Ultragenyx announced on December 30, 2025 that it has completed the rolling Biologics License Application submission to the U.S. FDA for DTX401, its AAV8 gene therapy for Glycogen Storage Disease Type Ia (GSDIa). The application is supported by data from a clinical program involving 52 treated patients with up to six years of follow-up. In the Phase 3 GlucoGene study, DTX401 demonstrated statistically significant reductions in both the quantity and frequency of daily cornstarch intake, maintenance of low hypoglycemia rates, improved fasting tolerance and euglycemia, and meaningful improvements on the Patient Global Impression of Change scale. The therapy has received Rare Pediatric Disease, orphan drug, Fast Track and RMAT designations from the FDA, as well as orphan drug and PRIME designations from the European Medicines Agency.

Shares of the company climbed by 15.5% on the day the rolling submission was completed, trading on volume of roughly 11 million shares versus a 30-day average of 1.7 million. Investors were buoyed by management’s guidance that, if approved, DTX401 would become the first therapy to directly address the underlying enzymatic defect in GSDIa, a disease estimated to affect 6,000 people in commercially accessible regions. Market watchers noted the jump occurred despite the company’s history of net losses and high R&D spending.

Following the announcement that two Phase 3 studies of setrusumab failed to meet their primary endpoints in osteogenesis imperfecta, a Wells Fargo analyst maintained an overweight rating while reducing his price target by 31%. The Orbit and Cosmic trials did achieve secondary endpoints, including bone mineral density improvements, and delivered favorable safety profiles. The analyst cited the upcoming FDA feedback on setrusumab’s bone density data, pointing to what he described as a “favorable risk-reward” scenario that still leaves potential upside.

Ultragenyx and its partner saw shares fall over 40% after disclosing that setrusumab did not achieve the primary endpoints in two pivotal studies. Despite secondary gains—statistically significant increases in bone mineral density—and an acceptable safety profile, investors expressed concern over the setback in what had been viewed as a key growth driver beyond the DTX401 filing. The dual outcomes underscore a bifurcated pipeline risk: regulatory milestones for gene therapy versus efficacy validation in rare bone disease.