The FDA granted accelerated approval to Denali Therapeutics’ Hunter syndrome treatment Avlayah (tividenofusp alfa), marking a notable shift in the rare-disease review environment after multiple recent tough calls. The approval comes months after the FDA rejected a Regenxbio gene therapy for the same condition, citing the need for more clinical data. The decision revives confidence in surrogate-endpoint pathways for certain neuronal mucopolysaccharidoses, as Avlayah leverages Denali’s blood-brain-barrier-shuttling drug delivery approach. In parallel, the FDA also cleared Denali’s therapy on an accelerated schedule that drew attention for its timing relative to prior agency feedback.