FDA greenlights Pasatru, first-in-class antibody for rare bone-forming disease

On August 19, 2026, FDA approved Pasatru (garetosmab-grts) for adults with fibrodysplasia ossificans progressiva (FOP), giving patients with the ultra-rare genetic disorder another approved treatment and the first designed to directly block Activin A, a key driver of abnormal bone formation.

FOP causes muscle, tendons, ligaments, and other connective tissues to progressively turn into bone, restricting movement and eventually causing severe disability. The disease results from mutations in the ACVR1 gene that cause abnormal signaling through the activin A receptor type 1. Pasatru is a fully human monoclonal antibody that neutralizes Activin A, interrupting the pathway that triggers heterotopic ossification (HO).

The approval is notable because Pasatru demonstrated reductions in both newly formed HO lesions and clinician-assessed disease flare-ups in a placebo-controlled trial. The other FDA-approved therapy for FOP, palovarotene (Sohonos), is a retinoid indicated to reduce new HO formation in females aged 8 years and older and males aged 10 years and older. Pasatru is currently approved only for adults.

In the phase 3 OPTIMA trial, 63 adults received Pasatru 10 mg/kg, Pasatru 3 mg/kg, or placebo by IV infusion every four weeks. At 56 weeks, investigators detected two new HO lesions among 23 patients receiving 10 mg/kg and one among 19 receiving 3 mg/kg, compared with 19 lesions among 21 placebo recipients. Clinician-assessed flare-ups numbered 9, 53, and 66, respectively. Patient-reported flare-ups, however, did not differ significantly between treatment groups.

The recommended starting dose is 10 mg/kg infused over 60 minutes every four weeks, with reduction to 3 mg/kg if the higher dose is not tolerated. The treatment can be administered in different care settings, including home infusion when appropriate.

Pasatru carries warnings for embryo-fetal toxicity, skin and soft tissue infections requiring treatment or hospitalization, and epistaxis requiring medical intervention. Common adverse reactions include epistaxis, increased hair growth, abscess, and acne.

“For people living with FOP, every irregular new bone formation is a step toward disability and potential loss of mobility,” said Kathryn Dahir, MD, professor at Vanderbilt University and a primary investigator for OPTIMA. “With the ability to reduce the number of new bone lesions and flare-ups, we now have a new treatment that can positively affect patients.”

Source: FDA. 2026 Aug 19. FDA Approves Second Treatment for Fibrodysplasia Ossificans Progressiva