Regeneron wins approval for a drug that slows bone invading muscle

The FDA approved Pasatru (garetosmab-grts) on 19 August 2026 to reduce new heterotopic ossification lesions and clinician-assessed flare-ups in adults with fibrodysplasia ossificans progressiva. It is the second drug approved for the disease.

FOP is an ultra-rare genetic disorder in which muscle, tendon, ligament and other connective tissue is progressively infiltrated by bone. When that happens at the jaw, spine, hip or rib cage, speaking, eating, walking and breathing become difficult in turn. Roughly 900 people worldwide are diagnosed; most use a wheelchair by age 30, and median survival is 56 years.

Pasatru is a fully human monoclonal antibody that blocks Activin A, a protein Regeneron scientists identified as critical to lesion formation. In the Phase 3 OPTIMA trial, the drug reduced new heterotopic ossification lesions by 90% or more at 56 weeks against placebo, with what the company describes as a reduction in clinician-assessed flare-ups. The recommended starting dose is 10 mg/kg infused intravenously over 60 minutes once every four weeks, reducible to 3 mg/kg if not tolerated.

Nothing is added to the body: the drug preserves movement by preventing lesions rather than by restoring what bone has already replaced. Regeneron says the infusion can be administered across a range of care settings, including home infusion where appropriate. The approval covers adults only.