Mirum Pharmaceuticals (NASDAQ: MIRM) began its BLOOM Phase 2 trial by enrolling the first male patient with a confirmed genetic diagnosis of Fragile X syndrome (FXS) on December 1 2025. The enrollment marks the first step toward evaluating the safety, tolerability, and potential cognitive benefits of MRM‑3379, Mirum’s investigational oral PDE4D inhibitor, in a population that has no approved therapies.
The BLOOM study will randomize 120 male participants aged 16 to 45 to one of three dose levels of MRM‑3379 or placebo for 12 weeks, with an open‑label cohort of boys 13 to 16 years old receiving the lowest dose. The primary endpoint is safety and tolerability, while the key secondary endpoint is the NIH Toolbox Crystallized Cognition Composite. The trial design is the first clinical evaluation of a selective PDE4D inhibitor aimed at improving cognition, language, and daily function in FXS.
Mirum’s pipeline expansion into neurodevelopmental disorders complements its established liver‑disease portfolio, which includes the approved drug LIVMARLI. The company has recently raised its 2025 revenue guidance to $4.4 billion from $4.3 billion, citing strong demand for its liver‑disease products and the momentum of its late‑stage volixibat program. The first‑patient enrollment signals that Mirum is moving its pipeline candidates toward data that could unlock billion‑dollar opportunities, reinforcing management’s stated goal of generating over $1 billion in peak revenue from its pipeline assets.
Chief Medical Officer Joanne Quan said, “Fragile X syndrome remains without an approved therapy. In preclinical models, MRM‑3379 shows improvement in multiple cognitive and behavioral domains associated with Fragile X syndrome.” CEO Chris Peetz added, “The initiation of the BLOOM study demonstrates our ability to translate scientific promise into clinical progress and positions Mirum to address a significant unmet need.”
Analysts have responded positively to the milestone, noting that the study launch aligns with Mirum’s broader strategy of combining strong commercial execution with a diversified pipeline. The company’s recent revenue guidance lift and the first‑patient enrollment are viewed as indicators of robust execution and a growing pipeline that could drive future growth. While valuation concerns remain, the market reaction reflects confidence in Mirum’s ability to deliver on its pipeline and commercial objectives.
The BLOOM study is expected to report top‑line data in 2027. If the safety profile is favorable and the cognitive endpoints show signal, MRM‑3379 could become a first‑in‑class therapy for FXS, potentially opening a new revenue stream and enhancing Mirum’s position in the rare‑disease market. The company’s continued focus on pipeline development, coupled with its solid commercial foundation, suggests a trajectory that could support long‑term growth and shareholder value.
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