The FDA approved Denali Therapeutics’ Hunter syndrome medicine Avlayah, a decision that arrives amid a more stringent posture toward rare-disease evidence. The agency’s approval is notable because it recently rejected Regenxbio’s Hunter syndrome gene therapy over what it deemed insufficient clinical data. Denali’s approval underscores that sponsors still have a pathway to market when programs satisfy the agency’s current expectations for clinical support. The contrast with Regenxbio’s rejection highlights how underwriting standards are being applied across gene and rare-disease categories, with regulators signaling they may require more mature or higher-volume clinical evidence. For biotech leaders, the approval is a timely reminder to stress-test trial design, endpoints, and dataset depth against FDA expectations—especially in rare inherited disorders where regulatory decisions are increasingly scrutinizing the strength and breadth of data packages.