X0306 4 2019-04-08 0 0001755237 Cyclerion Therapeutics, Inc. CYCN 0001117003 MCGUIRE TERRANCE C/O CYCLERION THERAPEUTICS, INC. 301 BINNEY STREET CAMBRIDGE MA 02142 1 0 0 0 Common Stock 2019-04-08 4 P 0 604482 16.00 A 604482 I By Polaris Partners VIII, L.P. Common Stock 2019-04-08 4 P 0 21635 16.00 A 21635 I By Polaris Entrepreneurs' Fund VIII, L.P. Common Stock 162 I By Polaris Venture Management Co. II, L.L.C. Common Stock 6911 I By Bartlett Partners, LLC Common Stock 11047 D These shares were acquired from unaffiliated stockholders in a negotiated, private transaction. The reportable securities are owned directly by Polaris Partners VIII, L.P. ("PP VIII"). Polaris Partners GP VIII, L.L.C. ("PPGP VIII") is the general partner of PP VIII. The Reporting Person, a member of the Issuer's Board of Directors, is an interest holder of PPGP VIII. Each of David Barrett, Brian Chee, Amir Nashat and Bryce Youngren are the managing members of PPGP VIII (collectively, the "Managing Members"). Each of the Reporting Person and the Managing Members, in their respective capacities with respect to PPGP VIII, may be deemed to have shared voting and dispositive power over the shares held by PP VIII. Each of PPGP VIII, the Reporting Person and the Managing Members disclaims beneficial ownership of these securities and this report shall not be deemed an admission that any one of them is the beneficial owner of such securities for purposes of Section 16 or for any other purpose, except to the extent of their respective pecuniary interests therein. The reportable securities are owned directly by Polaris Entrepreneurs' Fund VIII, L.P. ("PEF VIII"). PPGP VIII is the general partner of PEF VIII. The Reporting Person, a member of the Issuer's Board of Directors, is an interest holder of PPGP VIII. Each of the Reporting Person and the Managing Members, in their respective capacities with respect to PPGP VIII, may be deemed to have shared voting and dispositive power over the shares held by PEF VIII. Each of PPGP VIII, the Reporting Person and the Managing Members disclaims beneficial ownership of these securities and this report shall not be deemed an admission that any one of them is the beneficial owner of such securities for purposes of Section 16 or for any other purpose, except to the extent of their respective pecuniary interests therein. The Reporting Person and Jonathan Flint ("Flint") are the managing members of Polaris Venture Management Co. II, L.L.C., the beneficial owner of the securities. Each of the Reporting Person and Flint disclaims beneficial ownership of these securities and this report shall not be deemed an admission that any one of them is the beneficial owner of such securities for purposes of Section 16 or for any other purpose, except to the extent of their respective pecuniary interests therein. The Reporting Person is a managing member of Bartlett Partners, LLC, the beneficial owner of the securities. The Reporting Person disclaims beneficial ownership of these securities and this report shall not be deemed an admission that he is the beneficial owner of such securities for purposes of Section 16 or for any other purpose, except to the extent of their respective pecuniary interests therein. /s/ Larry Miller, Attorney-in-Fact 2019-04-10