BridgeBio Pharma announced Monday that its experimental oral therapy ribitol (BBP-418) succeeded in a Phase 3 trial for limb-girdle muscular dystrophy type 2I/R9, positioning the company to seek the first-ever approval for treating this rare genetic condition.
The study demonstrated that patients treated with ribitol achieved approximately 17% improvement in αDG glycosylation after three months compared to placebo, with this benefit sustained through 12 months of treatment. Levels of the glycosylated protein climbed from about 23% to nearly 40% after three months, representing a roughly 1.8-fold increase that exceeded Wall Street expectations.
Clinical Significance and Mechanism
αDG glycosylation serves as an important marker of muscle stability and was the trial's primary endpoint. The protein is part of a molecular system that acts as a shock absorber in muscle tissue. In patients with LGMD 2I/R9, this system doesn't function properly, leading to progressive muscle decline.
Ribitol is designed to boost the activity of an enzyme involved in glycosylating—or adding carbohydrates to—the αDG protein. Preclinical research and historical data suggested that achieving at least a 5% boost in glycosylated αDG levels should yield clinically meaningful benefits, according to Christine Siu, CEO of ML Bio Solutions, the BridgeBio subsidiary developing the therapy.
Comprehensive Functional Benefits
Beyond the primary endpoint, study participants receiving ribitol showed "statistically significant" and "clinically meaningful" improvements in all key secondary endpoints after one year of treatment. These included measures of walking ability and lung function—critical outcomes for patients whose condition can deprive them of mobility and shorten life by weakening the heart and lungs.
The company reported no new or unexpected safety findings during the trial period.
Addressing Significant Unmet Need
LGMD 2I/R9 affects approximately 7,000 people in the U.S. and Europe, according to BridgeBio estimates. Currently, no approved treatments exist for this condition, which is one subtype among a broad collection of over 30 genetic diseases that cause similar patterns of muscle loss.
If approved, ribitol could access a market opportunity worth more than $1 billion, Siu noted. The therapy has the potential to become the first approved treatment for this specific form of limb-girdle muscular dystrophy.
Regulatory Path Forward
BridgeBio plans to discuss its filing strategy with the FDA at an upcoming meeting later this year, with intentions to submit an approval application in the first half of 2026. Siu argues that the "preponderance of evidence will unite regulators, physicians, and the community to support an approval path," given that "even small changes in glycosylated αDG may be meaningful for patients."
Mizuho Securities analyst Salim Syed noted that the findings "exceeded" Wall Street's expectations, writing that "the key question" is now whether the data support a full approval instead of an accelerated clearance.
The positive results add to BridgeBio's growing portfolio success, as the company's market value has nearly doubled this year following the early launch success of Attruby, a drug for a deadly genetic heart condition.
