Ultragenyx's Genglycos Is the First Gene Therapy for GSDIa

The FDA granted accelerated approval on August 19 to Ultragenyx’s (RARE) Genglycos (pariglasgene brecaparvovec), the first gene therapy for glycogen storage disease type Ia (GSDIa). The AAV8 therapy delivers a working copy of the G6Pase gene to restore glucose release from the liver, and it is approved for adults and children eight and older. It is given as a one-time intravenous infusion. The decision came four days ahead of the August 23 PDUFA date, and Ultragenyx earned a priority review voucher with it. Shares closed at $25.32 on August 20.

GSDIa is an ultra-rare metabolic disorder affecting 1,500 to 2,500 people in the US and 6,000 to 8,000 worldwide. It is caused by a G6Pase deficiency that prevents the liver from releasing glucose during fasting, leaving patients at risk of severe hypoglycemia, seizures, and even death between meals. Standard care is a burdensome around-the-clock raw cornstarch regimen that still leaves patients with large glucose swings. Families describe waking through the night to dose cornstarch and the constant fear that a missed dose could trigger life-threatening low blood sugar. The Phase 3 GlucoGene study randomized 46 patients to Genglycos or placebo for 48 weeks; treated patients showed a significant reduction in daily cornstarch requirements (p<0.001).

This is Ultragenyx’s first gene therapy approval and fifth FDA approval overall, and it validates the AAV8 liver-targeting approach the company has built its rare-disease platform around. The FDA granted Genglycos regenerative medicine advanced therapy (RMAT) and Fast Track designations, reflecting the unmet need in a disease with no therapy addressing its underlying cause. The drug is manufactured at Ultragenyx’s own facility in Bedford, Massachusetts, which matters because scaling gene therapy production has historically been the bottleneck for rare-disease launches.

The accelerated approval means continued marketing depends on confirmatory data: Ultragenyx will supply two years of safety and efficacy data from 50 commercially treated patients and 20 controls through its Disease Monitoring Program, which will follow patients for up to 10 years. For how gene therapies price and what a one-time multimillion-dollar cure means for payers, see the gene therapy pricing guide, and for AAV versus lentivirus delivery, the AAV vs lentivirus vector explainer. The priority review voucher itself is a tradeable asset worth $100 million or more, as explained in the PRV guide.

What to watch next: the post-marketing confirmatory data. Ultragenyx must verify clinical benefit to keep the drug on the market, the same burden every accelerated gene therapy approval carries.

Source: Phase 3 GlucoGene study (DTX401) on ClinicalTrials.gov (NCT05139316); Ultragenyx Phase 3 DTX401 announcement