144 0001789545 XXXXXXXX LIVE 0001818794 Dyne Therapeutics, Inc. 001-39509 1560 TRAPELO ROAD WALTHAM MA 02451 (781) 786-8230 Scalzo Richard William Officer Common Stock Stifel Nicolaus & Company Inc.

501 N Broadway St Louis MO 63102

126073 4242356.00 100400798 08/19/2024 NASDAQ Common Stock 07/31/2020 Options Issuer N 9855 09/06/2024 Cash Common Stock 07/11/2022 Options Issuer N 29792 09/06/2024 Cash Common Stock 12/09/2022 Options Issuer N 18750 09/06/2024 Cash Common Stock 11/15/2023 Options Issuer N 6552 09/06/2024 Cash Common Stock 12/10/2021 Options Issuer N 16696 09/06/2024 Cash Common Stock 09/16/2020 Options Issuer N 34833 09/06/2024 Cash Common Stock 09/06/2024 Owned Shares Issuer N 9595 09/06/2024 Cash N Richard Scalzo

1560 TRAPELO ROAD WALTHAM MA 02451

Common Stock 06/11/2024 1331 41710.00 Richard Scalzo

1560 TRAPELO ROAD WALTHAM MA 02451

Common Stock 08/19/2024 2752 124028.00 09/06/2024 /s/ Dominick Iadicicco, as a duly authorized representative of STIFEL, as attorney-in-fact for Richard Scalzo