X0206 3 2020-09-16 0 0001818794 Dyne Therapeutics, Inc. DYN 0001577014 Rhodes Jason P C/O DYNE THERAPEUTICS, INC. 830 WINTER STREET WALTHAM MA 02451 1 0 1 0 Common Stock 2110404 I See footnote Series A Preferred Stock Common Stock 6029726 I See footnote Series B Preferred Stock Common Stock 1608785 I See footnote The shares are held directly by Atlas Venture Fund XI, L.P. ("Atlas Venture Fund XI"). The general partner of Atlas Venture Fund XI is Atlas Venture Associates XI, L.P. ("AVA XI LP"). Atlas Venture Associates XI, LLC ("AVA XI LLC") is the general partner of AVA XI LP. The reporting person is a member of AVA XI LLC and disclaims beneficial ownership of such securities held by Atlas Venture Fund XI, except to the extent of his pecuniary interest therein, if any. 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 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. The shares are held directly by Atlas Venture Opportunity Fund I, L.P. ("Atlas Venture Opportunity Fund I"). The general partner of Atlas Venture Opportunity Fund I is Atlas Venture Associates Opportunity I, L.P. ("AVAO I LP"). Atlas Venture Associates Opportunity I, LLC ("AVAO I LLC") is the general partner of AVAO I LP. The reporting person is a member of AVAO I LLC and disclaims beneficial ownership of such securities held by Atlas Venture Opportunity Fund I, except to the extent of his pecuniary interest therein, if any. Exhibit Index: 24.1 Power of Attorney /s/ Ommer Chohan, Attorney-in-Fact 2020-09-16