Frazier funds add Mirum (MIRM) stake via Bluejay merger and buys

Rhea-AI Filing Summary

Mirum Pharmaceuticals director Patrick J. Heron reported indirect fund activity in Mirum stock. On January 23, 2026, Frazier Life Sciences X, L.P., an investment fund associated with him, received 159,277 shares of Mirum common stock in connection with the merger of Bluejay Therapeutics into Mirum, when Mirum’s closing share price was $94.29. That same day, Frazier Life Sciences X, L.P. also purchased 131,425 shares of Mirum common stock at $68.48 per share.

After these transactions, Frazier Life Sciences X, L.P. held 459,010 Mirum shares indirectly reported by Heron, and Frazier Life Sciences IX, L.P. held 3,566,912 shares. Heron also reported 5,703 Mirum shares held directly in his own name. The footnotes state that the Frazier funds hold the shares directly and that Heron disclaims beneficial ownership of those fund-held securities except to the extent of his pecuniary interest.

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

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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^*

Heron Patrick J

(Last) (First) (Middle)

C/O MIRUM PHARMACEUTICALS, INC.

989 E. HILLSDALE BLVD., SUITE 300

(Street)

FOSTER CITY CA 94404

(City) (State) (Zip)

2. Issuer Name and Ticker or Trading Symbol
Mirum Pharmaceuticals, Inc. [ MIRM ]

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

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

3. Date of Earliest Transaction (Month/Day/Year)
01/23/2026

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	01/23/2026		J(1)		159,277	A	(1)	327,585	I	By Frazier Life Sciences X, L.P.(2)
Common Stock	01/23/2026		P		131,425	A	$68.48	459,010	I	By Frazier Life Sciences X, L.P.(2)
Common Stock								3,566,912	I	By Frazier Life Sciences IX, L.P.(3)
Common Stock								5,703	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. Frazier Life Sciences X, L.P. received these shares in connection with merger of Bluejay Therapeutics, Inc. into the Issuer (the "Merger"). On the effective date of the Merger, the closing price of the Issuer's Common Stock was $94.29 per share.

2. The shares are held directly by Frazier Life Sciences X, L.P. FHMLS X, L.P. is the general partner of Frazier Life Sciences X, L.P. and FHMLS X, L.L.C. is the general partner of FHMLS X, L.P. The Reporting Person is one of two managing members of FHMLS X, L.L.C. The Reporting Person disclaims beneficial ownership of such securities except to the extent of his pecuniary interest therein.

3. The shares are held directly by Frazier Life Sciences IX, L.P. FHMLS IX, L.P. is the general partner of Frazier Life Sciences IX, L.P. FHMLS IX, L.L.C. is the general partner of FHMLS IX, L.P. The Reporting Person is one of two managing members of FHMLS IX, L.L.C. The Reporting Person disclaims beneficial ownership of such securities except to the extent of his pecuniary interest therein.

	/s/ Jennifer Martin, Attorney-in-Fact For Patrick J. Heron	01/27/2026
	** Signature of Reporting Person	Date
Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
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FAQ

What insider activity did Mirum Pharmaceuticals (MIRM) report for Patrick J. Heron?

The filing shows that Patrick J. Heron, a director of Mirum Pharmaceuticals, reported indirect holdings through Frazier Life Sciences funds and a small direct position. The activity includes shares received and purchased by Frazier Life Sciences X, L.P. on January 23, 2026, plus existing holdings in Frazier Life Sciences IX, L.P. and 5,703 Mirum shares held directly by Heron.

How many Mirum Pharmaceuticals (MIRM) shares did Frazier Life Sciences X, L.P. receive and buy?

On January 23, 2026, Frazier Life Sciences X, L.P. received 159,277 Mirum common shares in connection with the Bluejay Therapeutics merger and purchased an additional 131,425 shares at $68.48 per share. After these transactions, it held 459,010 Mirum shares reported indirectly by Patrick J. Heron.

What is the connection between Mirum Pharmaceuticals (MIRM) and Bluejay Therapeutics in this Form 4?

The Form 4 states that Frazier Life Sciences X, L.P. received 159,277 Mirum common shares in connection with the merger of Bluejay Therapeutics, Inc. into Mirum. The footnote also notes that on the effective date of the merger, Mirum’s common stock closed at $94.29 per share.

How many Mirum Pharmaceuticals (MIRM) shares are held by Frazier Life Sciences IX, L.P. and directly by Patrick J. Heron?

The filing reports that Frazier Life Sciences IX, L.P. holds 3,566,912 Mirum common shares indirectly associated with Patrick J. Heron. Separately, Heron reports 5,703 Mirum shares held directly in his own name.

Does Patrick J. Heron personally control the Mirum Pharmaceuticals (MIRM) shares held by the Frazier funds?

The footnotes explain that the Mirum shares are held directly by Frazier Life Sciences X, L.P. and Frazier Life Sciences IX, L.P. and describe their general partners. They state that Patrick J. Heron is one of two managing members of the relevant general partner entities and that he disclaims beneficial ownership of the Frazier funds’ Mirum securities except to the extent of his pecuniary interest.

At what prices were the Mirum Pharmaceuticals (MIRM) shares valued or purchased in this insider report?

The filing notes that on the merger effective date, Mirum’s common stock had a closing price of $94.29 per share. It also reports that Frazier Life Sciences X, L.P. purchased 131,425 Mirum shares at a price of $68.48 per share on January 23, 2026.