Cyclerion Therapeutics (CYCN) 10-Q 9 Nov 21 2021 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2021	Nov. 05, 2021
Cover [Abstract]
Entity Registrant Name	CYCLERION THERAPEUTICS, INC.
Document Type	10-Q
Document Period End Date	Sep. 30, 2021
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		43,315,745
Entity Central Index Key	0001755237
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q3
Amendment Flag	false
Document Quarterly Report	true
Document Transition Report	false
Entity Tax Identification Number	83-1895370
Entity File Number	001-38787
Entity Incorporation, State or Country Code	MA
Entity Address, Address Line One	245 First Street, 18th Floor
Entity Address, City or Town	Cambridge
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02142
City Area Code	857
Local Phone Number	327-8778
Title of 12(b) Security	Common Stock, no par value
Trading Symbol	CYCN
Security Exchange Name	NASDAQ

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 62,503	$ 54,395
Accounts receivable	158	0
Related party accounts receivable	0	127
Prepaid expenses	562	816
Other current assets	459	3,163
Total current assets	63,682	58,501
Restricted cash, net of current portion	0	3,837
Property and equipment, net	112	6,865
Operating lease right-of-use asset	1,449	43,402
Other assets	2,499	2,773
Total assets	67,742	115,378
Current liabilities:
Accounts payable	1,174	1,149
Related party accounts payable	0	286
Accrued research and development costs	3,432	1,421
Accrued expenses and other current liabilities	3,240	7,294
Short-term note payable	3,509	3,509
Current portion of operating lease liabilities	0	3,293
Total current liabilities	11,355	16,952
Operating lease liabilities, net of current portion	0	38,933
Commitments and contingencies
Stockholders' equity
Common stock, no par value, 400,000,000 shares authorized and 43,310,089 issued and outstanding at September 30,2021 and 400,000,000 shares authorized and 34,047,300 issued and outstanding at December 31, 2020	0	0
Accumulated deficit	(204,300)	(163,429)
Paid-in capital	260,713	222,949
Accumulated other comprehensive loss	(26)	(27)
Total stockholders' equity	56,387	59,493
Total liabilities and stockholders' equity	$ 67,742	$ 115,378

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2021	Dec. 31, 2020
Statement Of Financial Position [Abstract]
Common stock, par value (in dollars per share)	$ 0	$ 0
Common stock, shares authorized	400,000,000	400,000,000
Common stock, shares issued	43,310,089	34,047,300
Common stock, shares outstanding	43,310,089	34,047,300

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Revenues:
Revenue from license agreement	$ 0	$ 0	$ 3,000	$ 0
Revenue from development agreement	77	0	138	0
Revenue from related party	0	400	0	2,163
Revenue from grants	271	0	271	0
Total revenues	348	400	3,409	2,163
Cost and expenses:
Research and development	7,032	13,703	27,178	44,322
General and administrative	4,601	8,033	16,207	21,551
(Gain) / loss on lease modification and termination	0	444	881	(1,669)
Total cost and expenses	11,633	22,180	44,266	64,204
Loss from operations	(11,285)	(21,780)	(40,857)	(62,041)
Sublease termination income, net	0	2,875	0	2,875
Interest and other income, net	(5)	93	(15)	592
Net loss	$ (11,290)	$ (18,812)	$ (40,872)	$ (58,574)
Net loss per share:
Basic and diluted net loss per share (in dollars per share)	$ (0.26)	$ (0.59)	$ (1.08)	$ (2.01)
Weighted average shares used in calculating:
Basic and diluted net loss per share (in shares)	43,291	32,096	37,730	29,196
Other comprehensive loss:
Net loss	$ (11,290)	$ (18,812)	$ (40,872)	$ (58,574)
Other comprehensive loss:
Foreign currency translation adjustment (loss) gain	0	3	1	(7)
Comprehensive loss	$ (11,290)	$ (18,809)	$ (40,871)	$ (58,581)

Condensed Consolidated and Comb

Condensed Consolidated and Combined Statements of Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Common stock	Paid-in capital	Accumulated deficit	Accumulated other comprehensive loss
Beginning balance at Dec. 31, 2019	$ 97,729		$ 183,376	$ (85,627)	$ (20)
Beginning balance (in shares) at Dec. 31, 2019		27,598,133
Net loss	(20,228)			(20,228)
Issuance of common stock upon exercise of stock options, RSUs and employee stock purchase plan	1		1
Issuance of common stock upon exercise of stock options, RSUs and employee stock purchase plan (in shares)		156,761
Share-based compensation expense related to issuance of stock options and RSUs to employees and employee stock purchase plan	4,036		4,036
Foreign currency translation adjustment (loss) gain	2				2
Ending balance at Mar. 31, 2020	81,540		187,413	(105,855)	(18)
Ending balance (in shares) at Mar. 31, 2020		27,754,894
Beginning balance at Dec. 31, 2019	97,729		183,376	(85,627)	(20)
Beginning balance (in shares) at Dec. 31, 2019		27,598,133
Net loss	(58,574)
Foreign currency translation adjustment (loss) gain	(7)
Ending balance at Sep. 30, 2020	75,354		219,582	(144,201)	(27)
Ending balance (in shares) at Sep. 30, 2020		33,961,555
Beginning balance at Mar. 31, 2020	81,540		187,413	(105,855)	(18)
Beginning balance (in shares) at Mar. 31, 2020		27,754,894
Net loss	(19,534)			(19,534)
Issuance of common stock upon exercise of stock options, RSUs and employee stock purchase plan	155		155
Issuance of common stock upon exercise of stock options, RSUs and employee stock purchase plan (in shares)		102,816
Share-based compensation expense related to issuance of stock options and RSUs to employees and employee stock purchase plan	3,952		3,952
Foreign currency translation adjustment (loss) gain	(12)				(12)
Ending balance at Jun. 30, 2020	66,101		191,520	(125,389)	(30)
Ending balance (in shares) at Jun. 30, 2020		27,857,710
Net loss	(18,812)			(18,812)
Issuance of common stock equity private placement and ATM	24,250		24,250
Issuance of common stock equity private placement and ATM (in shares)		6,062,500
Issuance of common stock upon exercise of stock options, RSUs and employee stock purchase plan	16		16
Issuance of common stock upon exercise of stock options, RSUs and employee stock purchase plan (in shares)		41,345
Share-based compensation expense related to issuance of stock options and RSUs to employees and employee stock purchase plan	3,796		3,796
Foreign currency translation adjustment (loss) gain	3				3
Ending balance at Sep. 30, 2020	75,354		219,582	(144,201)	(27)
Ending balance (in shares) at Sep. 30, 2020		33,961,555
Beginning balance at Dec. 31, 2020	$ 59,493		222,949	(163,429)	(27)
Beginning balance (in shares) at Dec. 31, 2020	34,047,300	34,047,300
Net loss	$ (13,399)			(13,399)
Issuance of common stock upon exercise of stock options, RSUs and employee stock purchase plan	27		27
Issuance of common stock upon exercise of stock options, RSUs and employee stock purchase plan (in shares)		82,625
Share-based compensation expense related to issuance of stock options and RSUs to employees and employee stock purchase plan	1,921		1,921
Share‑based compensation expense related to issuance of stock options to non-employees	391		391
Ending balance at Mar. 31, 2021	48,433		225,288	(176,828)	(27)
Ending balance (in shares) at Mar. 31, 2021		34,129,925
Beginning balance at Dec. 31, 2020	$ 59,493		222,949	(163,429)	(27)
Beginning balance (in shares) at Dec. 31, 2020	34,047,300	34,047,300
Net loss	$ (40,872)
Foreign currency translation adjustment (loss) gain	1
Ending balance at Sep. 30, 2021	$ 56,387		260,713	(204,300)	(26)
Ending balance (in shares) at Sep. 30, 2021	43,310,089	43,310,089
Beginning balance at Mar. 31, 2021	$ 48,433		225,288	(176,828)	(27)
Beginning balance (in shares) at Mar. 31, 2021		34,129,925
Net loss	(16,182)			(16,182)
Issuance of common stock equity private placement and ATM	30,497		30,497
Issuance of common stock equity private placement and ATM (in shares)		9,087,547
Issuance of common stock upon exercise of stock options, RSUs and employee stock purchase plan	133		133
Issuance of common stock upon exercise of stock options, RSUs and employee stock purchase plan (in shares)		57,777
Share-based compensation expense related to issuance of stock options and RSUs to employees and employee stock purchase plan	1,942		1,942
Share‑based compensation expense related to issuance of stock options to non-employees	398		398
Foreign currency translation adjustment (loss) gain	1				1
Ending balance at Jun. 30, 2021	65,222		258,258	(193,010)	(26)
Ending balance (in shares) at Jun. 30, 2021		43,275,249
Net loss	(11,290)			(11,290)
Issuance of common stock equity private placement and ATM	6		6
Issuance of common stock equity private placement and ATM (in shares)		1,500
Issuance of common stock upon exercise of stock options, RSUs and employee stock purchase plan	37		37
Issuance of common stock upon exercise of stock options, RSUs and employee stock purchase plan (in shares)		33,340
Share-based compensation expense related to issuance of stock options and RSUs to employees and employee stock purchase plan	2,018		2,018
Share‑based compensation expense related to issuance of stock options to non-employees	394		394
Foreign currency translation adjustment (loss) gain	0				0
Ending balance at Sep. 30, 2021	$ 56,387		$ 260,713	$ (204,300)	$ (26)
Ending balance (in shares) at Sep. 30, 2021	43,310,089	43,310,089

