Regeneron’s Pasatru has won US FDA approval for adults with fibrodysplasia ossificans progressiva, an ultra-rare genetic disorder in which soft tissues progressively turn to bone.

Approval rested on the Phase 3 OPTIMA trial in 63 adults. The 10 mg/kg dose cut new bone lesions by 90 per cent versus placebo, and the 3 mg/kg dose by 94 per cent. The higher dose also reduced clinician-assessed flare-ups by 88 per cent.

FOP affects about 900 people worldwide, and most become wheelchair-bound by age 30. Pasatru blocks Activin A, a protein that drives abnormal bone formation. It is the second FDA-approved FOP therapy after Ipsen’s Sohonos.

The drug is given by IV infusion every four weeks and carries warnings on fetal harm, skin infections and nosebleeds. A trial in children and adolescents is expected to begin later in 2026.

Ipsen’s Sohonos was the only approved FOP therapy before this. About 900 people worldwide have the condition. A paediatric trial, OPTIMA 2, is expected to begin later in 2026.