Dirk Kersten - 08 Aug 2024 Form 4/A Insider Report for Dyne Therapeutics, Inc. (DYN)

Footnote F1

This transaction was made pursuant to a Rule 10b5-1 trading plan adopted by Forbion Capital Fund IV Cooperatief U.A. ("FCF IV") on April 9, 2024.

Footnote F2

The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices within the range of $40.60 to $41.39, 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 the footnotes of this Form 4.

Footnote F3

The shares are held directly by FCF IV. Forbion IV Management B.V. ("Forbion Management"), the director of FCF IV, may be deemed to have voting and dispositive power over the shares held by FCF IV. Investment decisions with respect to the shares held by FCF IV can be made by FCPM III Services B.V., the director of Forbion Management, which may delegate such powers to its investment committee which may delegate such powers to the authorized representatives of Forbion Management. Messrs. Slootweg, van Osch, Mulder, van Houten, Reithinger and Boorsma (the "Partners") are partners of FCPM III Services B.V., which acts as the investment advisor to the directors of FCF IV. The Reporting Person is a partner of Forbion Management and a member of the investment committee of Forbion Management. The Reporting Person disclaims beneficial ownership of the shares, except to the extent of his pecuniary interest therein.

Footnote F4

The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices within the range of $41.605 to $42.435, inclusive.

Footnote F5

The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices within the range of $42.465 to $43.23, inclusive.

Footnote F6

The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices within the range of $41.985 to $42.98, inclusive.

Footnote F7

The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices within the range of $42.99 to $43.98, inclusive.

Footnote F8

The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices within the range of $43.995 to $44.06, inclusive.

Footnote F9

This Amendment to Form 4 is being filed to reflect a change in the Reporting Person's form of ownership of shares prior to the transactions reported herein. Such change was exempt from reporting pursuant to Rule 16a-13.

Footnote F10

The shares are held directly by ForDyne B.V. ("ForDyne"). ForDyne is jointly owned by FCF IV and Forbion Growth Opportunities Fund II Cooperatief U.A. ("FGO II"). Forbion Management may be deemed to have voting and dispositive power over 4,366,793 of the shares of common stock held by ForDyne. Investment decisions with respect to the shares held by ForDyne can be made by FCPM III Services B.V., the director of Forbion Management, which may delegate such powers to its investment committee which may delegate such powers to the authorized representatives of Forbion Management. The Partners are partners of FCPM III Services B.V., which acts as the investment advisor to the directors of ForDyne. The Reporting Person is a partner of Forbion Management and a member of the investment committee of Forbion Management.

Footnote F11

(Continued from footnote 10) Forbion Growth II Management B.V. ("FGO II Management"), the director of FGO II, may be deemed to have voting and dispositive power over 1,428,571 of the shares of common stock held by ForDyne. Investment decisions with respect to the shares held by ForDyne can be made by FCPM III Services B.V., the director of FGO II Management, which may delegate such powers to its investment committee which may delegate such powers to the authorized representatives of FGO II Management. The Partners are partners of FCPM III Services B.V., which acts as the investment advisor to the directors of ForDyne. The Reporting Person is a partner of FGO II Management and a member of the investment committee of FGO II Management. The Reporting Person disclaims beneficial ownership of the shares, except to the extent of his pecuniary interest therein.