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (40,872)	$ (58,574)
Adjustments to reconcile net loss to net cash (used in) operating activities:
Depreciation and amortization	424	1,827
Net loss on disposal of property and equipment	6,322	205
(Gain) / loss on lease modification and termination	881	(1,669)
Sublease termination income, net	0	(2,875)
Share-based compensation expense	7,064	11,785
Changes in operating assets and liabilities:
Accounts receivable	(158)	0
Related party accounts receivable	127	1,074
Prepaid expenses	254	748
Other current assets	1,254	(8)
Operating lease assets	(105)	(3,592)
Other assets	274	(979)
Accounts payable	25	(1,094)
Related party accounts payable	(286)	414
Accrued research and development costs	2,011	(38)
Operating lease liabilities	(1,048)	(2,000)
Accrued expenses and other current liabilities	(4,054)	(3,673)
Net cash (used in) operating activities	(27,887)	(58,449)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(7)	(1,489)
Proceeds from sale of property and equipment	1,464	71
Net cash provided by (used in) investing activities	1,457	(1,418)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from June 2021 equity private placement and ATM	30,503	24,250
Proceeds from exercises of stock options and ESPP	197	172
Proceeds from short-term note payable	0	3,509
Net cash provided by financing activities	30,700	27,931
Effect of exchange rate changes on cash, cash equivalents and restricted cash	1	(7)
Net increase (decrease) in cash, cash equivalents and restricted cash	4,271	(31,943)
Cash, cash equivalents and restricted cash, beginning of period	58,232	102,620
Cash, cash equivalents and restricted cash, end of period	62,503	70,677
Supplemental cash flow disclosure:
Cash paid for initial direct costs of lease modification	0	6,507
Non-cash investing activities
Fixed asset purchases in accounts payable and accrued expenses	$ 0	$ 4

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Cash Flows (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2021	Sep. 30, 2020
Reconciliation of cash, cash equivalents and restricted cash to the condensed consolidated balance sheets
Cash and cash equivalents	$ 62,503	$ 66,840
Restricted cash	0	3,837
Total cash, cash equivalents and restricted cash	$ 62,503	$ 70,677

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	1. Nature of Business Nature of Operations Cyclerion Therapeutics, Inc. (“Cyclerion”, the “Company” or “we”) is a clinical-stage biopharmaceutical company on a mission to develop treatments that restore cognitive function. Our lead asset, CY6463 (previously known as, IW-6463), is a pioneering, central nervous system (“CNS”)-penetrant, soluble guanylate cyclase (sGC) stimulator that is currently in clinical development for Alzheimer’s disease with vascular pathology (ADv), and Mitochondrial Encephalomyopathy, Lactic Acidosis and Stroke-like episodes (MELAS), and cognitive impairment associated with schizophrenia (CIAS). sGC stimulators are small molecules that act synergistically with nitric oxide (NO) as positive allosteric modulators of sGC to boost production of cyclic guanosine monophosphate (cGMP). cGMP is a key second messenger that, when produced by sGC, regulates diverse and critical biological functions in the CNS including neuronal function, neuroinflammation, cellular bioenergetics, and vascular function. Cyclerion GmbH, a wholly owned subsidiary, was incorporated in Zug, Switzerland on May 3, 2019. Cyclerion GmbH is an operational entity with one employee who is the Company’s Chief Scientific Officer. The functional currency is the Swiss franc. Cyclerion Securities Corporation, a wholly owned subsidiary, was incorporated in Massachusetts on November 15, 2019, and was granted securities corporation status in Massachusetts for the 2019 tax year. Cyclerion Securities Corporation has no employees. Company Overview The Company’s mission is to develop treatments that restore cognitive function. Its priorities are advancing its ongoing CY6463 clinical programs and next generation compound, CY3018. CNS assets. CY6463 is an orally administered CNS-penetrant sGC stimulator that is being developed as a symptomatic and potentially disease modifying therapy for serious CNS diseases. Nitric oxide sGC-cGMP is a fundamental CNS signaling network, but it has not yet been leveraged for its full therapeutic potential. CY6463 enhances the brain’s natural ability to produce cGMP, an important second messenger in the CNS, by stimulating sGC, a key node in the NO-sGC-cGMP pathway. This pathway is critical to basic CNS functions and deficient NO-sGC-cGMP signaling is believed to play an important role in the pathogenesis of neurodegenerative diseases. Agents that stimulate sGC to produce cGMP may compensate for deficient NO signaling. On January 13, 2020, we announced positive results from our Phase 1 first-in-human study that provided the foundation for continued development of CY6463. The Phase 1 healthy participant study results indicate that CY6463 was well tolerated. Pharmacokinetic (PK) data, obtained from both blood and cerebral spinal fluid (CSF), support once-daily dosing, with or without food, and demonstrated CY6463 penetration of the blood-brain-barrier with CSF concentrations expected to be pharmacologically active. On October 14, 2020, we announced positive topline results from our CY6463 Phase 1 translational pharmacology study in healthy elderly participants. Treatment with CY6463 for 15-days in this 24-subject study confirmed and extended results seen in the earlier first-in-human Phase 1 study: once daily oral treatment demonstrated blood-brain-barrier penetration with expected CNS exposure and target engagement. Results also showed significant improvements in neurophysiological and objective performance measures as well as in inflammatory biomarkers associated with aging and neurodegenerative diseases. CY6463 was shown to be safe and generally well tolerated. Significant effects on cerebral blood flow and markers of bioenergetics were not observed in this study of healthy elderly participants. We believe that these results, together with nonclinical data, support continued development of CY6463 as a potential new medicine for serious CNS diseases. We have initiated our CY6463 Phase 2a clinical trial in adult participants with MELAS. Startup activities are ongoing for our Phase 2a clinical trial in ADv, with enrollment expected to begin in 2021.The ADv study will be supported in part by a grant from the Alzheimer’s Association’s Part the Cloud-Gates Partnership Grant Program ("PTC Grant"), which provides Cyclerion with $2 million of funding over two years . Our phase 1b clinical study in CIAS has been activated and enrollment has begun. Our next generation CNS asset, CY3018, is a differentiated CNS-penetrant sGC stimulator with greater CSF-to-plasma exposure relative to CY6463. CY3018 is intended to expand the potential of sGC stimulation for the treatment of disorders of the CNS. Non-CNS assets. We have other assets that are outside of our current strategic focus. These non-core assets are not being internally developed at this time and with the exception of praliciguat, are available for licensing to a third-party partner. Praliciguat is an orally administered, once-daily systemic sGC stimulator. On June 3, 2021, we entered into a License Agreement with Akebia Therapeutics, Inc. (“Akebia”) relating to the exclusive worldwide license to Akebia of our rights to the development, manufacture, medical affairs and commercialization of pharmaceutical products containing the pharmaceutical compound praliciguat and other related products and forms thereof enumerated in such agreement. Olinciguat is an orally administered, once-daily, vascular sGC stimulator that was evaluated in a Phase 2 study of participants with sickle cell disease. We released topline results from this study in October 2020. The Separation On April 1, 2019, Ironwood Pharmaceuticals, Inc. (“Ironwood”) completed the separation of its sGC business, and certain other assets and liabilities, into a separate, independent publicly traded company by way of a pro-rata distribution of all of the outstanding shares of common stock of Cyclerion Therapeutics, Inc. through a dividend distribution of one share of the Company’s common stock, with no par value per share, for every 10 shares of Ironwood common stock held by Ironwood stockholders as of the close of business on March 19, 2019, the record date for the Distribution (the entire transaction being the “Separation”). As a result of the Separation, the Company became an independent public company and commenced trading under the symbol “CYCN” on the Nasdaq Global Select Market on April 2, 2019. 2020 Equity Private Placement On July 29, 2020, the Company entered into a Common Stock Purchase Agreement (the "2020 Equity Private Placement") for the private placement of 6,062,500 shares of the Company's common stock, for total gross proceeds of approximately $ 24.3 million. The closing of the 2020 Equity Private Placement occurred on July 29, 2020. The Company did not utilize the services of a placement agent or broker and accordingly incurred no material related transaction fees or commissions. June 2021 Equity Private Placement On June 3, 2021, the Company entered into a Common Stock Purchase Agreement (the “June 2021 Equity Private Placement”) for the private placement of 5,735,988 shares of the Company’s common stock, for total gross proceeds of approximately $ 18 million. The closing of the June 2021 Equity Private Placement occurred on June 7, 2021. The Company did not utilize the services of a placement agent or broker and accordingly incurred no material related transaction fees or commissions. At-the-Market Offering On July 24, 2020, the Company filed a Registration Statement on Form S-3 (the “Shelf”) with the Securities and Exchange Commission (the “SEC”) in relation to the registration of common stock, preferred stock, debt securities, warrants and units of any combination thereof for an aggregate initial offering price not to exceed $ 150.0 million. The Shelf was declared effective as of July 31, 2020. On September 3, 2020, the Company entered into a Sales Agreement (the “Sales Agreement”) with Jefferies LLC (“Jefferies”) with respect to an at-the-market offering (the “ATM Offering”) under the Shelf. Under the ATM Offering, 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 Jefferies as its sales agent. The Company will pay to Jefferies cash commissions of 3.0 percent of the gross proceeds of sales of common stock under the Sales Agreement. During the nine months ended September 30, 2021, the Company sold 3,353,059 shares of its common stock for net proceeds of $ 12.5 million under the ATM Offering, after deducting commissions paid to Jefferies of approximately $ 0.4 million. Basis of Presentation The condensed consolidated financial statements and the related disclosures are unaudited and have been prepared in accordance with accounting principles generally accepted in the U.S. Additionally, certain information and footnote disclosures normally included in the Company’s annual financial statements have been condensed or omitted. Accordingly, these interim condensed consolidated financial statements should be read in conjunction with the condensed consolidated financial statements and notes thereto contained in the Company’s Annual Report on Form 10-K for the year ended December 31, 2020, which was filed with the Securities and Exchange Commission on February 25, 2021. In the opinion of management, the unaudited interim condensed consolidated financial statements reflect all normal recurring adjustments considered necessary for a fair presentation of the Company’s financial position and the results of its operations for the interim periods presented. The results of operations for the three and nine months ended September 30, 2021 and 2020 are not necessarily indicative of the results that may be expected for the full year or any other subsequent interim period. The condensed consolidated financial statements include the financial statements of the Company and its wholly owned subsidiaries, Cyclerion GmbH, and Cyclerion Securities Corporation. All significant intercompany accounts and transactions have been eliminated in the preparation of the accompanying condensed consolidated financial statements. Going Concern At each reporting period, the Company evaluates whether there are conditions or events that raise substantial doubt about the Company’s ability to continue as a going concern within one year after the date that the financial statements are issued. The Company’s evaluation entails analyzing prospective operating budgets and forecasts for expectations of the Company’s cash needs and comparing those needs to the current cash and cash equivalent balances. The Company is required to make certain additional disclosures if it concludes substantial doubt exists and it is not alleviated by the Company’s plans or when its plans alleviate substantial doubt about the Company’s ability to continue as a going concern. The Company has experienced negative operating cash flows for all historical periods presented and the Company expects these losses to continue into the foreseeable future as the Company continues the development and clinical testing of its product candidate CY6463, CY3018 and its discovery research programs. Through September 30, 2021, the Company had raised an aggregate of $ 219.8 million in net proceeds from equity private placements and the ATM Offering. After considering the Company’s current research and development plans and the timing expectations related to the progress of its programs, and after considering its existing cash and cash equivalents as of September 30, 2021 , the Company did not identify conditions or events that would raise substantial doubt about the Company’s ability to continue as a going concern within one year from the date these financial statements were issued. 2. Summary of Significant Accounting Policies The accounting policies of the Company are set forth in Note 2. Summary of Significant Accounting Policies to the consolidated financial statements contained in the Company’s 2020 annual report on Form 10-K. The Company includes herein certain updates to those policies. Use of Estimates The preparation of consolidated financial statements in accordance with U.S. GAAP requires the Company’s management to make estimates and judgments that may affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the consolidated financial statements, and the amounts of expenses during the reported periods. On an ongoing basis, the Company’s management evaluates its estimates, judgments, and methodologies. Significant estimates and assumptions in the consolidated financial statements include those related to revenue, impairment of long-lived assets, valuation procedures for right-of-use assets and operating lease liabilities, income taxes, including the valuation allowance for deferred tax assets, research and development expenses, contingencies, share-based compensation and going concern. The Company bases its estimates on historical experience and on various other assumptions that are believed to be reasonable, the results of which form the basis for making judgments about the carrying values of assets and liabilities. Actual results may differ materially from these estimates under different assumptions or conditions. Changes in estimates are reflected in reported results in the period in which they become known. Revenue The Company generates revenue from research and development grants under contracts with third parties that do not create customer-vendor relationships. The Company’s research and development grants are non-exchange transactions and are not within the scope of ASC Topic 606, Revenue from Contracts with Customers (“ASC 606”). Contribution revenue earned from activities performed pursuant to research and development grants is reported as grant revenue in the Company’s condensed consolidated statements of operations. Revenue from these grants is recognized as the Company incurs qualifying expenses as stipulated by the terms of the respective grant. Cash received from grants in advance of incurring qualifying expenses is recorded as deferred revenue. The Company records revenue and a corresponding receivable when qualifying costs are incurred before receiving payment from the grants. New Accounting Pronouncements From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board (“FASB”) or other standard setting bodies that are adopted by the Company as of the specified effective date. Except as discussed elsewhere in the notes to the consolidated financial statements, the Company did not adopt any new accounting pronouncements during the nine months ended September 30, 2021 that had a material effect on its condensed consolidated financial statements. In June 2016 the FASB issued ASU 2016-13, Financial Instruments-Credit Losses. This standard requires entities to measure all expected credit losses for financial assets held at the reporting date based on historical experience, current conditions, and reasonable and supportable forecasts. As a smaller reporting company, ASU 2016-13 will become effective for the Company for fiscal years beginning after December 15, 2022, and early adoption is permitted. The Company is currently evaluating the impact that ASU 2016-13 will have on its financial statements and related disclosures. In May 2021 the FASB issued Accounting Standards Update No. 2021-04, Earnings Per Share (Topic 260), Debt-Modifications and Extinguishments (Subtopic 470-50), Compensation-Stock Compensation (Topic 718), and Derivatives and Hedging-Contracts in Entity’s Own Equity (Subtopic 815-40): Issuer’s Accounting for Certain Modifications or Exchanges of Freestanding Equity-Classified Written Call Options, a consensus of the Emerging Issues Task Force (EITF) , which amends the FASB Accounting Standards Codification (ASC or the “Codification”) to provide explicit guidance, and, thus, reduce diversity in practice, on accounting by issuers for modifications or exchanges of freestanding equity-classified written call options that remain equity classified after the modification or exchange. This amendment provides that for an entity that presents earnings per share (EPS) in accordance with Topic 260, the effects of a modification or an exchange of a freestanding equity-classified written call option that is recognized as a dividend should be an adjustment to net income (or net loss) in the basic EPS calculation. The amended guidance becomes mandatorily effective for all entities for fiscal years beginning after December 15, 2021, including interim periods within those fiscal years, and should be applied prospectively to modifications or exchanges occurring on or after the effective date. The Company is currently evaluating the impact that ASU 2021-04 will have on its financial statements and related disclosures. No other accounting standards known by the Company to be applicable to it that have been issued by the FASB or other standard-setting bodies and that do not require adoption until a future date are expected to have a material impact on the Company’s condensed consolidated financial statements upon adoption.

