Ultragenyx’s Gene Therapy UX111 Shows Durable Efficacy in Sanfilippo Syndrome Studies
Ultragenyx Pharmaceutical Inc. (NASDAQ: RARE) reported that its investigational gene therapy UX111 demonstrated sustained cognitive improvements and significant biomarker gains in long-term follow-up from two Sanfilippo syndrome type A studies, with up to 8.5 years of patient data. The results were presented at WORLDSymposium 2026, and come as the company recently resubmitted its biologics license application (BLA) to the U.S. Food and Drug Administration following a prior complete response letter that cited manufacturing issues. UX111 treatment showed about a 23.3-point improvement on the Bailey-III cognitive scale in younger patients versus untreated natural history comparators, alongside preservation of functional skills in older children. Biomarker data also indicated rapid and durable reductions in cerebrospinal fluid heparan sulfate, a disease-relevant marker.
- Long-term efficacy: UX111 sustained meaningful cognitive and functional benefits across developmental domains in patients with Sanfilippo A syndrome, with follow-ups extending nearly a decade.
- Regulatory progress: After receiving a complete response letter in mid-2025 citing non-clinical manufacturing issues, Ultragenyx resubmitted the BLA on Jan. 30, 2026, starting a six-month FDA review period.
- Unmet need: Sanfilippo syndrome type A is a rare, fatal lysosomal storage disorder with no approved disease-modifying treatments and profound neurodevelopmental decline in early childhood.
- Data significance: The results reinforce the potential of a one-time AAV9-based gene therapy to durably impact a severe genetic CNS disorder, a major unmet medical challenge in rare disease
