Mirum Pharmaceuticals Announces Commencement of Public Offering of Common Stock

Mirum Pharmaceuticals, Inc. (Nasdaq: MIRM), a biopharmaceutical company focused on the identification, acquisition, development and commercialization of novel therapies for debilitating rare and orphan diseases, today announced that it has commenced an underwritten public offering, subject to market and other conditions, to issue and sell $80.0 million of shares of its common stock. In connection with the proposed offering, Mirum expects to grant the underwriters a 30-day option to purchase up to an additional approximately $12.0 million of shares of common stock. There can be no assurance as to whether or when the proposed offering may be completed or as to the actual size or terms of the proposed offering.

J.P. Morgan, SVB Securities and Evercore ISI are acting as joint book-running managers for the proposed offering. Raymond James is acting as lead manager for the proposed offering.

The proposed offering is being made pursuant to a shelf registration statement on Form S-3, including a base prospectus, that was previously filed with the Securities and Exchange Commission (the "SEC") and was declared effective by the SEC on August 12, 2020. A preliminary prospectus supplement and accompanying prospectus relating to the proposed offering will be filed with the SEC and will be available for free on the SEC's website located at http://www.sec.gov. Copies of the preliminary prospectus supplement and the accompanying prospectus relating to the proposed offering, when available, may be obtained from:

J.P. Morgan Securities LLC, Attention: Broadridge Financial Solutions, 1155 Long Island Avenue, Edgewood, NY 11717, by email at [email protected] or by phone at (866) 803-9204; SVB Securities LLC, Attention: Syndicate Department, 53 State Street, 40th Floor, Boston, MA 02109, by email at [email protected] or by phone at (800) 808-7525, ext. 6105; or Evercore Group L.L.C., Attention: Equity Capital Markets, 55 East 52nd Street, New York, NY 10055, by email at [email protected] or by phone at (888) 474-0200.

This press release shall not constitute an offer to sell or a solicitation of an offer to buy, nor shall there be any sale of, these securities in any state or jurisdiction in which such offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of any such state or jurisdiction.

About Mirum Pharmaceuticals, Inc.

Mirum Pharmaceuticals, Inc. is a biopharmaceutical company dedicated to transforming the treatment of rare liver diseases. Mirum's approved medication is LIVMARLI® (maralixibat) oral solution which is approved in the U.S. for the treatment of cholestatic pruritus in patients with Alagille syndrome one year of age and older.

Mirum's late-stage pipeline includes two investigational treatments for debilitating liver diseases affecting children and adults. LIVMARLI, an oral ileal bile acid transporter (IBAT) inhibitor, is currently being evaluated in clinical trials for pediatric liver diseases and includes the MARCH Phase 3 clinical trial for progressive familial intrahepatic cholestasis (PFIC) and the EMBARK Phase 2b clinical trial for patients with biliary atresia. In addition, Mirum has an expanded access program open across multiple countries for eligible patients with ALGS and PFIC.

Mirum has submitted a Marketing Authorization Application to the European Medicines Agency for LIVMARLI for the treatment of cholestasis in patients with Alagille syndrome.

Mirum's second investigational treatment, volixibat, an oral IBAT inhibitor, is being evaluated in three potentially registrational studies including the VISTAS Phase 2b clinical trial for adults with primary sclerosing cholangitis, the OHANA Phase 2b clinical trial for pregnant women with intrahepatic cholestasis of pregnancy, and the VANTAGE Phase 2b clinical trial for adults with primary biliary cholangitis.

Forward Looking Statements

Statements contained in this press release regarding matters that are not historical facts are "forward-looking statements" within the meaning of the Private Securities Litigation Reform Act of 1995. Such forward-looking statements include statements regarding, among other things, the regulatory approval pathway for Mirum's product candidates, Mirum's expectations regarding the completion, timing and size of the proposed offering and Mirum's expectations with respect to granting the underwriters a 30-day option to purchase additional shares. Because such statements are subject to risks and uncertainties, actual results may differ materially from those expressed or implied by such forward-looking statements. Words such as "will," "may," "anticipate," "expects," "potential" and similar expressions are intended to identify forward-looking statements. These forward-looking statements are based upon Mirum's current expectations and involve assumptions that may never materialize or may prove to be incorrect. Actual results could differ materially from those anticipated in such forward-looking statements as a result of various risks and uncertainties, which include, without limitation, risks and uncertainties associated with Mirum's business in general, the impact of the COVID-19 pandemic, macroeconomic and geopolitical events, such as the ongoing military conflict between Ukraine and Russia and related sanctions and the other risks described in Mirum's filings with the SEC. All forward-looking statements contained in this press release speak only as of the date on which they were made and are based on management's assumptions and estimates as of such date. Mirum undertakes no obligation to update such statements to reflect events that occur or circumstances that exist after the date on which they were made, except as required by law.