Related Party Transactions

Related Party Transactions	9 Months Ended
	Sep. 30, 2021
Related Party Transactions [Abstract]
Related Party Transactions	3. Related Party Transactions Development Agreement with Ironwood As part of the Separation from Ironwood, the Company entered into a Development Agreement with Ironwood. Under the Development Agreement, the Company provided certain research and development services to Ironwood at mutually agreed upon rates and the amounts earned are recorded as revenue from related party for the three and nine months ended September 30, 2020. Such research and development activities were governed by a joint steering committee composed of representatives of both Ironwood and the Company. Ironwood and the Company have agreed not to renew the Development Agreement beyond the end of its initial term on March 31, 2021. These transactions under the Development Agreement were considered related party transactions due to Mark Currie’s role as President of the Company through December 31, 2020, and board member of Ironwood. In January 2021, Mark Currie’s role transitioned from President of the Company to a senior advisor on a consulting basis. Therefore, effective January 2021, transactions under the Development Agreement are no longer accounted for as related party transactions. The Company recorded approximately $ 0.4 million and $ 2.2 million as related party revenue for the three and nine months ended September 30, 2020 , respectively.

Fair Value of Financial Instrum

Fair Value of Financial Instruments	9 Months Ended
	Sep. 30, 2021
Fair Value Disclosures [Abstract]
Fair Value of Financial Instruments	4. Fair Value of Financial Instruments The Company’s cash equivalents are generally classified within Level 1 of the fair value hierarchy. The following tables present information about the Company’s financial assets measured at fair value on a recurring basis and indicate the level of the fair value hierarchy used to determine such fair values as of September 30, 2021 and December 31, 2020 (in thousands): Fair Value Measurements as of September 30, 2021: Level 1 Level 2 Level 3 Total Cash equivalents: Money market funds $ 61,451 $ — $ — $ 61,451 Cash equivalents $ 61,451 $ — $ — $ 61,451 Fair Value Measurements as of December 31, 2020: Level 1 Level 2 Level 3 Total Cash equivalents: Money market funds $ 53,240 $ — $ — $ 53,240 Cash equivalents $ 53,240 $ — $ — $ 53,240 During the nine months ended September 30, 2021 and 2020, there were no transfers between levels. The fair value of the Company’s cash equivalents, consisting of money market funds, is based on quoted market prices in active markets with no valuation adjustment. The Company believes the carrying amounts of its prepaid expenses and other current assets, restricted cash, accounts payable, and accrued expenses approximate their fair value due to the short-term nature of these amounts.

Property and Equipment

Property and Equipment	9 Months Ended
	Sep. 30, 2021
Property Plant And Equipment [Abstract]
Property and Equipment	5. Property and Equipment Property and equipment, net consisted of the following (in thousands): September 30, December 31, 2021 2020 Software $ 2,214 $ 2,214 Computer and office equipment 51 44 Leasehold improvements — 14,894 Property and equipment, gross 2,265 17,152 Less: accumulated depreciation and amortization ( 2,153 ) ( 10,287 ) Property and equipment, net $ 112 $ 6,865 As of September 30, 2021, and December 31, 2020, the Company’s property and equipment was primarily located in Cambridge, Massachusetts. Depreciation and amortization expense of the Company’s property and equipment was a de minimis amount and approximately $ 0.6 million for the three months ended September 30, 2021 and 2020, respectively, and approximately $ 0.4 million and $ 1.8 million for the nine months ended September 30, 2021 and 2020, respectively. During the nine months ended September 30, 2021 , the Company recorded a non-cash loss of $ 6.3 million, on the disposal of leasehold improvements as a result of its Head Lease (as defined below) termination (see Note 8 to the Condensed Consolidated Financial Statements). The non-cash loss on the disposal of leasehold improvements was recognized as a component of operating expenses in the condensed consolidated statements of operations and comprehensive loss for the nine months ended September 30, 2021 . The Company did no t record any disposal of property and equipment during the three months ended September 30, 2021 .

Accrued Expenses and Other Curr

Accrued Expenses and Other Current Liabilities	9 Months Ended
	Sep. 30, 2021
Accrued Liabilities And Other Liabilities [Abstract]
Accrued Expenses and Other Current Liabilities	6. Accrued Expenses and Other Current Liabilities Accrued expenses and other current liabilities consisted of the following (in thousands): September 30, December 31, 2021 2020 Accrued incentive compensation $ 957 $ 1,720 Salaries 450 514 Accrued vacation 338 555 Professional fees 503 689 Accrued severance and benefit costs 159 3,640 Other 833 176 Accrued expenses and other current liabilities $ 3,240 $ 7,294

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2021
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	7. Commitments and Contingencies Other Funding Commitments In the normal course of business, the Company enters into contracts with clinical research organizations and other third parties for clinical and preclinical research studies and other services and products for operating purposes. These contracts are generally cancellable, with notice, at the Company’s option and do not have any significant cancellation penalties. Guarantees On September 6, 2018, Cyclerion was incorporated in Massachusetts and its officers and directors are indemnified for certain events or occurrences while they are serving in such capacity. The Company enters into certain agreements with other parties in the ordinary course of business that contain indemnification provisions. These typically include agreements with directors and officers, business partners, contractors, clinical sites and customers. Under these provisions, the Company generally indemnifies and holds harmless the indemnified party for losses suffered or incurred by the indemnified party as a result of the Company’s activities. These indemnification provisions generally survive termination of the underlying agreements. The maximum potential amount of future payments the Company could be required to make under these indemnification provisions is unlimited. However, to date the Company has not incurred material costs to defend lawsuits or settle claims related to these indemnification provisions. As a result, the estimated fair value of these obligations is minimal. Accordingly, the Company did not have any liabilities recorded for these obligations as of September 30, 2021 and December 31, 2020 .

