FDA Grants Accelerated Approval to Denali's Avlayah for Hunter Syndrome, Defying Rare Disease Rejection Trend
On March 25, 2026, Denali Therapeutics announced that Avlayah (tividenofusp alfa, DNL310) received FDA accelerated approval for Hunter syndrome (mucopolysaccharidosis II, MPS II).3
This approval follows the FDA's rejection of REGENXBIO’s gene therapy RGX-121 on February 9, 2026, via a Complete Response Letter citing issues with eligibility criteria, natural history controls, and surrogate endpoints.1
Denali's therapy, a next-generation enzyme replacement therapy, had a target action date of April 5, 2026, and carries Breakthrough Therapy, Fast Track, Orphan Drug, and Rare Pediatric Disease designations with Priority Review.12
The approval bucks a recent trend of setbacks in Hunter syndrome treatments, including a prior FDA clinical hold on RGX-121 due to safety signals, with analysts estimating 70-80% approval odds for Denali.1
Denali's CEO highlighted 2026 as pivotal, with this decision marking a major advancement despite manufacturing challenges ahead.34
Sources:
1. https://www.biospace.com/drug-development/denalis-hunter-syndrome-candidate-in-the-spotlight-after-regenxbio-rejection
2. https://www.primetherapeutics.com/fda-decisions-expected-april-2026
3. https://www.marketscreener.com/news/denali-therapeutics-says-avlayah-receives-fda-accelerated-approval-in-hunter-syndrome-ce7e5ed3df89f620