Sanofi's Long-Delayed Rare Disease Drug Shows Promise for Neurological Gaucher, Falters in Fabry

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Sanofi's experimental therapy venglustat, a legacy asset from its 2011 acquisition of Genzyme, delivered mixed results in critical late-stage trials, the company announced Monday. The drug succeeded in a study for a neurological form of Gaucher disease but failed to meet its primary endpoint in a separate trial for Fabry disease.

The divergent outcomes mark a pivotal moment for a compound that has weathered a rocky development path. In the Phase 3 study for Fabry disease, venglustat—an oral pill designed to reduce toxic substrate buildup in cells—did not demonstrate a meaningful improvement in patient-reported pain scores compared to a placebo. Sanofi stated additional analyses are underway, with a second Fabry trial still ongoing.

The breakthrough came in the trial for Type 3 Gaucher disease, a rare, progressive disorder that impairs brain function and for which existing enzyme replacement therapies are ineffective. Sanofi reported that venglustat, tested against its own marketed therapy Cerezyme, met its primary goal and three key secondary endpoints. After one year, patients on venglustat showed statistically significant improvements on two measures of neurological symptoms. The company noted the drug was "well tolerated," though side effects like nausea and diarrhea were more frequent.

"These results represent a potential paradigm shift," said Dr. Houman Ashrafian, Sanofi's Head of R&D. "For the first time, we have evidence that an oral therapy could slow the neurological decline in Gaucher Type 3 patients, addressing a profound unmet need."

The venglustat data arrives as Sanofi seeks to bolster its pipeline following recent disappointments, including an eczema candidate that underwhelmed in late-stage testing. The company plans to submit the positive Gaucher data to global regulators, potentially paving the way for its first approval.

Expert Commentary:

Dr. Elena Rodriguez, Neurologist at Metropolitan Rare Disease Center: "This is cautiously optimistic news for the Gaucher community. The neurological component is devastating and utterly untreated. If these data hold, venglustat could become a cornerstone therapy. The Fabry failure is disappointing but not wholly surprising given the drug's mechanism."

Michael T. Brenner, Biotech Analyst at Veritas Capital: "Sanofi desperately needed a pipeline win. The Gaucher success validates their long-term investment in the Genzyme pipeline, but it's a niche market. The Fabry failure limits commercial upside and shows the fragility of repurposing drugs across multiple rare diseases."

Sarah Chen, Patient Advocate & Parent of a child with Gaucher Type 3: "We've been waiting for something—anything—that touches the brain. This feels like a flicker of light after years in the dark. But 'statistically significant' needs to translate to my child being able to hold a spoon longer. We'll celebrate when it's approved and accessible."

Prof. David K. Finch, Pharmaceutical Policy Researcher: "Another 'one step forward, one step back' result in rare diseases. It highlights the exorbitant risk and cost of development. Sanofi will price this Gaucher drug astronomically, citing R&D burdens, while writing off the Fabry loss. The system remains broken for patients and payers."