144 0001528826 XXXXXXXX LIVE 0001818794 Dyne Therapeutics, Inc. 001-39509 1560 TRAPELO ROAD WALTHAM MA 02451 (781) 786-8230 Brumm Joshua T Officer Director Common Stock Stifel Nicolaus & Company Inc

501 N Broadway St Louis MO 63102

363343 9247079.00 8195806 03/08/2024 NASDAQ Common Stock 07/31/2020 Option Exercise Issuer N 350000 03/08/2024 Cash Common Stock 02/15/2024 Owned Shares Issuer N 13343 03/08/2024 Cash N Joshua Brumm

1560 TRAPELO ROAD WALTHAM MA 02451

Common Stock 12/11/2023 7585 81334.00 Joshua Brumm

1560 TRAPELO ROAD WALTHAM MA 02451

Common Stock 01/03/2024 51183 989636.00 Joshua Brumm

1560 TRAPELO ROAD WALTHAM MA 02451

Common Stock 01/04/2024 218536 4046820.00 Joshua Brumm

1560 TRAPELO ROAD WALTHAM MA 02451

Common Stock 02/29/2024 5520 151813.00 Joshua Brumm

1560 TRAPELO ROAD WALTHAM MA 02451

Common Stock 03/01/2024 94480 2744016.00 03/08/2024 /s/ Dominick Iadicicco, as a duly authorized representative of STIFEL, as attorney-in-fact for Joshua Brumm