Leases

Leases	9 Months Ended
	Sep. 30, 2021
Leases [Abstract]
Leases	8. Leases On April 1, 2019, the Company entered into the Head Lease (the "Head Lease"), a direct operating lease for its former headquarters located at 301 Binney Street, Cambridge, MA originally consisting of approximately 114,000 rentable square feet of office and laboratory space on the first and second floors. The Head Lease had a term of 123 months with two five-year extension options and certain expansion rights. The Head Lease also included a letter of credit of $ 7.7 million, posted with the landlord as a security deposit, which was collateralized by a money market account recorded as restricted cash on the Company’s condensed consolidated balance sheets. The Company had also entered into customary non-disturbance arrangements with the building landlord’s mortgagee and with the property ground lessor recognizing Company’s leasehold interest in this property. On February 28, 2020, the Company amended the Head Lease (the "Lease Amendment"). The Lease Amendment partially terminated the Company’s rights and obligations with respect to an approximately 40,000 rentable square feet. The Company continued to lease the remaining space of approximately 74,000 square feet including the area covered by the subleased premise, discussed below. In connection with this Lease Amendment, the Company reduced its remaining lease payments through June 2029 by approximately $ 41.9 million and paid a $ 6.3 million termination fee and $ 0.2 million related to other initial direct costs, which were deferred and recognized over the remaining lease term. The Company’s security deposit was also reduced by approximately $ 2.7 million to approximately $ 5.0 million. The Lease Amendment was determined to be a lease modification that qualified as a change of accounting on the existing lease and not a separate contract. As such, the Right-of-Use (“ROU”) assets and operating lease liabilities were remeasured using an incremental borrowing rate at the date of modification of 9.7 %, which resulted in a reduction of the ROU asset of $ 21.4 million and a reduction in the operating lease liabilities of $ 23.5 million. The Company recorded the resulting gain of approximately $ 2.1 million as a component of operating expenses in the condensed consolidated statement of operations and comprehensive loss for the year ended December 31, 2020. On September 15, 2020, the Company entered into the Second Lease Amendment (the "Second Lease Amendment") to its Head Lease. The Second Lease Amendment partially terminated the Company’s rights and obligations with respect to approximately 17,000 rentable square feet (the “Surrender Space”), including 15,700 rentable square feet subleased by the Company to a subtenant. The Company continues to lease approximately 57,000 square feet of space under the terms of the Second Lease Amendment. The Company reduced its remaining lease payments through June 2029 by approximately $ 16.9 million. The Company paid no termination or other initial direct costs related to the execution of the Second Lease Amendment. The Company’s security deposit was reduced by approximately $ 1.2 million to approximately $ 3.8 million. The Second Lease Amendment was determined to be a lease modification that qualified as a change of accounting on the existing lease and not a separate contract. As such, the ROU assets and operating lease liabilities were remeasured using an incremental borrowing rate at the date of modification of 6.1 %, which resulted in a reduction of the ROU asset of $ 5.9 million and a reduction in the operating lease liabilities of $ 5.5 million. The Company recorded the resulting loss of approximately $ 0.4 million as a component of operating expenses in the condensed consolidated statement of operations and comprehensive loss for the year ended December 31, 2020. On April 30, 2021, the Company entered into a Termination Agreement (the "Termination Agreement") for its Head Lease as initially amended on February 28, 2020, and further amended on September 15, 2020. Pursuant to the Termination Agreement, the Company surrendered the leased space of approximately 57,000 square feet to the building’s landlord. The Company did not pay any termination fees in connection with the Termination Agreement. As a result of the termination of the Head Lease, the related right-of-use asset was written off, the lease liability was derecognized, and the $ 3.8 million security deposit was returned to the Company and recorded as part of our cash balance. In total, the Company recognized a loss on the termination of the Head Lease of $ 0.9 million during the nine months ended September 30, 2021. The loss is included in “General and administrative” expenses on our condensed consolidated statement of operations and comprehensive loss. The Company had an operating lease ROU asset of approximately $ 43.4 million related to the amended Head Lease recorded in its condensed consolidated balance sheets as of December 31, 2020. The Company had current and non-current operating lease liabilities of approximately $ 3.3 million and $ 38.9 million, respectively, related to the amended Head Lease recorded in its consolidated balance sheets as of December 31, 2020. Lease cost is recognized on a straight-line basis over the lease term. For the three and nine months ended September 30, 2021, the Company recognized a de minimis amount and a total of approximately $ 2.3 million of total lease costs related to the Head Lease, respectively, as amended. Variable lease costs not subject to an index or rate are recognized as incurred. For the nine months ended September 30, 2021, the Company recognized a total of approximately $ 0.7 million of variable lease costs related to the Head Lease, as amended. The Company did no t record any lease costs related to the Head Lease, as amended, during the three months ended September 30, 2021. For the three and nine months ended September 30, 2020, the Company recognized a total of approximately $ 2.0 million and $ 6.9 million, respectively, of total lease costs and $ 0.4 million and $ 1.9 million, respectively, of variable lease costs, related to the Head Lease, as amended. In May 2021 the Company signed a membership agreement to lease space with WeWork at 501 Boylston Street. The lease commenced on August 1, 2021 and was accounted for as a short term lease. The Company recorded a de minimis lease expense associated with the membership agreement during the three months ended September 30, 2021. Supplemental cash flow information related to leases for the nine months ended September 30, 2021 is as follows: Nine Months Ended 2021 2020 Decrease in right-of-use assets related to lease modifications and termination $ 42,058 $ 27,333 Decrease in operating lease liabilities due to lease modifications and termination $ 41,177 $ 29,002 Cash paid for amounts included in the measurement of lease liabilities (in thousands) $ — $ 6,076 Weighted-average remaining lease term of operating leases (in years) — 8.8 Weighted-average discount rate of operating leases — 6.1 % On October 18, 2019, the Company entered into an agreement with a third party to sublease 15,700 rentable square feet of its lease premises under the Head Lease. The sublease was scheduled to expire on June 30, 2029, unless earlier terminated in accordance with the sublease agreement, and had no extension options. The sublease provided for annual base rent of approximately $ 1.5 million in the first year, which increased on a yearly basis by 3.0 % (subject to an abatement of base rent of approximately $ 0.7 million for the first six months of the sublease). As part of the consideration for the sublease, the sublessee agreed to provide licensed rooms and services within the sublease premises to the Company over the sublease term free of charge. In addition, the sublessee was responsible for its pro rata share of certain costs, taxes and operating expenses related to the subleased space, the consideration for which is variable and is based on the actual operating costs of the lessor. The Company allocated the total consideration in the sublease agreement between the lease and non-lease components in the contract based on their relative standalone prices. The Company determined that the variable consideration related exclusively to non-lease components and would be recognized as incurred. The sublease included an initial security deposit of $ 0.5 million, which was provided by the sublessee in the form of a letter of credit, and an additional security deposit of $ 0.4 million within nine months of the sublease commencement. For the nine months ended September 30, 2020, gross sublease income of $ 1.5 million was recorded related to the sublease. Net sublease income of approximately $ 0.3 million was recorded in interest and other income in the condensed consolidated statements of operations and comprehensive loss for the nine months ended September 30, 2020. On September 15, 2020, concurrent with execution of the Second Lease Amendment, the Company entered into the Sublease Termination Agreement (the "Sublease Termination Agreement") to terminate its sublease of 15,700 rentable square feet. Under the terms of the Sublease Termination Agreement, the subtenant was relieved of its obligation to provide future cash rental payments to the Company. The agreements requiring the former subtenant to provide licensed rooms and services to the Company free of charge through the original sublease term survived the sublease termination. The Company gained access to the licensed rooms and services beginning in the third quarter of 2021. The letter of credit security deposit related to the sublease was released. The Company determined that the Sublease Termination Agreement constitutes a non-monetary exchange under ASC 845 Nonmonetary Transactions (“ASC 845”) where, in return for the free rooms and the services, the Company agreed to terminate its rights and obligations under the sublease agreement. In accordance with ASC 845, the Company determined that the accounting for the transaction should be based on the fair value of assets or services involved. The Company estimated the fair value of the rooms and services to be approximately $ 1.5 million and $ 2.9 million, respectively. Accordingly, prepaid rooms and services of $ 4.4 million were recorded upon the sublease termination. Termination fee income of $ 3.1 million was recognized related to the rooms and services, after considering the rent receivable balance of $ 1.3 million outstanding from the subtenant. The remaining unamortized direct costs of $ 0.2 million were written off. As of September 30, 2021, the Company had approximately $ 0.4 million and $ 2.5 million recorded in other current assets and other assets, respectively in the condensed consolidated balance sheets as of September 30, 2021 related to the services. The Company determined that the licensed rooms represent a lease under ASC 842. The Company obtained control of the rooms in the third quarter of 2021 and the prepaid rooms balance of approximately $ 1.4 million was reclassified from other assets to a ROU asset. The related lease expense is recognized on a straight-line basis over the lease term of 8.88 years. The Company recorded a de minimis amount of lease expense during the three months ended September 30, 2021. The Company determined that the licensed services represent a non-lease component, which is recognized separately from the lease component for this asset class. The expense related to the licensed services is recognized on a straight-line basis over the period the services are received. The Company recorded a de minimis amount for the three months ended September 30, 2021. Both the lease expense and services expense are recognized as a component of research and development costs in the condensed consolidated statements of operations and comprehensive loss.

