X0206 3 2020-09-16 0 0001818794 Dyne Therapeutics, Inc. DYN 0001823747 Forbion Capital Fund IV Cooperatief U.A. GOOIMEER 2-35 NAARDEN P7 1411 DC NETHERLANDS 0 0 1 0 Series A Preferred Stock Common Stock 4522293 D Series B Preferred Stock Common Stock 1608786 D The Series A Preferred Stock is convertible into common stock on a 3.3169-for-1 basis into the number of shares of common stock shown in Column 3 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 have 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. Each of the Partners disclaims beneficial ownership of such shares, except to the extent of his pecuniary interest therein. The Series B Preferred Stock is convertible into common stock on a 3.3169-for-1 basis into the number of shares of common stock shown in Column 3 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 have no expiration date. Forbion IV Management B.V., director of Forbion Capital Fund IV Cooperatief U.A., By: /s/ H.A. Slootweg and V. Van Houten as directors 2020-09-16