X0306 4 2021-12-10 0 0001818794 Dyne Therapeutics, Inc. DYN 0001789545 Scalzo Richard William C/O DYNE THERAPEUTICS, INC. 1560 TRAPELO ROAD WALTHAM MA 02451 0 1 0 0 See Remarks Common Stock 2021-12-10 4 A 0 16696 0.00 A 27302 D Stock Option (right to buy) 13.12 2021-12-10 4 A 0 25044 0.00 A 2031-12-09 Common Stock 25044 25044 D Consists of shares of Common Stock issuable under 16,696 restricted stock units ("RSUs"). Each RSU represents the right to receive one share of Common Stock upon vesting. These RSUs are scheduled to vest in equal quarterly installments over four years with the first installment vesting on March 10, 2022. Includes 25,295 unvested RSUs. Each unvested RSU represents the right to receive one share of Common Stock upon vesting. This option was granted on December 10, 2021. The shares underlying the option are scheduled to vest over four years in equal monthly installments through December 10, 2025. Vice President of Accounting and Administration and Treasurer /s/ Richard Scalzo 2021-12-14