X0306 4 2020-09-16 0 0001818794 Dyne Therapeutics, Inc. DYN 0001789545 Scalzo Richard William C/O DYNE THERAPEUTICS, INC. 830 WINTER STREET WALTHAM MA 02451 0 1 0 0 See Remarks Common Stock 2020-09-17 4 A 0 11465 0.00 A 11465 D Stock Option (right to buy) 19.00 2020-09-16 4 A 0 35575 0.00 A 2030-09-15 Common Stock 35575 35575 D Consists of shares of Common Stock issuable under 11,465 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 annual installments over four years with the first installment vesting on September 17, 2021. This option was granted on September 16, 2020. The shares underlying the option are scheduled to vest over four years in equal monthly installments through September 16, 2024. Vice President of Accounting and Administration and Treasurer /s/ Richard Scalzo 2020-09-18