May 16, 2019

Christopher Peetz
Chief Executive Officer
Mirum Pharmaceuticals, Inc.
950 Tower Lane, Suite 1050
Foster City, CA 94404

       Re: Mirum Pharmaceuticals, Inc.
           Draft Registration Statement on Form S-1
           Submitted April 18, 2019
           CIK No. 0001759425

Dear Mr. Peetz:

       We have reviewed your draft registration statement and have the
following comments. In
some of our comments, we may ask you to provide us with information so we may
understand your disclosure.

       Please respond to this letter by providing the requested information and
either submitting
an amended draft registration statement or publicly filing your registration
statement on
EDGAR. If you do not believe our comments apply to your facts and circumstances
or do not
believe an amendment is appropriate, please tell us why in your response.

      After reviewing the information you provide in response to these comments
and your
amended draft registration statement or filed registration statement, we may
have additional

Draft Registration Statement on Form S-1

Prospectus Summary
Our Solution, page 2

1.     Please revise to define the term "xanthomas" the first time it is used
in terms a lay person
       would understand.
2.     We refer to your statements on pages 2 to 3 that trial data from the
Phase 2 INDIGO trial
       demonstrated multi-parameter response and supported maralixibat's
breakthrough therapy
       designation for PFIC2. Please balance your discussion by disclosing that
the primary
       endpoint of sBA change was not met for the overall group. In addition,
expand your
       disclosure to explain that this designation may not lead to a faster
development or
       regulatory process, and that it does not increase the likelihood that it
will receive
 Christopher Peetz
FirstName LastNameChristopher Peetz
Mirum Pharmaceuticals, Inc.
Comapany NameMirum Pharmaceuticals, Inc.
May 16, 2019
May 16, 2019 Page 2
Page 2
FirstName LastName
         approval. Similarly, in your discussion of maralixibat trials in ALGS
on page 3, please
         balance your disclosure to explain that there were other Phase 2
trials that did not meet
         their primary endpoints.
3.       Please revise your last paragraph on page 2 to clarify that your Phase
3 MARCH trial will
         evaluate maralixibat at a higher dose of up to 600 g/kg twice daily
compared to the
         INDIGO trial dosage of 280 g/kg once daily, and disclose the highest
dosage previously
         tested on a long-term basis.
4.       Please revise the last paragraph in this section to explain that
volixibat has been evaluated
         primarily for the treatment of non-alcoholic steatohepatitis, and has
not been evaluated in
         either PSC or ICP, which you discuss in your risk factors on page 12.
5.       Your product candidate table discloses that you intend to initiate a
Phase 3 trial for biliary
         atresia. We also note your disclosure on page 14 that you have not had
any meeting with
         the FDA regarding a Phase 3 trial, you do not have any safety data for
patients under the
         age of 12 months, which is the target age group you would seek to
treat, and the FDA may
         require you to first conduct such safety studies. Please explain why
you believe it is
         appropriate to indicate that you expect to initiate a Phase 3 trial in
this table.
Our Company, page 3

6.       You state that you are well-positioned to deliver on your mission of
developing therapies
         for patients suffering from debilitating liver diseases. Please
balance your disclosure by
         explaining that you have not yet completed a clinical trial as a
company, and also that you
         do not currently have the necessary internal research and development
capabilities, as you
         explain on pages 10 and 29.
Implications of Being an Emerging Growth Company and Smaller Reporting Company,
page 4

7.       Please supplementally provide us with copies of all written
communications, as defined in
         Rule 405 under the Securities Act, that you, or anyone authorized to
do so on your behalf,
         present to potential investors in reliance on Section 5(d) of the
Securities Act, whether or
         not they retain copies of the communications.
Risks Associated with Our Business, page 4

8.       Expand your discussion to add a bullet disclosing that even if
approved, the FDA may
         only approve maralixibat for the narrower indication of pruritus
associated with PFIC, or a
         subset of the PFIC patient population, rather than for the treatment
of PFIC generally, as
         you more fully explain on page 11.
Our principal stockholders and management own a significant percentage. . .,
page 56

