$ 3	217
Employee share purchases (in shares)		13,193
Shares issued for cash under employee share purchase plan	110		110
Share-based compensation expense	1,693		1,693
Net loss	$ (20,126)			(20,126)
Ending balance (in shares) at Sep. 30, 2017	21,886,568	21,886,568
Ending balance at Sep. 30, 2017	$ 38,985	$ 219	$ 125,973	$ (87,207)
Ending balance (in shares) at Feb. 13, 2017					0
Ending balance at Feb. 13, 2017					$ 0

Condensed Consolidated Stateme6

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Cash flows from operating activities:
Net loss	$ (20,126)	$ (11,300)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	227	253
Share-based compensation expense	1,693	129
Non-cash interest expense	85	125
Change in fair value of preferred stock warrants	0	2
Unrealized gain on short term investments	0	9
Changes in operating assets and liabilities:
Accounts receivable	(615)	(9)
Prepaid expenses and other assets	(719)	(545)
Deferred revenue	0	(439)
Accounts payable	(598)	(586)
Accrued liabilities	(871)	893
Net cash used in operating activities	(20,924)	(11,468)
Cash flows from investing activities:
Cash acquired in reverse merger	1,280	0
Purchases of property and equipment	(212)	(240)
Purchases of short-term investments	0	1,010
Net cash provided by (used in) investing activities	1,068	(1,250)
Cash flows from financing activities:
Proceeds from issuance of redeemable convertible preferred stock	0	16,091
Payments of principal on notes payable	(1,500)	0
Proceeds from the exercise of stock options	220	0
Proceeds from employee stock purchases	110	0
Net cash provided by financing activities	40,557	16,081
Net increase in cash and cash equivalents	20,701	3,363
Cash and cash equivalents at beginning of period	22,104	21,235
Cash and cash equivalents at end of period	42,805	24,598
Supplemental disclosure of cash flow information
Interest paid	112	124
Supplemental disclosure of non-cash investing and financing activities
Conversion of preferred stock to common stock	76,981	0
Liabilities assumed, net of non-cash assets received in reverse merger	1,076	0
Transfer of common stock issuance costs from prepaid expenses and other current assets to equity (private financing and at the market sales)	339	0
Reclassification of preferred stock warrant (accrued liability) to common stock warrant (equity)	51	0
Accretion of redeemable convertible preferred stock to redemption value	5	37
Unpaid common stock issuance costs included in prepaid expenses and other assets, accounts payable, and accrued liabilities	3	0
Private Financing
Cash flows from financing activities:
Proceeds from the sale of common stock	40,703	0
Payment of issuance costs associated with the sale of common stock	(1,216)	0
Convertible Preferred Stock
Cash flows from financing activities:
Payment of issuance costs associated with the sale of common stock	0	(10)
At-the-Market Offering
Cash flows from financing activities:
Proceeds from the sale of common stock	2,711	0
Payment of issuance costs associated with the sale of common stock	(172)	0
Shelf Registration
Cash flows from financing activities:
Payment of issuance costs associated with the sale of common stock	$ (299)	$ 0

Description of Business

Description of Business	9 Months Ended
	Sep. 30, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Description of Business	DESCRIPTION OF BUSINESS Miragen Therapeutics, Inc., a Delaware corporation (the “Company” or “Miragen”), is a clinical-stage biopharmaceutical company discovering and developing proprietary RNA-targeted therapeutics with a specific focus on microRNAs and their roles in diseases where there is a high unmet medical need. microRNAs are short RNA molecules, or oligonucleotides, that regulate gene expression or activity and play vital roles in influencing the pathways responsible for many disease processes. The Company’s two lead product candidates, MRG-106 and MRG-201, are currently in clinical development. MRG-106 is an inhibitor of microRNA-155, which is found at abnormally high levels in malignant cells of several blood cancers. MRG-201 is a replacement for microRNA-29 (“miR-29”), which is found at abnormally low levels in a number of pathological fibrotic conditions, including cutaneous, cardiac, renal, hepatic, pulmonary, and ocular fibrosis, as well as in systemic sclerosis. Miragen is also developing MRG-110, an inhibitor of microRNA-92, under a License and Collaboration Agreement (the “Servier Collaboration Agreement”) with Les Laboratoires Servier and Institut de Recherches Servier (collectively, “Servier”). MRG-110 is being developed for the treatment of heart failure and other ischemic disease. In addition to these programs, the Company continues to develop a pipeline of wholly-owned preclinical product candidates. The goal of the Company’s translational medicine strategy is to progress rapidly to first-in-human trials once it has adequately established the pharmacokinetics (the movement of drug into, through, and out of the body), pharmacodynamics (the effect and mechanism of action of a drug), safety, and manufacturability of the product candidate in preclinical studies. Miragen Therapeutics Europe Limited (“Miragen Europe”), the Company’s wholly-owned subsidiary, was formed in January 2011 for the sole purpose of submitting regulatory filings in Europe. Miragen Europe has no employees or operations. On February 13, 2017, the Company, then known as Signal Genetics, Inc. (“Signal”), completed its merger with Miragen Therapeutics, Inc., a then privately-held Delaware corporation (“Private Miragen”). Pursuant to the Agreement and Plan of Merger and Reorganization (the “Merger Agreement”) by and among the Company, Private Miragen, and Signal Merger Sub, Inc., a wholly-owned subsidiary of the Company (“Merger Sub”), Merger Sub merged with and into Private Miragen, with Private Miragen surviving as a wholly-owned subsidiary of the Company (the “Merger”). Immediately, following the Merger, Private Miragen merged with and into the Company, with the Company as the surviving corporation (the “Short-Form Merger” and, together with the Merger, the “Mergers”). In connection with the Short-Form Merger, the Company changed its corporate name to “Miragen Therapeutics, Inc.” The holders of shares of Private Miragen common stock outstanding immediately prior to the Merger received approximately 0.7031 shares of the Company’s common stock in exchange for each share of Private Miragen common stock in the Merger. Following the Merger on February 13, 2017, the combined company had 21,309,440 shares of common stock outstanding at a par value of $0.01 per share (the “Common Stock”) as compared to the par value of Private Miragen’s common stock of $0.001 per share. The accompanying unaudited condensed consolidated financial statements and notes to the unaudited condensed consolidated financial statements give retroactive effect to the exchange ratio and change in par value for all periods presented. Liquidity The Company has incurred annual net operating losses since its inception. As of September 30, 2017 , the Company had an accumulated deficit of $87.2 million and net losses of $5.8 million and $20.1 million for the three and nine months ended September 30, 2017 , respectively. On February 13, 2017, the date of the Merger, Private Miragen received $40.7 million in cash, before offering expenses, from the issuance of common stock to investors. Additionally, on March 31, 2017, the Company entered into an at the market issuance Common Stock Sales Agreement (the “ATM Agreement”) with Cowen and Company, LLC (“Cowen”) under which the Company may offer and sell, from time to time at its sole discretion, shares of its Common Stock having an aggregate offering price of up to $50,000,000 through Cowen, as its sales agent. As of September 30, 2017, the Company has sold, pursuant to the terms of such ATM Agreement, an aggregate of 297,653 shares of its Common Stock, at a weighted average price of $9.11 per share, for aggregate gross proceeds of approximately $2.7 million . Net proceeds received during the nine months ended September 30, 2017 were approximately $2.5 million , including initial expenses for executing the “at the market offering” and commissions to Cowen as sales agent. The Company’s management believes that the $42.8 million of cash and cash equivalents on hand at September 30, 2017 will be sufficient to fund its operations in the normal course of business and allow the Company to meet its liquidity needs through the end of 2018.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2017
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Basis of Presentation The accompanying condensed consolidated financial statements include the accounts of the Company and its wholly-owned subsidiary, Miragen Europe. The financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“U.S. GAAP”) and follow the requirements of the Securities and Exchange Commission (the “SEC”) for interim reporting. As permitted under those rules, certain footnotes or other financial information that are normally required by U.S. GAAP can be condensed or omitted. These financial statements have been prepared on the same basis as the Company’s annual financial statements and, in the opinion of management, reflect all adjustments, consisting only of normal recurring adjustments, which are necessary for a fair statement of the Company’s financial information. These interim results are not necessarily indicative of the results to be expected for the year ending December 31, 2017, or for any other interim period, or for any other future year. The balance sheet as of December 31, 2016 has been derived from audited consolidated financial statements at that date but does not include all the information required by U.S. GAAP for complete financial statements. All intercompany balances and transactions have been eliminated in consolidation. The accompanying unaudited condensed consolidated financial statements and related financial information should be read in conjunction with the audited consolidated financial statements of the Company and the notes thereto contained in the Company’s Form 8-K/A for the year ended December 31, 2016, filed with the SEC on March 31, 2017. The Company’s management performed an evaluation of its activities through the date of filing of these financial statements and concluded that there are no subsequent events requiring disclosure, other than as disclosed. Use of Estimates The Company’s consolidated financial statements are prepared in accordance with U.S. GAAP, which requires it to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and contingent liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Although these estimates are based on the Company’s knowledge of current events and actions it may take in the future, actual results may ultimately differ from these estimates and assumptions. Revenue Recognition The Company recognizes revenue principally from its strategic alliance and collaboration agreement. Revenue is recognized from upfront payments for licenses and milestone payments that are generated from defined research or development events, as well as from the reimbursement of amounts for research and development services under its strategic alliance and collaboration agreement. The Company recognizes revenue when all four of the following criteria are met: (1) persuasive evidence of an arrangement exists; (2) products have been delivered or services rendered; (3) the selling price is fixed or determinable; and (4) collectability is reasonably assured. Multiple-element arrangements are examined to determine whether the deliverables can be separated or must be accounted for as a single unit of accounting. The Servier Collaboration Agreement with Servier, for example, includes a combination of upfront license fees, payments for research and development activities, and milestone payments that are evaluated to determine whether each deliverable under the agreement has value to the customer on a stand-alone basis and whether reliable evidence of fair value for the deliverable exists. Deliverables in an arrangement that do not meet this separation criteria are treated as a single unit of accounting, generally applying applicable revenue recognition guidance for the final deliverable to the combined unit of accounting. The Company recognizes revenue from non-refundable upfront license fees over the term of performance under the Servier Collaboration Agreement. When the performance period is not specified, the Company estimates the performance period based upon provisions contained within the agreement, such as the duration of the research or development term, the existence, or likelihood, of achievement of development commitments, and any other significant commitments. These advance payments are deferred and recorded as deferred revenue upon receipt, pending recognition, and are classified as a short-term or long-term liability in the accompanying condensed consolidated balance sheets. Expected performance periods are reviewed periodically and, if applicable, the amortization period is adjusted, which may accelerate or decelerate revenue recognition. The timing of revenue recognition, specifically as it relates to the amortization of upfront license fees, is significantly influenced by the Company’s estimates. Share-Based Compensation The Company accounts for share-based compensation expense related to stock options granted to employees and members of its board of directors under its 2008 Equity Incentive Plan (the “2008 Plan”) and under its 2016 Equity Incentive Plan (the “2016 Plan”) by estimating the fair value of each stock option or award on the date of grant using the Black-Scholes option pricing model. The Company recognizes share-based compensation expense on a straight-line basis over the vesting term. The Company accounts for stock options issued to non-employees by valuing the award using an option pricing model and remeasuring such awards to the current fair value until the awards are vested or a performance commitment has otherwise been reached. Research and Development Research and development costs are expensed as incurred in performing research and development activities. The costs include employee-related expense including salaries, benefits, share-based compensation, fees for acquiring and maintaining licenses under third party license agreements, consulting fees, costs of research and development activities conducted by third parties on the Company’s behalf, laboratory supplies, depreciation, and facilities and overhead costs. The Company defers and capitalizes non-refundable advance payments for research and development activities until the related goods are received or services performed. In circumstances where amounts have been paid in excess of costs incurred, the Company records a prepaid expense. The Company records upfront and milestone payments to acquire contractual rights to licensed technology as research and development expenses when incurred if there is uncertainty in the Company receiving future economic benefit from the acquired contractual rights. The Company considers future economic benefits from acquired contractual rights to licensed technology to be uncertain until such a drug candidate is approved by the U.S. Food and Drug Administration or when other significant risk factors are abated. Clinical Trial and Preclinical Study Accruals The Company makes estimates of accrued expenses as of each balance sheet date in its condensed consolidated financial statements based on certain facts and circumstances at that time. The Company’s accrued expenses for clinical trials and preclinical studies are based on estimates of costs incurred for services provided by clinical research organizations, manufacturing organizations, and other providers. Payments under the Company’s agreements with external service providers depend on a number of factors, such as site initiation, patient screening, enrollment, delivery of reports, and other events. In accruing for these activities, the Company obtains information from various sources and estimates the level of effort or expense allocated to each period. Adjustments to the Company’s research and development expenses may be necessary in future periods as its estimates change. Cash and Cash Equivalents All highly-liquid investments that have maturities of 90 days or less at the date of purchase are classified as cash equivalents. Cash equivalents are reported at cost, which approximates fair value due to the short maturities of these instruments. Fair Value of Financial Instruments The following tables present information about the Company’s financial assets and liabilities that have been measured at fair value and indicate the fair value of the hierarchy of the valuation inputs utilized to determine such fair value. In general, fair values determined by Level 1 inputs utilize quoted prices (unadjusted) in active markets for identical assets or liabilities. Fair value determined by Level 2 inputs utilize observable inputs other than Level 1 prices, such as quoted prices, for similar assets or liabilities, quoted market prices in markets that are not active or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the related assets or liabilities. Fair values determined by Level 3 inputs are unobservable data points for the asset or liability, and include situations where there is little, if any, market activity for the asset or liability. September 30, December 31, Level 1 Level 3 Level 1 Level 3 (in thousands) Assets: Money market funds (included in cash and cash equivalents) (1) $ 44,112 $ — $ 22,189 $ — Liabilities: Preferred and common stock warrants (included in accrued and other liabilities) $ — $ 82 $ — $ 133 ______________________ (1) Amounts presented for each period above differ from cash and cash equivalents reported in the condensed consolidated balance sheets due to outstanding disbursements and deposits. A reconciliation of the beginning and ending balances of the Company’s liabilities measured at fair value using significant unobservable, or Level 3, inputs are as follows for the nine months ended September 30, 2017 (in thousands): Balance of liability as of December 31, 2016 $ 133 Reclassification of preferred stock warrant to common stock warrant (51 ) Balance of liability as of September 30, 2017 $ 82 Certain of the Company’s financial instruments are not measured at fair value on a recurring basis but are recorded at amounts that approximate their fair value due to the short-term nature of their maturities, such as cash and cash equivalents, accounts receivable, accounts payable, and accrued expenses. The carrying amount of the Company’s note payable approximates its fair value (a Level 2 fair value measurement), reflecting interest rates currently available to the Company. The Company accounts for its warrants to purchase common and preferred stock pursuant to ASC Topic 480, Distinguishing Liabilities from Equity , and classifies warrants for redeemable preferred stock and certain warrants for common stock as liabilities. The warrants are reported at their estimated fair value and any changes in fair value are reflected in interest expense and other related expenses. Concentrations of Credit Risk Financial instruments that potentially subject the Company to concentrations of credit risk consist primarily of cash equivalents, which include short-term investments that have maturities of less than three months. The Company maintains deposits in federally insured financial institutions in excess of federally insured limits. The Company has not experienced any losses in such accounts. The Company invests its excess cash primarily in deposits and money market funds held with two financial institutions. Property and Equipment The Company carries its property and equipment at cost, less accumulated depreciation and amortization. Depreciation is computed using the straight-line method over the estimated useful lives of the assets, generally three to five years . Leasehold improvements are amortized over the shorter of the life of the lease (including any renewal periods that are deemed to be reasonably assured) or the estimated useful life of the assets. Construction in progress is not depreciated until placed in service. Repairs and maintenance costs are expensed as incurred and expenditures for major improvements are capitalized. Impairment of Long-Lived Assets The Company assesses the carrying amount of its property and equipment whenever events or changes in circumstances indicate the carrying amount of such assets may not be recoverable. No impairment charges were recorded during the three and nine months ended September 30, 2017 and 2016 . Net Loss per Share Basic net loss per share is calculated by dividing the net loss applicable to common stockholders by the weighted average number of shares of Common Stock outstanding during the period without consideration of Common Stock equivalents. Since the Company was in a loss position for all periods presented, diluted net loss per share is the same as basic net loss per share for all periods, as the inclusion of all potential common shares outstanding is anti-dilutive. Comprehensive Loss Comprehensive loss is defined as the change in equity during a period from transactions and other events and/or circumstances from non-owner sources. If the Company had comprehensive gains (losses), they would be reflected in the statement of operations and comprehensive loss and as a separate component in the statement of stockholders’ equity (deficit). There were no elements of comprehensive loss during the three and nine months ended September 30, 2017 and 2016 . Income Taxes The Company accounts for income taxes by using an asset and liability method of accounting for deferred 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. A valuation allowance is recorded to the extent it is more likely than not that a deferred tax asset will not be realized. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in operations in the period that includes the enactment date. The Company’s significant deferred tax assets are for net operating loss carryforwards, tax credits, and capitalized start-up costs. The Company has provided a valuation allowance for its entire net deferred tax assets since inception as, due to its history of operating losses, the Company has concluded that it is more likely than not that its deferred tax assets will not be realized. The Company has no unrecognized tax benefits. The Company classifies interest and penalties arising from the underpayment of income taxes in the condensed consolidated statements of operations as general and administrative expenses. No such expenses have been recognized during the three and nine months ended September 30, 2017 and 2016 . Segment Information The Company operates in one operating segment and, accordingly, no segment disclosures have been presented herein. All equipment, leasehold improvements, and other fixed assets are physically located within the United States and all agreements with the Company’s partners are denominated in U.S. dollars, except where noted. Recent Accounting Pronouncements – Not Yet Adopted Revenue Recognition In May 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ ASU”) No. 2014-09 , Revenue from Contracts with Customers (Topic 606) , which outlines a single comprehensive model for entities to use in accounting for revenue arising from contracts with customers and supersedes most current revenue recognition guidance, including industry-specific guidance. The core principle of the revenue model is that “an entity recognizes revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services.” The standard provides enhancements to the quality and consistency of how revenue is reported by companies, while also improving comparability in the financial statements of companies reporting using International Financial Reporting Standards or U.S. GAAP. The new standard also will require enhanced revenue disclosures, provide guidance for transactions that were not previously addressed comprehensively and improve guidance for multiple-element arrangements. This accounting standard becomes effective for the Company for reporting periods beginning after December 15, 2018, and interim reporting periods thereafter. Early adoption is permitted for annual reporting periods (including interim periods) beginning after December 15, 2016. This new standard permits the use of either the retrospective or cumulative effect transition method. In March 2016, the FASB issued ASU No. 2016-08 , Revenue from Contracts with Customers (Topic 606): Principal versus Agent Considerations . The purpose of this standard is to clarify the implementation of guidance on principal versus agent considerations related to ASU 2014-09. The standard has the same effective date as ASU 2014-09 described above. In April 2016, the FASB issued ASU No. 2016-10, Revenue from Contracts with Customer, which provides clarity related to ASU 2014-09 regarding identifying performance obligations and licensing implementation. The standard has the same effective date as ASU 2014-09 described above. In May 2016, the FASB issued ASU 2016-12: Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Practical Expedients , which provides narrow scope improvements and practical expedients related to ASU 2014-09. The purpose of this standard is to clarify certain narrow aspects of ASU 2014-09, such as assessing the collectability criterion, presentation of sales taxes, and other similar taxes collected from customers, noncash consideration, contract modifications at transition, completed contracts at transition, and technical correction. The standard has the same effective date as ASU 2014-09 described above. In December 2016, the FASB issued ASU 2016-20: Technical Corrections and Improvements to Topic 606, Revenue from Contracts with Customers . The amendments in this standard affect narrow aspects of guidance issued in ASU 2014-09. The standard has the same effective date as ASU 2014-09 described above. The Company plans to adopt these new standards in the first quarter of 2019. As of September 30, 2017 , there were limited contracts that will be in effect (actively) as of the transition date and, accordingly, the Company has not yet determined the effect of the standard on its condensed consolidated financial statements. The Company’s selected implementation transition method will be dependent upon contracts that are in place closer to the transition date. Deferred Taxes In November 2015, the FASB issued ASU No. 2015-17 , Balance Sheet Classification of Deferred Taxes . ASU No. 2015-17 requires that deferred tax liabilities and assets be classified as noncurrent in a classified statement of financial position. This standard is effective for the Company for financial statements issued for fiscal years beginning after December 15, 2017, and interim periods thereafter. The Company does not believe the adoption of this standard will have a material impact on its condensed consolidated financial statements due to the full valuation allowance on all net deferred tax assets. Leases In February 2016, the FASB issued ASU No. 2016-02 , Leases (Topic 842), which supersedes FASB ASC Topic 840, Leases (Topic 840), and provides principles for the recognition, measurement, presentation and disclosure of leases for both lessees and lessors. In September 2017, the FASB issued ASU 2017-13, Revenue Recognition (Topic 605), Revenue from Contracts with Customers (Topic 606), Leases (Topic 840), and Leases (Topic 842), which provides additional implementation guidance on the previously issued ASU 2016-02 Leases (Topic 842) . ASU 2016-02 requires lessees to apply a dual approach, classifying leases as either finance or operating leases based on the principle of whether or not the lease is effectively a financed purchase by the lessee. This classification will determine whether lease expense is recognized based on an effective interest method or on a straight-line basis over the term of the lease, respectively. A lessee is also required to record a right-of-use asset and a lease liability for all leases with a term of greater than twelve months regardless of classification. Leases with a term of twelve months or less will be accounted for similar to existing guidance for operating leases. The standard is effective for the Company for fiscal years beginning after December 15, 2019, and interim periods thereafter, with early adoption permitted. At adoption, this update will be applied using a modified retrospective approach. The Company is currently evaluating the impact of this standard on its condensed consolidated financial statements. Share-based Compensation In March 2016, the FASB issued ASU No. 2016-09 , Compensation—Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting , which is intended to simplify accounting for equity share-based payment transactions, including the income tax consequences, classification of awards as either equity or liabilities, and classification on the statement of cash flows. This standard is effective for the Company for annual periods beginning after December 15, 2017, and interim periods thereafter. Amendments related to the timing of when excess tax benefits are recognized, minimum statutory withholding requirements, forfeitures, and intrinsic value should be applied using a modified retrospective transition method by means of a cumulative-effect adjustment to equity as of the beginning of the period in which the guidance is adopted. Amendments related to the presentation of employee taxes paid on the statement of cash flows when an employer withholds shares to meet the minimum statutory withholding requirement should be applied retrospectively. Amendments requiring recognition of excess tax benefits and tax deficiencies in the income statement and the practical expedient for estimating the expected term should be applied prospectively. An entity may elect to apply the amendments related to the presentation of excess tax benefits on the statement of cash flows using either a prospective transition method or a retrospective transition method. The Company is currently evaluating the impact of this standard on its condensed consolidated financial statements. Other new pronouncements issued but not effective as of September 30, 2017 are not expected to have a material impact on the Company’s condensed consolidated financial statements.

