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

2672 67530.00 8195806 03/11/2024 NASDAQ Common Stock 12/10/2021 Restricted Stock Units Issuer N 1044 03/11/2024 Compensation Common Stock 12/09/2022 Restricted Stock Units Issuer N 1937 03/11/2024 Compensation N Richard Scalzo

1560 TRAPELO ROAD WALTHAM MA 02451

Common Stock 12/11/2023 1380 14797.00 Richard Scalzo

1560 TRAPELO ROAD WALTHAM MA 02451

Common Stock 12/14/2023 2376 28558.00 Richard Scalzo

1560 TRAPELO ROAD WALTHAM MA 02451

Common Stock 01/03/2024 13000 244500.00 Richard Scalzo

1560 TRAPELO ROAD WALTHAM MA 02451

Common Stock 01/26/2024 13000 316441.00 Richard Scalzo

1560 TRAPELO ROAD WALTHAM MA 02451

Common Stock 02/29/2024 3429 94310.00 Richard Scalzo

1560 TRAPELO ROAD WALTHAM, MA 02451

Common Stock 03/01/2024 9311 263005.00 Richard Scalzo

1560 TRAPELO ROAD, WALTHAM MA 02451

Common Stock 03/08/2024 86252 2261389.00 03/11/2024 /s/ Dominick Iadicicco, as a duly authorized representative of STIFEL, as attorney-in-fact for Richard Scalzo