Share-based Compensation Plans

Share-based Compensation Plans	9 Months Ended
	Sep. 30, 2021
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Share-based Compensation Plans	9. Share-based Compensation Plans In 2019, Cyclerion adopted share-based compensation plans. Specifically, Cyclerion adopted the 2019 Employee Stock Purchase Plan (“2019 ESPP”) and the 2019 Equity Incentive Plan (“2019 Equity Plan”). Under the 2019 ESPP, eligible employees may use payroll deductions to purchase shares of stock in offerings under the plan, and thereby acquire an interest in the future of the Company. The 2019 Equity Plan provides for stock options and restricted stock units (“RSUs”). Cyclerion also mirrored two of Ironwood’s existing plans, the Amended and Restated 2005 Stock Incentive Plan (“2005 Equity Plan”) and the Amended and Restated 2010 Employee, Director and Consultant Equity Incentive Plan (“2010 Equity Plan). These mirror plans were adopted to facilitate the exchange of Ironwood equity awards for Cyclerion equity awards upon the Separation as part of the equity conversion. As a result of the Separation and in accordance with the EMA, employees of both companies retained their existing Ironwood vested options and received a pro-rata share of Cyclerion options, regardless of which company employed them post-Separation. For employees that were ultimately employed by Cyclerion, unvested Ironwood options and RSUs were converted to unvested Cyclerion options and RSUs. The following table provides share-based compensation reflected in the Company’s condensed consolidated statements of operations and comprehensive loss for the three and nine months ended September 30, 2021 and 2020 (in thousands): Three Months Ended Nine Months Ended 2021 2020 2021 2020 Research and development $ 957 $ 1,784 $ 2,874 $ 5,584 General and administrative 1,455 2,012 4,190 6,200 $ 2,412 $ 3,796 $ 7,064 $ 11,784 A summary of stock option activity for the nine months ended September 30, 2021, is as follows: Weighted Weighted Average Average Average Remaining Intrinsic Number Exercise Contractual Value (in of Options Price Term (Years) thousands) Outstanding as of December 31, 2020 7,426,356 $ 11.87 7.0 1,178 Granted 834,250 3.40 Exercised ( 58,055 ) 2.21 Cancelled or forfeited ( 1,237,123 ) 10.24 Outstanding as of September 30, 2021 6,965,428 $ 11.22 6.7 $ 873 Exercisable at September 30, 2021 4,373,344 $ 13.72 5.7 $ 301 As of September 30, 2021, the unrecognized share-based compensation expense, net of estimated forfeitures, related to all unvested time-based stock options held by the Company’s employees is $ 9.6 million and the weighted average period over which that expense is expected to be recognized is 3.2 years. A summary of RSU activity for the nine months ended September 30, 2021 is as follows: Weighted Average Number Grant Date of Shares Fair Value Unvested as of December 31, 2020 294,913 $ 14.52 Granted 39,369 3.17 Vested ( 88,217 ) 15.06 Forfeited ( 97,704 ) 14.41 Unvested as of September 30, 2021 148,361 $ 11.25 As of September 30, 2021, the unrecognized share-based compensation expense, net of estimated forfeitures, related to all unvested restricted stock units by the Company’s employees is $ 1 million and the weighted-average period over which that expense is expected to be recognized is 0.94 years. The Company has granted to certain employees performance-based options to purchase shares of common stock. These options are subject to performance-based milestone vesting. During the three and nine months ended September 30, 2021 and 2020 there were no shares that vested as a result of performance milestone achievements. The Company recorded no share-based compensation expense related to these performance-based options for the three and nine months ended September 30, 2021 and 2020. The Company also has granted to certain employees stock options containing market conditions that vest upon the achievement of specified price targets of the Company’s share price for a period through December 31, 2024. Vesting is measured based upon the average closing price of the Company’s share price for any thirty consecutive trading days, subject to certain service requirements. Stock compensation cost is expensed on a straight-line basis over the derived service period for each stock price target within the award, ranging from approximately 4.0 to 4.6 years. The Company accelerates expense when a stock price target is achieved prior to the derived service period. The Company does not reverse expense recognized if the share price target(s) are ultimately not achieved but expense is reversed when a stock award recipient has a break in service prior to the completion of the derived service period. For each of the three months ended September 30, 2021 and 2020, the Company recorded a de minimis amount of share-based compensation expense, respectively related to these stock options containing market conditions. During the nine months ended September 30, 2021, 150,000 stock options containing market conditions were forfeited with a weighted average exercise price of $ 2.01 . As of September 30, 2021, there were 450,000 outstanding stock options containing market conditions with a weighted average exercise price of $ 2.01 . As of September 30, 2021, there was $ 0.2 million of unrecognized compensation costs related to stock options containing market conditions, which is expected to be recognized over a weighted-average period of 2.42 years.

Loss per share

Loss per share	9 Months Ended
	Sep. 30, 2021
Earnings Per Share [Abstract]
Loss per share	10. Loss per share Basic and diluted net loss per common share is computed by dividing net loss by the weighted average number of common shares outstanding during the period as follows: Three Months Ended Nine Months Ended 2021 2020 2021 2020 Numerator: Net loss (in thousands) $ ( 11,290 ) $ ( 18,812 ) $ ( 40,872 ) $ ( 58,574 ) Denominator: Weighted average shares used in calculating net loss per share — basic and diluted (in thousands) 43,291 32,096 37,730 29,196 Net loss per share — basic and diluted $ ( 0.26 ) $ ( 0.59 ) $ ( 1.08 ) $ ( 2.01 ) For both the three and nine months ended September 30, 2021 there were 6,965,428 shares of common stock related to stock options and 148,361 shares of common stock related to RSUs excluded from the calculation of diluted net loss per share since the inclusion of such shares would be anti-dilutive. For the three months ended September 30, 2020, 7,439,901 shares of common stock related to stock options and 428,077 shares of common stock related to RSU’s were excluded from the calculation of diluted net loss per share since the inclusion of such shares would be anti-dilutive.

Defined Contribution Plan

Defined Contribution Plan	9 Months Ended
	Sep. 30, 2021
Compensation And Retirement Disclosure [Abstract]
Defined Contribution Plan	11. Defined Contribution Plan Subsequent to the Separation, Cyclerion adopted a defined contribution 401(k) Savings Plan similar to the plan in place at Ironwood. The plan assets under the Ironwood defined contribution 401(k) Savings Plan were transferred to the Cyclerion plan. Subject to certain IRS limits, eligible employees may elect to contribute from 1 % to 100 % of their compensation. Cyclerion contributions to the plan are at the sole discretion of the board of directors. Currently, Cyclerion provides a matching contribution of 75 % of the employee’s contributions, up to $ 6,000 annually. Included in compensation expense is a de minimis amount and approximately $ 0.5 million related to the defined contribution 401(k) Savings Plan for the three and nine months ended September 30, 2021, respectively, and a de minimis amount, and approximately $ 0.4 million for the three and nine months ended September 30, 2020 , respectively.

Workforce Reduction

Workforce Reduction	9 Months Ended
	Sep. 30, 2021
Restructuring And Related Activities [Abstract]
Workforce Reduction	12. Workforce Reduction 2019 Workforce Reduction On October 30, 2019, the Company began a reduction of its current workforce by approximately thirty (30) full-time employees to align its resources with its ongoing clinical and preclinical programs, innovation strategy and partnering efforts. The total one-time costs related to the workforce reduction were approximately $ 3.0 million of which approximately $ 2.8 million were recorded during the year ended December 31, 2019 and the remaining $ 0.2 million were recorded during the three months ended March 31, 2020. The following table summarizes the accrued liabilities activity recorded in connection with the reduction in workforce for the nine months ended September 30, 2020 (in thousands): Amounts Charges Amount Adjustments Amounts October 2019 workforce reduction $ 2,009 $ 158 $ 2,137 $ ( 30 ) $ 0 Total $ 2,009 $ 158 $ 2,137 $ ( 30 ) $ 0 2020 Workforce Reduction On November 5, 2020, the Company began a reduction of its current workforce by approximately forty-eight ( 48 ) full-time employees to align its resources with its current priorities of focusing on the MELAS study, the planned ADv study and further characterization of CY6463 novel pharmacology. The total one-time costs related to the 2020 Workforce Reduction were approximately $ 5.0 million, including approximately $ 0.1 million in stock-based compensation from the modification of certain share-based equity awards. The Company reduced its workforce by approximately thirty-one ( 31 ) employees in the fourth quarter of 2020 and recorded approximately $ 4.1 million of severance and benefits costs in accordance with ASC Topic 420, Exit or Disposal Cost Obligations , or ASC 420, including a de minimis amount of stock-based compensation expense, for the year ended December 31, 2020. The workforce reduction was completed by the end of the first quarter of 2021. The following table summarizes the accrued liabilities activity recorded in connection with the reduction in workforce for the nine months ended September 30, 2021 (in thousands): Amounts Charges Amount Adjustments Amounts 2020 workforce reduction $ ( 3,640 ) $ ( 858 ) $ 4,339 $ — $ ( 159 ) Total $ ( 3,640 ) $ ( 858 ) $ 4,339 $ — $ ( 159 )

License Agreement

License Agreement	9 Months Ended
	Sep. 30, 2021
License Agreement [Abstract]
License Agreements	13. License Agreement Akebia License Agreement On June 3, 2021, the Company and Akebia entered into a License Agreement (the “License Agreement”) relating to the exclusive worldwide license by the Company to Akebia of our rights to the development, manufacture, medical affairs and commercialization of pharmaceutical products containing the pharmaceutical compound known as praliciguat and other related products and forms thereof enumerated in the License Agreement (collectively, the “Products”). Pursuant to the License Agreement, Akebia will be responsible for all future research, development, regulatory, and commercialization activities for the Products. Akebia paid a $ 3.0 million up-front payment to the Company upon signing of the License Agreement and the Company is eligible to receive additional milestone cash payments of up to $ 12.0 million in the next 18 months. Further milestone cash payments by Akebia are scheduled in the License Agreement based on the initiation of phase 3 clinical trials in the U.S. for Products for first and second indication, for FDA approvals, for approvals in certain other major markets, and for certain sales milestones. In addition to these cash milestone payments, Akebia will pay the Company tiered royalty payments on net sales in certain major markets at percentages ranging from the mid-single digits to the high-teens, subject to certain reductions and offsets. Pursuant to the License Agreement, the Company determined the License Agreement represents a service arrangement under the scope of ASC 606. Given the reversion of the rights under the License Agreement represents a penalty in substance for a termination by Akebia, the contract term would be the stated term of the License Agreement. The Company determined that the grant of license to our patents and trademarks, know how transfer, the assignment of regulatory submissions and trademarks and additional knowledge transfer assistance obligations represent a single promise and performance obligation to be transferred to Akebia over time due to the nature of the promises in the contract. The provision of development materials on hand was identified as a separate performance obligation. However, it is immaterial in the context of the contract as the development materials are low value and do not have an alternative use to the Company. The consideration related to sales-based milestone payments, including royalties, will be recognized when the related sales occur as these amounts have been determined to relate predominantly to the license. The Company will re-evaluate the probability of achievement of the milestones and any related constraints each reporting period. Akebia Supply Agreement On August 3, 2021, the Company and Akebia entered into a Supply Agreement (the “Supply Agreement”) relating to the manufacturing by the Company of the Initial Supply of the Drug Product and placebo ("Initial Supply") for Akebia's use pursuant to the License Agreement. Akebia will pay the Company for the manufacturing costs at mutually agreed upon rates. The Company determined the Supply Agreement has stand-alone value under the scope of ASC 606 and should not be combined with the License Agreement. Given that the Supply Agreement can be terminated at any time without cause with 30 days notice, the Company deemed the Supply Agreement to be a month-to-month contract. The manufacturing of the Initial Supply by the Company represents a single performance obligation and consideration related to the manufacturing costs will be recognized over time as costs are incurred. The Company recorded a de minimis amount as revenue from the Supply Agreement in the three and nine months ended September 30, 2021.