Strategic Alliance and Collabor

Strategic Alliance and Collaboration with Servier	9 Months Ended
	Sep. 30, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Strategic Alliance and Collaboration with Servier	STRATEGIC ALLIANCE AND COLLABORATION WITH SERVIER In October 2011, the Company entered into the Servier Collaboration Agreement with Servier for the research, development, and commercialization of RNA-targeting therapeutics in cardiovascular disease, which was subsequently amended. Under the Servier Collaboration Agreement, the Company granted Servier an exclusive license to research, develop, and commercialize RNA-targeting therapeutics for three targets in the cardiovascular field. In 2017, the Company and Servier agreed to amend the Servier Collaboration Agreement to remove three existing targets, add one named target, and provide Servier with the right to add one additional target through September 2019. Under the terms of the amended agreement, the term of the Research Collaboration has been extended through September 2019. Servier’s rights to each named target is limited to therapeutics in the cardiovascular field in their territory, which is worldwide except for the United States and Japan. The Company retains all rights in the United States and Japan. The Company is eligible to receive development milestone payments of €5.8 million to €13.8 million ( $6.9 million to $16.3 million as of September 30, 2017 ) and regulatory milestone payments of €10.0 million to €40.0 million ( $11.8 million to $47.3 million as of September 30, 2017 ) for each target. Additionally, the Company may receive up to €175 million ( $206.7 million as of September 30, 2017 ) in commercialization milestones, as well as quarterly royalty payments expressed in percentages ranging from the low-double digits to the mid-teens (subject to reductions for patent expiration, generic competition, third-party royalty, and costs of goods) on the net sales of any licensed product commercialized by Servier. Servier is obligated to make royalty payments for a period specified under the Servier Collaboration Agreement. As part of the Servier Collaboration Agreement, the Company established a multiple-year research collaboration, under which it jointly performs agreed upon research activities directed to the identification and characterization of named targets and oligonucleotides in the cardiovascular field, which is referred to as the Research Collaboration. The current term of the Research Collaboration extends through September 2019. Servier is responsible for funding the costs of the Research Collaboration, as defined under the Servier Collaboration Agreement. During the three months ended September 30, 2017 and 2016 , the Company recognized as revenue amounts reimbursable under the Servier Collaboration Agreement of $1.5 million and $0.6 million , respectively. During the nine months ended September 30, 2017 and 2016 , the Company recognized as revenue amounts reimbursable under the Servier Collaboration Agreement of $2.0 million and $2.0 million , respectively. The development of each product candidate (commencing with registration enabling toxicology studies) under the Servier Collaboration Agreement is performed pursuant to a mutually agreed upon development plan to be conducted by the parties as necessary to generate data useful for both parties to obtain regulatory approval of such product candidates. Servier is responsible for a specified percentage of the cost of research and development activities under the development plan through the completion of one or more Phase 2 clinical trials and will reimburse the Company for a specified portion of such costs it incurs. The costs of Phase 3 clinical trials for each product candidate will be allocated between the parties at a specified percentage of costs. The applicable percentage for each product candidate will be based upon whether certain events under the Servier Collaboration Agreement occur, including if the Company enters into a third-party agreement for the development and/or commercialization of a product in the United States at least 180 days before the initiation of the first Phase 3 clinical trial, or if the Company subsequently enters into a U.S. partner agreement, or if it does not enter into a U.S. partner agreement but files for approval in the United States using data from the Phase 3 clinical trial. Under the Servier Collaboration Agreement, the Company also granted Servier a royalty-free, non-exclusive license to develop a companion diagnostic in its territory for any therapeutic product that may be developed by Servier under the Servier Collaboration Agreement. The Company also granted Servier an exclusive, royalty-free license to commercialize such a companion diagnostic in its territory for use in connection with the development and commercialization of such therapeutic product in its territory. The Servier Collaboration Agreement will expire as to each underlying product candidate when Servier’s royalty obligations as to such product candidate have expired. Servier may also terminate the Servier Collaboration Agreement for (i) convenience upon a specified number of days’ prior notice to the Company or (ii) upon determination of a safety issue relating to development under the agreement upon a specified number of days’ prior notice to the Company. Either party may terminate the Servier Collaboration Agreement upon a material breach by the other party which is not cured within a specified number of days. The Company may also terminate the agreement if Servier challenges any of the patents licensed by the Company to Servier. The Company determined that the elements within the Servier Collaboration Agreement should be treated as a single unit of accounting because the delivered elements, the licenses, did not have stand-alone value to Servier at the time the license was granted. As such, the Company recognized license fees earned under the Servier Collaboration Agreement as revenue on a proportional performance basis over the estimated period to complete the activities under the Research Collaboration. The total period of performance is equal to the estimated term of the Research Collaboration. The Company measures its progress under the proportional performance method based on actual and estimated full-time equivalents. The Company received a total of $12.4 million ( €9.0 million ) in non-refundable license fees under the Servier Collaboration Agreement. Based on earlier estimates of the term of the Research Collaboration, these license fees had been fully recognized as revenue during the period from October 2011 through December 2016. Accordingly, no amounts were recognized as revenue during the three and nine months ended September 30, 2017 . During the three months and nine months ended September 30, 2016 , the Company recognized license revenue of $0.1 million and $0.5 million , respectively. In total, for the three months ended September 30, 2017 and 2016 , the Company recognized $1.5 million and $0.7 million , respectively, as revenue under the Servier Collaboration Agreement. For the nine months ended September 30, 2017 and 2016 , the Company recognized $2.0 million and $2.5 million , respectively, as revenue under the Servier Collaboration Agreement. Amounts incurred but not billed to Servier for research and related intellectual property activities totaled $1.4 million and $0.3 million as of September 30, 2017 and December 31, 2016 , respectively. These amounts are included in prepaid expenses and other current assets in the Company’s condensed consolidated balance sheets. As of September 30, 2017 , accounts receivable for Servier research and related intellectual property activities totaled $0.5 million . At December 31, 2016 , the Company had no amounts billed to Servier included in accounts receivable.

