The FDA has approved Mirum Pharmaceuticals' Atebrioz (zilurgisertib) as a once-daily oral treatment for fibrodysplasia ossificans progressiva (FOP) in patients aged 12 and older. FOP is an ultra-rare genetic disorder that turns muscle and connective tissue into bone. Atebrioz, licensed from Incyte, is the third FOP therapy approved in the U.S., setting up a commercial rivalry with Regeneron's infused drug Pasatru and Ipsen's Sohonos.
FDA approval of Atebrioz
- ▪Atebrioz received Fast Track and Orphan Drug designations from the FDA prior to its approval.
- ▪The FDA approved Mirum Pharmaceuticals' once-daily oral medication Atebrioz, also known as zilurgisertib, on September 25, 2026, to treat fibrodysplasia ossificans progressiva in patients aged 12 and older.
Atebrioz mechanism and origins
- ▪Novartis originally discovered Atebrioz before Incyte licensed the drug for clinical development.
- ▪Atebrioz is an oral small molecule designed to inhibit activin receptor-like kinase 2 (ALK2), a receptor that regulates bone growth and is overly active in patients with fibrodysplasia ossificans progressiva.
Phase 2 PROGRESS trial results
- ▪In the Phase 2 PROGRESS trial of Atebrioz, an 81% decline in new bone growth occurrences missed statistical significance due to the small study population of 63 patients.
- ▪The most common side effects reported in the Phase 2 PROGRESS trial of Atebrioz were headache, joint pain, upper respiratory tract infection, nosebleeds, and nausea.
- ▪Patients treated with Atebrioz in the Phase 2 PROGRESS trial demonstrated a 99% reduction in the total volume of new bone growth in soft tissue compared to the placebo group at 24 weeks.
Atebrioz licensing and development
- ▪In April 2026, Mirum Pharmaceuticals licensed Atebrioz's global commercial rights from Incyte for $16 million upfront, with Incyte eligible for up to $63 million in milestone payments, royalties, and a rare pediatric disease priority review voucher.
- ▪Incyte conducted the Phase 2 clinical trial of Atebrioz before licensing the drug's global commercial rights to Mirum Pharmaceuticals.
Overview of fibrodysplasia ossificans progressiva
- ▪Fibrodysplasia ossificans progressiva affects approximately 900 patients worldwide, including an estimated 300 individuals in the United States.
- ▪Fibrodysplasia ossificans progressiva is an ultra-rare genetic disorder that causes muscle, tendons, and ligaments to progressively turn into bone, restricting mobility and breathing.
Comparison with competing FOP treatments
- ▪Atebrioz may hold a commercial advantage over Regeneron's Pasatru because Atebrioz is a daily oral pill approved for patients aged 12 and older, whereas Pasatru is an intravenous infusion approved only for adults.
- ▪Atebrioz is the third FDA-approved treatment for fibrodysplasia ossificans progressiva, joining Ipsen's Sohonos approved in 2023 and Regeneron Pharmaceuticals' Pasatru approved in August 2026.
Debatable claims
- ▪The FDA was justified in approving Atebrioz despite its trial missing statistical significance
- ▪Million-dollar price tags for ultra-rare disease treatments are justified to incentivize drug development
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