Recruiting: Mirum Launches Clinical Trial of MRM-3379 for Fragile X Syndrome

December 1, 2025
Dr. Gary Feldman, Principal Investigator for the MRM-3379 Phase 2 clinical trial at the Irvine, California site, standing with an individual with Fragile X syndrome.
Dr. Gary Feldman, Principal Investigator for the MRM-3379 Phase 2 clinical trial at the Irvine, California site, with an individual with Fragile X syndrome.

Mirum Pharmaceuticals has launched a Phase 2 clinical trial of MRM-3379, a selective PDE4D inhibitor, as a potential treatment for Fragile X syndrome. The study is now open for males ages 13 to 45 with Fragile X syndrome.

The trial (ClinicalTrials.gov ID: NCT07209462) will evaluate the safety, tolerability, and early efficacy signals of MRM-3379, focusing on improvements in cognitive function, behavior, and daily living. This marks an important step forward in developing targeted treatments for Fragile X syndrome.

Michael Tranfaglia, MD

It’s incredibly encouraging to see a company like Mirum step into the Fragile X space with a potential therapy that holds real promise. This study is actively enrolling, and we encourage eligible families to consider participation in this important research.

Michael Tranfaglia, MD
Medical Director and Co-Founder
FRAXA Research Foundation

A Promising Path Toward Advancing PDE4D Therapies in Fragile X

MRM-3379 targets the phosphodiesterase type 4D (PDE4D) enzyme. This approach builds on years of science, much of it spearheaded and funded by FRAXA, which identified PDE4D inhibitors as a promising treatment strategy based on their ability to restore signaling pathways disrupted in Fragile X.

FRAXA-funded studies helped support the development of Shionogi’s zatolmilast, another PDE4D inhibitor that showed cognitive improvement in a Phase 2 trial and is currently in Phase 3 development.

Mirum’s MRM-3379 potentially offers a new generation of PDE4D-targeting therapy with differentiated pharmacological properties.

Understanding the MRM-3379 Trial and How to Take Part

The clinical trial will run for 12 weeks, during which males ages 16 to 45 receive MRM-3379 or placebo. In addition, males ages 13 to <16 can receive open-label MRM-3379. Sites in California and Pennsylvania are recruiting now, and additional sites in Boston and Cincinnati will be coming on line soon.

For complete eligibility details and the full list of recruiting sites, see the MRM-3379 entry on ClinicalTrials.gov.

Enrollment Information

Amnova Clinical Research, LLC
Irvine, California
Maggie Wang
(949) 358-7447
maggie@amnovaresearch.com

Suburban Research Associates
Media, Pennsylvania
Alex Hollis
(610) 891-9024
ahollis@suburbanresearch.com

Why Advancing Multiple Treatment Options Is Critical in Fragile X

The launch of this trial is a major milestone for the Fragile X community. MRM-3379 adds to a growing pipeline of therapies that aim to address the root biological mechanisms of Fragile X, not just the symptoms. No single medicine will be right for everyone, so it is important to have multiple drugs in development. FRAXA is proud to see our early investments in Fragile X research helping drive PDE4D discoveries into clinical trials. As more biotech companies like Mirum enter this space, we move closer to real-world treatments.

As with all trials, progress depends on participation. To stay up to date on this and other clinical trials, visit our Clinical Trials Hub or reach out to our team at info@fraxa.org.