Reverse Merger

Reverse Merger	9 Months Ended
	Sep. 30, 2017
Business Combinations [Abstract]
Reverse Merger	REVERSE MERGER On February 13, 2017, Private Miragen completed the Merger as discussed in Note 1. For accounting purposes, Private Miragen is considered to be acquiring Signal in the Merger. Private Miragen was determined to be the accounting acquirer based upon the terms of the Merger and other factors including: (i) the Private Miragen security holders own approximately 95.2% of the combined company’s outstanding common stock immediately following the closing of the Merger; (ii) former Private Miragen directors hold all of the board seats in the combined company; and (iii) Private Miragen management holds key management positions of the combined company. The Merger has been accounted for as an asset acquisition rather than business combination because the assets acquired and liabilities assumed by Private Miragen do not meet the definition of a business as defined by U.S. GAAP. The net assets acquired in connection with this transaction were recorded at their estimated acquisition date fair values as of February 13, 2017, the date the Mergers were completed. Immediately prior to the effective date of the Merger, all shares of preferred stock of Private Miragen converted into shares of common stock of Private Miragen on a one -for-one basis. At the effective date of the Merger, the Company issued shares of its Common Stock to Private Miragen stockholders, at an exchange rate of approximately 0.7031 shares of Signal Common Stock in exchange for each share of Private Miragen common stock outstanding immediately prior to the Merger. The exchange rate was calculated by a formula that was determined through arms-length negotiations between the Company and Private Miragen. The combined company assumed all of the outstanding options, whether or not vested, under the 2008 Plan with such options representing the right to purchase a number of shares of Common Stock equal to approximately 0.7031 multiplied by the number of shares of Private Miragen common stock previously represented by such options. Immediately after the Merger on February 13, 2017, there were 21,309,440 shares of Common Stock outstanding. In addition, immediately after the Merger, Private Miragen stockholders, warrant holders, and option holders owned approximately 95.9% of the aggregate number of shares of Common Stock, and the stockholders of the Company immediately prior to the Merger owned approximately 4.1% of the aggregate number of shares of Common Stock (each on a fully diluted basis). On February 13, 2017, prior to the effectiveness of the Merger, Signal had 1,024,960 shares of Common Stock outstanding and a market capitalization of $12.6 million . The estimated fair value of the net assets of Signal on February 13, 2017, prior to the Merger, was $0.2 million . The fair value of Common Stock on the Merger closing date, prior to the Merger, was above the fair value of the Company’s net assets. As the Company’s net assets were predominantly comprised of cash offset by current liabilities, the fair value of the Company’s net assets as of February 13, 2017, prior to the Merger, is considered to be the best indicator of the fair value and, therefore, the estimated preliminary purchase consideration. The following table summarizes the net assets acquired based on their estimated fair values as of February 13, 2017, prior to the Merger (in thousands): Cash and cash equivalents $ 1,280 Prepaid and other assets 248 Accrued liabilities (1,324 ) Net acquired tangible assets $ 204

Property and Equipment

Property and Equipment	9 Months Ended
	Sep. 30, 2017
Property, Plant and Equipment [Abstract]
Property and Equipment	PROPERTY AND EQUIPMENT Property and equipment, net, consisted of the following: September 30, December 31, (in thousands) Lab equipment $ 2,219 $ 2,163 Furniture and fixtures 77 51 Computer hardware and software 361 281 Leasehold improvements 729 688 Property and equipment, gross 3,386 3,183 Less: accumulated depreciation and amortization (2,776 ) (2,558 ) Property and equipment, net $ 610 $ 625 During the three months ended September 30, 2017 and 2016 , depreciation and amortization expense was $0.1 million for each period. During the nine months ended September 30, 2017 and 2016 , depreciation and amortization expense was $0.2 million and $0.3 million , respectively. Depreciation and amortization expense is recorded primarily in research and development expense on the condensed consolidated statements of operations.

Accrued Liabilities

Accrued Liabilities	9 Months Ended
	Sep. 30, 2017
Payables and Accruals [Abstract]
Accrued Liabilities	ACCRUED LIABILITIES Accrued liabilities consisted of the following: September 30, December 31, (in thousands) Accrued outsourced clinical and preclinical studies $ 1,635 $ 1,684 Accrued employee compensation and related taxes 1,061 928 Accrued legal fees and expenses 607 759 Accrued other professional service fees 457 124 Accrued equipment and lab materials 156 — Value of liability-classified stock purchase warrants 82 133 Deferred and accrued facility lease obligations 70 221 Other accrued liabilities 74 60 Total accrued liabilities $ 4,142 $ 3,909

Notes Payable

Notes Payable	9 Months Ended
	Sep. 30, 2017
Debt Disclosure [Abstract]
Notes Payable	NOTES PAYABLE 2015 Silicon Valley Bank Loan Agreement In April 2015, Private Miragen entered into a loan and security agreement with Silicon Valley Bank (the “2015 SVB Loan Agreement”) to borrow up to $10.0 million in two separate tranches. The first tranche of $5.0 million was funded in May 2015 and had a 30 -month payment period following an 18 -month interest-only payment period that ended in November 2016. Amounts outstanding bear interest at the prime rate minus 0.25% ( 4.00% at September 30, 2017 ), with a final payment fee equal to 5.50% of amounts borrowed. Borrowings are secured by a priority security interest, right, and title in all business assets, excluding the Company’s intellectual property, which is subject to a negative pledge. In connection with the first tranche, in April 2015, Private Miragen issued detachable warrants to purchase up to 11,718 shares of Private Miragen preferred stock at an adjusted exercise price of $8.53 per share. At issuance, the warrants were classified as a liability subject to remeasurement at each balance sheet date. Immediately prior to the Merger, these warrants became exercisable for Private Miragen common stock, which was immediately exchanged for the right to purchase the Company’s Common Stock. The Company determined that although the warrants were no longer exercisable for redeemable preferred stock, the warrants continued to be classified as a liability after the Merger due to the right of the holder to require the Company to repurchase the warrants for $0.1 million under certain circumstances. As of September 30, 2017 , the Company estimated the fair value of the warrants to be $0.1 million using a probability adjusted present value method with the following assumptions: term of two years, discount rate of 6.8% , and probability of 90.0% . In December 2016, the 2015 SVB Loan Agreement was amended to extend the end of the draw period from December 31, 2016 to July 31, 2017. The Company chose not to draw the second $5.0 million tranche prior to the expiration of the draw period in July 2017. Amounts outstanding under notes payable are as follows: September 30, December 31, (in thousands) Principal amount outstanding $ 3,167 $ 4,667 Unamortized debt discount (6 ) (14 ) Unamortized debt issuance costs (14 ) (31 ) Accreted final payment fee 227 167 Total notes payable 3,374 4,789 Less: current maturities (1,983 ) (1,969 ) Long-term notes payable, net of current portion $ 1,391 $ 2,820 Future annual minimum principal payments of notes payable are as follows: September 30, (in thousands) 2017 (remainder of year) $ 500 2018 2,000 2019 667 Total $ 3,167

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	COMMITMENTS AND CONTINGENCIES Indemnification Agreements The Company has entered into indemnification agreements with each of its directors and officers whereby it has agreed to indemnify such persons for certain events or occurrences while the individual is, or was, serving as a director, officer, employee, or other agent of the Company. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is unlimited. Employment Agreements The Company has entered into agreements with its executives that provide for base salary, severance, eligibility for bonuses, and other generally available benefits. The agreements provide that the Company may terminate the employment of its executives at any time, with or without cause. If an executive is terminated without cause, as defined in the employment agreements, or an executive resigns for good reason, as defined in the employment agreements, then the executive is entitled to receive, upon the execution of a release agreement, a severance package consisting of: (i) the equivalent of 12 months of the executive’s base salary in effect immediately prior to date of termination, (ii) acceleration of vesting of the equivalent of 12 months of vesting of the executive’s outstanding unvested stock options or other equity awards that were outstanding as of the effective date of the executive’s employment agreement, and (iii) 12 months of continued health coverage. If an executive is terminated without cause or resigns for good reason within one month prior to or 12 months following a change of control, as defined in the employment agreements, the executive is entitled to receive, upon the execution of a release agreement, a severance package consisting of: (i) the equivalent of 12 months of the executive’s base salary in effect immediately prior to date of termination, (ii) the vesting in full of the executive’s then-outstanding stock options or other equity awards subject to time-based vesting, and (iii) 12 months of continued health coverage. Solely in the case of the Company’s Chief Executive Officer, if such termination occurs one month before or 12 months following a change of control, then, upon the execution of a release agreement, the executive is entitled to: (i) the equivalent of 24 months of the executive’s base salary in effect immediately prior to the date of termination, (ii) the vesting in full of the executive’s outstanding stock options or other equity awards subject to time-based vesting, and (iii) 12 months of continued health coverage. License Agreements with the University of Texas As of September 30, 2017 , the Company had five exclusive patent license agreements (the “UT License Agreements”) with the Board of Regents of The University of Texas System (the “University of Texas”). Under each of the UT License Agreements, the University of Texas granted the Company exclusive and nonexclusive licenses to certain patent and technology rights. The University of Texas is a minority stockholder of the Company. In consideration of rights granted by the University of Texas, the Company is required to: (i) pay a nonrefundable upfront license documentation fee in the amount of $10 thousand per license; (ii) pay an annual license maintenance fee in the amount of $10 thousand per license starting one year from the date of each agreement; (iii) reimburse the University of Texas for actual costs incurred in conjunction with the filing, prosecution, enforcement, and maintenance of patent rights prior to the effective date; and (iv) bear all future costs of and manage the filing, prosecution, enforcement, and maintenance of patent rights. During the nine months ended September 30, 2017 and 2016, the Company incurred immaterial upfront and maintenance fees, which were recorded as research and development expense. All costs related to the filing, prosecution, and maintenance of patent and technology rights are recorded as general and administrative expense when incurred. Under the terms of the UT License Agreements, the Company may be obligated to make the following future milestone payments for each licensed product candidate: (i) up to approximately $0.6 million upon the initiation of defined clinical trials; (ii) $2.0 million upon regulatory approval in the United States; and (iii) $0.5 million per region upon regulatory approval in other specified regions. Additionally, if the Company or its sublicensees successfully commercializes any product candidate subject to the UT License Agreements, it is responsible for royalty payments in the low-single digits based upon net sales of such licensed products and payments at a percentage in the mid-teens of any sublicense income, subject to specified exceptions. The University of Texas’s right to these royalty payments will expire as to each license agreement upon the expiration of the last patent claim subject to the applicable UT License Agreement. The license term extends on a product by product and country by country basis until the expiration of the last to expire of the licensed patents that covers such product in such country. Upon expiration of the royalty payment obligation, the Company will have a fully paid license in such country. The Company may also terminate each UT License Agreement for convenience upon a specified number of days’ prior notice to the University of Texas. The University of Texas also has the right to earlier terminate the UT License Agreements after a defined date under specified circumstances where the Company has effectively abandoned its research and development efforts or has no sales. The UT License Agreements will terminate under customary termination provisions including automatic termination upon the Company’s bankruptcy or insolvency, upon notice of an uncured material breach, and upon mutual written consent. All charges incurred under the UT License Agreements have been expensed to date due to the uncertainty as to future economic benefit from the acquired rights. License Agreement with Roche Innovation Center Copenhagen A/S (formerly Santaris Pharma A/S) In June 2010, Private Miragen entered into a license agreement with the Santaris Pharma A/S, which was acquired by F. Hoffmann-La Roche Ltd (“Roche”) in 2014 and subsequently changed its name to Roche Innovation Center Copenhagen A/S (“RICC”). The agreement was amended in October 2011 and amended and restated in December 2012 (the “RICC License Agreement”). Under the RICC License Agreement, the Company has received exclusive and nonexclusive licenses from RICC to use specified technology of RICC (the “RICC Technology”) for specified uses including research, development, and commercialization of pharmaceutical products using this technology worldwide. Under the RICC License Agreement, the Company has the right to develop and commercialize the RICC Technology directed to four specified targets and the option to obtain exclusive product licenses for up to six additional targets. The acquisition of Santaris Pharma A/S by Roche was considered a change-of-control under the RICC License Agreement, and as such, certain terms and conditions of the RICC License Agreement changed, as contemplated and in accordance with the RICC License Agreement. These changes primarily relate to milestone payments reflected in the disclosures below. As consideration for the grant of the license and option, Private Miragen previously paid RICC $2.3 million and issued RICC 856,806 shares of Private Miragen’s Series A convertible preferred stock, which subsequently converted to 602,420 shares of Common Stock. If the Company exercises its option to obtain additional product licenses or to replace the target families, it will be required to make additional payments to RICC. Under the terms of the RICC License Agreement, milestone payments were previously decreased by a specified percentage as a result of the change of control by RICC referenced above. The Company is obligated to make future milestone payments for each licensed product for up to $5.2 million , which is inclusive of a potential product license option fee. Certain of these milestones will be increased by a specified percentage if the Company undergoes a change in control during the term of the RICC License Agreement. If the Company grants a third party a sublicense to the RICC Technology, it is required to remit to Roche up to a specified percentage of the upfront and milestone and other specified payments it receives under its sublicense, and if such sublicense covers use of the RICC Technology in the United States or the entire European Union, the Company will not have any further obligation to pay the fixed milestone payments noted above. If the Company or its sublicensee successfully commercializes any product candidate subject to the RICC License Agreements, then RICC is entitled to royalty payments in the mid-single digits on the net sales of such product, provided that if such net sales are made by a sublicensee under the RICC License Agreement, RICC is entitled to royalty payments equal to the lesser of a percentage in the mid-single digits on the net sales of such product or a specified percentage of the royalties paid to the Company by such sublicensee, subject to specified restrictions. The Company is obligated to make any such royalty payments until the later of: (i) a specified anniversary of the first commercial sale of the applicable product or (ii) the expiration of the last valid patent claim licensed by RICC under the RICC License Agreement underlying such product. Upon the occurrence of specified events, the royalty owed to RICC will be decreased by a specified percentage. The RICC License Agreement will terminate upon the latest of the expiration of all of RICC’s royalty rights, the termination of the last Miragen target, or the expiration of its right to obtain a product license for a new target under the RICC License Agreement. The Company may also terminate the RICC License Agreement for convenience upon a specified number of days’ prior notice to RICC, subject to specified terms and conditions. Either party may terminate the RICC License Agreement upon an uncured material breach by the other party and RICC may terminate the RICC License Agreement upon the occurrence of other specified events immediately or after such event is not cured within a specified number of days, as applicable. All charges incurred under the RICC License Agreement have been expensed to date due to the uncertainty as to future economic benefit from the acquired rights. For the nine months ended September 30, 2017 and 2016, the Company paid $0.5 million and $0.2 million , respectively, to Roche for raw materials to be used in its drug manufacturing process. Subcontract Agreement with Yale University In October 2014, Private Miragen and Yale University (“Yale”) entered into a subcontract agreement and into a subaward agreement in March 2015 (the “Yale Agreements”), which was subsequently amended. Under the Yale Agreements, the Company is providing specified services regarding the development of a proprietary compound that targets miR-29 in the indication of idiopathic pulmonary fibrosis. Yale entered into the Yale Agreements in connection with a grant that Yale received from the National Institutes of Health (“NIH”) for the development of a miR-29 mimic as a potential therapy for pulmonary fibrosis. In consideration of the Company’s services under the Yale Agreements, Yale has agreed to pay the Company up to $1.1 million over five years , subject to the availably of funds under the grant and continued eligibility. Under the terms of the Yale Agreements, the Company retains all rights to any and all intellectual property developed solely by the Company in connection with the Yale Agreements. Yale has also agreed to provide the Company with an exclusive option to negotiate in good faith for an exclusive, royalty-bearing license from Yale for any intellectual property developed by Yale or jointly by the parties under the Yale Agreements. Yale is responsible for filing, prosecuting, and maintaining foreign and domestic patent applications and patents on all inventions jointly developed by the parties under the Yale Agreements. Through September 30, 2017 , the Company has received $0.1 million under the Yale Agreements. The Yale Agreements terminate automatically on the date that Yale delivers its final research report to the NIH under the terms of the grant underlying the Yale Agreements. Each party may also terminate the Yale Agreements upon a specified number of days’ notice in the event that the NIH’s grant funding is reduced or terminated or upon material breach by the other party. License Agreements with the t2cure GmbH In October 2010, Private Miragen entered into a license and collaboration agreement (the “t2cure Agreement”) with t2cure GmbH (“t2cure”), which was subsequently amended. Under the t2cure Agreement, the Company has received a worldwide, royalty-bearing, and exclusive license to specified patent and technology rights relating to miR-92. In consideration of rights granted by t2cure, Private Miragen paid an upfront fee of $46 thousand and agreed to: (i) pay an annual license maintenance fee in the amount of €3 thousand ( $3 thousand as of September 30, 2017 ); and (ii) reimburse t2cure for costs incurred in conjunction with the filing, prosecution, enforcement, and maintenance of patent rights. Under the terms of the t2cure Agreement, the Company is obligated to make the following future milestone payments for each licensed product: (i) up to approximately $0.7 million upon the initiation of certain defined clinical trials; (ii) $2.5 million upon regulatory approval in the United States; and (iii) up to $1.5 million per region upon regulatory approval in the European Union or Japan. Additionally, if the Company or its sublicensees successfully commercialize any product candidate subject to the t2cure Agreement, it is responsible for royalty payments equal to percentages in the low-single digits upon net sales of licensed products and sublicense fees equal to a percentage in the low-twenties of sublicense income received by it. The Company is obligated to make any such royalty payment until the later of (i) the tenth anniversary of the first commercial sale of the applicable product or (ii) the expiration of the last valid claim to a patent licensed by t2cure under the t2cure Agreement covering such product. If such patent claims expire prior to the end of the ten -year term, then the royalty owed to t2cure will be decreased by a specified percentage. The Company also has the right to decrease its royalty payments by a specified percentage for royalties paid to third parties for licenses to certain third-party intellectual property. The license term extends on a country by country basis until the later of: (i) the tenth anniversary of the first commercial sale of a licensed product in a country and (ii) the expiration of the last to expire valid claim that claims such licensed product in such country. Upon expiration of the royalty payment obligation, the Company will have a fully paid license in such country. The Company has the right to terminate the t2cure Agreement at will, on a country-by-country basis, after 60 days’ written notice. The t2cure Agreement will also automatically terminate upon the Company’s bankruptcy or insolvency or upon notice of an uncured material breach. The Company has expensed all charges incurred under the t2cure Agreement to date, due to the uncertainty as to future economic benefit from the acquired rights. License Agreement with The Brigham and Women’s Hospital In May 2016, Private Miragen and The Brigham and Women’s Hospital (“BWH”) entered into an exclusive patent license agreement (the “BWH License Agreement”). Under the BWH License Agreement, the Company has an exclusive, worldwide license, including a right to sublicense, to specified patent rights and a nonexclusive, worldwide license, including a right to sublicense, to specified technology rights of BWH, each related to certain microRNAs believed to be involved in various neurodegenerative disorders. As consideration for these rights, the Company is obligated to pay a specified annual license fee. BWH is also entitled to milestone payments of up to approximately $2.6 million for each of the Company’s product candidates developed based on the patent rights subject to the BWH License Agreement plus a one-time sales milestone payment of $0.3 million for all product candidates developed based on the patent rights subject to the BWH License Agreement. If the Company were to successfully commercialize any product candidate subject to the BWH License Agreement, then BWH is entitled to royalty payments in the low-single digits on the net sales of such product. BWH’s right to these royalty payments will expire on a product by product and country by country basis upon the expiration of the last patent claim in such country that is subject to the BWH License Agreement and covers the product, and the Company’s license to such product in such country will become fully paid at such time. BWH is also entitled to a percentage in the low-double digits of any sublicense income from such product, subject to specified exceptions. The Company is also responsible for all costs associated with the preparation, filing, prosecution, and maintenance of the patent rights subject to the BWH License Agreement. Additionally, the Company is obligated to use commercially reasonable efforts to develop a product under the BWH License Agreement and to meet specified diligence milestones thereunder. The BWH License Agreement will terminate upon the expiration of all issued patents and patent applications subject to the patent rights under the agreement. The Company may also terminate the BWH License Agreement for convenience upon a specified number of days’ prior notice to BWH. BWH may terminate the BWH License Agreement upon a breach by the Company of its payment obligations and upon the occurrence of other specified events that are not cured within a specified number of days, provided that such termination is automatic upon the Company’s bankruptcy or insolvency. During the nine months ended September 30, 2017 , the Company paid the first annual license fee, which was immaterial. To date, the Company has not met any milestones that have required milestone payments. Facility Lease In December 2010, Private Miragen entered into a multi-year lease agreement for its current office and lab space. The agreement was subsequently amended to extend the term through August 2020. This lease is noncancelable. Minimum base lease payments, including the impact of tenant improvement allowances, under the operating lease are recognized on a straight-line basis over the full term of the lease. During the three months ended September 30, 2017 and 2016 , rent expense was $0.1 million for each period. During the nine months ended September 30, 2017 and 2016 , rent expense was $0.2 million and $0.3 million , respectively. The Company is also required to pay for operating expenses. During the three months ended September 30, 2017 and 2016 , operating expenses were $0.1 million for each period. During the nine months ended September 30, 2017 and 2016 , operating expenses related to the leased space were $0.2 million for each period. Future annual minimum payments under the lease are as follows: September 30, (in thousands) 2017 (remainder of year) $ 95 2018 391 2019 404 2020 277 Total $ 1,167

