X0206 3 2020-09-16 0 0001818794 Dyne Therapeutics, Inc. DYN 0001708269 Atlas Venture Fund XI, L.P. 400 TECHNOLOGY SQUARE, 10TH FLOOR CAMBRIDGE MA 02139 0 0 1 0 0001780067 Atlas Venture Associates XI, LLC 400 TECHNOLOGY SQUARE, 10TH FLOOR CAMBRIDGE MA 02139 0 0 1 0 0001780068 Atlas Venture Associates XI, L.P. 400 TECHNOLOGY SQUARE, 10TH FLOOR CAMBRIDGE MA 02139 0 0 1 0 0001759241 Atlas Venture Opportunity Fund I, L.P. 400 TECHNOLOGY SQUARE, 10TH FLOOR CAMBRIDGE MA 02139 0 0 1 0 0001780065 Atlas Venture Associates Opportunity I, L.P. 400 TECHNOLOGY SQUARE, 10TH FLOOR CAMBRIDGE MA 02139 0 0 1 0 0001780066 Atlas Venture Associates Opportunity I, LLC 400 TECHNOLOGY SQUARE, 10TH FLOOR CAMBRIDGE MA 02139 0 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. Each of AVA XI LP and AVA XI LLC disclaims Section 16 beneficial ownership of the securities held by Atlas Venture Fund XI, except to the extent of its 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. Each of AVAO I LP and AVAO I LLC disclaims Section 16 beneficial ownership of the securities held by Atlas Venture Opportunity Fund I, except to the extent of its pecuniary interest therein, if any. /s/ Atlas Venture Fund XI, LP, By: Atlas Venture Associates XI, L.P., it's general partner, By: Atlas Venture Associates XI, LLC, its general partner, By: Ommer Chohan, Chief Financial Officer, /s/ Ommer Chohan 2020-09-16 /s/ Atlas Venture Associates XI, LP, By: Atlas Venture Associates XI, LLC, it's general partner, By: Ommer Chohan, Chief Financial Officer, /s/ Ommer Chohan 2020-09-16 /s/ Atlas Venture Associates XI, LLC, By: Ommer Chohan, Chief Financial Officer, /s/ Ommer Chohan 2020-09-16 /s/ Atlas Venture Opportunity Fund I, L.P., By: Atlas Venture Associates Opportunity I, L.P., its general partner, By: Atlas Venture Associates Opportunity I, LLC, its general partner, By: Ommer Chohan, Chief Financial Officer, /s/ Ommer Chohan 2020-09-16 /s/ Atlas Venture Associates Opportunity I, L.P., By: Atlas Venture Associates Opportunity I, LLC, its general partner, By: Ommer Chohan, Chief Financial Officer, /s/ Ommer Chohan 2020-09-16 /s/ Atlas Venture Associates Opportunity I, LLC, By: Ommer Chohan, Chief Financial Officer, /s/ Ommer Chohan 2020-09-16