Entity linked to Dyne Therapeutics director sells stock

Dyne Therapeutics director Dirk Kersten, through ForDyne B.V., reported two indirect open-market sales totaling 261,460 shares of common stock on July 27, 2026, at weighted average prices of $25.5024 and $26.0428 per share.

Rhea-AI Filing Summary

Dyne Therapeutics director Dirk Kersten, through ForDyne B.V., reported two indirect open-market sales totaling 261,460 shares of common stock on July 27, 2026, at weighted average prices of $25.5024 and $26.0428 per share. These trades were executed under a Rule 10b5-1 trading plan adopted by ForDyne on November 11, 2025. ForDyne is jointly owned by Forbion funds, and Kersten disclaims beneficial ownership of the shares except to the extent of his pecuniary interest.

Insider Trade Summary 10b5-1

Net Seller: 261,460 shares

Net Sell 2 txns

Insider Kersten Dirk

Role Director

Sold 261,460 shs ($6.67M)

Type	Security	Shares	Price	Value
Sale	Common Stock F1, F2, F3, F4	256,072	$25.5024	$6.53M
Sale	Common Stock F1, F5, F3, F4	5,388	$26.0428	$140K

Holdings After Transaction: Common Stock — 3,586,796 shares (Indirect, See footnote)

Footnotes (5)

1. F1. This transaction was made pursuant to a Rule 10b5-1 trading plan adopted by ForDyne B.V. ("ForDyne") on November 11, 2025.
2. 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 $25.00 to $25.995, 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.
3. F3. The shares are held directly by ForDyne. ForDyne is jointly owned by Forbion Capital Fund IV Cooperatief U.A. ("FCF IV") and Forbion Growth Opportunities Fund II Cooperatief U.A. ("FGO II"). Forbion IV Management B.V. ("Forbion Management") may be deemed to have voting and dispositive power over 2,160,426 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. 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 ForDyne. The Reporting Person is a partner of Forbion Management and a member of the investment committee of Forbion Management.
4. F4. (Continued from Footnote 3) Forbion Growth II Management B.V. ("FGO II Management"), the director of FGO II, may be deemed to have voting and dispositive power over 1,426,370 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.
5. 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 $26.00 to $26.12, 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.

Key Figures

Total shares sold: 261,460 shares First block shares sold: 256,072 shares First block price range: $25.00 to $25.995 +4 more

7 metrics

Total shares sold 261,460 shares Indirect common stock sales via ForDyne B.V. on 2026-07-27

First block shares sold 256,072 shares Common stock sold at weighted average price $25.5024 per share

First block price range $25.00 to $25.995 Multiple transactions within this range for the 256,072-share sale

Second block shares sold 5,388 shares Common stock sold at weighted average price $26.0428 per share

Second block price range $26.00 to $26.12 Multiple transactions within this range for the 5,388-share sale

Shares under Forbion Management power 2,160,426 shares Common stock held by ForDyne over which Forbion IV Management B.V. may have power

Shares under FGO II Management power 1,426,370 shares Common stock held by ForDyne over which FGO II Management B.V. may have power

Key Terms

Rule 10b5-1 trading plan, weighted average price, voting and dispositive power, beneficial ownership, +1 more

5 terms

Rule 10b5-1 trading plan regulatory

"This transaction was made pursuant to a Rule 10b5-1 trading plan adopted"

A Rule 10b5-1 trading plan is a pre-arranged schedule that allows company insiders to buy or sell stock at specific times, even if they have inside information. It helps prevent accusations of unfair trading by making these transactions look planned and transparent, rather than sneaky or illegal.

weighted average price financial

"The price reported in Column 4 is a weighted average price."

Weighted average price is the average price of a security where each trade or component is counted according to its size, so bigger trades pull the average more than smaller ones. Think of it like calculating the average cost of a grocery haul where items you bought more of have greater influence on the final per-item cost. Investors use it to understand the true average price paid or received, judge execution quality, and compare trading performance against market movement.

voting and dispositive power financial

"may be deemed to have voting and dispositive power over 2,160,426 of the shares"

beneficial ownership financial

"The Reporting Person disclaims beneficial ownership of the shares, except"

Beneficial ownership means the person or entity that actually enjoys the benefits of owning shares or other assets — such as receiving dividends, voting rights, or price gains — even if the legal title is held in another name. For investors it matters because knowing who truly controls and profits from a company reveals who can influence decisions, exposes potential conflicts of interest or hidden concentration of power, and affects transparency and risk in the stock.

pecuniary interest financial

"disclaims beneficial ownership of the shares, except to the extent of his pecuniary interest"

FAQ

AI-generated questions and answers. How Rhea-AI works. Not financial advice.

What insider transaction did Dyne Therapeutics (DYN) disclose?

Dyne Therapeutics reported that an entity associated with director Dirk Kersten, ForDyne B.V., sold 261,460 shares of common stock on July 27, 2026. The sales were indirect and executed in two separate open-market transactions.

How many Dyne Therapeutics (DYN) shares were sold and at what prices?

ForDyne B.V. sold 256,072 shares at a weighted average price of $25.5024 and 5,388 shares at a weighted average price of $26.0428. The shares in each block traded within stated price ranges around those averages.