9.       Expand your disclosure to explain that all of your current directors
have been appointed
         by investors pursuant to a voting agreement, as you more fully explain
on page 129.
 Christopher Peetz
FirstName LastNameChristopher Peetz
Mirum Pharmaceuticals, Inc.
Comapany NameMirum Pharmaceuticals, Inc.
May 16, 2019
May 16, 2019 Page 3
Page 3
FirstName LastName
Use of Proceeds, page 65

10.      Please revise to state the approximate amount of net proceeds intended
to be used for your
         development of maralixibat and volixibat. Refer to Item 504 of
Regulation S-K.
Our Product Pipeline, page 84

11.      We refer to your statements on pages 86 and 87 that volixibat has a
favorable safety
         profile. Given that safety determinations are within the authority of
the FDA and other
         regulatory authorities, please revise to remove these statements.
Similarly, please delete
         your reference in the last paragraph on page 102 to the "durable
efficacy" for maralixibat
         in the treatment of ALGS.
Historical Clinical Development of Maralixibat, page 92

12.      For the INDIGO trial, expand your discussion of the pruritus results
to explain whether
         this endpoint was met. As we also note that you state in the chart
that the INDIGO trial is
         ongoing, please update your narrative disclosures accordingly to
discuss the ongoing
         portion of this trial, including when you expect the results from the
ongoing portion.
Phase 2 INDIGO Trial, page 94

13.      You state that PFIC2 responders demonstrated improvement in pruritus
and an increase in
         quality of life. However, the patient represented by the green line
appears to show an
         increase in the itch score and a decrease in the quality of life.
Please revise your
         disclosures to clarify this discrepancy.
Future Clinical Development of Maralixibat, page 103

14.      Please revise to discuss the secondary endpoints you intend to measure
in the MARCH
         trial. Also revise to explain the meaning of submitting data together
with natural history
         data set comparisons, and whether this approach has been previously
discussed with the
         FDA in connection with this trial. Provide similar disclosure for the
ALGS trial.
Safety and Tolerability Data for Maralixibat, page 103

15.      Please revise to disclose all serious adverse events, not only those
that were the most
         commonly reported. Also provide similar disclosure for volixibat on
page 104.
License Agreements, page 105

16.      You state in the last paragraph on page 105 that in addition to the
disclosed milestones,
         you are required to also pay an additional amount upon regulatory
approval of maralixibat
         for each and every other indication. Please revise your disclosure of
the total aggregate
         development and regulatory milestones that may be payable to include
these amounts.
 Christopher Peetz
Mirum Pharmaceuticals, Inc.
May 16, 2019
Page 4
17.    For each of your license agreements, to the extent not otherwise
disclosed, please revise to
       clarify the duration of the royalty obligations and the terms of the
agreements, including
       by disclosing the expiration dates of the underlying patents and patent
Phase 2 NASH Clinical Trial, page 105

18.    Please expand on your disclosure in the first paragraph to explain the
"clinical proof of
       mechanism" to which you refer.
Intellectual Property, page 109

19.    Please revise to disclose the foreign jurisdictions in which you have
issued or
       pending patent applications.

20.    Once you have an estimated offering price or range, please explain to us
how you
       determined the fair value of the common stock underlying your equity
issuances and the
       reasons for any differences between the recent valuations of your common
stock leading
       up to the IPO and the estimated offering price. This information will
help facilitate our
       review of your accounting for equity issuances including stock
compensation and asset
21.    Please provide us proofs of all graphics, visual, or photographic
information you will
       provide in the printed prospectus prior to its use, for example in a
preliminary prospectus.
       Please note that we may have comments regarding this material.
       You may contact Paul Cline at 202-551-3851 or Angela Connell at
202-551-3426 if you
have questions regarding comments on the financial statements and related
matters. Please
contact Dorrie Yale at 202-551-8776 or Mary Beth Breslin at 202-551-3625 with
any other

FirstName LastNameChristopher Peetz
                                                             Division of
Corporation Finance
Comapany NameMirum Pharmaceuticals, Inc.
                                                             Office of
Healthcare & Insurance
May 16, 2019 Page 4
cc:       Jason L. Kent - Cooley LLP
FirstName LastName