Capital Stock

Capital Stock	9 Months Ended
	Sep. 30, 2017
Equity [Abstract]
Capital Stock	CAPITAL STOCK Common Stock The Company is authorized to issue 105,000,000 shares of its stock, of which 100,000,000 shares have been designated as Common Stock and 5,000,000 shares have been designated as preferred stock with a par value of $0.01 per share. The number of authorized shares of Common Stock may be increased or decreased by the affirmative vote of the holders of a majority of the Company’s stock who are entitled to vote. Each share of Common Stock is entitled to one vote. The holders of Common Stock are entitled to receive dividends when and as declared or paid by its board of directors. At the effective date of the Merger, each outstanding share of Private Miragen common stock was converted into the right to receive approximately 0.7031 shares of the Company’s Common Stock. On February 13, 2017, immediately prior to the Merger and in accordance with subscription agreements entered into with certain investors in October 2016, Private Miragen issued and sold an aggregate of 9,045,126 shares of Private Miragen’s common stock at a price per share of $4.50 , or 6,359,628 shares of Common Stock at a price per share of $6.40 as adjusted for the exchange ratio in the Merger, for aggregate consideration of $40.7 million , offset by associated financing fees of $1.5 million . Series Preferred In February 2017, in conjunction with the Merger, all of the outstanding redeemable convertible preferred stock of Private Miragen converted into Private Miragen common stock at a ratio of 1 :1 and was immediately exchanged for the Company’s Common Stock at an exchange ratio of 0.7031 as a result of the Merger. A summary of the conversion by class of preferred stock is summarized as follows (in thousands, except share data): Series A Series B Series C Total Shares Amount Shares Amount Shares Amount Shares Amount Balance at December 31, 2016 7,149,176 $ 23,124 2,166,651 $ 12,975 9,268,563 $ 40,877 18,584,390 $ 76,976 Accretion of redeemable convertible preferred stock to redemption value — 1 — 1 — 3 — 5 Conversion of preferred stock to common stock (7,149,176 ) (23,125 ) (2,166,651 ) (12,976 ) (9,268,563 ) (40,880 ) (18,584,390 ) (76,981 ) Balance at February 13, 2017 — $ — — $ — — $ — — $ — As of September 30, 2017 , the Company had no shares of preferred stock outstanding and had not designated the rights, preferences, or privileges of any class or series of preferred stock. Although the Company’s board of directors has the authority to issue preferred stock at its discretion in one or more classes or series and to fix the designations, powers, preferences and rights, and the qualifications, limitations, or restrictions thereof, including dividend rights, conversion right, voting rights, terms of redemption, liquidation preferences, and the number of shares constituting any class or series of preferred stock, without further vote or action by the stockholders. Common Stock Sales Agreement On March 31, 2017, the Company entered into an ATM Agreement with Cowen, under which the Company may offer and sell, from time to time at its sole discretion, shares of its Common Stock having an aggregate offering price of up to $50.0 million through Cowen as its sales agent. Cowen may sell the Common Stock by any method permitted by law deemed to be an “at the market offering” as defined in Rule 415 of the Securities Act of 1933, as amended, including without limitation sales made by means of ordinary brokers’ transactions on The NASDAQ Capital Market or otherwise at market prices prevailing at the time of sale, in block transactions, or as otherwise directed by the Company. Cowen will use commercially reasonable efforts to sell the Common Stock from time to time, based upon instructions from the Company (including any price, time or size limits or other customary parameters or conditions the Company may impose). The Company will pay Cowen a commission equal to 3.0% of the gross sales proceeds of any Common Stock sold through Cowen under the ATM Agreement, and also has provided Cowen with customary indemnification rights. The Company is not obligated to make any sales of Common Stock under the ATM Agreement. The offering of shares of Common Stock pursuant to the ATM Agreement will terminate upon the earlier of: (i) the sale of all Common Stock subject to the ATM Agreement or (ii) termination of the ATM Agreement in accordance with its terms. As of September 30, 2017 , the Company has sold, pursuant to the terms of the ATM Agreement, 297,653 shares of Common Stock, at a weighted average price of $9.11 per share, for aggregate gross proceeds of approximately $2.7 million . Net proceeds received during the nine months ended September 30, 2017 were approximately $2.5 million , including initial expenses for executing the “at the market offering” and commissions to Cowen as sales agent. See Note 13 for a discussion of sales of Common Stock made under the ATM Agreement after September 30, 2017 . The Company has incurred approximately $0.4 million in offering costs for the ATM Agreement, including costs for the related shelf filing, but excluding the commissions paid to Cowen as sales agent. The costs incurred are initially included in prepaid expenses and other current assets and are being amortized to a reduction of offering costs as shares are sold under the ATM Agreement. The costs reflected in the condensed consolidated statement of cash flows include the 3.0% commission paid to Cowen on shares sold ( $0.1 million through September 30, 2017 ) along with $8 thousand of amortized offering costs. WARRANTS Stock purchase warrant activity is as follows for the nine months ended September 30, 2017 : Common Stock Warrants Preferred Stock Warrants Number Weighted Average Exercise Price Number Weighted Average Exercise Price Outstanding at December 31, 2016 7,031 $ 0.57 25,779 $ 6.21 Warrants acquired in Merger 13,534 $ 80.70 — $ — Preferred stock warrants converted into Common Stock warrants 25,779 $ 6.21 (25,779 ) $ 6.21 Exercises (21,092 ) $ 3.04 — $ — Outstanding at September 30, 2017 25,252 $ 47.21 — $ — A summary of outstanding Common Stock purchase warrants as of September 30, 2017 is as follows: Number of Underlying Shares Exercise Price Expiration Date 13,534 $80.70 2019 & 2020 11,718 $8.53 2025 25,252 In connection with the Merger, Private Miragen assumed 13,534 outstanding warrants to purchase shares of the Company’s Common Stock at a weighted average exercise price of $80.70 per share. The assumed warrants expire on various dates in 2019 and 2020.

