[Form 4] Avidity Biosciences, Inc. Insider Trading Activity

Rhea-AI Filing Summary

Eric Mosbrooker, Chief Commercial Officer of Avidity Biosciences, Inc. (RNA), reported option exercise and concurrent sales executed on 09/03/2025 under a previously adopted Rule 10b5-1 trading plan. He exercised 6,563 stock options at an exercise price of $9.05 per share, resulting in ownership of 61,563 shares after the transaction. On the same date he sold 6,563 shares in multiple transactions at a weighted-average price of $47.0723 (prices ranged $46.13–$47.66). The reporting person adopted the 10b5-1 plan on September 11, 2024. Option vesting is monthly at 1/48th starting January 1, 2024, with full vesting on the fourth anniversary.

Positive

• Exercise at a low strike ($9.05) followed by sales at a much higher weighted-average price ($47.0723), realizing a significant spread
• Sales executed under a documented Rule 10b5-1 plan, indicating pre-planned transactions that limit concerns about opportunistic timing
• Filing includes vesting schedule details, improving transparency about option economics and future potential issuances

Negative

• Insider sold all shares acquired through the exercise on the same date, modestly reducing immediate insider-held shares
• Weighted-average sale price disclosed only as a range with further breakdowns available upon request, leaving some granularity unspecified

Insights

Securities Analyst

TL;DR: Routine option exercise and contemporaneous sale under a 10b5-1 plan; economically captures gain from a low strike price.

The transaction shows a standard exercise of stock options at a $9.05 strike followed by sales at a weighted-average of $47.0723, locking in a material per-share spread. Because the sales were executed pursuant to a 10b5-1 plan adopted in September 2024, timing is pre-planned rather than ad hoc. The post-transaction beneficial ownership of 61,563 shares remains disclosed. This is a routine insider liquidity event rather than an operational signal about company performance.

Corporate Governance Expert

TL;DR: Disclosure meets Section 16 requirements; use of 10b5-1 plan reduces signaling risk but warrants transparency on plan terms.

The Form 4 properly reports exercise and sales, cites the 10b5-1 plan adoption date, and provides weighted-average sale price range. The filing includes vesting details for the option award, including monthly vesting from January 1, 2024. From a governance perspective, the filing is complete and aligns with standard insider reporting practices, supporting compliance and market transparency.

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^*

Mosbrooker Eric

(Last) (First) (Middle)

C/O AVIDITY BIOSCIENCES, INC.

3020 CALLAN RD.

(Street)

SAN DIEGO CA 92121

(City) (State) (Zip)

2. Issuer Name and Ticker or Trading Symbol
Avidity Biosciences, Inc. [ RNA ]

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

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

3. Date of Earliest Transaction (Month/Day/Year)
09/03/2025

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

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

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

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	09/03/2025		M(1)		6,563	A	$9.05	61,563	D
Common Stock	09/03/2025		S(1)		6,563	D	$47.0723(2)	55,000	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
Stock Option (Right to Buy)	$9.05	09/03/2025		M(1)			6,563	(3)	12/31/2033	Common Stock	6,563	$0	183,750	D

Explanation of Responses:

1. The sales reported on this Form 4 were effected pursuant to a Rule 10b5-1 trading plan previously adopted by the Reporting Person on September 11, 2024.

2. This represents a weighted-average price. These shares were sold in multiple transactions at prices ranging from $46.13 to $47.66. The Reporting Person undertakes to provide the Issuer, any securityholder 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 set forth in this footnote.

3. 1/48th of the total number of shares subject to the option shall vest on each monthly anniversary of January 1, 2024 (the "Vesting Commencement Date"), subject to the Reporting Person's continuous service to the Issuer on each such vesting date, so that the options shall be fully vested on the fourth anniversary of the Vesting Commencement Date.

Remarks:

	/s/ John B. Moriarty, Jr., J.D., Attorney-in-Fact	09/05/2025
	** 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.

FAQ

What transactions did Eric Mosbrooker report on Form 4 for RNA?

On 09/03/2025 he exercised 6,563 options at $9.05 and sold 6,563 shares at a weighted-average price of $47.0723.

Were the sales made under a Rule 10b5-1 plan for RNA insider Mosbrooker?

Yes. The sales were effected pursuant to a 10b5-1 trading plan adopted on September 11, 2024.

How many RNA shares does Mosbrooker beneficially own after these transactions?

The Form 4 reports that he beneficially owns 61,563 shares following the reported transactions.

What is the option vesting schedule disclosed in the Form 4?

Options vest at 1/48th of the total each month starting on January 1, 2024, with full vesting on the fourth anniversary.

What price range were the sold RNA shares transacted at?

Sales occurred at prices ranging from $46.13 to $47.66, yielding a weighted-average of $47.0723.