Mirum and Incyte secure FDA approval for Atebrioz in FOP
Mirum Pharmaceuticals and Incyte have received US Food and Drug Administration (FDA) approval for Atebrioz (zilurgisertib), an oral treatment designed to reduce the volume of total new heterotopic ossification (HO) in adult and paediatric patients aged 12 years and older with fibrodysplasia ossificans progressiva (FOP).
The FDA approved a recommended dose of 100 mg once daily. Mirum expects Atebrioz to become commercially available in the US in October through its Mirum Access Plus (MAP) patient support programme.
The approval gives Mirum a new commercial product in the ultra-rare disease market while expanding treatment options for patients with FOP. Incyte originally developed zilurgisertib and licensed worldwide development and commercialisation rights to Mirum.
FDA approves Atebrioz for patients aged 12 and older
Atebrioz is an activin receptor-like kinase 2 (ALK2) inhibitor targeting a biological pathway associated with FOP.
FOP is a rare genetic disorder in which abnormal activation of the ALK2 pathway can cause bone to form in muscles, tendons, ligaments and other soft tissues. This process, known as heterotopic ossification, can progressively restrict movement and impair mobility and daily function.
The FDA said its approval was based on a randomised, double-blind, placebo-controlled study involving 63 patients. In the 24-week double-blind period, patients receiving Atebrioz experienced an average 3.2 cm³ decrease in total new HO volume, compared with a 24.6 cm³ increase among patients receiving placebo.
The treatment was generally well tolerated during the placebo-controlled period. Reported adverse reactions included headache, joint pain, upper respiratory tract infection, nosebleeds and nausea. The FDA prescribing information also includes a warning concerning potential fetal harm based on animal studies.
Mirum prepares US commercial launch
The FDA decision moves zilurgisertib from clinical development into commercialisation for Mirum in the US.
Mirum said Atebrioz will be distributed through Mirum Access Plus, which is intended to support patients, families and healthcare providers with insurance access, financial assistance for eligible patients and other treatment-support services.
The company expects the medicine to be commercially available in the US in October.
The commercial launch adds another product to Mirum’s rare-disease portfolio. The company already markets therapies including LIVMARLI and CTEXLI and is advancing additional programmes across rare diseases. Its pipeline includes development programmes targeting cholestatic liver diseases and chronic hepatitis delta virus infection.
Zilurgisertib adds to Mirum-Incyte commercial relationship
The approval also advances the commercial value of Mirum’s agreement with Incyte.
Mirum entered into an exclusive worldwide licence agreement with Incyte for zilurgisertib in April 2026. Under the agreement, Incyte received an upfront payment of $16 million and became eligible for additional development and regulatory milestone payments, sales-based milestones and tiered royalties on worldwide net sales.
For Incyte, the arrangement provides an economic interest in the commercial development of zilurgisertib without requiring the company to lead worldwide commercialisation of the product.
For Mirum, the approval provides the basis for a US launch while its development programme continues in younger FOP populations.
Development programme extends to younger patients
The current FDA indication covers adults and children aged 12 years and older, but the PROGRESS development programme is continuing to investigate zilurgisertib in younger patients.
Cohort 2 is evaluating patients aged six to under 12 years, while Cohort 3 is evaluating children aged two to under 12 years. Mirum has reported that enrolment in Cohort 2 has been completed and enrolment in Cohort 3 is underway.
The company has also said that a marketing authorisation application for zilurgisertib is under review by the European Medicines Agency.
The US approval therefore represents a commercial milestone within a broader development programme rather than the end of clinical development for the medicine.
What the Atebrioz approval means for the rare-disease market
The approval strengthens Mirum’s position in rare-disease commercialisation and gives the company an opportunity to build a new US revenue stream around an ultra-rare condition.
FOP affects approximately 300 people in the US and 900 worldwide, according to Mirum and Incyte. The limited patient population means that commercialisation of an FOP therapy involves a highly specialised treatment and patient-access infrastructure rather than a conventional mass-market pharmaceutical model.
The immediate business focus will be the US launch, patient identification and access, while Mirum continues regulatory and clinical activities in other markets and younger patient groups.
The FDA approval also came with a Rare Pediatric Disease Priority Review Voucher issued to Incyte. Such a voucher can be used for a subsequent eligible drug application to obtain priority review.
For Mirum and Incyte, the next developments to watch include the US commercial launch of Atebrioz, regulatory progress in Europe and clinical development of zilurgisertib in younger children.
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