Warrants

Warrants	9 Months Ended
	Sep. 30, 2017
Other Liabilities Disclosure [Abstract]
Warrants	CAPITAL STOCK Common Stock The Company is authorized to issue 105,000,000 shares of its stock, of which 100,000,000 shares have been designated as Common Stock and 5,000,000 shares have been designated as preferred stock with a par value of $0.01 per share. The number of authorized shares of Common Stock may be increased or decreased by the affirmative vote of the holders of a majority of the Company’s stock who are entitled to vote. Each share of Common Stock is entitled to one vote. The holders of Common Stock are entitled to receive dividends when and as declared or paid by its board of directors. At the effective date of the Merger, each outstanding share of Private Miragen common stock was converted into the right to receive approximately 0.7031 shares of the Company’s Common Stock. On February 13, 2017, immediately prior to the Merger and in accordance with subscription agreements entered into with certain investors in October 2016, Private Miragen issued and sold an aggregate of 9,045,126 shares of Private Miragen’s common stock at a price per share of $4.50 , or 6,359,628 shares of Common Stock at a price per share of $6.40 as adjusted for the exchange ratio in the Merger, for aggregate consideration of $40.7 million , offset by associated financing fees of $1.5 million . Series Preferred In February 2017, in conjunction with the Merger, all of the outstanding redeemable convertible preferred stock of Private Miragen converted into Private Miragen common stock at a ratio of 1 :1 and was immediately exchanged for the Company’s Common Stock at an exchange ratio of 0.7031 as a result of the Merger. A summary of the conversion by class of preferred stock is summarized as follows (in thousands, except share data): Series A Series B Series C Total Shares Amount Shares Amount Shares Amount Shares Amount Balance at December 31, 2016 7,149,176 $ 23,124 2,166,651 $ 12,975 9,268,563 $ 40,877 18,584,390 $ 76,976 Accretion of redeemable convertible preferred stock to redemption value — 1 — 1 — 3 — 5 Conversion of preferred stock to common stock (7,149,176 ) (23,125 ) (2,166,651 ) (12,976 ) (9,268,563 ) (40,880 ) (18,584,390 ) (76,981 ) Balance at February 13, 2017 — $ — — $ — — $ — — $ — As of September 30, 2017 , the Company had no shares of preferred stock outstanding and had not designated the rights, preferences, or privileges of any class or series of preferred stock. Although the Company’s board of directors has the authority to issue preferred stock at its discretion in one or more classes or series and to fix the designations, powers, preferences and rights, and the qualifications, limitations, or restrictions thereof, including dividend rights, conversion right, voting rights, terms of redemption, liquidation preferences, and the number of shares constituting any class or series of preferred stock, without further vote or action by the stockholders. Common Stock Sales Agreement On March 31, 2017, the Company entered into an ATM Agreement with Cowen, under which the Company may offer and sell, from time to time at its sole discretion, shares of its Common Stock having an aggregate offering price of up to $50.0 million through Cowen as its sales agent. Cowen may sell the Common Stock by any method permitted by law deemed to be an “at the market offering” as defined in Rule 415 of the Securities Act of 1933, as amended, including without limitation sales made by means of ordinary brokers’ transactions on The NASDAQ Capital Market or otherwise at market prices prevailing at the time of sale, in block transactions, or as otherwise directed by the Company. Cowen will use commercially reasonable efforts to sell the Common Stock from time to time, based upon instructions from the Company (including any price, time or size limits or other customary parameters or conditions the Company may impose). The Company will pay Cowen a commission equal to 3.0% of the gross sales proceeds of any Common Stock sold through Cowen under the ATM Agreement, and also has provided Cowen with customary indemnification rights. The Company is not obligated to make any sales of Common Stock under the ATM Agreement. The offering of shares of Common Stock pursuant to the ATM Agreement will terminate upon the earlier of: (i) the sale of all Common Stock subject to the ATM Agreement or (ii) termination of the ATM Agreement in accordance with its terms. As of September 30, 2017 , the Company has sold, pursuant to the terms of the ATM Agreement, 297,653 shares of Common Stock, at a weighted average price of $9.11 per share, for aggregate gross proceeds of approximately $2.7 million . Net proceeds received during the nine months ended September 30, 2017 were approximately $2.5 million , including initial expenses for executing the “at the market offering” and commissions to Cowen as sales agent. See Note 13 for a discussion of sales of Common Stock made under the ATM Agreement after September 30, 2017 . The Company has incurred approximately $0.4 million in offering costs for the ATM Agreement, including costs for the related shelf filing, but excluding the commissions paid to Cowen as sales agent. The costs incurred are initially included in prepaid expenses and other current assets and are being amortized to a reduction of offering costs as shares are sold under the ATM Agreement. The costs reflected in the condensed consolidated statement of cash flows include the 3.0% commission paid to Cowen on shares sold ( $0.1 million through September 30, 2017 ) along with $8 thousand of amortized offering costs. WARRANTS Stock purchase warrant activity is as follows for the nine months ended September 30, 2017 : Common Stock Warrants Preferred Stock Warrants Number Weighted Average Exercise Price Number Weighted Average Exercise Price Outstanding at December 31, 2016 7,031 $ 0.57 25,779 $ 6.21 Warrants acquired in Merger 13,534 $ 80.70 — $ — Preferred stock warrants converted into Common Stock warrants 25,779 $ 6.21 (25,779 ) $ 6.21 Exercises (21,092 ) $ 3.04 — $ — Outstanding at September 30, 2017 25,252 $ 47.21 — $ — A summary of outstanding Common Stock purchase warrants as of September 30, 2017 is as follows: Number of Underlying Shares Exercise Price Expiration Date 13,534 $80.70 2019 & 2020 11,718 $8.53 2025 25,252 In connection with the Merger, Private Miragen assumed 13,534 outstanding warrants to purchase shares of the Company’s Common Stock at a weighted average exercise price of $80.70 per share. The assumed warrants expire on various dates in 2019 and 2020.

Share-Based Compensation

Share-Based Compensation	9 Months Ended
	Sep. 30, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-Based Compensation	SHARE-BASED COMPENSATION Equity Incentive Plans In February 2017, the Company’s 2014 Stock Incentive Plan (the “2014 Plan”) was terminated as a result of the Merger. There are no awards outstanding under the 2014 Plan and no future awards will be issued under the 2014 Plan. As of September 30, 2017 , there were 2,060,993 options outstanding and no remaining equity awards available for future issuances under the 2008 Plan. All awards granted under the 2008 Plan that, after February 13, 2017, expire or terminate for any reason prior to exercise or settlement, are forfeited, or are reacquired, withheld, or not issued to satisfy a tax withholding obligation or to satisfy the exercise price of a stock award, will become available for grant under the 2016 Plan in accordance with its terms. The 2016 Plan provides for the grant of incentive stock options, nonstatutory stock options, stock appreciation rights, restricted stock awards, restricted stock unit awards, other stock awards, and performance awards that may be settled in cash, stock, or other property. All employees and non-employee directors are eligible to participate in the 2016 Plan and may receive all types of awards other than incentive stock options. Incentive stock options may be granted under the 2016 Plan only to employees (including officers) and employees of the Company’s affiliates. The aggregate number of shares of Common Stock that may be issued under the 2016 Plan will not exceed 4,182,404 shares, which number is the sum of: (i) 1,681,294 shares, plus (ii) the number of shares subject to outstanding stock awards that were granted under the 2008 Plan, that, from and after the closing date of the Merger, expire or terminate for any reason prior to exercise or settlement, are forfeited because of the failure to meet a contingency or condition required to vest such shares, or are reacquired, withheld, or not issued to satisfy a tax withholding obligation in connection with an award or to satisfy the purchase price or exercise price of a stock award, if any, as such shares become available from time to time. As of September 30, 2017 , there were 908,227 equity awards outstanding and 773,067 remaining equity awards available for future issuances under the 2016 Plan. Options granted under the 2008 Plan and 2016 Plan have an exercise price equal to the market value of the Common Stock at the date of grant and expire ten years from the date of grant. Generally, options vest 25% on the first anniversary of the vesting commencement date and 75% ratably in equal monthly installments over the remaining 36 months . The Company has also granted options that vest in equal monthly or quarterly amounts over periods up to 48 months . A summary of Common Stock option activity is as follows: Number of Options Weighted Average Exercise Price Outstanding at December 31, 2016 2,321 $ 1.44 Granted 956 $ 11.48 Exercised (274 ) $ (0.80 ) Forfeited (34 ) $ (11.40 ) Outstanding at September 30, 2017 2,969 $ 4.62 Fair Value Assumptions The Company uses the Black-Scholes option pricing model to estimate the fair value of stock options granted. The Black-Scholes model requires inputs for risk-free interest rate, dividend yield, volatility, and expected lives of the options. Because the Company has a limited history of stock purchase and sale activity, expected volatility is based on historical data from public companies similar to the Company in size and nature of operations. The Company will continue to use similar entity volatility information until its historical volatility is relevant to measure expected volatility for option grants. The Company has not applied a forfeiture rate to its assumptions as the impact would not be material to the consolidated financial statements. The risk-free rate for periods within the contractual life of each option is based on the U.S. Treasury yield curve in effect at the time of the grant for a period commensurate with the expected term of the grant. The expected term (without regard to forfeitures) for options granted represents the period of time that options granted are expected to be outstanding and is derived from the contractual terms of the options granted and expected option exercise behaviors. Prior to the Merger, Private Miragen estimated the fair value of underlying shares of common stock using a third-party valuation report that derived the fair value using the probability-weighted expected return method. After the Merger, the fair value of the underlying Common Stock is based on the closing price of the Common Stock on the NASDAQ Capital Market at the date of grant. Stock Options Granted to Employees The weighted-average fair value of options granted during the nine months ended September 30, 2017 and 2016 was $8.32 and $0.70 , respectively. The fair value was determined by the Black-Scholes option pricing model using the following assumptions: Nine Months Ended 2017 2016 Expected term, in years 6.44 5.00 Expected volatility 83.8 % 84.0 % Risk-free interest rate 2.1 % 1.1 % Expected dividend yield — % — % Weighted average grant date fair value of underlying Common Stock $ 11.48 $ 1.05 Stock Options Granted to Non-Employees The Company determines the value of Common Stock options issued to non-employees using the Black-Scholes option pricing model and adjusting the value of such awards to current fair value each reporting period until the awards are vested or a performance commitment has otherwise been reached. No Common Stock options were issued to non-employees during the nine months ended September 30, 2017 and 2016 . Employee Stock Purchase Plan The 2016 Employee Stock Purchase Plan (“ESPP”) allows qualified employees to purchase shares of the Company's Common Stock at a price equal to 85% of the lower of: (i) the closing price at the beginning of the offering period or (ii) the closing price at the end of the offering period. The Company expects that a new 6-month offering period will begin each August 22 and February 22. As of September 30, 2017 , the Company had 0.2 million shares available for issuance and 13 thousand shares had been issued under the ESPP. Share-Based Compensation Expense Share-based compensation related to all equity awards issued pursuant to the 2008 Plan and 2016 Plan and for estimated shares to be issued under the ESPP for the current purchase period is included in the condensed consolidated statements of operations as follows: Three Months Ended Nine Months Ended 2017 2016 2017 2016 (in thousands) Research and development $ 263 $ 5 $ 643 $ 22 General and administrative 416 40 1,050 107 Total share-based compensation expense $ 679 $ 45 $ 1,693 $ 129 As of September 30, 2017 , the Company had $7.4 million of total unrecognized employee share-based compensation costs, which the Company expects to recognize over a weighted-average remaining period of 3.2 years. As of September 30, 2017 , based on the current estimate of fair value, the Company estimates that the remaining unrecognized share-based compensation expense related to non-employees of $0.1 million will be recorded to expense over a weighted-average remaining period of 0.9 years.

Net Loss Per Share

Net Loss Per Share	9 Months Ended
	Sep. 30, 2017
Earnings Per Share [Abstract]
Net Loss Per Share	NET LOSS PER SHARE Basic net loss per share is computed by dividing the net loss available to common stockholders by the weighted-average number of Common Stock outstanding. Diluted net loss per share is computed similarly to basic net loss per share except that the denominator is increased to include the number of additional shares of Common Stock that would have been outstanding if the potential shares of Common Stock had been issued and if the additional shares of Common Stock were dilutive. Diluted net loss per share is the same as basic net loss per share of Common Stock, since the effects of potentially dilutive securities are antidilutive. Potentially dilutive securities include the following: September 30, 2017 September 30, 2016 (in thousands) Options to purchase Common Stock 2,969 2,265 Warrants to purchase Common Stock 25 7 Redeemable convertible preferred stock — 13,067 Warrants to purchase redeemable convertible preferred stock — 26 Total 2,994 15,365

Subsequent Events

Subsequent Events	9 Months Ended
	Sep. 30, 2017
Subsequent Events [Abstract]
Subsequent Events	SUBSEQUENT EVENTS Subsequent to September 30, 2017 , and through November 7, 2017 , the Company sold, pursuant to the terms of the ATM Agreement, an aggregate of 403,306 shares of Common Stock, at a weighted average price of $9.65 per share, for aggregate gross proceeds of approximately $3.9 million . Net proceeds were approximately $3.8 million , including commissions to Cowen, as sales agent.