Grant Revenue

Grant Revenue	9 Months Ended
	Sep. 30, 2021
Grant [Member]
Disaggregation of Revenue [Line Items]
Grant Revenue	14. Grant Revenue In August 2021, the Company was approved to receive funding from the PTC Grant for the Phase 2 study of CNS sGC stimulation in AD with vascular features. The granting period is July 1, 2021, to December 31, 2022, and the Company will receive an award of up to $ 2 million. The Company determined that this transaction is non-reciprocal as there is not considered to be a commensurate value exchanged with the Alzheimer's Association as the funding provider. Where commensurate value is not exchanged for goods and services provided, a recipient assesses whether the grant is conditional or unconditional. The Company considered all conditions and barriers associated with this grant and determined the grant is conditional and revenue will be recognized upon achieving certain milestones and incurring internal costs specifically covered by this grant. Under ASC 958-605, revenues will be recognized as the Company incurs expenses related to the PTC Grant. The Company incurred approximately $ 0.3 million of allowable expenses and recognized a corresponding amount of grant revenue for the three and nine months ended September 30, 2021. The Company had a deferred revenue balance of approximately $ 0.4 million related to advance billings as of September 30, 2021.

Subsequent Events

Subsequent Events	9 Months Ended
	Sep. 30, 2021
Subsequent Events [Abstract]
Subsequent Events	15. Subsequent Events In August 2021, the Company applied with the SBA for forgiveness of the PPP loan and was notified on November 4, 2021 that the SBA has approved our application to forgive the entire amount of the loan and accrued interest. In November 2021, the Company will record a gain on extinguishment of debt of $ 3.5 million representing the principal and a deminimis amount of accrued interest for the PPP Loan.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The condensed consolidated financial statements and the related disclosures are unaudited and have been prepared in accordance with accounting principles generally accepted in the U.S. Additionally, certain information and footnote disclosures normally included in the Company’s annual financial statements have been condensed or omitted. Accordingly, these interim condensed consolidated financial statements should be read in conjunction with the condensed consolidated financial statements and notes thereto contained in the Company’s Annual Report on Form 10-K for the year ended December 31, 2020, which was filed with the Securities and Exchange Commission on February 25, 2021. In the opinion of management, the unaudited interim condensed consolidated financial statements reflect all normal recurring adjustments considered necessary for a fair presentation of the Company’s financial position and the results of its operations for the interim periods presented. The results of operations for the three and nine months ended September 30, 2021 and 2020 are not necessarily indicative of the results that may be expected for the full year or any other subsequent interim period. The condensed consolidated financial statements include the financial statements of the Company and its wholly owned subsidiaries, Cyclerion GmbH, and Cyclerion Securities Corporation. All significant intercompany accounts and transactions have been eliminated in the preparation of the accompanying condensed consolidated financial statements.
Use of Estimates	Use of Estimates The preparation of consolidated financial statements in accordance with U.S. GAAP requires the Company’s management to make estimates and judgments that may affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the consolidated financial statements, and the amounts of expenses during the reported periods. On an ongoing basis, the Company’s management evaluates its estimates, judgments, and methodologies. Significant estimates and assumptions in the consolidated financial statements include those related to revenue, impairment of long-lived assets, valuation procedures for right-of-use assets and operating lease liabilities, income taxes, including the valuation allowance for deferred tax assets, research and development expenses, contingencies, share-based compensation and going concern. The Company bases its estimates on historical experience and on various other assumptions that are believed to be reasonable, the results of which form the basis for making judgments about the carrying values of assets and liabilities. Actual results may differ materially from these estimates under different assumptions or conditions. Changes in estimates are reflected in reported results in the period in which they become known.
Revenue	Revenue The Company generates revenue from research and development grants under contracts with third parties that do not create customer-vendor relationships. The Company’s research and development grants are non-exchange transactions and are not within the scope of ASC Topic 606, Revenue from Contracts with Customers (“ASC 606”). Contribution revenue earned from activities performed pursuant to research and development grants is reported as grant revenue in the Company’s condensed consolidated statements of operations. Revenue from these grants is recognized as the Company incurs qualifying expenses as stipulated by the terms of the respective grant. Cash received from grants in advance of incurring qualifying expenses is recorded as deferred revenue. The Company records revenue and a corresponding receivable when qualifying costs are incurred before receiving payment from the grants.
New Accounting Pronouncements	New Accounting Pronouncements From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board (“FASB”) or other standard setting bodies that are adopted by the Company as of the specified effective date. Except as discussed elsewhere in the notes to the consolidated financial statements, the Company did not adopt any new accounting pronouncements during the nine months ended September 30, 2021 that had a material effect on its condensed consolidated financial statements. In June 2016 the FASB issued ASU 2016-13, Financial Instruments-Credit Losses. This standard requires entities to measure all expected credit losses for financial assets held at the reporting date based on historical experience, current conditions, and reasonable and supportable forecasts. As a smaller reporting company, ASU 2016-13 will become effective for the Company for fiscal years beginning after December 15, 2022, and early adoption is permitted. The Company is currently evaluating the impact that ASU 2016-13 will have on its financial statements and related disclosures. In May 2021 the FASB issued Accounting Standards Update No. 2021-04, Earnings Per Share (Topic 260), Debt-Modifications and Extinguishments (Subtopic 470-50), Compensation-Stock Compensation (Topic 718), and Derivatives and Hedging-Contracts in Entity’s Own Equity (Subtopic 815-40): Issuer’s Accounting for Certain Modifications or Exchanges of Freestanding Equity-Classified Written Call Options, a consensus of the Emerging Issues Task Force (EITF) , which amends the FASB Accounting Standards Codification (ASC or the “Codification”) to provide explicit guidance, and, thus, reduce diversity in practice, on accounting by issuers for modifications or exchanges of freestanding equity-classified written call options that remain equity classified after the modification or exchange. This amendment provides that for an entity that presents earnings per share (EPS) in accordance with Topic 260, the effects of a modification or an exchange of a freestanding equity-classified written call option that is recognized as a dividend should be an adjustment to net income (or net loss) in the basic EPS calculation. The amended guidance becomes mandatorily effective for all entities for fiscal years beginning after December 15, 2021, including interim periods within those fiscal years, and should be applied prospectively to modifications or exchanges occurring on or after the effective date. The Company is currently evaluating the impact that ASU 2021-04 will have on its financial statements and related disclosures. No other accounting standards known by the Company to be applicable to it that have been issued by the FASB or other standard-setting bodies and that do not require adoption until a future date are expected to have a material impact on the Company’s condensed consolidated financial statements upon adoption.

Fair Value of Financial Instr_2

Fair Value of Financial Instruments (Tables)	9 Months Ended
	Sep. 30, 2021
Fair Value Disclosures [Abstract]
Schedule of financial assets measured at fair value on a recurring basis and indicating the level of the fair value hierarchy	The Company’s cash equivalents are generally classified within Level 1 of the fair value hierarchy. The following tables present information about the Company’s financial assets measured at fair value on a recurring basis and indicate the level of the fair value hierarchy used to determine such fair values as of September 30, 2021 and December 31, 2020 (in thousands): Fair Value Measurements as of September 30, 2021: Level 1 Level 2 Level 3 Total Cash equivalents: Money market funds $ 61,451 $ — $ — $ 61,451 Cash equivalents $ 61,451 $ — $ — $ 61,451 Fair Value Measurements as of December 31, 2020: Level 1 Level 2 Level 3 Total Cash equivalents: Money market funds $ 53,240 $ — $ — $ 53,240 Cash equivalents $ 53,240 $ — $ — $ 53,240

Property and Equipment (Tables)

Property and Equipment (Tables)	9 Months Ended
	Sep. 30, 2021
Property Plant And Equipment [Abstract]
Schedule of property and equipment, net	Property and equipment, net consisted of the following (in thousands): September 30, December 31, 2021 2020 Software $ 2,214 $ 2,214 Computer and office equipment 51 44 Leasehold improvements — 14,894 Property and equipment, gross 2,265 17,152 Less: accumulated depreciation and amortization ( 2,153 ) ( 10,287 ) Property and equipment, net $ 112 $ 6,865

Accrued Expenses and Other Cu_2

Accrued Expenses and Other Current Liabilities (Tables)	9 Months Ended
	Sep. 30, 2021
Accrued Liabilities And Other Liabilities [Abstract]
Schedule of accrued expenses and other current liabilities	Accrued expenses and other current liabilities consisted of the following (in thousands): September 30, December 31, 2021 2020 Accrued incentive compensation $ 957 $ 1,720 Salaries 450 514 Accrued vacation 338 555 Professional fees 503 689 Accrued severance and benefit costs 159 3,640 Other 833 176 Accrued expenses and other current liabilities $ 3,240 $ 7,294

Leases (Tables)

Leases (Tables)	9 Months Ended
	Sep. 30, 2021
Leases [Abstract]
Schedule of supplemental cash flow information related to leases	Supplemental cash flow information related to leases for the nine months ended September 30, 2021 is as follows: Nine Months Ended 2021 2020 Decrease in right-of-use assets related to lease modifications and termination $ 42,058 $ 27,333 Decrease in operating lease liabilities due to lease modifications and termination $ 41,177 $ 29,002 Cash paid for amounts included in the measurement of lease liabilities (in thousands) $ — $ 6,076 Weighted-average remaining lease term of operating leases (in years) — 8.8 Weighted-average discount rate of operating leases — 6.1 %

