Ultragenyx Announces FDA Clearance of Investigational New Drug (IND) Application for UX053, an mRNA for the Treatment of Glycogen Storage Disease Type III

NOVATO, Calif. – Ultragenyx Pharmaceutical Inc., a biopharmaceutical company focused on the development and commercialization of novel products for serious rare and ultra-rare genetic diseases, today announced that the U.S. Food and Drug Administration (FDA) has cleared the Investigational New Drug (IND) application for UX053, an investigational mRNA therapy being evaluated for the treatment of Glycogen Storage Disease Type III (GSDIII). Enrollment in a Phase 1/2 study is expected to begin in the second half of 2021.

“FDA IND clearance paves the way for UX053 to enter the clinic as the first possible pharmacologic treatment option for patients with GSDIII,” said Camille L. Bedrosian, M.D., Chief Medical Officer of Ultragenyx. “UX053 is the most advanced of our investigational mRNA therapies, with multiple others in earlier preclinical development, and will be one of the first mRNA programs to enter clinical development for rare genetic diseases.”

Ultragenyx is developing UX053 and a number of other mRNA therapies in the preclinical stage for undisclosed indications. These mRNA therapies come out of a long-term collaboration with Arcturus Therapeutics, a clinical-stage messenger RNA medicines company.

Study Design

The two-part Phase 1/2 clinical trial will evaluate the safety, tolerability, and efficacy of UX053 in adults with GSDIII. Part 1 is open label and will enroll up to 12 patients who receive a single ascending dose of UX053. Part 2 is a randomized, double-blind, placebo-controlled multi-ascending study of 5 doses. It will enroll up to 16 patients across four cohorts randomized 3:1 to UX053 or placebo. In addition to safety, tolerability, and pharmacokinetics, study endpoints include clinician- and patient-reported outcomes, muscle strength, and biomarkers of liver, cardiac, and muscle health.

About Glycogen Storage Disease Type III

Our preclinical candidate UX053 is being developed for the treatment of GSDIII, a disease caused by a glycogen debranching enzyme (AGL) deficiency that results in glycogen accumulation in the liver and muscle. GSDIII can cause hepatomegaly, hypoglycemia, hyperlipidemia, some progressive liver cirrhosis, and skeletal and cardiac muscle disease. There are no approved treatment options for GSDIII and the current standard of care is a strict diet, including frequent doses of cornstarch, to reduce the risk of hypoglycemia. GSDIII affects more than 10,000 patients in the developed world.

About UX053

UX053 is an investigational mRNA-based biologic therapy encoding full-length, glycogen debranching enzyme encapsulated in a lipid nanoparticle (LNP) designed to provide the deficient protein in GSDIII.

About Ultragenyx Pharmaceutical Inc.
Ultragenyx is a biopharmaceutical company committed to bringing novel products to patients for the treatment of serious rare and ultra-rare genetic diseases. The company has built a diverse portfolio of approved therapies and product candidates aimed at addressing diseases with high unmet medical need and clear biology for treatment, for which there are typically no approved therapies treating the underlying disease.

The company is led by a management team experienced in the development and commercialization of rare disease therapeutics. Ultragenyx’s strategy is predicated upon time- and cost-efficient drug development, with the goal of delivering safe and effective therapies to patients with the utmost urgency.

For more information on Ultragenyx, please visit the company’s website at: www.ultragenyx.com.


Ultragenyx Pharmaceutical Inc.
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Joshua Higa