On Aug. 19, 2026, Ultragenyx Pharmaceutical announced that the U.S. Food and Drug Administration (FDA) has granted accelerated approval for GENGLYCOS™ (pariglasgene brecaparvovec-opnr), also known as DTX401, in adult and pediatric patients eight years and older with glycogen storage disease type Ia (GSDIa).

GSDIa is an ultra-rare genetic metabolic disorder caused by a deficiency of the enzyme needed to release glucose from the liver to the bloodstream. The deficiency reduces the liver’s ability to control glucose levels and is associated with potentially life-threatening hypoglycemia episodes and other serious complications, requiring rigorous nutritional management that involves a burdensome, around-the-clock regimen of raw cornstarch intake as an oral glucose replacement therapy. Glucose control with cornstarch is crude with large swings in glucose, and patients instead end up spending a large fraction of their day significantly hyperglycemic to avoid hypoglycemic episodes. GSDIa affects 1,500-2,500 patients in the U.S. and 6,000-8,000 worldwide within commercially accessible geographies.

The approval of GENGLYCOS is based on positive data from the 48-week randomized, double-blind, placebo-controlled Phase 3 GlucoGene study which treated 46 participants aged eight years and older with DTX401 (1.0 x 10^13 GC/kg dose) or placebo, showing a reduction in the cornstarch requirements in the treated group (p<0.001). There were 44 participants in the modified intention-to-treat (mITT) population providing efficacy data within the Week 48 analysis period following treatment with DTX401 (n=20) or placebo (n=24). At Week 48, eligible participants crossed over and received the alternate treatment. After crossover, participants continued to be followed, with analyses conducted at Week 96 and Week 144.

As part of accelerated approval, Ultragenyx has agreed to provide two years of safety and efficacy clinical data from open-label commercial treatment of 50 patients and 20 control patients through enhancement of its existing GSDIa Disease Monitoring Program (DMP). The control group will consist of patients who sought commercial treatment but cannot be treated with GENGLYCOS due to the presence of anti-AAV8 antibodies. The study will provide more data to support the reduction in cornstarch clinical burden, fasting tolerance, and other measures in a post-marketing setting where patients can know their immediate glucose levels, and their cornstarch and diet can be managed more promptly by their physician. The DMP will also evaluate previously treated clinical trial participants as well as these new commercial patients for a total of 10 years.  

Ultragenyx will provide support to help enrolled patients and caregivers navigate access to treatment through its UltraCare^® program, which now includes specially trained UltraCare^® Gene Therapy Guides to help understand insurance coverage, assist in obtaining treatment support, and answer questions about the treatment process.