Summary of Significant Accoun20

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2017
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying condensed consolidated financial statements include the accounts of the Company and its wholly-owned subsidiary, Miragen Europe. The financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“U.S. GAAP”) and follow the requirements of the Securities and Exchange Commission (the “SEC”) for interim reporting. As permitted under those rules, certain footnotes or other financial information that are normally required by U.S. GAAP can be condensed or omitted. These financial statements have been prepared on the same basis as the Company’s annual financial statements and, in the opinion of management, reflect all adjustments, consisting only of normal recurring adjustments, which are necessary for a fair statement of the Company’s financial information. These interim results are not necessarily indicative of the results to be expected for the year ending December 31, 2017, or for any other interim period, or for any other future year. The balance sheet as of December 31, 2016 has been derived from audited consolidated financial statements at that date but does not include all the information required by U.S. GAAP for complete financial statements. All intercompany balances and transactions have been eliminated in consolidation. The accompanying unaudited condensed consolidated financial statements and related financial information should be read in conjunction with the audited consolidated financial statements of the Company and the notes thereto contained in the Company’s Form 8-K/A for the year ended December 31, 2016, filed with the SEC on March 31, 2017. The Company’s management performed an evaluation of its activities through the date of filing of these financial statements and concluded that there are no subsequent events requiring disclosure, other than as disclosed.
Use of Estimates	Use of Estimates The Company’s consolidated financial statements are prepared in accordance with U.S. GAAP, which requires it to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and contingent liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Although these estimates are based on the Company’s knowledge of current events and actions it may take in the future, actual results may ultimately differ from these estimates and assumptions.
Revenue Recognition	Revenue Recognition The Company recognizes revenue principally from its strategic alliance and collaboration agreement. Revenue is recognized from upfront payments for licenses and milestone payments that are generated from defined research or development events, as well as from the reimbursement of amounts for research and development services under its strategic alliance and collaboration agreement. The Company recognizes revenue when all four of the following criteria are met: (1) persuasive evidence of an arrangement exists; (2) products have been delivered or services rendered; (3) the selling price is fixed or determinable; and (4) collectability is reasonably assured. Multiple-element arrangements are examined to determine whether the deliverables can be separated or must be accounted for as a single unit of accounting. The Servier Collaboration Agreement with Servier, for example, includes a combination of upfront license fees, payments for research and development activities, and milestone payments that are evaluated to determine whether each deliverable under the agreement has value to the customer on a stand-alone basis and whether reliable evidence of fair value for the deliverable exists. Deliverables in an arrangement that do not meet this separation criteria are treated as a single unit of accounting, generally applying applicable revenue recognition guidance for the final deliverable to the combined unit of accounting. The Company recognizes revenue from non-refundable upfront license fees over the term of performance under the Servier Collaboration Agreement. When the performance period is not specified, the Company estimates the performance period based upon provisions contained within the agreement, such as the duration of the research or development term, the existence, or likelihood, of achievement of development commitments, and any other significant commitments. These advance payments are deferred and recorded as deferred revenue upon receipt, pending recognition, and are classified as a short-term or long-term liability in the accompanying condensed consolidated balance sheets. Expected performance periods are reviewed periodically and, if applicable, the amortization period is adjusted, which may accelerate or decelerate revenue recognition. The timing of revenue recognition, specifically as it relates to the amortization of upfront license fees, is significantly influenced by the Company’s estimates.
Stock-Based Compensation	Share-Based Compensation The Company accounts for share-based compensation expense related to stock options granted to employees and members of its board of directors under its 2008 Equity Incentive Plan (the “2008 Plan”) and under its 2016 Equity Incentive Plan (the “2016 Plan”) by estimating the fair value of each stock option or award on the date of grant using the Black-Scholes option pricing model. The Company recognizes share-based compensation expense on a straight-line basis over the vesting term. The Company accounts for stock options issued to non-employees by valuing the award using an option pricing model and remeasuring such awards to the current fair value until the awards are vested or a performance commitment has otherwise been reached.
Research and Development	Research and Development Research and development costs are expensed as incurred in performing research and development activities. The costs include employee-related expense including salaries, benefits, share-based compensation, fees for acquiring and maintaining licenses under third party license agreements, consulting fees, costs of research and development activities conducted by third parties on the Company’s behalf, laboratory supplies, depreciation, and facilities and overhead costs. The Company defers and capitalizes non-refundable advance payments for research and development activities until the related goods are received or services performed. In circumstances where amounts have been paid in excess of costs incurred, the Company records a prepaid expense. The Company records upfront and milestone payments to acquire contractual rights to licensed technology as research and development expenses when incurred if there is uncertainty in the Company receiving future economic benefit from the acquired contractual rights. The Company considers future economic benefits from acquired contractual rights to licensed technology to be uncertain until such a drug candidate is approved by the U.S. Food and Drug Administration or when other significant risk factors are abated.
Clinical Trials and Preclinical Study Accruals	Clinical Trial and Preclinical Study Accruals The Company makes estimates of accrued expenses as of each balance sheet date in its condensed consolidated financial statements based on certain facts and circumstances at that time. The Company’s accrued expenses for clinical trials and preclinical studies are based on estimates of costs incurred for services provided by clinical research organizations, manufacturing organizations, and other providers. Payments under the Company’s agreements with external service providers depend on a number of factors, such as site initiation, patient screening, enrollment, delivery of reports, and other events. In accruing for these activities, the Company obtains information from various sources and estimates the level of effort or expense allocated to each period. Adjustments to the Company’s research and development expenses may be necessary in future periods as its estimates change.
Cash and Cash Equivalents	Cash and Cash Equivalents All highly-liquid investments that have maturities of 90 days or less at the date of purchase are classified as cash equivalents. Cash equivalents are reported at cost, which approximates fair value due to the short maturities of these instruments.
Fair Value of Financial Instruments	Certain of the Company’s financial instruments are not measured at fair value on a recurring basis but are recorded at amounts that approximate their fair value due to the short-term nature of their maturities, such as cash and cash equivalents, accounts receivable, accounts payable, and accrued expenses. The carrying amount of the Company’s note payable approximates its fair value (a Level 2 fair value measurement), reflecting interest rates currently available to the Company. The Company accounts for its warrants to purchase common and preferred stock pursuant to ASC Topic 480, Distinguishing Liabilities from Equity , and classifies warrants for redeemable preferred stock and certain warrants for common stock as liabilities. The warrants are reported at their estimated fair value and any changes in fair value are reflected in interest expense and other related expenses. Fair Value of Financial Instruments The following tables present information about the Company’s financial assets and liabilities that have been measured at fair value and indicate the fair value of the hierarchy of the valuation inputs utilized to determine such fair value. In general, fair values determined by Level 1 inputs utilize quoted prices (unadjusted) in active markets for identical assets or liabilities. Fair value determined by Level 2 inputs utilize observable inputs other than Level 1 prices, such as quoted prices, for similar assets or liabilities, quoted market prices in markets that are not active or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the related assets or liabilities. Fair values determined by Level 3 inputs are unobservable data points for the asset or liability, and include situations where there is little, if any, market activity for the asset or liability.
Concentrations of Credit Risk	Concentrations of Credit Risk Financial instruments that potentially subject the Company to concentrations of credit risk consist primarily of cash equivalents, which include short-term investments that have maturities of less than three months. The Company maintains deposits in federally insured financial institutions in excess of federally insured limits. The Company has not experienced any losses in such accounts. The Company invests its excess cash primarily in deposits and money market funds held with two financial institutions.
Property and Equipment	Property and Equipment The Company carries its property and equipment at cost, less accumulated depreciation and amortization. Depreciation is computed using the straight-line method over the estimated useful lives of the assets, generally three to five years . Leasehold improvements are amortized over the shorter of the life of the lease (including any renewal periods that are deemed to be reasonably assured) or the estimated useful life of the assets. Construction in progress is not depreciated until placed in service. Repairs and maintenance costs are expensed as incurred and expenditures for major improvements are capitalized.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets The Company assesses the carrying amount of its property and equipment whenever events or changes in circumstances indicate the carrying amount of such assets may not be recoverable.
Net Loss per Share	Net Loss per Share Basic net loss per share is calculated by dividing the net loss applicable to common stockholders by the weighted average number of shares of Common Stock outstanding during the period without consideration of Common Stock equivalents. Since the Company was in a loss position for all periods presented, diluted net loss per share is the same as basic net loss per share for all periods, as the inclusion of all potential common shares outstanding is anti-dilutive.
Comprehensive Loss	Comprehensive Loss Comprehensive loss is defined as the change in equity during a period from transactions and other events and/or circumstances from non-owner sources. If the Company had comprehensive gains (losses), they would be reflected in the statement of operations and comprehensive loss and as a separate component in the statement of stockholders’ equity (deficit).
Income Taxes	Income Taxes The Company accounts for income taxes by using an asset and liability method of accounting for deferred 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. A valuation allowance is recorded to the extent it is more likely than not that a deferred tax asset will not be realized. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in operations in the period that includes the enactment date. The Company’s significant deferred tax assets are for net operating loss carryforwards, tax credits, and capitalized start-up costs. The Company has provided a valuation allowance for its entire net deferred tax assets since inception as, due to its history of operating losses, the Company has concluded that it is more likely than not that its deferred tax assets will not be realized. The Company has no unrecognized tax benefits. The Company classifies interest and penalties arising from the underpayment of income taxes in the condensed consolidated statements of operations as general and administrative expenses.
Segment Information	Segment Information The Company operates in one operating segment and, accordingly, no segment disclosures have been presented herein. All equipment, leasehold improvements, and other fixed assets are physically located within the United States and all agreements with the Company’s partners are denominated in U.S. dollars, except where noted.
Recent Accounting Pronouncements - Adopted and Not Yet Adopted	Recent Accounting Pronouncements – Not Yet Adopted Revenue Recognition In May 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ ASU”) No. 2014-09 , Revenue from Contracts with Customers (Topic 606) , which outlines a single comprehensive model for entities to use in accounting for revenue arising from contracts with customers and supersedes most current revenue recognition guidance, including industry-specific guidance. The core principle of the revenue model is that “an entity recognizes revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services.” The standard provides enhancements to the quality and consistency of how revenue is reported by companies, while also improving comparability in the financial statements of companies reporting using International Financial Reporting Standards or U.S. GAAP. The new standard also will require enhanced revenue disclosures, provide guidance for transactions that were not previously addressed comprehensively and improve guidance for multiple-element arrangements. This accounting standard becomes effective for the Company for reporting periods beginning after December 15, 2018, and interim reporting periods thereafter. Early adoption is permitted for annual reporting periods (including interim periods) beginning after December 15, 2016. This new standard permits the use of either the retrospective or cumulative effect transition method. In March 2016, the FASB issued ASU No. 2016-08 , Revenue from Contracts with Customers (Topic 606): Principal versus Agent Considerations . The purpose of this standard is to clarify the implementation of guidance on principal versus agent considerations related to ASU 2014-09. The standard has the same effective date as ASU 2014-09 described above. In April 2016, the FASB issued ASU No. 2016-10, Revenue from Contracts with Customer, which provides clarity related to ASU 2014-09 regarding identifying performance obligations and licensing implementation. The standard has the same effective date as ASU 2014-09 described above. In May 2016, the FASB issued ASU 2016-12: Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Practical Expedients , which provides narrow scope improvements and practical expedients related to ASU 2014-09. The purpose of this standard is to clarify certain narrow aspects of ASU 2014-09, such as assessing the collectability criterion, presentation of sales taxes, and other similar taxes collected from customers, noncash consideration, contract modifications at transition, completed contracts at transition, and technical correction. The standard has the same effective date as ASU 2014-09 described above. In December 2016, the FASB issued ASU 2016-20: Technical Corrections and Improvements to Topic 606, Revenue from Contracts with Customers . The amendments in this standard affect narrow aspects of guidance issued in ASU 2014-09. The standard has the same effective date as ASU 2014-09 described above. The Company plans to adopt these new standards in the first quarter of 2019. As of September 30, 2017 , there were limited contracts that will be in effect (actively) as of the transition date and, accordingly, the Company has not yet determined the effect of the standard on its condensed consolidated financial statements. The Company’s selected implementation transition method will be dependent upon contracts that are in place closer to the transition date. Deferred Taxes In November 2015, the FASB issued ASU No. 2015-17 , Balance Sheet Classification of Deferred Taxes . ASU No. 2015-17 requires that deferred tax liabilities and assets be classified as noncurrent in a classified statement of financial position. This standard is effective for the Company for financial statements issued for fiscal years beginning after December 15, 2017, and interim periods thereafter. The Company does not believe the adoption of this standard will have a material impact on its condensed consolidated financial statements due to the full valuation allowance on all net deferred tax assets. Leases In February 2016, the FASB issued ASU No. 2016-02 , Leases (Topic 842), which supersedes FASB ASC Topic 840, Leases (Topic 840), and provides principles for the recognition, measurement, presentation and disclosure of leases for both lessees and lessors. In September 2017, the FASB issued ASU 2017-13, Revenue Recognition (Topic 605), Revenue from Contracts with Customers (Topic 606), Leases (Topic 840), and Leases (Topic 842), which provides additional implementation guidance on the previously issued ASU 2016-02 Leases (Topic 842) . ASU 2016-02 requires lessees to apply a dual approach, classifying leases as either finance or operating leases based on the principle of whether or not the lease is effectively a financed purchase by the lessee. This classification will determine whether lease expense is recognized based on an effective interest method or on a straight-line basis over the term of the lease, respectively. A lessee is also required to record a right-of-use asset and a lease liability for all leases with a term of greater than twelve months regardless of classification. Leases with a term of twelve months or less will be accounted for similar to existing guidance for operating leases. The standard is effective for the Company for fiscal years beginning after December 15, 2019, and interim periods thereafter, with early adoption permitted. At adoption, this update will be applied using a modified retrospective approach. The Company is currently evaluating the impact of this standard on its condensed consolidated financial statements. Share-based Compensation In March 2016, the FASB issued ASU No. 2016-09 , Compensation—Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting , which is intended to simplify accounting for equity share-based payment transactions, including the income tax consequences, classification of awards as either equity or liabilities, and classification on the statement of cash flows. This standard is effective for the Company for annual periods beginning after December 15, 2017, and interim periods thereafter. Amendments related to the timing of when excess tax benefits are recognized, minimum statutory withholding requirements, forfeitures, and intrinsic value should be applied using a modified retrospective transition method by means of a cumulative-effect adjustment to equity as of the beginning of the period in which the guidance is adopted. Amendments related to the presentation of employee taxes paid on the statement of cash flows when an employer withholds shares to meet the minimum statutory withholding requirement should be applied retrospectively. Amendments requiring recognition of excess tax benefits and tax deficiencies in the income statement and the practical expedient for estimating the expected term should be applied prospectively. An entity may elect to apply the amendments related to the presentation of excess tax benefits on the statement of cash flows using either a prospective transition method or a retrospective transition method. The Company is currently evaluating the impact of this standard on its condensed consolidated financial statements. Other new pronouncements issued but not effective as of September 30, 2017 are not expected to have a material impact on the Company’s condensed consolidated financial statements.

Summary of Significant Accoun21

Summary of Significant Accounting Policies (Tables)	9 Months Ended
	Sep. 30, 2017
Accounting Policies [Abstract]
Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis	The following tables present information about the Company’s financial assets and liabilities that have been measured at fair value and indicate the fair value of the hierarchy of the valuation inputs utilized to determine such fair value. In general, fair values determined by Level 1 inputs utilize quoted prices (unadjusted) in active markets for identical assets or liabilities. Fair value determined by Level 2 inputs utilize observable inputs other than Level 1 prices, such as quoted prices, for similar assets or liabilities, quoted market prices in markets that are not active or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the related assets or liabilities. Fair values determined by Level 3 inputs are unobservable data points for the asset or liability, and include situations where there is little, if any, market activity for the asset or liability. September 30, December 31, Level 1 Level 3 Level 1 Level 3 (in thousands) Assets: Money market funds (included in cash and cash equivalents) (1) $ 44,112 $ — $ 22,189 $ — Liabilities: Preferred and common stock warrants (included in accrued and other liabilities) $ — $ 82 $ — $ 133 ______________________ (1) Amounts presented for each period above differ from cash and cash equivalents reported in the condensed consolidated balance sheets due to outstanding disbursements and deposits.
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation	A reconciliation of the beginning and ending balances of the Company’s liabilities measured at fair value using significant unobservable, or Level 3, inputs are as follows for the nine months ended September 30, 2017 (in thousands): Balance of liability as of December 31, 2016 $ 133 Reclassification of preferred stock warrant to common stock warrant (51 ) Balance of liability as of September 30, 2017 $ 82

Reverse Merger (Tables)

Reverse Merger (Tables)	9 Months Ended
	Sep. 30, 2017
Business Combinations [Abstract]
Schedule of Business Acquisitions, by Acquisition	The following table summarizes the net assets acquired based on their estimated fair values as of February 13, 2017, prior to the Merger (in thousands): Cash and cash equivalents $ 1,280 Prepaid and other assets 248 Accrued liabilities (1,324 ) Net acquired tangible assets $ 204

Property and Equipment (Tables)

Property and Equipment (Tables)	9 Months Ended
	Sep. 30, 2017
Property, Plant and Equipment [Abstract]
Components of Property and Equipment	Property and equipment, net, consisted of the following: September 30, December 31, (in thousands) Lab equipment $ 2,219 $ 2,163 Furniture and fixtures 77 51 Computer hardware and software 361 281 Leasehold improvements 729 688 Property and equipment, gross 3,386 3,183 Less: accumulated depreciation and amortization (2,776 ) (2,558 ) Property and equipment, net $ 610 $ 625

Accrued Liabilities (Tables)

