Dyne Therapeutics (DYN) director buys 2,500 Common Stock shares

Rhea-AI Filing Summary

Dyne Therapeutics, Inc. director Brian S. Posner reported an open-market purchase of 2,500 shares of Common Stock on May 20, 2026 at $17.12 per share. Following this transaction, he directly owns a total of 18,000 Dyne Therapeutics shares.

Insider Trade Summary

Net Buyer: 2,500 shares ($42,800)

Net Buy 1 txn

Insider Posner Brian S

Role null

Bought 2,500 shs ($43K)

Type	Security	Shares	Price	Value
Purchase	Common Stock	2,500	$17.12	$43K

Holdings After Transaction: Common Stock — 18,000 shares (Direct, null)

Footnotes (1)

Key Figures

Shares purchased: 2,500 shares Purchase price: $17.12 per share Total holdings after transaction: 18,000 shares +1 more

4 metrics

Shares purchased 2,500 shares Open-market purchase of Common Stock on May 20, 2026

Purchase price $17.12 per share Price paid in the reported open-market transaction

Total holdings after transaction 18,000 shares Direct ownership by Brian S. Posner following the purchase

Net shares bought 2,500 shares Net buy according to transaction summary

Key Terms

open-market purchase, Common Stock, direct ownership

3 terms

open-market purchase financial

"transaction_action: "open-market purchase""

An open-market purchase is when an investor or a company buys shares on a public stock exchange at the going market price, rather than through a private deal. It matters to investors because these purchases change how many shares are available, can push the stock price up or signal confidence from large buyers, and often affect per-share metrics like earnings—think of it like someone buying lots of apples off a grocery shelf, reducing supply and potentially raising the price.

Common Stock financial

"security_title: "Common Stock""

Common stock represents ownership shares in a company, giving investors a stake in its success and a say in important decisions through voting rights. It is the most common type of stock traded on markets and can provide income through dividends, as well as potential for value growth. For investors, holding common stock means sharing in the company’s profits and risks.

direct ownership financial

"ownership_type: "direct" and ownership_code: "D""

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).

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^*

Posner Brian S

(Last) (First) (Middle)

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)
05/20/2026

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	05/20/2026		P		2,500	A	$17.12	18,000	D

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:

	/s/ Ron Caponigro, Attorney-in-Fact	05/22/2026
	** 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 transaction did Dyne Therapeutics (DYN) disclose?

Dyne Therapeutics disclosed that director Brian S. Posner bought 2,500 shares of Common Stock in an open-market transaction. This purchase reflects a personal increase in his equity stake in the company through direct ownership of additional shares.

At what price did the Dyne Therapeutics director buy shares?

Brian S. Posner purchased 2,500 Dyne Therapeutics Common Stock shares at $17.12 per share. This open-market transaction sets a clear reference price for the trade and indicates the cost he paid to increase his direct holdings in the company.

How many Dyne Therapeutics shares does Brian S. Posner now hold?

After the reported transaction, Brian S. Posner directly holds 18,000 Dyne Therapeutics Common Stock shares. This total includes the newly acquired 2,500 shares from the open-market purchase disclosed in the Form 4 insider trading report.

Was the Dyne Therapeutics insider trade a purchase or a sale?

The Dyne Therapeutics insider trade was a purchase. Director Brian S. Posner executed an open-market buy of 2,500 Common Stock shares, increasing his direct ownership position rather than disposing of or selling any existing shares.

What does an open-market purchase mean for Dyne Therapeutics insiders?

An open-market purchase means the insider bought shares on the public market at prevailing prices. For Dyne Therapeutics, director Brian S. Posner acquired 2,500 shares this way, using personal capital rather than receiving shares through grants or option exercises.