FDA Approves Denali Therapeutics' Avlayah for Hunter Syndrome, First Treatment for Neurologic Manifestations

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The FDA approved Avlayah (tividenofusp alfa-eknm), an IV infusion from Denali Therapeutics, to treat neurologic manifestations of Hunter syndrome (MPS II) in pediatric patients weighing at least 5 kg, presymptomatic or symptomatic before advanced impairment.1

Avlayah is the first approved drug addressing neurologic complications of Hunter syndrome, a rare X-linked disorder affecting about 500 people in the US, mostly males.13

Approval was accelerated based on a Phase 1/2 trial in 47 pediatric patients showing a 91% average reduction in cerebrospinal fluid heparan sulfate (CSF HS) at Week 24, with 93% of patients below the upper limit of normal.14

The approval follows recent FDA rejections of other rare disease therapies, including a Hunter syndrome gene therapy from Regenxbio, marking a win for the rare disease community.2

Avlayah received breakthrough therapy, fast track, priority review, and orphan drug designations; common side effects include upper respiratory infections, fever, and anemia, with a boxed warning for anaphylaxis.1

Sources:

1. https://www.fda.gov/news-events/press-announcements/fda-approves-drug-treat-neurologic-manifestations-hunter-syndrome

2. https://www.statnews.com/2026/03/25/denali-therapeutics-hunter-syndrome-rare-disease/

3. https://www.fiercepharma.com/pharma/fda-approves-denali-hunter-syndrome-drug-breaking-streak-rare-disease-rejections

4. https://www.investing.com/news/stock-market-news/denali-shares-jump-on-fda-approval-of-hunter-syndrome-drug-93CH-4580538