The U.S. Food and Drug Administration (FDA) has approved Atebrioz (zilurgisertib) to treat fibrodysplasia ossificans progressiva (FOP), an extremely rare genetic disorder in which soft tissues gradually turn into bone.
The once-daily oral medicine, developed by Mirum Pharmaceuticals, is approved for adults and children aged 12 years and older with FOP. The recommended starting dose is 100 milligrams once daily.
FOP is caused by mutations affecting the activin A receptor type 1 (ACVR1/ALK2) pathway. The disorder can cause muscles, tendons and ligaments to progressively transform into bone outside the normal skeleton, known as heterotopic ossification. This can severely restrict movement and lead to deformities and disability.
According to Mirum, FOP affects approximately 300 people in the United States and around 900 worldwide, with diagnosis typically occurring during early childhood.
Zilurgisertib works by inhibiting ALK2, a receptor that is abnormally active in most people with FOP and plays a key role in abnormal bone formation.
The FDA’s approval was based on a randomized, double-blind, placebo-controlled trial involving 63 patients. After 24 weeks, patients receiving Atebrioz had an average 3.2 cubic-centimeter decrease in the volume of new heterotopic bone formation, while the placebo group recorded an average 24.6 cubic-centimeter increase.
The FDA said the most common side effects reported with Atebrioz include headache, joint pain, upper respiratory tract infection, nosebleeds and nausea. The agency also warned that the medicine can cause fetal harm based on animal studies.
Atebrioz is the third FDA-approved treatment for FOP. The FDA approved Pasatru (garetosmab-grts) for adults in August 2026, while another treatment, Sohonos (palovarotene), is also approved for certain patients with FOP.
Mirum has said it is preparing to launch Atebrioz in the U.S., with commercial availability and pricing details to follow.