Sanofi reported mixed Phase 3 results for its glucosylceramide synthase (GCS) inhibitor venglustat: the drug met its primary endpoint in Gaucher disease but failed a separate Phase 3 trial in Fabry disease. The contrasting outcomes highlight disease‑specific biology and raise questions about the compound’s broader utility across lysosomal disorders. Sanofi will advance the Gaucher program while reassessing the Fabry asset and its development strategy. The result underscores the risk of single‑mechanism approaches across distinct rare diseases and will influence resource allocation, labeling prospects, and potential partner interest for venglustat.