Sec Form 4 Filing - O'Donnell Niall @ Mirum Pharmaceuticals, Inc. - 2019-07-22

FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

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, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person O'Donnell Niall 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) (Last) (First) (Middle) C/O RIVERVEST VENTURE PARTNERS, 101 SOUTH HANLEY ROAD, STE. 1850 3. Date of Earliest Transaction (MM/DD/YY) 07/22/2019 (Street) ST. LOUIS, MO63105 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) __ X __ Form filed by One Reporting Person _____ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 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 07/22/2019 C 1,496,118 ( 1 ) A 1,621,118 I By RiverVest Venture Fund IV, L.P. ( 2 ) Common Stock 07/22/2019 P( 3 ) 300,000 A $ 15 1,921,118 I By RiverVest Venture Fund IV, L.P. ( 2 )

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 (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 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 (MM/DD/YY) 7. Title and Amount of Underlying Securities (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 of Derivative Security: 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 Series A Preferred Stock ( 1 ) 07/22/2019 C 11,968,944 ( 1 ) ( 1 ) Common Stock 1,496,118 ( 1 ) $ 0 0 I By RiverVest Venture Fund IV, L.P. ( 2 )

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other O'Donnell Niall C/O RIVERVEST VENTURE PARTNERS 101 SOUTH HANLEY ROAD, STE. 1850 ST. LOUIS, MO63105 X Signatures /s/ Jody Howe, Attorney-in-Fact 07/24/2019 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Automatic conversion, in connection with the Issuer's initial public offering, of each share of the Issuer's Series A preferred stock into 0.125 shares of the Issuer's common stock. The shares have no expiration date. ( 2 )RiverVest Venture Partners IV, L.P. is the general partner of RiverVest Venture Fund IV, L.P. The Reporting Person is a manager of RiverVest Venture Partners IV, LLC, the sole general partner of RiverVest Venture Partners IV, L.P., and as a result may be deemed to share dispositive voting and investment power with respect to the shares held by RiverVest Venture Partners IV, L.P. The Reporting Person disclaims beneficial ownership of all shares held by RiverVest Venture Partners IV, L.P. except to the extent of his pecuniary interests therein. ( 3 )The shares were purchased in the Issuer's initial public offering.

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).

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