FDA changes rare disease tune again as it clears path for Regenxbio’s gene therapy

The US Food and Drug Administration agreed to reconsider Regenxbio's gene therapy Navsunli for treating Hunter syndrome. The agency originally issued a complete response letter in February 2026 citing concerns about study design and patient criteria. After four months, the FDA determined that existing clinical data is sufficient for accelerated approval pathway without requiring additional patient enrollment or new studies. Regenxbio plans to meet with the FDA in July with a biologics license application resubmission scheduled for Q3 2026. Hunter syndrome is a rare genetic disease caused by enzyme deficiency affecting approximately 2,000 patients worldwide, with more than 500 babies born annually with the condition. This regulatory shift reflects the FDA's broader trend toward less stringent approaches to gene therapies for rare diseases, coinciding with recent leadership changes at the agency.