Director-linked fund trims 337K Dyne Therapeutics (DYN) shares under 10b5-1 plan

Rhea-AI Filing Summary

Dyne Therapeutics, Inc. reported that investment entity ForDyne B.V., which is associated with director Dirk Kersten, sold a total of 337,248 shares of common stock in open-market transactions under a pre-arranged Rule 10b5-1 trading plan.

ForDyne sold 211,974 shares at a weighted average price of $20.2916 on April 17, 2026 and 125,274 shares at a weighted average price of $20.0672 on April 20, 2026, across price ranges disclosed in the footnotes. Following these sales, entities linked to ForDyne continued to hold 4,207,525 shares indirectly, and Kersten disclaims beneficial ownership beyond his pecuniary interest.

Insider Trade Summary 10b5-1

Net Seller: 337,248 shares ($6,815,190)

Net Sell 2 txns

Insider Kersten Dirk

Role null

Sold 337,248 shs ($6.82M)

Type	Security	Shares	Price	Value
Sale	Common Stock	125,274	$20.0672	$2.51M
Sale	Common Stock	211,974	$20.2916	$4.30M

Holdings After Transaction: Common Stock — 4,207,525 shares (Indirect, See footnote)

Footnotes (1)

1. This transaction was made pursuant to a Rule 10b5-1 trading plan adopted by ForDyne B.V. ("ForDyne") on November 11, 2025. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices within the range of $20.00 to $20.75, 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. 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 2,781,155 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. (Continued from Footnote 2) 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. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices within the range of $21.00 to $21.20, 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

Shares sold 2026-04-17: 211,974 shares at $20.2916 Shares sold 2026-04-20: 125,274 shares at $20.0672 Total shares sold: 337,248 shares +4 more

7 metrics

Shares sold 2026-04-17 211,974 shares at $20.2916 Open-market sale by ForDyne B.V.

Shares sold 2026-04-20 125,274 shares at $20.0672 Open-market sale by ForDyne B.V.

Total shares sold 337,248 shares Combined net sales in this Form 4

Shares held after sales 4,207,525 shares Indirect holdings linked to ForDyne B.V.

Price range 2026-04-20 $20.00–$20.75 Multiple trades, weighted average $20.0672

Price range 2026-04-17 $21.00–$21.20 Multiple trades, weighted average $20.2916

10b5-1 plan adoption date November 11, 2025 Rule 10b5-1 trading plan for ForDyne B.V.

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 by ForDyne B.V."

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

"Forbion IV Management B.V. may be deemed to have voting and dispositive power over 2,781,155 of the shares"

beneficial ownership financial

"The Reporting Person disclaims beneficial ownership of the shares, except to the extent of his pecuniary interest therein."

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

"The Reporting Person disclaims beneficial ownership of the shares, except to the extent of his pecuniary interest therein."

Form 4 Insider Transactions: What Each Field Means →

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)
04/17/2026

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	04/17/2026		S(1)		211,974	D	$20.2916(2)	4,332,799	I	See footnote(3)(4)
Common Stock	04/20/2026		S(1)		125,274	D	$20.0672(5)	4,207,525	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 $20.00 to $20.75, 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 2,781,155 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 2) 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 $21.00 to $21.20, 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	04/21/2026
	** 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)

FAQ

What insider transactions were reported for DYN in this Form 4?

The filing reports two open-market sales of Dyne Therapeutics common stock by ForDyne B.V. totaling 337,248 shares. These took place on April 17, 2026 and April 20, 2026, with weighted average prices just above $20 per share.

Who actually sold Dyne Therapeutics (DYN) shares in this filing?

Shares were sold by ForDyne B.V., an investment entity associated with funds managed by Forbion. Director Dirk Kersten is a partner in related management entities but disclaims beneficial ownership of the shares beyond his pecuniary interest as described in the footnotes.

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

ForDyne sold 211,974 shares at a weighted average of $20.2916 and 125,274 shares at a weighted average of $20.0672. The footnotes state these were executed in multiple trades within price ranges of $20.00–$20.75 and $21.00–$21.20, respectively.

How many Dyne Therapeutics (DYN) shares remain held after these insider sales?

After the reported transactions, entities linked to ForDyne B.V. continued to hold 4,207,525 shares of Dyne Therapeutics common stock indirectly. The footnotes explain how different Forbion-related management companies may be deemed to have voting and dispositive power over portions of this position.

Were the Dyne Therapeutics (DYN) insider sales made under a trading plan?

Yes. A footnote states the transactions were made pursuant to a Rule 10b5-1 trading plan adopted by ForDyne B.V. on November 11, 2025. Such plans are pre-arranged programs that systematically execute trades according to preset instructions.

What does the weighted average price disclosure mean in this Dyne Therapeutics Form 4?

The filing states that reported prices are weighted averages for multiple trades within specified ranges. ForDyne undertakes to provide detailed breakdowns of the exact number of shares sold at each individual price within those ranges upon request to the issuer, security holders, or SEC staff.