Ultragenyx wins first gene therapy approval with Genglycos for glycogen storage disease

Aug 20, 2026

On August 19, 2026, the FDA approved Ultragenyx's Glenglycos, the first gene therapy for glycogen storage disease type Ia (GSDIa), priced at $2.7 million per patient. The accelerated approval requires two years of follow-up data. Ultragenyx plans to sell the accompanying priority review voucher to help achieve profitability by 2027, while also awaiting a September 19, 2026 FDA decision on its UX111 gene therapy.

Glenglycos FDA approval for GSDIa

▪Glycogen storage disease type Ia (GSDIa) is a rare genetic condition where a mutation leaves patients without a critical enzyme that helps the body stabilize blood sugar levels between meals
▪Patients with glycogen storage disease type Ia (GSDIa) typically ingest a cornstarch slurry every four hours to prevent hypoglycemia, and the FDA approved Glenglycos based on data showing it reduced cornstarch intake
▪On August 19, 2026, the FDA approved Ultragenyx's gene therapy, Glenglycos, as the first treatment for patients with glycogen storage disease type Ia (GSDIa)
▪Glenglycos is a one-time gene therapy designed to deliver a functional gene to the liver, aiming to restore the missing enzyme in patients with glycogen storage disease type Ia (GSDIa)

Gene therapy pricing model

▪Ultragenyx plans to make Glenglycos available at specialized treatment centers within 30 to 60 days of its August 19, 2026 approval
▪William Blair analyst Sami Corwin expects peak sales of Glenglycos to reach $362 million
▪Ultragenyx set the wholesale acquisition cost of Glenglycos at $2.7 million per patient

Priority review voucher sale

▪The FDA approval of Glenglycos awarded Ultragenyx a priority review voucher, which the company plans to sell to support its path to profitability
▪Ultragenyx Chief Financial Officer Howard Horn stated on August 19, 2026, that the company expects to reach profitability in 2027

UX111 regulatory resubmission

▪The FDA previously rejected Ultragenyx's UX111 application in 2025 due to manufacturing concerns and deemed a subsequent response incomplete before accepting the resubmission in April 2026
▪Ultragenyx is seeking FDA approval for UX111, a gene therapy for Sanfilippo syndrome Type A, with an FDA action deadline set for September 19, 2026

GTX-102 pivotal trial results

▪William Blair analyst Sami Corwin stated that investors are highly focused on the pivotal trial results for GTX-102, an Angelman syndrome treatment, expected in September or October 2026
▪William Blair analyst Sami Corwin wrote that the upcoming pivotal trial results for GTX-102 will be a significant catalyst for Ultragenyx's stock

Accelerated approval pathway requirements

▪The FDA cleared Glenglycos under its accelerated approval process, requiring Ultragenyx to provide longer-term data showing clinical benefit
▪Ultragenyx plans to monitor Glenglycos patients and a control group for 10 years, although the FDA only requires two years of additional data for full approval