FDA Approves Genglycos as First GSDIa Therapy

The FDA granted accelerated approval to pariglasgene brecaparvovec-opnr (Genglycos, Ultragenyx Pharmaceutical) for adults and children aged 8 years and older with glycogen storage disease type Ia (GSDIa). The gene therapy is approved as an adjunct to nutritional management to reduce daily cornstarch intake and is the first approved treatment for the inherited disorder.

GSDIa is caused by glucose-6-phosphatase deficiency, which prevents the liver and kidneys from releasing sufficient glucose into the bloodstream during fasting. Patients can develop dangerous hypoglycemia and long-term metabolic complications. Management has historically required frequent meals, avoidance of certain simple sugars, close monitoring, and repeated doses of uncooked or specially formulated cornstarch.

The FDA based the accelerated approval on trial evidence that treatment reduced daily cornstarch requirements when used with an appropriate diet. Cornstarch reduction served as a surrogate endpoint considered reasonably likely to predict clinical benefit. The manufacturer must complete additional studies to confirm effectiveness.

Serious adverse reactions reported included anaphylaxis, adrenal insufficiency, elevated lactate levels, and hypoglycemia, while the most common were elevated transaminases, nausea, headache, constipation, and hyperglycemia. The prescribing information includes warnings for anaphylaxis, liver toxicity, adrenal insufficiency, and potential development of tumors.

The approval does not eliminate the need for nutritional management. GSDIa management typically includes careful medical monitoring. It introduces a disease-targeted option for a population whose treatment has centered on intensive dietary measures designed to prevent hypoglycemia.

Source: U.S. Food and Drug Administration. FDA approves first therapy for patients aged 8 years and older with glycogen storage disease type Ia. News release. FDA; August 19, 2026. Accessed August 20, 2026.