Share-based Compensation Plans

Share-based Compensation Plans (Tables)	9 Months Ended
	Sep. 30, 2021
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Schedule of share-based compensation expense	The following table provides share-based compensation reflected in the Company’s condensed consolidated statements of operations and comprehensive loss for the three and nine months ended September 30, 2021 and 2020 (in thousands): Three Months Ended Nine Months Ended 2021 2020 2021 2020 Research and development $ 957 $ 1,784 $ 2,874 $ 5,584 General and administrative 1,455 2,012 4,190 6,200 $ 2,412 $ 3,796 $ 7,064 $ 11,784
Schedule of stock option activity	A summary of stock option activity for the nine months ended September 30, 2021, is as follows: Weighted Weighted Average Average Average Remaining Intrinsic Number Exercise Contractual Value (in of Options Price Term (Years) thousands) Outstanding as of December 31, 2020 7,426,356 $ 11.87 7.0 1,178 Granted 834,250 3.40 Exercised ( 58,055 ) 2.21 Cancelled or forfeited ( 1,237,123 ) 10.24 Outstanding as of September 30, 2021 6,965,428 $ 11.22 6.7 $ 873 Exercisable at September 30, 2021 4,373,344 $ 13.72 5.7 $ 301
Summary of RSU activity	A summary of RSU activity for the nine months ended September 30, 2021 is as follows: Weighted Average Number Grant Date of Shares Fair Value Unvested as of December 31, 2020 294,913 $ 14.52 Granted 39,369 3.17 Vested ( 88,217 ) 15.06 Forfeited ( 97,704 ) 14.41 Unvested as of September 30, 2021 148,361 $ 11.25

Loss per share (Tables)

Loss per share (Tables)	9 Months Ended
	Sep. 30, 2021
Earnings Per Share [Abstract]
Schedule of basic and diluted earnings per share	Basic and diluted net loss per common share is computed by dividing net loss by the weighted average number of common shares outstanding during the period as follows: Three Months Ended Nine Months Ended 2021 2020 2021 2020 Numerator: Net loss (in thousands) $ ( 11,290 ) $ ( 18,812 ) $ ( 40,872 ) $ ( 58,574 ) Denominator: Weighted average shares used in calculating net loss per share — basic and diluted (in thousands) 43,291 32,096 37,730 29,196 Net loss per share — basic and diluted $ ( 0.26 ) $ ( 0.59 ) $ ( 1.08 ) $ ( 2.01 )

Workforce Reduction (Tables)

Workforce Reduction (Tables)	9 Months Ended
	Sep. 30, 2021
Restructuring And Related Activities [Abstract]
Schedule of accrued liabilities activity allocated to Cyclerion in connection with the reduction in workforce	The following table summarizes the accrued liabilities activity recorded in connection with the reduction in workforce for the nine months ended September 30, 2020 (in thousands): Amounts Charges Amount Adjustments Amounts October 2019 workforce reduction $ 2,009 $ 158 $ 2,137 $ ( 30 ) $ 0 Total $ 2,009 $ 158 $ 2,137 $ ( 30 ) $ 0 The following table summarizes the accrued liabilities activity recorded in connection with the reduction in workforce for the nine months ended September 30, 2021 (in thousands): Amounts Charges Amount Adjustments Amounts 2020 workforce reduction $ ( 3,640 ) $ ( 858 ) $ 4,339 $ — $ ( 159 ) Total $ ( 3,640 ) $ ( 858 ) $ 4,339 $ — $ ( 159 )

Nature of Business (Details)

Nature of Business (Details) $ in Thousands

Jun. 03, 2021USD ($)shares

Sep. 03, 2020USD ($)

Jul. 29, 2020USD ($)shares

Apr. 01, 2019

Sep. 30, 2021USD ($)

Jun. 30, 2021USD ($)

Sep. 30, 2020USD ($)

Sep. 30, 2021USD ($)shares

Sep. 30, 2020USD ($)

Jul. 24, 2020USD ($)

Nov. 15, 2019Employee

May 03, 2019Employee

Nature of Business

Health care trust fund, Description

We have initiated our CY6463 Phase 2a clinical trial in adult participants with MELAS. Startup activities are ongoing for our Phase 2a clinical trial in ADv, with enrollment expected to begin in 2021.The ADv study will be supported in part by a grant from the Alzheimer’s Association’s Part the Cloud-Gates Partnership Grant Program ("PTC Grant"), which provides Cyclerion with $2 million of funding over two years

Common stock dividend issued (shares of Cyclerion per ten shares of Ironwood)

0.1

Proceeds from June 2021 equity private placement and ATM

$ 30,503

$ 24,250

Proceeds from 2020 Equity private placement and ATM

30,503

$ 24,250

Issuance of common stock equity private placement and ATM

$ 6

$ 30,497

$ 24,250

Private Placement

Nature of Business

Issuance of common stock equity private placement and ATM (in shares) | shares

5,735,988

6,062,500

Proceeds from June 2021 equity private placement and ATM

$ 18,000

$ 24,300

Proceeds from 2020 Equity private placement and ATM

$ 18,000

$ 24,300

Net proceeds from issuance of shares to accredited investors

$ 219,800

IPO

Nature of Business

Maximum amount of Aggregate initial offering price

$ 150,000

ATM Offering | Jefferies LLC

Nature of Business

Issuance of common stock equity private placement and ATM (in shares) | shares

3,353,059

Cash commission of gross proceeds of sales of common stock, percentage

3.00%

Net Proceeds from Issuance of Common Stock

$ 12,500

Commission Paid From Gross Proceeds Of Sales Of Common Stock

$ 400

ATM Offering | Maximum | Jefferies LLC

Nature of Business

Issuance of common stock equity private placement and ATM

$ 50,000

Cyclerion GmbH

Nature of Business

Number of employees | Employee

1

Cyclerion Securities Corporation

Nature of Business

Number of employees | Employee

0

Related Party Transactions (Det

Related Party Transactions (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2020
Ironwood | Development agreement
Related Party Transaction [Line Items]
Revenue from related party	$ 0.4	$ 2.2

Fair Value of Financial Instr_3

Fair Value of Financial Instruments (Details) - Recurring - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Cash equivalents:
Total cash equivalents	$ 61,451	$ 53,240
Level 1
Cash equivalents:
Total cash equivalents	61,451	53,240
Money market funds
Cash equivalents:
Total cash equivalents	61,451	53,240
Money market funds | Level 1
Cash equivalents:
Total cash equivalents	$ 61,451	$ 53,240

Property and Equipment (Details

Property and Equipment (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Property and Equipment
Property and equipment. gross	$ 2,265		$ 2,265		$ 17,152
Less: accumulated depreciation and amortization	(2,153)		(2,153)		(10,287)
Property and equipment, net	112		112		6,865
Depreciation and amortization	600	$ 600	424	$ 1,827
Gain (Loss) on Termination of Lease			6,300
Gain Loss On Sale Of Property Plant Equipment	0		(6,322)	$ (205)
Software
Property and Equipment
Property and equipment. gross	2,214		2,214		2,214
Computer and office equipment
Property and Equipment
Property and equipment. gross	51		51		44
Leasehold improvements
Property and Equipment
Property and equipment. gross	$ 0		$ 0		$ 14,894

Accrued Expenses and Other Cu_3

Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Accrued Liabilities And Other Liabilities [Abstract]
Accrued incentive compensation	$ 957	$ 1,720
Salaries	450	514
Accrued vacation	338	555
Professional fees	503	689
Accrued severance and benefit costs	159	3,640
Other	833	176
Accrued expenses and other current liabilities	$ 3,240	$ 7,294

Leases - Summary (Details)

Leases - Summary (Details) $ in Thousands	Apr. 30, 2021USD ($)ft²	Sep. 15, 2020USD ($)ft²	Feb. 28, 2020USD ($)ft²	Apr. 01, 2019USD ($)ft²Item	Sep. 30, 2021USD ($)	Sep. 30, 2020USD ($)	Sep. 30, 2021USD ($)	Sep. 30, 2020USD ($)	Dec. 31, 2020USD ($)	Oct. 18, 2019ft²
Leases
Rentable space terminated from lease agreement (in square feet) | ft²		15,700
Decrease in right-of-use assets related to lease modification							$ 42,058	$ 27,333
Decrease in operating lease liabilities due to lease modification							41,177	29,002
Gain (loss) on lease modification					$ 0	$ (444)	(881)	1,669
Current portion of operating lease liabilities					0		0		$ 3,293
Noncurrent lease liability					0		0		38,933
Operating lease right-of-use asset					1,449		1,449		43,402
Gain (Loss) on Termination of Lease							6,300
Total lease costs						2,000		6,900
Head Lease
Leases
Rented space (in square feet) | ft²				114,000
Term of lease				123 months
Number of extension option | Item				2
Renewal term				5 years
Letter of credit posted with the landlord as a security deposit				$ 7,700
Space subleased to subtenant (in square feet) | ft²										15,700
Total lease costs					2,300		2,300
Lease Amendment
Leases
Rented space (in square feet) | ft²			74,000
Letter of credit posted with the landlord as a security deposit			$ 5,000
Rentable space terminated from lease agreement (in square feet) | ft²			40,000
Decrease in security deposit			$ 2,700
Decrease in remaining operating lease payments			41,900
Cash paid for lease termination fees			6,300
Cash paid for initial direct costs of lease modification			$ 200
Incremental borrowing rate (as a percent)			9.70%
Decrease in right-of-use assets related to lease modification			$ 21,400
Decrease in operating lease liabilities due to lease modification			$ 23,500
Gain (loss) on lease modification									2,100
Second Lease Amendment
Leases
Rented space (in square feet) | ft²		57,000
Letter of credit posted with the landlord as a security deposit					3,800		3,800
Rentable space terminated from lease agreement (in square feet) | ft²		17,000
Decrease in security deposit							1,200
Decrease in remaining operating lease payments		$ 16,900
Cash paid for lease termination fees		0
Cash paid for initial direct costs of lease modification		$ 0
Incremental borrowing rate (as a percent)		6.10%
Decrease in right-of-use assets related to lease modification		$ 5,900
Decrease in operating lease liabilities due to lease modification		$ 5,500
Gain (loss) on lease modification									(400)
Space subleased to subtenant (in square feet) | ft²		15,700
Current portion of operating lease liabilities									3,300
Noncurrent lease liability									38,900
Operating lease right-of-use asset									$ 43,400
Total lease costs					$ 0
Variable lease costs						$ 400	$ 700	$ 1,900
Termination Agreement
Leases
Surrendered Lease Space | ft²	57,000
Security Deposit Returned	$ 3,800
Gain (Loss) on Termination of Lease	$ 900