Were the Dyne Therapeutics (DYN) insider sales under a Rule 10b5-1 plan?

Yes. The filing states the transactions were made pursuant to a Rule 10b5-1 trading plan adopted by ForDyne B.V. on November 11, 2025. Such pre-arranged plans automate trading and can reduce the informational value of trade timing.

Who actually holds the Dyne Therapeutics (DYN) shares reported by Dirk Kersten?

The common shares are held directly by ForDyne B.V., which is jointly owned by Forbion Capital Fund IV Cooperatief U.A. and Forbion Growth Opportunities Fund II Cooperatief U.A. Kersten’s interest is through his roles in related management entities, not direct share ownership.

Does Dirk Kersten claim beneficial ownership of all reported Dyne Therapeutics (DYN) shares?

No. A footnote explains that Kersten disclaims beneficial ownership of the ForDyne-held shares, except to the extent of his pecuniary interest. The structure emphasizes that investment power resides primarily with Forbion-managed entities.

Which entities have voting and dispositive power over the Dyne Therapeutics (DYN) shares?

Footnotes state Forbion IV Management B.V. may have voting and dispositive power over 2,160,426 shares, and FGO II Management B.V. over 1,426,370 shares, all held by ForDyne B.V. under the Forbion investment structure.

AI-generated analysis. How Rhea-AI works. Not financial advice.

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Available on EDGAR 07/29/2026 - 04:15 PM Accepted by SEC EDGAR 07/29/2026 - 04:15 PM Learn about SEC filing dates

SEC Form 4

FORM 4

UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934
or Section 30(h) of the Investment Company Act of 1940

OMB APPROVAL

OMB Number:			3235-0287
Estimated average burden
hours per response:			0.5

Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

X

Check this box to indicate that a transaction was made pursuant to a contract, instruction or written plan for the purchase or sale of equity securities of the issuer that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c). See Instruction 10.

1. Name and Address of Reporting Person^*

Kersten Dirk

(Last) (First) (Middle)

C/O DYNE THERAPEUTICS, INC.

1560 TRAPELO ROAD

(Street)

WALTHAM MASSACHUSETTS 02451

(City) (State) (Zip)

UNITED STATES

(Country)

2. Issuer Name and Ticker or Trading Symbol
Dyne Therapeutics, Inc. [ DYN ]

5. Relationship of Reporting Person(s) to Issuer
(Check all applicable)

X	Director		10% Owner
	Officer (give title below)		Other (specify below)

2a. Foreign Trading Symbol

3. Date of Earliest Transaction (Month/Day/Year)
07/27/2026

6. Individual or Joint/Group Filing (Check Applicable Line)

X	Form filed by One Reporting Person
	Form filed by More than One Reporting Person

4. If Amendment, Date of Original Filed (Month/Day/Year)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1. Title of Security (Instr. 3)	2. Transaction Date (Month/Day/Year)	2A. Deemed Execution Date, if any (Month/Day/Year)	3. Transaction Code (Instr. 8)		4. Securities Acquired (A) or Disposed Of (D) (Instr. 3, 4 and 5)			5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4)	6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	7. Nature of Indirect Beneficial Ownership (Instr. 4)
			Code	V	Amount	(A) or (D)	Price
Common Stock	07/27/2026		S(1)		256,072	D	$25.5024(2)	3,592,184	I	See footnote(3)(4)
Common Stock	07/27/2026		S(1)		5,388	D	$26.0428(5)	3,586,796	I	See footnote(3)(4)

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 3)	2. Conversion or Exercise Price of Derivative Security	3. Transaction Date (Month/Day/Year)	3A. Deemed Execution Date, if any (Month/Day/Year)	4. Transaction Code (Instr. 8)		5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5)		6. Date Exercisable and Expiration Date (Month/Day/Year)		7. Title and Amount of Securities Underlying Derivative Security (Instr. 3 and 4)		8. Price of Derivative Security (Instr. 5)	9. Number of derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)	10. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	11. Nature of Indirect Beneficial Ownership (Instr. 4)
				Code	V	(A)	(D)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares

Explanation of Responses:

1. This transaction was made pursuant to a Rule 10b5-1 trading plan adopted by ForDyne B.V. ("ForDyne") on November 11, 2025.

2. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices within the range of $25.00 to $25.995, 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.

3. The shares are held directly by ForDyne. ForDyne is jointly owned by Forbion Capital Fund IV Cooperatief U.A. ("FCF IV") and Forbion Growth Opportunities Fund II Cooperatief U.A. ("FGO II"). Forbion IV Management B.V. ("Forbion Management") may be deemed to have voting and dispositive power over 2,160,426 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. 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 ForDyne. The Reporting Person is a partner of Forbion Management and a member of the investment committee of Forbion Management.

4. (Continued from Footnote 3) Forbion Growth II Management B.V. ("FGO II Management"), the director of FGO II, may be deemed to have voting and dispositive power over 1,426,370 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.

5. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices within the range of $26.00 to $26.12, 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.

	/s/ Dirk Kersten	07/29/2026
	** Signature of Reporting Person	Date
Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
* If the form is filed by more than one reporting person, see Instruction 4 (b)(v).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB Number.
* Form 4: SEC 1474 (03-26)