Accrued Liabilities (Tables)	9 Months Ended
	Sep. 30, 2017
Payables and Accruals [Abstract]
Components of Accrued Liabilities	Accrued liabilities consisted of the following: September 30, December 31, (in thousands) Accrued outsourced clinical and preclinical studies $ 1,635 $ 1,684 Accrued employee compensation and related taxes 1,061 928 Accrued legal fees and expenses 607 759 Accrued other professional service fees 457 124 Accrued equipment and lab materials 156 — Value of liability-classified stock purchase warrants 82 133 Deferred and accrued facility lease obligations 70 221 Other accrued liabilities 74 60 Total accrued liabilities $ 4,142 $ 3,909

Notes Payable (Tables)

Notes Payable (Tables)	9 Months Ended
	Sep. 30, 2017
Debt Disclosure [Abstract]
Composition of Notes Payable	Amounts outstanding under notes payable are as follows: September 30, December 31, (in thousands) Principal amount outstanding $ 3,167 $ 4,667 Unamortized debt discount (6 ) (14 ) Unamortized debt issuance costs (14 ) (31 ) Accreted final payment fee 227 167 Total notes payable 3,374 4,789 Less: current maturities (1,983 ) (1,969 ) Long-term notes payable, net of current portion $ 1,391 $ 2,820
Future Annual Minimum Principal Payments of Notes Payable	Future annual minimum principal payments of notes payable are as follows: September 30, (in thousands) 2017 (remainder of year) $ 500 2018 2,000 2019 667 Total $ 3,167

Commitments and Contingencies (

Commitments and Contingencies (Tables)	9 Months Ended
	Sep. 30, 2017
Commitments and Contingencies Disclosure [Abstract]
Schedule of Future Minimum Rental Payments for Operating Leases	Future annual minimum payments under the lease are as follows: September 30, (in thousands) 2017 (remainder of year) $ 95 2018 391 2019 404 2020 277 Total $ 1,167

Capital Stock (Tables)

Capital Stock (Tables)	9 Months Ended
	Sep. 30, 2017
Equity [Abstract]
Summary of Series Preferred Stock	A summary of the conversion by class of preferred stock is summarized as follows (in thousands, except share data): Series A Series B Series C Total Shares Amount Shares Amount Shares Amount Shares Amount Balance at December 31, 2016 7,149,176 $ 23,124 2,166,651 $ 12,975 9,268,563 $ 40,877 18,584,390 $ 76,976 Accretion of redeemable convertible preferred stock to redemption value — 1 — 1 — 3 — 5 Conversion of preferred stock to common stock (7,149,176 ) (23,125 ) (2,166,651 ) (12,976 ) (9,268,563 ) (40,880 ) (18,584,390 ) (76,981 ) Balance at February 13, 2017 — $ — — $ — — $ — — $ —

Warrants (Tables)

Warrants (Tables)	9 Months Ended
	Sep. 30, 2017
Other Liabilities Disclosure [Abstract]
Summary of Warrants	Stock purchase warrant activity is as follows for the nine months ended September 30, 2017 : Common Stock Warrants Preferred Stock Warrants Number Weighted Average Exercise Price Number Weighted Average Exercise Price Outstanding at December 31, 2016 7,031 $ 0.57 25,779 $ 6.21 Warrants acquired in Merger 13,534 $ 80.70 — $ — Preferred stock warrants converted into Common Stock warrants 25,779 $ 6.21 (25,779 ) $ 6.21 Exercises (21,092 ) $ 3.04 — $ — Outstanding at September 30, 2017 25,252 $ 47.21 — $ — A summary of outstanding Common Stock purchase warrants as of September 30, 2017 is as follows: Number of Underlying Shares Exercise Price Expiration Date 13,534 $80.70 2019 & 2020 11,718 $8.53 2025 25,252

Share-Based Compensation (Table

Share-Based Compensation (Tables)	9 Months Ended
	Sep. 30, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock Option Activity	A summary of Common Stock option activity is as follows: Number of Options Weighted Average Exercise Price Outstanding at December 31, 2016 2,321 $ 1.44 Granted 956 $ 11.48 Exercised (274 ) $ (0.80 ) Forfeited (34 ) $ (11.40 ) Outstanding at September 30, 2017 2,969 $ 4.62
Fair Value Assumptions for Stock Options	The fair value was determined by the Black-Scholes option pricing model using the following assumptions: Nine Months Ended 2017 2016 Expected term, in years 6.44 5.00 Expected volatility 83.8 % 84.0 % Risk-free interest rate 2.1 % 1.1 % Expected dividend yield — % — % Weighted average grant date fair value of underlying Common Stock $ 11.48 $ 1.05
Allocation of Share-based Compensation Expense	Share-based compensation related to all equity awards issued pursuant to the 2008 Plan and 2016 Plan and for estimated shares to be issued under the ESPP for the current purchase period is included in the condensed consolidated statements of operations as follows: Three Months Ended Nine Months Ended 2017 2016 2017 2016 (in thousands) Research and development $ 263 $ 5 $ 643 $ 22 General and administrative 416 40 1,050 107 Total share-based compensation expense $ 679 $ 45 $ 1,693 $ 129

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	9 Months Ended
	Sep. 30, 2017
Earnings Per Share [Abstract]
Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share	Potentially dilutive securities include the following: September 30, 2017 September 30, 2016 (in thousands) Options to purchase Common Stock 2,969 2,265 Warrants to purchase Common Stock 25 7 Redeemable convertible preferred stock — 13,067 Warrants to purchase redeemable convertible preferred stock — 26 Total 2,994 15,365

Description of Business - Narra

Description of Business - Narrative (Details)	Feb. 13, 2017USD ($)$ / sharesshares	Sep. 30, 2017USD ($)$ / sharesshares	Sep. 30, 2016USD ($)	Sep. 30, 2017USD ($)$ / sharesshares	Sep. 30, 2017USD ($)$ / sharesshares	Sep. 30, 2016USD ($)	Feb. 12, 2017$ / sharesshares	Dec. 31, 2016USD ($)$ / sharesshares	Dec. 31, 2015USD ($)
Description of Business [Line Items]
Common stock, shares outstanding (in shares) | shares		21,886,568		21,886,568	21,886,568			833,744
Common stock, par value (in dollars per share) | $ / shares		$ 0.01		$ 0.01	$ 0.01			$ 0.01
Accumulated deficit		$ (87,207,000)		$ (87,207,000)	$ (87,207,000)			$ (67,076,000)
Net loss		(5,834,000)	$ (4,153,000)		(20,126,000)	$ (11,300,000)
Proceeds from the sale of common stock	$ 40,700,000
Cash and cash equivalents		$ 42,805,000	$ 24,598,000	42,805,000	42,805,000	24,598,000		$ 22,104,000	$ 21,235,000
Private Financing
Description of Business [Line Items]
Proceeds from the sale of common stock					40,703,000	0
ATM Agreement
Description of Business [Line Items]
Proceeds from the sale of common stock					2,711,000	$ 0
Aggregate offering				$ 2,700,000	$ 2,500,000
Shares sold (in shares) | shares				297,653
Sale price (in usd per share) | $ / shares		$ 9.11		$ 9.11	$ 9.11
ATM Agreement | Maximum
Description of Business [Line Items]
Aggregate offering					$ 50,000,000
Authorized transaction amount					$ 50,000,000
Signal
Description of Business [Line Items]
Common stock, shares outstanding (in shares) | shares	21,309,440						1,024,960
Common stock, par value (in dollars per share) | $ / shares	$ 0.01						$ 0.001
Signal Shares issued to Miragen Common Shareholders | Signal
Description of Business [Line Items]
Exchange rate of common stock	0.7031

Summary of Significant Accoun32

Summary of Significant Accounting Policies - Assets and Liabilities Measured on a Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Level 1
Assets:
Assets, fair value disclosure	$ 44,112	$ 22,189
Liabilities:
Liabilities, fair value disclosure	0	0
Level 3
Assets:
Assets, fair value disclosure	0	0
Liabilities:
Liabilities, fair value disclosure	$ 82	$ 133

Summary of Significant Accoun33

Summary of Significant Accounting Policies - Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2017USD ($)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 133
Reclassification of preferred stock warrant to common stock warrant	51
Ending balance	$ 82

Summary of Significant Accoun34

Summary of Significant Accounting Policies - Narrative (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2017USD ($)	Sep. 30, 2016USD ($)	Sep. 30, 2017USD ($)segment	Sep. 30, 2016USD ($)
Accounting Policies [Abstract]
Impairment charges	$ 0	$ 0	$ 0	$ 0
Income tax penalties and interest expense	$ 0	$ 0	$ 0	$ 0
Number of operating segments | segment			1
Minimum
Property, Plant and Equipment [Line Items]
Estimated useful lives			3 years
Maximum
Property, Plant and Equipment [Line Items]
Estimated useful lives			5 years

Strategic Alliance and Collab35

Strategic Alliance and Collaboration with Servier - Narrative (Details) € in Millions	3 Months Ended		9 Months Ended		63 Months Ended
	Sep. 30, 2017USD ($)	Sep. 30, 2016USD ($)	Sep. 30, 2017USD ($)	Sep. 30, 2016USD ($)	Dec. 31, 2016EUR (€)	Dec. 31, 2016USD ($)	Sep. 30, 2017EUR (€)	Sep. 30, 2017USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue	$ 1,493,000	$ 715,000	$ 1,991,000	$ 2,479,000
Servier Collaboration Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential commercialization milestone payments							€ 175	$ 206,700,000
Revenue from research and development activities	1,500,000	600,000	2,000,000	2,000,000
Licenses revenue	0	100,000	0	500,000	€ 9	$ 12,400,000
Collaboration revenue	$ 1,500,000	$ 700,000	$ 2,000,000	$ 2,500,000
Amounts incurred but not yet billed						300,000		1,439,871
Accounts receivable						$ 0		500,000
Minimum | Servier Collaboration Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential development milestone payments							5.8	6,900,000
Potential regulatory milestone payments							10	11,800,000
Maximum | Servier Collaboration Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential development milestone payments							13.8	16,300,000
Potential regulatory milestone payments							€ 40	$ 47,300,000

Reverse Merger - Narrative (Det

Reverse Merger - Narrative (Details) $ in Thousands	Sep. 30, 2017shares	Feb. 28, 2017	Feb. 13, 2017USD ($)shares	Feb. 12, 2017USD ($)shares	Dec. 31, 2016shares
Business Acquisition [Line Items]
Common stock, shares outstanding (in shares) | shares	21,886,568				833,744
Preferred stock
Business Acquisition [Line Items]
Exchange rate of common stock		1		1
Signal
Business Acquisition [Line Items]
Common stock, shares outstanding (in shares) | shares			21,309,440	1,024,960
Market capitalization | $				$ 12,600
Net acquired tangible assets | $			$ 204
Signal | Signal Shares issued to Miragen Common Shareholders
Business Acquisition [Line Items]
Exchange rate of common stock			0.7031
Signal | Pre-Merger MIragen Stockholders, Warrantholders, and Optionholders
Business Acquisition [Line Items]
Ownership percentage			95.20%
Signal | Signal Shareholders
Business Acquisition [Line Items]
Ownership interest prior to merger			95.90%
Signal | Miragen Shareholders
Business Acquisition [Line Items]
Ownership interest prior to merger			4.10%

Reverse Merger - Summary of Ass

Reverse Merger - Summary of Assets Acquired and Liabilities Assumed (Details) - Signal $ in Thousands	Feb. 13, 2017USD ($)
Business Acquisition [Line Items]
Cash and cash equivalents	$ 1,280
Prepaid and other assets	248
Accrued liabilities	(1,324)
Net acquired tangible assets	$ 204

Property and Equipment - Compon

Property and Equipment - Components of Property and Equipment (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Property and equipment	$ 3,386	$ 3,183
Less: accumulated depreciation and amortization	(2,776)	(2,558)
Property and equipment, net	610	625
Lab equipment
Property, Plant and Equipment [Line Items]
Property and equipment	2,219	2,163
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property and equipment	77	51
Computer hardware and software
Property, Plant and Equipment [Line Items]
Property and equipment	361	281
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment	$ 729	$ 688

Property and Equipment - Narrat

Property and Equipment - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Property, Plant and Equipment [Abstract]
Depreciation and amortization	$ 100	$ 100	$ 227	$ 253

Accrued Liabilities - Component

Accrued Liabilities - Components of Accrued Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Payables and Accruals [Abstract]
Accrued outsourced clinical and preclinical studies	$ 1,635	$ 1,684
Accrued employee compensation and related taxes	1,061	928
Accrued legal fees and expenses	607	759
Accrued other professional service fees	457	124
Accrued equipment and lab materials	156	0
Value of liability-classified stock purchase warrants	82	133
Deferred and accrued facility lease obligations	70	221
Other accrued liabilities	74	60
Total accrued liabilities	$ 4,142	$ 3,909

Notes Payable - Narrative (Deta

Notes Payable - Narrative (Details) $ / shares in Units, $ in Millions	1 Months Ended		9 Months Ended
	May 31, 2015USD ($)	Apr. 30, 2015USD ($)tranche$ / sharesshares	Sep. 30, 2017USD ($)
Detachable Warrants - Series B Redeemable Convertible Preferred Stock | Income Approach Valuation Technique | Warrants Not Settleable in Cash
Debt Instrument [Line Items]
Expected term			2 years
Discount rate			6.80%
Probability of exercise			90.00%
Silicon Valley Bank Agreement | Notes Payable to Banks
Debt Instrument [Line Items]
Face amount		$ 10
Number of tranches | tranche		2
2015 Notes Payable to Silicon Valley Bank - Tranche One | Detachable Warrants - Series B Redeemable Convertible Preferred Stock
Debt Instrument [Line Items]
Shares eligible for purchase under warrants (in shares) | shares		11,718
Warrant exercise price (in usd per share) | $ / shares		$ 8.53
Fair value of warrants			$ 0.1
2015 Notes Payable to Silicon Valley Bank - Tranche One | Notes Payable to Banks
Debt Instrument [Line Items]
Face amount	$ 5
Repayment period	30 months
Interest-only period	18 months
2015 Notes Payable to Silicon Valley Bank - Tranche One | Notes Payable to Banks | Prime Rate
Debt Instrument [Line Items]
Variable rate		0.25%
Interest rate at period end			4.00%
Final payment fee percent	5.50%
2015 Notes Payable to Silicon Valley Bank - Tranche Two | Notes Payable to Banks
Debt Instrument [Line Items]
Face amount	$ 5

Notes Payable - Composition of

Notes Payable - Composition of Notes Payable (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Debt Disclosure [Abstract]
Principal amount outstanding	$ 3,167	$ 4,667
Unamortized debt discount	(6)	(14)
Unamortized debt issuance costs	(14)	(31)
Accreted final payment fee	227	167
Total notes payable	3,374	4,789
Less: current maturities	(1,983)	(1,969)
Long-term notes payable, net of current portion	$ 1,391	$ 2,820

