Ultragenyx Wins FDA Approval for GENGLYCOS, Its First Gene Therapy

Key Points

• Ultragenyx received FDA accelerated approval for GENGLYCOS (DTX401), its first gene therapy, for adults and children aged 8 and older with GSD1A who lack AAV8 antibodies. The therapy is designed to reduce dependence on frequent cornstarch dosing by helping the liver produce glucose during fasting.
• Approval was supported by a Phase 3 trial of 46 patients showing a significant reduction in daily cornstarch intake while maintaining glycemic control. Because the approval uses cornstarch reduction as a surrogate endpoint, Ultragenyx must conduct post-marketing studies to confirm long-term clinical benefit and improved fasting tolerance.
• GENGLYCOS is expected to launch in the U.S. within 30–60 days at a $2.7 million wholesale price per patient. Ultragenyx has treatment centers and commercial inventory in place, but will delay revenue guidance until it gains more visibility into reimbursement and market demand.

Ultragenyx Pharmaceutical NASDAQ: RARE said the U.S. Food and Drug Administration has approved GENGLYCOS, also known as DTX401, for glycogen storage disease type 1A, or GSD1A. The approval marks the company’s first gene therapy approval and its fifth approved medicine.

GENGLYCOS is indicated for adults and pediatric patients ages 8 and older with GSD1A who do not have antibodies to AAV8. The liver-directed gene therapy is designed to address the underlying cause of the disease by enabling the liver to break down glycogen and produce glucose during fasting or metabolic stress, according to the company.

Emil Kakkis, Ultragenyx’s chief executive officer and president, said the treatment provides a new option for patients who have historically relied on cornstarch slurry every three to four hours, including overnight, to help avoid life-threatening hypoglycemia.

Accelerated Approval and Confirmatory Data

The FDA granted GENGLYCOS accelerated approval after deciding late in its review to consider reduced cornstarch use as a surrogate endpoint. Ultragenyx will need to generate additional evidence showing that the reduction is associated with clinical benefit and improved fasting tolerance over time.

The biologics license application was supported by a Phase 3 randomized, double-blind, placebo-controlled study involving 46 patients ages 8 and older. The study met its primary endpoint, showing a statistically significant reduction in daily cornstarch intake versus placebo while maintaining glycemic control, Ultragenyx said. The company also reported positive results across multiple secondary endpoints.

Eric Crombez, chief medical officer, said the broader clinical program includes 52 treated patients and up to eight years of follow-up. GENGLYCOS was well tolerated, according to the company, with transient liver-enzyme elevations representing the most common treatment-related events. Those events were generally non-serious and managed with a prophylactic corticosteroid regimen.

As part of its post-marketing commitment, Ultragenyx plans to collect two years of data from 50 commercially treated patients through its disease monitoring program. The program will assess daily cornstarch intake and time to hypoglycemia during a controlled fasting challenge. The company will also follow 20 untreated patients with AAV8 antibodies as a control group.

The two-year evaluation will be conducted in an open-label setting, allowing patients and physicians to receive real-time glucose measurements. Ultragenyx said it believes this structure could enable greater cornstarch reduction and improved metabolic control than a blinded study without real-time glucose information.

Commercial Launch Plans

Erik Harris, chief commercial officer, said Ultragenyx has established UltraCare Gene Therapy Guides to help patients navigate insurance coverage, treatment support and questions related to the gene therapy process. GENGLYCOS will be administered through a national network of qualified treatment centers selected for GSD1A and gene therapy experience.

The company said it has enough treatment centers under contract to meet initial demand and expects the network could double by year-end. It plans to continue adding centers as demand grows. Ultragenyx said roughly 75% of GSD1A providers overlap with physicians it already knows through its MEPSEVII and DOJOLVI commercial activities.

Ultragenyx set a U.S. wholesale acquisition cost of $2.7 million per patient for GENGLYCOS. The company expects initial access to proceed through single-case agreements while insurers develop coverage policies. Management said it has had extensive discussions with state Medicaid programs and large national payers, which have recognized the severity of GSD1A and the potential clinical relevance of reduced cornstarch dependence.

Management expects GENGLYCOS to be commercially available within 30 to 60 days, subject to final steps in the product-release process. The company did not provide a launch revenue forecast, citing the need to first assess reimbursement processes and market dynamics.

Manufacturing, Revenue Outlook and Priority Review Voucher

GENGLYCOS is manufactured entirely in-house at Ultragenyx’s Bedford, Massachusetts, gene therapy facility. The company said it has commercial inventory to meet anticipated demand and will scale production as the launch progresses.

Howard Horn, chief financial officer, said Ultragenyx intends to provide revenue guidance once it has sufficient visibility into market dynamics, which historically has been about six quarters after launch. In the meantime, the company expects to report measures including treatment-center network growth and the number of patients treated.

Ultragenyx also received a priority review voucher with the approval and plans to monetize the voucher to support its balance sheet and path to profitability. Horn said the company has previously discussed an average net-pricing range of $1 million to $2 million and expects GENGLYCOS net pricing to be at or near the upper end of that range.

Beyond the U.S., Ultragenyx said it has filed or plans to file in other territories and expects to pursue commercialization globally, though it did not provide specific regulatory timelines. Management said pricing and reimbursement pressure may differ outside the U.S., but the company sees potential for substantial revenue in international markets as well.

About Ultragenyx Pharmaceutical (NASDAQ:RARE)

Ultragenyx Pharmaceutical Inc is a biopharmaceutical company focused on developing and commercializing therapies for rare and ultra-rare genetic disorders. Since its founding in 2010 and headquarters in Novato, California, the company has built expertise in protein replacement therapies, small molecules and gene therapy approaches to address high-unmet medical needs. Ultragenyx applies a precision medicine model, leveraging both in-house research and strategic collaborations to advance its product pipeline from discovery through regulatory approval.

The company's commercial portfolio includes Crysvita (burosumab-tmyl) for X-linked hypophosphatemia, Mepsevii (vestronidase alfa-vjbk) for mucopolysaccharidosis VII and Dojolvi (triheptanoin) for long-chain fatty acid oxidation disorders.

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