On August 19, 2026, the U.S. Food and Drug Administration approved Regeneron’s PASATRU™ (garetosmab-grts) for the treatment of adults with fibrodysplasia ossificans progressiva (FOP), an ultra-rare genetic diso
rder characterized by progressive heterotopic ossification (HO), the formation of bone in muscles, tendons, ligaments, and other connective tissues. According to Regeneron, PASATRU is the first and only FDA-approved treatment shown in a placebo-controlled trial to reduce both new heterotopic ossification (HO) lesions and clinician-assessed flare-ups in adults with FOP.
The approval is based on results from the Phase 3 OPTIMA trial, in which PASATRU demonstrated a 90% or greater reduction in new HO lesions at 56 weeks compared to placebo. The trial also showed a substantial reduction in clinician-assessed disease flare-ups among treated patients.
FOP is caused by mutations in the ACVR1 gene and results in the progressive replacement of soft tissue with bone, leading to severe disability and loss of mobility. PASATRU (garetosmab-grts) is a fully human IgG4 monoclonal antibody that works by blocking Activin A, a protein identified as a key driver of aberrant bone formation in patients with FOP.
While FOP affects only approximately 900 diagnosed patients worldwide, the successful development of an Activin A-targeting antibody underscores the potential of precision biologics to address highly specialized genetic diseases with well-defined molecular drivers.