X0508 4 2023-12-04 0 0001818794 Dyne Therapeutics, Inc. DYN 0001789545 Scalzo Richard William C/O DYNE THERAPEUTICS, INC. 1560 TRAPELO ROAD WALTHAM MA 02451 0 1 0 0 See Remarks 1 Common Stock 2023-12-04 4 S 0 681 12.01 D 129856 D Common Stock 2023-12-06 4 S 0 1872 12.01 D 127984 D The sales reported in this Form 4 were effected pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person on July 11, 2023. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices within the range of $12.00 to $12.04, inclusive. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range(s) set forth in this footnote of this Form 4. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices within the range of $12.00 to $12.04, inclusive. Senior Vice President, Head of Finance and Administration /s/ Richard Scalzo 2023-12-06