Notes Payable - Future Annual M

Notes Payable - Future Annual Minimum Principal Payments (Details) $ in Thousands	Sep. 30, 2017USD ($)
Debt Disclosure [Abstract]
2017 (remainder of year)	$ 500
2,018	2,000
2,019	667
Total	$ 3,167

Commitments and Contingencies -

Commitments and Contingencies - Narrative (Details) € in Thousands	1 Months Ended		3 Months Ended		9 Months Ended		36 Months Ended
	Oct. 31, 2010EUR (€)	Oct. 31, 2010USD ($)	Sep. 30, 2017USD ($)arrangement	Sep. 30, 2016USD ($)	Sep. 30, 2017USD ($)arrangementshares	Sep. 30, 2016USD ($)	Sep. 30, 2017USD ($)arrangement
Commitments and Contingencies [Line Items]
Rent expense			$ 100,000	$ 100,000	$ 200,000	$ 300,000
Operating expenses of leases			100,000	$ 100,000	200,000	200,000
Yale University
Commitments and Contingencies [Line Items]
Potential cash proceeds from agreement			$ 1,100,000		$ 1,100,000		$ 1,100,000
Term of agreement					5 years
Proceeds from collaboration							$ 100,000
University of Texas
Commitments and Contingencies [Line Items]
Number of arrangements | arrangement			5		5		5
Nonrefundable upfront license documentation fee					$ 10,000
Annual license maintenance fee					10,000
Potential milestone payment for initiation of defined clinical trials			$ 600,000		600,000		$ 600,000
University of Texas | United States
Commitments and Contingencies [Line Items]
Potential milestone payment for regulatory approval			2,000,000		2,000,000		2,000,000
University of Texas | Other Regions
Commitments and Contingencies [Line Items]
Potential milestone payment for regulatory approval			500,000		500,000		500,000
RICC
Commitments and Contingencies [Line Items]
Payments for the grant of license and option					2,300,000
Potential future milestone payments per licensed product			5,200,000		5,200,000		5,200,000
Payments for raw materials					$ 500,000	$ 200,000
RICC | Series A
Commitments and Contingencies [Line Items]
Shares issued in agreement (in shares) | shares					856,806
Shares issued in conversion (in shares) | shares					602,420
t2cure
Commitments and Contingencies [Line Items]
Nonrefundable upfront license documentation fee		$ 46,000
Annual license maintenance fee	€ 3	$ 3,000
Potential milestone payment for initiation of defined clinical trials			700,000		$ 700,000		700,000
Term of agreement					10 years
Period to terminate agreement					60 days
t2cure | United States
Commitments and Contingencies [Line Items]
Potential milestone payment for regulatory approval			2,500,000		$ 2,500,000		2,500,000
t2cure | European Union or Japan
Commitments and Contingencies [Line Items]
Potential milestone payment for regulatory approval			$ 1,500,000		1,500,000		$ 1,500,000
BWH
Commitments and Contingencies [Line Items]
Potential milestone payments					2,600,000
One-time sales milestone payment					$ 300,000

Commitments and Contingencies45

Commitments and Contingencies - Future Minimum Rental Payments (Details) $ in Thousands	Sep. 30, 2017USD ($)
Commitments and Contingencies Disclosure [Abstract]
2017 (remainder of year)	$ 95
2,018	391
2,019	404
2,020	277
Total	$ 1,167

Capital Stock - Narrative (Deta

Capital Stock - Narrative (Details) $ / shares in Units, $ in Thousands	Mar. 31, 2017	Feb. 13, 2017USD ($)$ / sharesshares	Sep. 30, 2017USD ($)$ / sharesshares	Sep. 30, 2017USD ($)$ / sharesshares	Sep. 30, 2017USD ($)$ / sharesshares	Sep. 30, 2016USD ($)	Feb. 28, 2017	Feb. 12, 2017$ / shares	Dec. 31, 2016$ / sharesshares
Class of Stock [Line Items]
Shares authorized (in shares) | shares			105,000,000	105,000,000	105,000,000
Common stock, shares authorized (in shares) | shares			100,000,000	100,000,000	100,000,000				100,000,000
Preferred stock, shares authorized (in shares) | shares			5,000,000	5,000,000	5,000,000
Common stock, par value (in dollars per share) | $ / shares			$ 0.01	$ 0.01	$ 0.01				$ 0.01
Preferred stock, par value (in usd per share) | $ / shares			$ 0.01	$ 0.01	$ 0.01
Proceeds from the sale of common stock		$ 40,700
Payments of stock issuance costs		$ 1,500
Offering costs incurred					$ 400
Offering costs			$ 100	$ 100	100
Accumulated amortization, offering costs			$ 8	$ 8	$ 8
ATM Agreement
Class of Stock [Line Items]
Issuance of common stock to investors, net of issuance cost (in shares) | shares			297,653
Sale price (in usd per share) | $ / shares			$ 9.11	$ 9.11	$ 9.11
Proceeds from the sale of common stock					$ 2,711	$ 0
Payments of stock issuance costs					172	$ 0
Aggregate offering				$ 2,700	2,500
Commission fee percent	3.00%
Maximum | ATM Agreement
Class of Stock [Line Items]
Aggregate offering					$ 50,000
Preferred stock
Class of Stock [Line Items]
Exchange rate of common stock							1	1
Signal
Class of Stock [Line Items]
Common stock, par value (in dollars per share) | $ / shares		$ 0.01						$ 0.001
Signal Shares issued to Miragen Common Shareholders | Signal
Class of Stock [Line Items]
Exchange rate of common stock		0.7031
Pre-Merger
Class of Stock [Line Items]
Issuance of common stock to investors, net of issuance cost (in shares) | shares		9,045,126
Sale price (in usd per share) | $ / shares		$ 4.50
Post-Merger
Class of Stock [Line Items]
Issuance of common stock to investors, net of issuance cost (in shares) | shares		6,359,628
Sale price (in usd per share) | $ / shares		$ 6.40

Capital Stock - Summary of Seri

Capital Stock - Summary of Series Preferred Stock (Details) - USD ($) $ in Thousands	2 Months Ended	9 Months Ended
	Feb. 13, 2017	Sep. 30, 2017	Sep. 30, 2016
Redeemable Convertible Preferred Stock
Conversion of preferred stock to common stock		$ 76,981	$ 0
Series A
Redeemable Convertible Preferred Stock
Beginning balance (in shares)	7,149,176	7,149,176
Beginning balance	$ 23,124	$ 23,124
Accretion of redeemable convertible preferred stock to redemption value	$ 1
Conversion of preferred stock to common stock (in shares)	(7,149,176)
Conversion of preferred stock to common stock	$ (23,125)
Ending balance (in shares)	0
Ending balance	$ 0	$ 0
Series B
Redeemable Convertible Preferred Stock
Beginning balance (in shares)	2,166,651	2,166,651
Beginning balance	$ 12,975	$ 12,975
Accretion of redeemable convertible preferred stock to redemption value	$ 1
Conversion of preferred stock to common stock (in shares)	(2,166,651)
Conversion of preferred stock to common stock	$ (12,976)
Ending balance (in shares)	0
Ending balance	$ 0	$ 0
Series C
Redeemable Convertible Preferred Stock
Beginning balance (in shares)	9,268,563	9,268,563
Beginning balance	$ 40,877	$ 40,877
Accretion of redeemable convertible preferred stock to redemption value	$ 3
Conversion of preferred stock to common stock (in shares)	(9,268,563)
Conversion of preferred stock to common stock	$ (40,880)
Ending balance (in shares)	0
Ending balance	$ 0	$ 0
Total
Redeemable Convertible Preferred Stock
Beginning balance (in shares)	18,584,390	18,584,390
Beginning balance	$ 76,976	$ 76,976
Accretion of redeemable convertible preferred stock to redemption value	$ 5	$ 5
Conversion of preferred stock to common stock (in shares)	(18,584,390)	(18,584,390)
Conversion of preferred stock to common stock	$ (76,981)	$ (76,981)
Ending balance (in shares)	0	0
Ending balance	$ 0	$ 0

Warrants - Stock Warrant Activi

Warrants - Stock Warrant Activity (Details)	9 Months Ended
	Sep. 30, 2017$ / sharesshares
Common Stock Warrants
Number
Beginning balance (in shares) | shares	7,031
Warrants acquired in Merger (in shares) | shares	13,534
Preferred stock warrants converted into common stock warrants (in shares) | shares	25,779
Cashless exercise (in shares) | shares	(21,092)
Ending balance (in shares) | shares	25,252
Weighted Average Exercise Price
Beginning balance (in usd per share) | $ / shares	$ 0.57
Warrants acquired in Merger (in usd per share) | $ / shares	80.70
Preferred stock warrants converted into common stock warrants (in usd per share) | $ / shares	6.21
Cashless exercise (in usd per share) | $ / shares	3.04
Ending balance (in usd per share) | $ / shares	$ 47.21
Preferred Stock Warrants
Number
Beginning balance (in shares) | shares	25,779
Warrants acquired in Merger (in shares) | shares	0
Preferred stock warrants converted into common stock warrants (in shares) | shares	(25,779)
Cashless exercise (in shares) | shares	0
Ending balance (in shares) | shares	0
Weighted Average Exercise Price
Beginning balance (in usd per share) | $ / shares	$ 6.21
Warrants acquired in Merger (in usd per share) | $ / shares	0
Preferred stock warrants converted into common stock warrants (in usd per share) | $ / shares	6.21
Cashless exercise (in usd per share) | $ / shares	0
Ending balance (in usd per share) | $ / shares	$ 0

Warrants - Stock Warrants Outst

Warrants - Stock Warrants Outstanding (Details) - $ / shares	Sep. 30, 2017	Dec. 31, 2016
Common Stock Warrants
Class of Warrant or Right [Line Items]
Number of Underlying Shares (in shares)	25,252
Exercise price (in usd per share)	$ 47.21	$ 0.57
Expiration Date 2019 and 2020
Class of Warrant or Right [Line Items]
Number of Underlying Shares (in shares)	13,534
Exercise price (in usd per share)	$ 80.70
Expiration Date 2025
Class of Warrant or Right [Line Items]
Number of Underlying Shares (in shares)	11,718
Exercise price (in usd per share)	$ 8.53

Warrants - Narrative (Details)

Warrants - Narrative (Details) - Common Stock Warrants	9 Months Ended
	Sep. 30, 2017$ / sharesshares
Class of Warrant or Right [Line Items]
Warrants acquired in Merger (in shares) | shares	13,534
Warrants acquired in Merger (in usd per share) | $ / shares	$ 80.70

Share-Based Compensation - Narr

Share-Based Compensation - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity awards outstanding	908,227
Remaining equity awards available for future issuances	773,067
Unrecognized employee stock-based compensation costs	$ 7.4
Remaining weighted-average period for RSUs	3 years 2 months 11 days
Options to purchase Common Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares outstanding (in shares)	2,969,000		2,321,000
Expiration period	10 years
Weighted average fair value per option (in usd per share)	$ 8.32	$ 0.70
Shares issued in period (in shares)	956,000
Options to purchase Common Stock | Initial vesting period
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percent	25.00%
Options to purchase Common Stock | Subsequent vesting period
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percent	75.00%
Vesting period	36 months
Options to purchase Common Stock | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	48 months
Non-employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized stock-based compensation expense for non-employees	$ 0.1
Weighted-average remaining period for recognition of non-employee stock-based compensation expense	11 months 12 days
Non-employee Stock Option | Non-employees
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued in period (in shares)	0	0
2008 Equity Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares outstanding (in shares)	2,060,993
2016 Equity Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares authorized for issuance (in shares)	4,182,404
Basis for equity incentive plan (in shares)	1,681,294
Common stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available for issuance under ESPP (in shares)	200,000
Employee share purchases (in shares)	13,193

Share-Based Compensation - Stoc

Share-Based Compensation - Stock Option Activity (Details) - Options to purchase Common Stock - $ / shares shares in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Number of Options (in thousands)
Beginning balance (in shares)	2,321
Granted (in shares)	956
Exercised (in shares)	(274)
Forfeited (in shares)	(34)
Ending balance (in shares)	2,969
Weighted Average Exercise Price
Beginning balance (in usd per share)	$ 1.44
Granted (in usd per share)	11.48	$ 1.05
Exercised (in usd per share)	(0.80)
Forfeited (in usd per share)	(11.40)
Ending balance (in usd per share)	$ 4.62

Share-Based Compensation - Fair

Share-Based Compensation - Fair Value Assumption for Stock Options (Details) - Options to purchase Common Stock - $ / shares	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term, in years	6 years 5 months 9 days	5 years
Expected volatility	83.80%	84.00%
Risk-free interest rate	2.10%	1.10%
Expected dividend yield	0.00%	0.00%
Weighted average grant date fair value of underlying common stock (in usd per share)	$ 11.48	$ 1.05

Share-Based Compensation - Allo

Share-Based Compensation - Allocation of Share-based Compensation Expense on Statements of Operations (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total share-based compensation expense	$ 679	$ 45	$ 1,693	$ 129
Research and development
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total share-based compensation expense	263	5	643	22
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total share-based compensation expense	$ 416	$ 40	$ 1,050	$ 107

Net Loss Per Share - Summary of

Net Loss Per Share - Summary of Potential Dilutive Securities (Details) - shares shares in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Dilutive securities (in shares)	2,994	15,365
Options to purchase Common Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Dilutive securities (in shares)	2,969	2,265
Warrants to purchase Common Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Dilutive securities (in shares)	25	7
Redeemable convertible preferred stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Dilutive securities (in shares)	0	13,067
Warrants to purchase redeemable convertible preferred stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Dilutive securities (in shares)	0	26

Subsequent Events - Narrative (

Subsequent Events - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands	Feb. 13, 2017	Nov. 07, 2017	Sep. 30, 2017	Sep. 30, 2017	Sep. 30, 2016
Subsequent Event [Line Items]
Proceeds from the sale of common stock	$ 40,700
At-the-Market Offering
Subsequent Event [Line Items]
Shares sold (in shares)			297,653
Sale price (in usd per share)			$ 9.11	$ 9.11
Proceeds from the sale of common stock				$ 2,711	$ 0
Net proceeds from offering			$ 2,700	$ 2,500
At-the-Market Offering | Subsequent Event
Subsequent Event [Line Items]
Shares sold (in shares)		403,306
Sale price (in usd per share)		$ 9.65
Proceeds from the sale of common stock		$ 3,900
Net proceeds from offering		$ 3,800