27 SEP 2026 — The US Food and Drug Administration approved a third treatment for fibrodysplasia ossificans progressiva on 25 September. The drug, zilurgisertib, sold as Atebrioz, treats FOP, a rare genetic disease in which muscle, tendon and ligament gradually turn into bone.
It is the second approval for the disease in five weeks.
What the disease does
In fibrodysplasia ossificans progressiva, usually shortened to FOP, the body builds bone where it should not. Soft tissue turns into what doctors call heterotopic ossification (bone outside the skeleton), often after an injury or a flare-up. Over time joints lock in place and movement is restricted, including the chest movement needed to breathe.
The extra bone cannot simply be removed. Surgery to cut it out tends to trigger more of it, which is why a drug that slows new growth matters.
What the approval rests on
The FDA's announcement says 63 patients were randomly assigned to 100 mg of zilurgisertib or a placebo once a day for 24 weeks, followed by a long open-label extension in which everyone could take the drug.
The FDA based efficacy on the change in the volume of new abnormal bone, measured by whole-body CT scans. At week 24, patients on the drug had an average decrease of 3.2 cubic centimetres; patients on placebo had an average increase of 24.6.
The approval covers adults and children aged 12 and over. The drug is a tablet taken by mouth, and it received fast track, priority review and orphan drug designation.
Three drugs, three approaches
Atebrioz joins palovarotene (Ipsen's Sohonos) and garetosmab (Regeneron's Pasatru), Healio reports. The FDA's list of novel drug approvals for 2026 shows garetosmab-grts approved on 19 August.
Zilurgisertib targets ALK2, the receptor that is overactive in FOP because of the genetic change behind the disease. The drug was developed by Incyte and is being brought to market by Mirum Pharmaceuticals.
Doctors and families now have three approved options. The trials behind each drug measured different things over different periods, so the approvals do not say which works best or for whom.
Warnings and side effects
The FDA says the drug can cause harm to a foetus, based on animal studies. The most common side effects were headache, joint pain, upper respiratory tract infections, nosebleeds and nausea.
What the numbers do not show yet
Twenty-four weeks is short for a disease that progresses over a lifetime, and the controlled comparison covered only that period. The open-label extension will show whether the effect holds, though without a placebo group for comparison.
The measure also counts bone volume, not what patients can do. The question that matters most to people with FOP is whether slowing new bone translates into keeping movement in a shoulder or a jaw over years, and that will take longer to answer.
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