[Form 4] Ultragenyx Pharmaceutical Inc. Insider Trading Activity

Rhea-AI Filing Summary

Theodore Alan Huizenga, SVP and Chief Accounting Officer and director of Ultragenyx Pharmaceutical Inc. (RARE), reported a sale of 64 shares of common stock on 09/18/2025 at a price of $29.17 per share. The filing states the shares were sold to pay required tax withholdings related to the vesting of restricted stock units (RSUs). After the transaction, the reporting person beneficially owned 50,242 shares. The Form 4 was signed by an attorney-in-fact on 09/19/2025.

Positive

• Transaction disclosed as tax-withholding for RSU vesting, clarifying the non-discretionary nature of the sale
• Insider retains significant ownership after the sale: 50,242 shares remain beneficially owned
• Form 4 filed with required details including transaction date, price, and signature by attorney-in-fact

Negative

• None.

Insights

Financial Analyst

TL;DR: A small, routine insider sale of 64 shares to cover RSU tax withholding; immaterial to company valuation.

The sale is explicitly described as a tax-withholding disposition tied to RSU vesting, indicating a non-discretionary liquidity event rather than a cash-raising or directional bet on the stock. The reported quantity (64 shares) and the post-transaction holding (50,242 shares) suggest the insider retains substantial exposure. This type of Form 4 typically has negligible impact on market perception or valuation.

Corporate Governance Expert

TL;DR: Proper and timely disclosure of an RSU-related sale demonstrates compliance with Section 16 reporting obligations.

The form identifies the reporting person, relation to issuer, transaction date, and rationale (tax withholding for vested RSUs), matching common governance practices. The signature by an attorney-in-fact is noted, which is acceptable procedural practice. There are no indications of rule exceptions or material governance concerns in this filing.

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
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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^*

Huizenga Theodore Alan

(Last) (First) (Middle)

C/O ULTRAGENYX PHARMACEUTICAL INC.

60 LEVERONI COURT

(Street)

NOVATO CA 94949

(City) (State) (Zip)

2. Issuer Name and Ticker or Trading Symbol
Ultragenyx Pharmaceutical Inc. [ RARE ]

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

	Director		10% Owner
X	Officer (give title below)		Other (specify below)
	SVP, Chief Accounting Officer

3. Date of Earliest Transaction (Month/Day/Year)
09/18/2025

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	09/18/2025		S(1)		64	D	$29.17	50,242(2)	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:

1. Represents shares sold to pay required tax withholdings due to the vesting of RSUs.

2. Includes previously reported shares of common stock underlying RSUs granted to the Reporting Person, which are subject to certain vesting conditions.

	/s/ Karah Parschauer, attorney-in-fact	09/19/2025
	** 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 did Ultragenyx insider Theodore Huizenga report on Form 4 (RARE)?

He reported the sale of 64 shares on 09/18/2025 at $29.17 per share, recorded as a tax-withholding sale related to RSU vesting.

How many shares does the reporting person own after the transaction?

The filing states the reporting person beneficially owned 50,242 shares following the reported transaction.

Why were the shares sold according to the Form 4?

The filing explains the shares were sold to pay required tax withholdings due to the vesting of restricted stock units (RSUs).

When was the Form 4 signed and by whom?

The Form 4 bears a signature by an attorney-in-fact, dated 09/19/2025.