Phase 2 trial of experimental oral treatment enrolling fragile X males
MRM-3379 designed to restore disrupted brain signaling that marks disorder
Mirum Pharmaceuticals has launched a proof-of-concept Phase 2 clinical trial to test its experimental oral treatment MRM-3379 in boys and men with fragile X syndrome.
The therapy, acquired by the company last year, is designed to restore the disrupted brain signaling that characterizes fragile X syndrome, which is expected to alleviate disease symptoms.
The placebo-controlled Phase 2 trial (NCT07209462) is recruiting up to 60 boys and men, ages 13 to 45 years, with the condition at sites in the U.S. Plans for the trial to start this year were announced in late 2024.
“We … made important progress across the pipeline, including … initiating our Phase 2 study in Fragile X Syndrome,” Chris Peetz, the CEO of Mirum, said in a company press release reporting the latest financial results and business updates. “Mirum is well-positioned heading into 2026 with strong commercial momentum and multiple upcoming [trial readouts].”
Treatment aimed at easing Fragile X symptoms
In fragile X syndrome, a neurodevelopmental disorder, mutations in the FMR1 gene prevent the production of functional FMRP. This protein regulates the production of other proteins critical for communication between nerve cells.
Without FMRP, brain signaling becomes disrupted, leading to fragile X symptoms such as learning difficulties, developmental delays, anxiety, and hyperactive or autistic behaviors, which tend to be more pronounced in males.
MRM-3379 is an investigational oral therapy that works by selectively blocking phosphodiesterase 4D (PDE4D), an enzyme that normally breaks down cAMP, a molecule essential for nerve cell communication.
PDE4D is most active in brain regions involved in learning, memory, and emotional regulation, and cAMP levels are reduced in people with fragile X.
By reducing PDE4D activity, MRM-3379 is expected to restore cAMP balance, rebuild healthy nerve cell communication networks in the brain, and ultimately ease fragile X symptoms.
According to a previous company presentation, the therapy has demonstrated efficacy in preclinical models of memory and was well-tolerated in Phase 1 clinical trials, where it was tested in both single and multiple ascending doses.
In the Phase 2 trial, males with fragile X syndrome, ages 16 to 45, will be randomly assigned to receive one of three oral dose levels of MRM-3379 or a placebo for 12 weeks, or about three months. A separate group of boys with fragile X, ages 13 to 16, will receive the lowest MRM-3379 dose for exploratory evaluation.
The trial’s main goal is to assess the safety and tolerability of MRM-3379, as measured by the occurrence and severity of adverse events and discontinuations linked to those events. Secondary and exploratory outcomes will evaluate whether MRM-3379 can also ease disease symptoms.
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