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# Ultragenyx Gets Complete Response on Gene Therapy
- URL: https://www.fdaweb.com/ultragenyx-gets-complete-response-on-gene-therapy/
- Published: 2025-07-14T12:00:00.000Z
- Updated: 2026-09-14T15:16:31.000Z
- Author: David McFarland
- Tags: Drugs, #legacy-id-D5159496

FDA has issued Ultragenyx Pharmaceutical a complete response letter (CRL) on its BLA for UX111 (ABO-102), an investigational gene therapy for Sanfilippo syndrome Type A, a rare and fatal neurodegenerative disorder affecting children. The letter cites outstanding issues related to chemistry, manufacturing, and controls (CMC), particularly observations from recent inspections of Ultragenyx’s manufacturing facilities, according to the company. It says the agency did not raise concerns with the therapy’s clinical data or patient outcomes, and acknowledged that the neurodevelopmental and biomarker data provided to date are “robust” and supportive.

“While the CRL will delay the potential approval of UX111 to 2026, we are working with urgency to resolve the remaining CMC observations,” the company says.

According to Ultragenyx, FDA’s concerns primarily relate to facilities and manufacturing processes and are not directly linked to the quality of the gene therapy itself. The company indicated that many of the issues have already been addressed, and it plans to resubmit the BLA once all observations are resolved. A six-month review period is expected following resubmission.

Ultragenyx describes UX111 as an AAV9-based gene therapy designed to deliver a functional copy of the SGSH gene to the brain via a single intravenous infusion. The product aims to correct the underlying enzyme deficiency in patients with the condition, which leads to toxic buildup of heparan sulfate in brain cells and results in rapid neurological decline. Originally developed by Abeona Therapeutics, the program was transferred to Ultragenyx for late-stage development and commercialization.