X0306 4 2020-09-16 0 0001818794 Dyne Therapeutics, Inc. DYN 0001824542 Beskrovnaya Oxana 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 19289 0.00 A 19289 D Stock Option (right to buy) 19.00 2020-09-16 4 A 0 59857 0.00 A 2030-09-15 Common Stock 59857 59857 D Consists of shares of Common Stock issuable under 19,289 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. Senior Vice President, Head of Research /s/ Richard Scalzo, Attorney-in-Fact 2020-09-18