Ultragenyx Announces Significant Longer-Term Results for GSDIa AAV Gene Therapy

NOVATO, Calif., Sept. 08, 2025 (GLOBE NEWSWIRE) — Ultragenyx Pharmaceutical Inc. today announced compelling longer-term results from its Phase 3 GlucoGene study of DTX401 AAV gene therapy for the treatment of glycogen storage disease type Ia (GSDIa). The data, presented at the International Congress of Inborn Errors of Metabolism (ICIEM) 2025, showed sustained and even greater clinical benefits at Week 96 compared to the previously reported 48-week data.

At Week 48, patients treated with DTX401 (n=20) experienced a statistically significant mean reduction in daily cornstarch intake of 41% compared to a 10% reduction in the placebo group (n=24). By Week 96, these improvements deepened, with both the DTX401 group and the crossover group (n=19) achieving a mean reduction in daily cornstarch intake of 61% from baseline. This included a mean reduction in nighttime cornstarch of 70% and 75% for the two groups, respectively. Importantly, participants were able to maintain low levels of hypoglycemia and improved euglycemia despite the substantial reduction in cornstarch dependency.

“The current treatment for GSDIa with multiple doses of uncooked cornstarch provides a heavy burden for individuals with this disease and requires continuous vigilance,” said Dr. John Mitchell, a study investigator. “Treatment with DTX401 resulted in an impressive reduction of both cornstarch quantity and dosing frequency while maintaining glucose levels in the target range… The most significant result from the study is the reduction in the number of cornstarch doses overnight. Uninterrupted sleep leads to improvement in quality of life and less fatigue for patients and their families.”

The clinical benefits directly translated to improvements in patient-reported quality of life. At Week 96, 83% of the DTX401 group and 95% of the crossover group reported improvements in disease burden, according to the Patient Global Impression of Change (PGIC) questionnaire. Participants frequently cited a reduction in cornstarch intake, less hypoglycemia, and less tiredness.

The study demonstrated that DTX401 was well-tolerated with an acceptable safety profile, consistent with Phase 1/2 results. No AAV8 class effects such as dorsal root ganglion toxicity, malignancy, or thrombotic microangiopathy were observed.

This investigational AAV gene therapy is designed to deliver a functional copy of the G6PC gene, allowing the liver to produce glucose and reduce the constant threat of severe or fatal hypoglycemia.