Company: MIRM
Filing Date: 2025-04-14
Form Type: DEFA14A
Source: 0001759425-25-000024
Chunk: 0

Company: Mirum Pharmaceuticals, Inc.
Filing Date: 2025-04-14
Form: DEFA14A
Chunk 0
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### UNITED STATES

### SECURITIES AND EXCHANGE COMMISSION

#### Washington, D.C. 20549

#### SCHEDULE 14A INFORMATION

#### Proxy Statement Pursuant to Section 14(a) of the

#### Securities Exchange Act of 1934
<div align='center'>(Amendment No. )

________________</div>

| Filed by the Registrantx |     | Filed by a party other than the Registranto |

Check the appropriate box:

| o |     | Preliminary Proxy Statement                                                     |
| o |     | Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2)) |
| o |     | Definitive Proxy Statement                                                      |
| x |     | Definitive Additional Materials                                                 |
| o |     | Soliciting Material Pursuant to § 240.14a-12                                    |

| Mirum Pharmaceuticals, Inc.                                             |
| (Name of Registrant as Specified In Its Charter)                        |
| N/A                                                                     |
| (Name of Person(s) Filing Proxy Statement if other than the Registrant) |

Payment of Filing Fee (Check all boxes that apply)

| x |     | No fee required                                                                                     |
| o |     | Fee paid previously with preliminary materials                                                      |
| o |     | Fee computed on table in exhibit required by Item 25(b) per Exchange Act Rules 14a-6(i)(1) and 0-11 |