X0306 4 2022-12-09 0 0001818794 Dyne Therapeutics, Inc. DYN 0001824542 Beskrovnaya Oxana C/O DYNE THERAPEUTICS, INC. 1560 TRAPELO ROAD WALTHAM MA 02451 0 1 0 0 Chief Scientific Officer Common Stock 2022-12-09 4 A 0 40000 0.00 A 90825 D Common Stock 2022-12-12 4 S 0 680 10.87 D 90145 D Stock Option (right to buy) 10.72 2022-12-09 4 A 0 63000 0.00 A 2032-12-08 Common Stock 63000 63000 D Consists of shares of Common Stock issuable under 40,000 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, 2023. Includes 79,323 unvested RSUs. Represents shares automatically sold by the Reporting Person to satisfy tax withholding obligations in connection with the vesting of restricted stock units granted to the Reporting Person on December 10, 2021. The automatic sale of the Reporting Person's shares is provided for in a restricted stock unit agreement constituting a "binding contract" consistent with the affirmative defense to liability under Rule 10b5-1 and the sale does not represent a discretionary trade by the Reporting Person. Includes 77,041 unvested RSUs. This option was granted on December 9, 2022. The shares underlying the option are scheduled to vest over four years in equal monthly installments through December 10, 2026. /s/ Richard Scalzo, Attorney-in-Fact 2022-12-13