Mirum Pharmaceuticals Enrolls First Participant in BLOOM Phase 2 Study Evaluating MRM-3379 for Fragile X Syndrome
Mirum Pharmaceuticals, Inc., a biopharmaceutical company focused on developing and delivering innovative therapies for rare diseases, announced today a key milestone in its development pipeline: the enrollment of the first participant in the BLOOM Phase 2 clinical study evaluating MRM-3379 for the treatment of Fragile X syndrome (FXS).
Fragile X syndrome, caused by a mutation in the FMR1 gene, represents the most common inherited cause of intellectual disability and autism spectrum disorder and continues to present substantial unmet needs for affected individuals and their families. With an estimated 50,000 males impacted in the United States and Europe, yet no approved therapies available that directly target the condition, the initiation of the BLOOM study marks a meaningful advance in research efforts for this vulnerable population.
The Phase 2 BLOOM clinical trial is designed to investigate the safety, tolerability, and potential clinical benefit of MRM-3379 in male participants who have received a confirmed genetic diagnosis of Fragile X syndrome. The development of this investigational therapy represents Mirum’s strategic expansion into neurological and genetic developmental disorders, complementing its existing portfolio in rare hepatic and metabolic diseases.
Joanne Quan, M.D., Chief Medical Officer at Mirum Pharmaceuticals, emphasized the significance of this moment in advancing treatment possibilities for Fragile X syndrome:
Despite decades of research and the life-changing impact Fragile X syndrome has on individuals and their families, there are currently no approved therapies for this condition. MRM-3379 offers a promising mechanism that, in preclinical models, has demonstrated improvements across measurable cognitive and behavioral domains relevant to Fragile X. With strong safety and tolerability findings already observed in healthy volunteers, this study marks an important step toward evaluating whether MRM-3379 may transform daily functioning, cognition, and quality of life for patients living with FXS.”
The launch of the study has generated considerable interest and optimism within the Fragile X clinical and advocacy community, where families and researchers have long awaited new therapeutic options capable of meaningfully addressing symptoms and improving long-term outcomes.
Michael Tranfaglia, M.D., Medical Director and Co-Founder of FRAXA Research Foundation, affirmed the importance of Mirum’s entry into the space:
“It is incredibly encouraging to see a company with the capabilities and commitment of Mirum advance a carefully designed clinical study in Fragile X syndrome. Families and researchers have waited many years for new trials with targeted approaches such as this one. We encourage eligible families to consider participation, as clinical research remains essential to unlocking future progress.”
Echoing this sentiment, Hilary Rosselot, Executive Director of the National Fragile X Foundation, stated:
The entire Fragile X community is energized by this milestone. Every new clinical program brings renewed hope and strengthens the pathway to potential breakthroughs. We applaud Mirum for taking on this important work and advancing an approach that could ultimately expand treatment options for families who have long been underserved.”
Families, caregivers, and healthcare providers seeking additional information about the BLOOM study or considering enrollment may visit clinicaltrials.gov and reference study ID NCT07209462.
MRM-3379 is an investigational, orally administered therapy licensed by Mirum and currently being evaluated for the treatment of Fragile X syndrome. The therapy works as a selective phosphodiesterase-4D (PDE4D) inhibitor, a mechanism designed to enhance cAMP (cyclic adenosine monophosphate) signaling—an important cellular signaling pathway that is disrupted in Fragile X syndrome. By modulating this pathway, MRM-3379 has the potential to support brain functions associated with learning, memory, cognition, and communication.
Early research has shown encouraging signals across preclinical models, including improvements in behavioral markers, learning-associated tasks, and neurological pathways relevant to the condition. Mirum continues to pursue a disciplined and data-driven development plan to determine whether these preclinical findings can translate into meaningful clinical outcomes in patients.
The BLOOM Phase 2 study will include male participants age 16 to 45, who will be randomly assigned to receive either placebo or one of three escalating dose levels of MRM-3379 for a 12-week treatment period. To further explore therapeutic potential in earlier developmental stages, the study also includes an open-label cohort enrolling boys ages 13 to 16 who will receive the lowest dose.
The primary focus of the study is to assess safety and tolerability. In addition, key secondary and exploratory endpoints—such as the NIH Toolbox Crystallized Cognition Composite (CCC) and multiple measures of mood, behavior, daily functioning, and emotional regulation—are designed to provide a comprehensive picture of how the therapy may impact symptoms and daily life in individuals with Fragile X syndrome.
About Fragile X Syndrome (FXS)
Fragile X syndrome is a rare, inherited neurodevelopmental disorder and the most common known inherited cause of intellectual disability and autism spectrum disorder. The condition is caused by a full mutation in the FMR1 gene located on the X chromosome, resulting in loss or severe reduction of FMRP, a protein critical to synaptic development and neuronal communication. This disruption contributes to challenges including speech and language delay, learning difficulties, hypersensitivity to sensory stimuli, behavioral challenges, and reduced adaptive functioning.
Although multiple symptomatic treatments exist to support learning, behavioral regulation, and anxiety, there are currently no approved therapies specifically developed to address the underlying biological cause of Fragile X syndrome.
About Mirum Pharmaceuticals, Inc.
Mirum Pharmaceuticals (NASDAQ: MIRM) is a science-driven rare disease company committed to developing life-changing medicines for patients with limited or no therapeutic options. With a growing global commercial presence and a robust development pipeline, Mirum focuses on diseases where deep expertise, strong community engagement, and purposeful research can accelerate patient impact.
Mirum’s commercial portfolio includes:
- LIVMARLI® (maralixibat) for Alagille syndrome (ALGS) and progressive familial intrahepatic cholestasis (PFIC)
- CHOLBAM® (cholic acid) for bile-acid synthesis disorders
- CTEXLI® (chenodiol) for cerebrotendinous xanthomatosis (CTX)
The company’s clinical-stage programs include:
- Volixibat, an IBAT inhibitor in late-stage development for primary sclerosing cholangitis (PSC) and primary biliary cholangitis (PBC)
- MRM-3379, a selective PDE4D inhibitor in development for Fragile X syndrome
With a mission centered on scientific rigor, collaboration with patient communities, and disciplined execution, Mirum continues to build a pipeline intended to reshape expectations in rare disease treatment.
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