Novato, California, August 19, 2026

Ultragenyx Pharmaceutical Inc. has announced that the U.S. Food and Drug Administration (FDA) granted accelerated approval for GENGLYCOS™ (pariglasgene brecaparvovec-opnr), also known as DTX401, for adult and pediatric patients aged eight years and older with glycogen storage disease type Ia (GSDIa). The approval represents a major milestone for rare-disease treatment, making GENGLYCOS the first-ever FDA-approved gene therapy for GSDIa and the first gene therapy approved by Ultragenyx. The therapy is designed to address the underlying genetic cause of the ultra-rare metabolic disorder and reduce patients’ daily dependence on cornstarch as part of nutritional management.

GENGLYCOS Targets the Underlying Cause of GSDIa

GSDIa is a serious inherited metabolic disorder caused by pathogenic variants in the G6PC gene, which encodes glucose-6-phosphatase, an enzyme essential for releasing glucose from glycogen and other metabolic sources. Deficiency of this enzyme can lead to severe hypoglycemia during fasting and overnight periods, excess glycogen accumulation in the liver, metabolic abnormalities, and other serious complications. Current disease management relies heavily on a demanding schedule of raw cornstarch intake throughout the day and night to provide an external source of glucose. According to Ultragenyx, GSDIa affects approximately 1,500–2,500 people in the United States and 6,000–8,000 people worldwide within commercially accessible geographies. GENGLYCOS is designed to restore the normal breakdown of glycogen to produce glucose during fasting or metabolic stress, offering a potential approach that directly addresses the disease mechanism rather than relying solely on dietary management.

Phase 3 Data Support Accelerated Approval

The FDA’s accelerated approval was supported by results from the 48-week randomized, double-blind, placebo-controlled Phase 3 GlucoGene study, which enrolled 46 participants aged eight years and older. Participants received either DTX401 at a dose of 1.0 × 10^13 genome copies per kilogram or placebo. The study demonstrated a statistically significant reduction in cornstarch requirements among treated participants, with a reported p-value of less than 0.001. Following the Week 48 analysis, eligible participants crossed over to the alternate treatment and continued to be followed, with additional analyses planned at Weeks 96 and 144. Under the accelerated-approval pathway, Ultragenyx has also agreed to provide two years of additional safety and efficacy data from an open-label commercial treatment program involving 50 treated patients and 20 controls. The existing GSDIa Disease Monitoring Program is expected to follow participants for up to 10 years and assess cornstarch burden, fasting tolerance, and other measures of clinical benefit. Continued approval may depend on confirmation of clinical benefit through required post-marketing studies.

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Gene Therapy Manufacturing and Patient Access

Ultragenyx plans to make GENGLYCOS available through a national network of Qualified Treatment Centers, where specialized teams will administer the gene therapy. The company will also support eligible patients and caregivers through its UltraCare® program, including specially trained Gene Therapy Guides focused on treatment access, insurance coverage, and patient support. GENGLYCOS is manufactured entirely at Ultragenyx’s Gene Therapy Manufacturing Facility in Bedford, Massachusetts, giving the company direct manufacturing capabilities for its gene therapy program. The approval also resulted in Ultragenyx receiving a Priority Review Voucher, adding another significant regulatory milestone to the company’s first gene therapy approval. While GENGLYCOS offers a new treatment approach for GSDIa, the prescribing information includes important safety considerations, including risks of hypersensitivity and infusion reactions, hepatotoxicity, adrenal insufficiency, and potential risks associated with AAV vector integration. The approval therefore marks both a major scientific advance and an important next stage of long-term clinical monitoring for patients receiving the therapy.

Source: Ultragenyx Pharmaceutical press relese