Foster City, California & Wilmington, Delaware, September 25, 2026
Mirum Pharmaceuticals and Incyte have announced a major regulatory milestone with the U.S. Food and Drug Administration (FDA) approval of ATEBRIOZ™ (zilurgisertib) for adults and pediatric patients aged 12 years and older living with fibrodysplasia ossificans progressiva (FOP). The once-daily oral treatment is approved to reduce the volume of total new heterotopic ossification (HO), a debilitating process in which bone forms abnormally in muscles, tendons, ligaments and other soft tissues. The approval adds a new treatment option for people affected by this ultra-rare genetic disorder and represents an important development in the treatment of progressive abnormal bone formation.
FDA Approves Once-Daily ALK2 Inhibitor for FOP
ATEBRIOZ contains zilurgisertib, an oral activin receptor-like kinase 2 (ALK2) inhibitor designed to address abnormal ALK2 signaling associated with FOP. The disease is linked to pathogenic variants in the ACVR1 gene, which can result in excessive activation of the ALK2 pathway and progressive heterotopic bone formation. Under the FDA approval, the recommended dose of ATEBRIOZ is 100 mg orally once daily, with or without food. The treatment is specifically indicated to reduce the volume of total new HO in patients aged 12 years and older. The regulatory decision was supported by findings from the PROGRESS study, a randomized, double-blind, placebo-controlled clinical trial evaluating zilurgisertib in patients with FOP. According to the FDA, 63 patients were randomized to receive either ATEBRIOZ 100 mg once daily or placebo during the 24-week double-blind treatment period, followed by a long-term open-label extension. At Week 24, patients receiving zilurgisertib experienced an average 3.2 cm³ decrease in total new HO volume, compared with a 24.6 cm³ increase among patients receiving placebo. These measurements were based on whole-body CT assessments.
Clinical Development Continues in Younger Children
The approval covers adult and pediatric patients 12 years and older, while Mirum and Incyte continue to investigate zilurgisertib in younger children through the PROGRESS pediatric development program. Enrollment has been completed in the cohort evaluating children aged 6 to under 12 years, while enrollment is continuing in another cohort involving children aged 2 to under 12 years. This ongoing research is intended to expand the clinical understanding of zilurgisertib across younger pediatric populations with FOP. The companies reported that ATEBRIOZ was generally well tolerated during the 24-week placebo-controlled period. Reported adverse reactions included headache, arthralgia, upper respiratory tract infection, epistaxis and nausea, with most reported events described as mild or moderate. The FDA also notes that ATEBRIOZ may cause fetal harm based on animal-study data and includes reproductive and drug-interaction considerations in its prescribing information.
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A New Treatment Option for a Rare Genetic Disease
FOP is an ultra-rare genetic disorder in which abnormal bone formation progressively restricts movement and can cause significant disability. Because the disease is associated with abnormal ALK2 activity, targeting this pathway represents an important therapeutic approach under investigation in FOP. The FDA approval makes ATEBRIOZ the third treatment approved in the United States for FOP, according to the agency.
Mirum expects ATEBRIOZ to become commercially available in the United States in October 2026 through Mirum Access Plus, its patient-support program. Meanwhile, an application for marketing authorization in the European Union remains under review by the European Medicines Agency. With U.S. approval now secured for patients aged 12 and older and pediatric development continuing, zilurgisertib represents an important addition to the evolving therapeutic landscape for FOP.
Source: Mirum Pharmaceuticals press release
