X0306 4 2020-07-31 0 0001818794 Dyne Therapeutics, Inc. DYN 0001823682 Kersten Dirk C/O DYNE THERAPEUTICS, INC. 830 WINTER STREET WALTHAM MA 02451 1 0 1 0 Common Stock 2020-09-21 4 C 0 6131079 A 6131079 I See footnote Series A Preferred Stock 2020-07-31 4 P 0 5250000 1.00 A Common Stock 1582803 15000000 I See footnote Series B Preferred Stock 2020-08-07 4 P 0 5336179 2.811 A Common Stock 1608786 5336179 I See footnote Series A Preferred Stock 2020-09-21 4 C 0 15000000 0.00 D Common Stock 4522293 0 I See footnote Series B Preferred Stock 2020-09-21 4 C 0 5336179 0.00 D Common Stock 1608786 0 I See footnote On September 21, 2020, the Series A Preferred Stock automatically converted into Common Stock on a 3.3169-for-one basis without payment of further consideration upon closing of the initial public offering of the Issuer's common stock. The shares had no expiration date. On September 21, 2020, the Series B Preferred Stock automatically converted into Common Stock on a 3.3169-for-one basis without payment of further consideration upon closing of the initial public offering of the Issuer's common stock. The shares had no expiration date. The shares are held directly by Forbion Capital Fund IV Cooperatief U.A ("FCF IV"). Forbion IV Management B.V. ("Forbion Management") the director of FCF IV, may be deemed to have voting and dispositive power over the shares held by FCF IV. Investment decisions with respect to the shares held by FCF IV can be made by FCPM III Services B.V., the director of Forbion Management, which may delegate such powers to its investment committee which may delegate such powers to the authorized representatives of Forbion Management. Messrs. Slootweg, van Osch, Mulder, van Houten, Reithinger and Boorsma (the "Partners") are partners of FCPM III Services B.V., which acts as the investment advisor to the directors of FCF IV. The Reporting Person is a partner of Forbion Management and a member of the investment committee of Forbion Management. The Reporting Person disclaims beneficial ownership of the shares, except to the extent of his pecuniary interest therein. The Series A Preferred Stock was convertible into common stock on a 3.3169-for-one basis into the number of shares of common stock shown in Column 7 without payment of further consideration at the holder's election or upon closing of the initial public offering of the Issuer's common stock. The shares had no expiration date. The Series B Preferred Stock was convertible into common stock on a 3.3169-for-one basis into the number of shares of common stock shown in Column 7 without payment of further consideration at the holder's election or upon closing of the initial public offering of the Issuer's common stock. The shares had no expiration date. /s/ Richard Scalzo, Attorney-in-Fact 2020-09-23