The FDA’s accelerated approval of GENGLYCOS™ (pariglasgene brecaparvovec-opnr), also known as DTX401, introduces the first FDA-approved treatment option for glycogen storage disease type Ia (GSDIa). The FDA granted approval on August 19, 2026, for adult and pediatric patients eight years and older with GSDIa.
GSDIa is an ultra-rare genetic metabolic disorder caused by mutations in the G6PC gene which impair the enzyme needed to release glucose from the liver into the bloodstream. This deficiency reduces the liver’s ability to regulate glucose levels and is associated with potentially life-threatening hypoglycemia and other serious complications. Management requires rigorous nutritional support, including an around-the-clock regimen of raw cornstarch intake as oral glucose replacement therapy. Constant vigilance is required because a single episode of low blood sugar can cause severe hypoglycemia, potentially leading to seizure, coma, or death. GSDIa affects an estimated 1,500 to 2,500 patients in the US and 6,000 to 8,000 patients worldwide within commercially accessible geographies.
GENGLYCOS is a one-time adeno-associated virus (AAV8) vector-based gene therapy designed to deliver a functional G6PC gene to the liver, aiming to restore the deficient enzyme required to release stored glucose and maintain stable blood sugar levels during fasting. It is administered as a single intravenous infusion.
As stated by the FDA, the effectiveness of GENGLYCOS was evaluated in a randomized, double-blind, placebo-controlled study in patients with GSDIa followed over 48 weeks after dosing. Patients treated with GENGLYCOS demonstrated a statistically significant mean reduction from baseline in daily cornstarch intake of 31% compared with placebo, the study’s primary endpoint. A mean reduction from baseline of one cornstarch dose per day was observed in the GENGLYCOS group compared with placebo, the study’s secondary endpoint. GENGLYCOS-treated patients experienced a numerical mean increase of 3% in the percentage of glucose values in the hypoglycemic range (<70 mg/dL) compared with placebo.
GENGLYCOS is manufactured in Bedford, Massachusetts, and will be available through a national network of Qualified Treatment Centers (QTCs) with specialized expertise and training to safely administer gene therapy. The current QTC listing is available at GENGLYCOS-QTC-List_8.21.26-new.pdf.
GENGLYCOS has a U.S. wholesale acquisition cost of $2.7 million per patient and is expected to be available within 30 to 60 days. Financial and patient support is available through UltraCare – Rare Disease Patient Services & Treatment Suite.
Article by Kathy Clark, RN, BSN, CMCN, RIT, Vice President, Director of Managed Care. For more information about how the impact on your plan, please contact your Summit ReSources care specialist. The following sources were used as reference material for this article:
(1) Ultragenyx Pharmaceutical Inc. (2026, August 20). Ultragenyx announces U.S. FDA approval of GENEGLOSC™ gene therapy. Ultragenyx. https://ir.ultragenyx.com/news-releases/news-release-details/ultragenyx-announces-us-fda-approval-genglycostm-gene-therapy. Accessed 8/25/2026.
(2) U.S. Food and Drug Administration. (2026, August 20). FDA approves first therapy for patients aged 8 years and older with glycogen storage disease type Ia. U.S. Department of Health and Human Services. https://www.fda.gov/news-events/press-announcements/fda-approves-first-therapy-patients-aged-8-years-and-older-glycogen-storage-disease-type-ia. Accessed 8/25/2026.
(3) Healio. (2026, August 20). FDA approves first gene therapy to treat glycogen storage disease type Ia. Healio Endocrinology. https://www.healio.com/news/endocrinology/20260820/fda-approves-first-gene-therapy-to-treat-glycogen-storage-disease-type-ia. Accessed 8/25/2026.
(4) Highlights of Prescribing information: https://www.ultragenyx.com/wp-content/uploads/2026/08/GENGLYCOS_USPI.pdf Accessed 8/25/2026.
(5) Smith, J. (2026, August 20). FDA approves $2.7 million gene therapy for rare metabolic disorder. Managed Healthcare Executive. https://www.managedhealthcareexecutive.com/view/fda-approves-2-7-million-gene-therapy-for-rare-metabolic-disorder . Accessed 8/25/2026.
(6) Ernst, D. (2026, August 25). First gene therapy approved for glycogen storage disease type Ia. Endocrinology Advisor. https://www.endocrinologyadvisor.com/news/fda-approves-genglycos-gene-therapy-gsdia/. Accessed 8/25/2026