Leases - Schedule of supplement

Leases - Schedule of supplemental cash flow information related to leases (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Leases [Abstract]
Decrease in right-of-use assets related to lease modification	$ 42,058	$ 27,333
Decrease in operating lease liabilities due to lease modification	$ 41,177	29,002
Cash paid for amounts included in the measurement of lease liabilities (in thousands)		$ 6,076
Weighted-average remaining lease term of operating leases (in years)		8 years 9 months 18 days
Weighted-average discount rate of operating leases		6.10%

Leases - Sublease as Lessor (De

Leases - Sublease as Lessor (Details) $ in Thousands	Oct. 18, 2019USD ($)ft²Item	Sep. 30, 2021USD ($)	Sep. 30, 2020USD ($)	Sep. 30, 2021USD ($)	Sep. 30, 2020USD ($)	Dec. 31, 2020USD ($)	Sep. 15, 2020ft²
Sublease as lessor
Rentable space terminated from lease agreement (in square feet) | ft²							15,700
Sublease termination agreement estimated fair value of rooms		$ 1,500		$ 1,500
Sublease termination agreement estimated fair value of services		2,900		2,900
Sublease termination agreement prepaid of rooms and services		4,400		4,400
Other current assets		459		459		$ 3,163
Gain (loss) on lease modification		0	$ (444)	(881)	$ 1,669
Prepaid rooms balance reclassified from other assets		$ 1,400
Lease expense term		8 years 10 months 17 days
Head Lease
Sublease as lessor
Space subleased to subtenant (in square feet) | ft²	15,700
Sublease, Annual base rent	$ 1,500
Sublease, Increase in base rent over the term of the lease (as a percent)	3.00%
Sublease, Abatement of base rent	$ 700
Sublease, Abatement period	6 months
Sublease, Number of extension options | Item	0
Sublease, Initial security deposit received	$ 500
Sublease, Additional security deposit to be received	$ 400
Sublease, additional security deposit period	9 months
Gross sublease income, net of rent expense				1,500
Net sublease income				300
Sublease Termination Agreement
Sublease as lessor
Other current assets		$ 400		400
Other assets		2,500		2,500
Gain (loss) on lease modification				3,100
Rent receivables outstanding from subtenant		$ 1,300		1,300
Write off lease unamortized direct cost				$ 200

Share-based Compensation Plan_2

Share-based Compensation Plans (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2021USD ($)$ / sharesshares	Sep. 30, 2020USD ($)shares	Sep. 30, 2021USD ($)TradingDay$ / sharesshares	Sep. 30, 2020USD ($)shares	Dec. 31, 2020$ / sharesshares
Share-based Compensation Plans
Share-based compensation	$ 2,412,000	$ 3,796,000	$ 7,064,000	$ 11,784,000
Expected period to recognize the expense			2 years 5 months 1 day
Unrecognized share-based compensation expense | $	$ 200,000		$ 200,000
Stock options forfeited | shares			150,000
Cancelled or forfeited (in dollars per share) | $ / shares			$ 2.01
outstanding stock options | shares	450,000		450,000
weighted average exercise price | $ / shares	$ 2.01		$ 2.01
Research and development
Share-based Compensation Plans
Share-based compensation	$ 957,000	1,784,000	$ 2,874,000	5,584,000
General and administrative
Share-based Compensation Plans
Share-based compensation	1,455,000	2,012,000	4,190,000	6,200,000
Restricted Stock Units
Share-based Compensation Plans
Unrecognized share-based compensation expense	1,000,000		$ 1,000,000
Expected period to recognize the expense			11 months 8 days
Stock options
Share-based Compensation Plans
Unrecognized share-based compensation expense	$ 9,600,000		$ 9,600,000
Expected period to recognize the expense			3 years 2 months 12 days
Stock options forfeited | shares			1,237,123
Cancelled or forfeited (in dollars per share) | $ / shares			$ 10.24
outstanding stock options | shares	6,965,428		6,965,428		7,426,356
weighted average exercise price | $ / shares	$ 11.22		$ 11.22		$ 11.87
Performance stock options
Share-based Compensation Plans
Share-based compensation	$ 0	$ 0	$ 0	$ 0
Number of shares vested | shares	0	0	0	0
Threshold consecutive trading days, used as a base for measurement of vesting of stock awards | TradingDay			30
Performance stock options | Minimum [Member]
Share-based Compensation Plans
Expected option term (in years)			4 years
Performance stock options | Maximum
Share-based Compensation Plans
Expected option term (in years)			4 years 7 months 6 days

Share-based Compensation Plan_3

Share-based Compensation Plans - Stock Options (Details) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Number of Options
Cancelled or forfeited (in shares)	(150,000)
Outstanding at end of the year (in shares)	450,000
Weighted Average Exercise Price
Cancelled or forfeited (in dollars per share)	$ 2.01
Outstanding at end of the year (in dollars per share)	$ 2.01
Stock options
Number of Options
Outstanding at beginning of the year (in shares)	7,426,356
Granted (in shares)	834,250
Exercised (in shares)	(58,055)
Cancelled or forfeited (in shares)	(1,237,123)
Outstanding at end of the year (in shares)	6,965,428	7,426,356
Exercisable (in shares)	4,373,344
Weighted Average Exercise Price
Outstanding at beginning of the year (in dollars per share)	$ 11.87
Granted (in dollars per share)	3.40
Exercised (in dollars per share)	2.21
Cancelled or forfeited (in dollars per share)	10.24
Outstanding at end of the year (in dollars per share)	11.22	$ 11.87
Exercisable (in dollars per share)	$ 13.72
Weighted Average Remaining Contractual Term (years)
Weighted Average Remaining Contractual Term (years)	6 years 8 months 12 days	7 years
Weighted Average Remaining Contractual Term (years)	5 years 8 months 12 days
Aggregate Intrinsic Value, Outstanding	$ 873	$ 1,178
Aggregate Intrinsic Value, Exercisable	$ 301

Share-based Compensation Plan_4

Share-based Compensation Plans - Restricted Stock Units and Restricted Stock Awards (Details) - Restricted Stock Units	9 Months Ended
	Sep. 30, 2021$ / sharesshares
Number of Shares
Unvested at the beginning of the period (in shares | shares	294,913
Granted (in shares) | shares	39,369
Vested (in shares) | shares	(88,217)
Forfeited (in shares) | shares	(97,704)
Unvested the end of the period (in shares) | shares	148,361
Weighted-Average Grant Date Fair Value
Unvested at the beginning of the period (in shares | $ / shares	$ 14.52
Granted (in dollars per share) | $ / shares	3.17
Vested (in dollars per share) | $ / shares	15.06
Forfeited (in dollars per share) | $ / shares	14.41
Unvested restricted common stock at the end of the period (in dollars per share) | $ / shares	$ 11.25

Loss per share (Details)

Loss per share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
Numerator:
Net loss	$ (11,290)	$ (16,182)	$ (13,399)	$ (18,812)	$ (19,534)	$ (20,228)	$ (40,872)	$ (58,574)
Denominator:
Weighted average shares used in calculating net loss per share — basic and diluted (in thousands)	43,291,000			32,096,000			37,730,000	29,196,000
Net loss per share — basic and diluted	$ (0.26)			$ (0.59)			$ (1.08)	$ (2.01)
Stock options
Denominator:
Anti-dilutive securities excluded from the calculation of diluted loss per share	6,965,428			7,439,901			6,965,428	7,439,901
Restricted Stock Units
Denominator:
Anti-dilutive securities excluded from the calculation of diluted loss per share	148,361			428,077			148,361	428,077

Defined Contribution Plan (Deta

Defined Contribution Plan (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Defined Contribution Plan
401 (k) Savings Plan	us-gaap:QualifiedPlanMember		us-gaap:QualifiedPlanMember
Matching contribution (as a percent of employee's contributions)			75.00%
Maximum amount of employer matching contribution			$ 6,000
Compensation expense related to the defined contribution 401(k) Savings Plan	$ 500,000	$ 400,000	$ 500,000	$ 400,000
Minimum
Defined Contribution Plan
Percent of compensation eligible employees may elect to contribute			1.00%
Maximum
Defined Contribution Plan
Percent of compensation eligible employees may elect to contribute			100.00%

Workforce Reduction (Details)

Workforce Reduction (Details) $ in Thousands	Nov. 05, 2020USD ($)Employees	Oct. 30, 2019USD ($)Employees	Dec. 31, 2020USD ($)Employees	Mar. 31, 2020USD ($)	Sep. 30, 2021USD ($)	Sep. 30, 2020USD ($)	Dec. 31, 2019USD ($)
October 2019 Workforce Reduction
Restructuring Cost and Reserve [Line Items]
Beginning of period			$ 0	$ 2,009		$ 2,009
Charges						158
Amount paid						2,137
Adjustments						(30)
End of period					$ 0	$ 0	$ 2,009
2020 Workforce Reduction
Restructuring Cost and Reserve [Line Items]
Beginning of period					3,640
Charges					(858)
Amount paid					4,339
Adjustments					0
End of period			$ 3,640		$ 159
Current workforce reductions | October 2019 Workforce Reduction
Restructuring Cost and Reserve [Line Items]
Reduction in workforce, number of employees | Employees		30
Restructuring costs		$ 3,000		$ 200			$ 2,800
Current workforce reductions | November 2020 Workforce Reduction
Restructuring Cost and Reserve [Line Items]
Reduction in workforce, number of employees | Employees	48		31
Restructuring costs	$ 5,000
Severance and benefits costs			$ 4,100
Stock-based compensation from the modification of share based equity awards	$ 100

License Agreement - Additional

License Agreement - Additional Information (Detail) - Akebia Research License Agreement [Member] - USD ($) $ in Millions	Jun. 03, 2021	Mar. 31, 2023
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Up Front Payment Received	$ 3
Forecast [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Additional milestone cash payment		$ 12

Grant Revenue (Additional Infor

Grant Revenue (Additional Information) (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended	18 Months Ended
	Sep. 30, 2021	Sep. 30, 2021	Dec. 31, 2022
Revenue Recognition and Deferred Revenue [Abstract]
PTC Grant Award			$ 2
Allowable Expenses on Grant Revenue	$ 0.3	$ 0.3
Deferred Revenue	$ 0.4	$ 0.4

Subsequent Events (Additional I

Subsequent Events (Additional Information) (Details) $ in Millions	1 Months Ended
	Nov. 30, 2021USD ($)
Subsequent Event [Member]
Subsequent Event [Line Items]
Gain (loss) on extinguishment of debt	$ 3.5