Ultragenyx Pharmaceutical Inc. filed a new Biologics License Application for UX111, a self‑complementary AAV9 gene therapy targeting Sanfilippo syndrome type A, on January 30, 2026. The resubmission follows a July 2025 Complete Response Letter that highlighted chemistry, manufacturing, and controls (CMC) observations from facility inspections. By addressing those concerns and adding new data, Ultragenyx aims to secure a priority review and a PDUFA date in the third quarter of 2026.
The updated application incorporates 8.5 years of long‑term clinical data that demonstrate durable neurological benefit, a milestone that could establish UX111 as the first approved treatment for a disease with no current disease‑modifying options. In addition, the company has supplied cerebrospinal fluid heparan sulfate biomarker data to support an intermediate clinical endpoint, strengthening the evidence base for accelerated approval. These additions respond directly to the FDA’s requests and provide a more robust case for efficacy and safety.
Ultragenyx’s CEO, Emil D. Kakkis, emphasized the urgency of the therapy, noting that families of children with Sanfilippo syndrome type A face a rapid decline in communication, mobility, and feeding ability, often leading to death by the mid‑teens. “Today, with no approved treatment options to address the relentless progression of Sanfilippo syndrome type A, families must watch helplessly as their children lose the ability to communicate, play, move, and even eat before ultimately succumbing to this devastating and fatal disease,” Kakkis said. He added that the company believes it has addressed all FDA concerns to avoid further delays, underscoring a commitment to patient access.
Financially, Ultragenyx reported preliminary unaudited revenue of $672–$674 million for 2025, a 20% increase over 2024, reflecting strong performance in its core rare‑disease portfolio. While the BLA resubmission is a regulatory milestone, the company also faces setbacks in other pipeline areas, such as the failure of its setrusumab trials for osteogenesis imperfecta. The contrast highlights the company’s focus on advancing UX111 while navigating broader development challenges.
The resubmission positions Ultragenyx to potentially capture a sizable market for a first‑in‑class therapy, which could significantly alter its revenue mix and strengthen its standing in the rare‑disease gene‑therapy sector. A successful FDA review would not only provide a new treatment option for patients but also validate the company’s platform and manufacturing capabilities, potentially opening doors for future gene‑therapy candidates.
The FDA’s priority review designation and the anticipated PDUFA date in Q3 2026 signal a focused regulatory path, but the company remains cognizant of the inherent risks of a complex gene‑therapy approval process. Ultragenyx’s leadership remains optimistic, citing the robust long‑term data and the company’s ability to address CMC concerns as key factors that could accelerate the approval timeline.
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