Sec Form 3 Filing - Frazier Life Sciences IX, L.P. @ Mirum Pharmaceuticals, Inc. - 2019-07-17

FORM 3 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 Frazier Life Sciences IX, L.P. 2. Issuer Name and Ticker or Trading Symbol Mirum Pharmaceuticals, Inc. [ MIRM] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director X __ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) 70 WILLOW ROAD, STE. 200 3. Date of Earliest Transaction (MM/DD/YY) 07/17/2019 (Street) MENLO PARK, CA94025 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) _____ Form filed by One Reporting Person __ X __ 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

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 ) ( 1 ) ( 1 ) Common Stock 3,116,912 ( 2 ) D ( 3 )

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other Frazier Life Sciences IX, L.P. 70 WILLOW ROAD, STE. 200 MENLO PARK, CA94025 X FHMLS IX, L.P. 70 WILLOW ROAD, STE. 200 MENLO PARK, CA94025 X FHMLS IX, L.L.C. 70 WILLOW ROAD, STE. 200 MENLO PARK, CA94025 X Topper James N 70 WILLOW ROAD, STE. 200 MENLO PARK, CA94025 X Signatures Frazier Life Sciences IX, L.P. By: FHMLS IX, L.P., its general partner, By: FHMLS IX, L.C.C., its general partner,By: /s/ Steve R. Bailey, Chief Financial Officer 07/17/2019 Signature of Reporting Person Date FHMLS IX, L.P. By: FHMLS IX, L.L.C., its general partner, By: /s/ Steve Bailey, Chief Financial Officer 07/17/2019 Signature of Reporting Person Date FHMLS IX, L.L.C. By: /s/ Steve Bailey, Chief Financial Officer 07/17/2019 Signature of Reporting Person Date /s/ Steve Bailey, Attorney-in-Fact for James N. Topper 07/17/2019 Signature of Reporting Person Date

Explanation of Responses:

( 1 )The shares of Series A Preferred Stock have no expiration date and are convertible at any time at the election of the holder without payment of further consideration. Each share of Series A Preferred Stock will automatically convert into 0.125 shares of Common Stock upon the closing of the Issuer's initial public offering. ( 2 )Share numbers give effect to the reverse split of each share of the Issuer's Common Stock into 0.125 shares of Common Stock effected on July 3, 2019, which will be effective for the Preferred Stock upon its conversion to Common Stock upon the closing of the Issuer's initial public offering. ( 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. James N. Topper and Patrick Heron are the managing members of FHMLS IX, L.L.C.and share voting and dispositive power over the shares held by Frazier Life Sciences IX, L.P. Mr. Topper, FHMLS IX, L.P. and FHMLS IX, L.L.C. disclaim beneficialownership of the shares held by Frazier Life Sciences IX, L.P., except to the extent of his or its pecuniary interest therein, if any.

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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