Aug 20, 2026 —
Ultragenyx has received U.S. Food and Drug Administration (FDA) approval for Glenglycos, a one-time gene therapy for glycogen storage disease type Ia (GSDIa), marking the company’s first approved gene therapy and the first treatment cleared for this rare metabolic condition.
GSDIa is caused by a genetic mutation that leaves patients without a critical enzyme needed to stabilize blood sugar between meals, which can lead to potentially life-threatening episodes of hypoglycemia. Standard management typically requires ingesting a slurry of cornstarch every four hours, day and night, alongside strict dietary control and continuous monitoring.
Glenglycos is designed as a one-time, adeno-associated virus (AAV) vector-based therapy that delivers a functional copy of the gene to the liver, aiming to restore enzyme activity and reduce the metabolic burden of the disease. The initial approval, granted through the FDA’s accelerated approval pathway, was based on data showing that treated patients were able to reduce their cornstarch intake.
Because the clearance was granted under accelerated approval, Ultragenyx will provide longer-term confirmatory data. Company officials said they plan to monitor treated patients alongside a control group for 10 years, while the FDA is requiring two additional years of data to support full approval. The therapy is expected to be available within 30 to 60 days at specialized treatment centers, and the approval carries a priority review voucher.
The approval described by an FDA official as “a great milestone in using a gene therapy to treat this disease,” adds to a growing list of AAV gene therapies reaching the market for rare genetic diseases, and underscores the continued need for scalable, high-quality viral vector manufacturing to support one-time genetic medicines.
