The FDA has approved Pasatru (garetosmab-grts), a Regeneron antibody for fibrodysplasia ossificans progressiva (FOP) — an ultra-rare, disabling disorder often called “stone man disease,” in which muscles, tendons and ligaments progressively turn to bone.
FOP is vanishingly rare, with only about 900 people diagnosed worldwide. As abnormal bone (heterotopic ossification) accumulates, mobility is lost; most patients are wheelchair-bound by age 30, and median survival is around 56. Pasatru, approved August 20, 2026, is a monoclonal antibody that blocks Activin A, a protein that drives the bony lesions. It is given by intravenous injection once monthly, starting at 10 mg/kg with an option to reduce to 3 mg/kg.
What the trial showed
In the Phase 3 OPTIMA trial — 63 patients over 56 weeks — the higher dose produced up to a 90% reduction in new heterotopic ossification lesions versus placebo, and both dose levels reduced painful flare-ups. “For people living with FOP, every irregular new bone formation is a step toward disability and potential loss of mobility,” said OPTIMA investigator Dr. Kathryn Dahir.
Why it matters
Until now, the only approved FOP therapy was Ipsen’s Sohonos (palovarotene), which carries a list price of $624,000; Regeneron has not disclosed Pasatru’s price. For a community with almost no options, a second approved therapy — one that sharply curbs the process that steals mobility — is a meaningful milestone.