On March 25, 2026, the U.S. Food and Drug Administration (FDA) approved Avlayah for the treatment of certain patients with Hunter syndrome. Hunter syndrome is a rare inherited lysosomal storage disorder that can affect multiple organs including the skeleton, heart, respiratory system, and brain.
Avlayah is the first drug approved to target the neurological manifestations of Hunter syndrome. It is indicated for pediatric patients weighing at least 5 kg, prior to the onset of significant neurological impairment, and is administered via weekly intravenous infusion. The drug received accelerated approval based on clinical trial results demonstrating a significant reduction in cerebrospinal fluid heparan sulfate—a surrogate endpoint reasonably likely to predict clinical benefit.
In a clinical trial involving 47 patients, after 24 weeks of treatment, 93% of patients had cerebrospinal fluid heparan sulfate levels below the upper limit of normal. The drug carries a boxed warning for allergic reactions, including anaphylaxis. Common side effects include upper respiratory tract infections, fever, and anemia.
Avlayah had previously received breakthrough therapy, priority review, and orphan drug designations. The marketing authorization holder is Denali Therapeutics.
