Fibrodysplasia ossificans progressiva, or FOP, is a rare inherited condition in which bone forms in soft tissue where it should not. The extra bone can progressively limit movement. The disorder involves changes in ACVR1, which encodes the ALK2 receptor. A treatment aimed at that signaling pathway gives clinicians a different way to intervene, but an approval does not mean existing abnormal bone disappears.
On September 25, 2026, the FDA approved Mirum Pharmaceuticals' Atebrioz (zilurgisertib) to reduce the volume of new heterotopic bone formation in adults and children aged 12 and older with FOP. It is a once-daily oral ALK2 inhibitor and the third approved US FOP treatment, after Sohonos and Regeneron's Pasatru.
