Ultragenyx Pharmaceutical Inc. announced that the U.S. Food and Drug Administration (FDA) has issued a Complete Response Letter (CRL) for its Biologics License Application (BLA) for UX111 (ABO-102) AAV gene therapy as a treatment for patients with Sanfilippo syndrome type A (MPS IIIA). 

“Our goal is to get UX111 to patients as quickly as possible knowing how critical this first therapy is to the Sanfilippo community. We have been diligently responding to the recent CMC observations and our priority is to resolve them so that we can resubmit the BLA as soon as possible,” said Emil D. Kakkis, M.D., Ph.D., chief executive officer and president of Ultragenyx. “We believe the CMC observations are readily addressable and many have already been addressed. While the CRL will delay the potential approval of UX111 to 2026, we are working with urgency to respond and resubmit.”

In the CRL, the FDA requested that the company provide additional information and improvements related to specific aspects of CMC and observations from the recently completed manufacturing facility inspections. The company believes that these observations are readily addressable, related to facilities and processes, and are not directly related to the quality of the product. The company will be working with the FDA over the next few months to resolve the observations. Once resolution is achieved, the company expects to resubmit the BLA and anticipates up to a 6-month review period to follow the resubmission.

Clinical review had been ongoing and the FDA has acknowledged that the neurodevelopmental outcome data provided to date are robust and the biomarker data provide additional supportive evidence. The CRL did not note any review issues related to the clinical data package nor clinical inspections, and asked that updated clinical data from current patients be included in the resubmission.