Phase 3 Randomized Trial Results of DTX401 AAV Gene Therapy for the Treatment of GSDIa.

John J Mitchell, Jose E Abdenur, Foekje de Boer, Monica Boyer, Margo Sheck Breilyn, María-Luz Couce, Diva D De Leon, Terry G Derks, Areeg El-Gharbawy, Andrea B Haijer-Schreuder, Karen Loechner, Nicola Longo, Allan M Lund, Miguel Angel Martinez Olmos, Shawn E McCandless, Bibiana Mello de Oliveira, Malaya Mount, Nicole Muschol, Kristina Pytlak, Kadakkal Radhakrishnan, Rebecca Riba-Wolman, David F Rodriguez-Buritica, Alessandro La Rosa, Alessandro Rossi, Heather Saavedra, René Santer, Brian Shayota, G Peter A Smit, Carolina F Moura De Souza, Melanie M van der Klauw, David A Weinstein, Joseph I Wolfsdorf, Anne Blake, Andrew A Grimm, Deepali Mitragotri, Syeda Rahman, Diane M Turner-Bowker, Richard Collis

Journal: Journal of inherited metabolic disease 2026;49(5):e70241

PMID: 42674977

Abstract

Glycogen storage disease type Ia (GSDIa) is a rare, life-threatening inherited carbohydrate metabolism disorder caused by biallelic pathogenic G6PC gene variants resulting in deficiency of glucose-6-phosphatase. DTX401 is an investigational AAV8 vector containing the human G6PC gene. DTX401-CL301 is a pivotal, phase 3, double-blind, randomized, placebo-controlled trial of DTX401 in patients ≥ 8 years with GSDIa. The primary endpoint was percent change from Baseline to Week 48 in daily cornstarch intake for the DTX401 versus placebo group. Participants were randomly assigned (1:1) to blinded DTX401 or placebo. After the 48-week Primary Efficacy Analysis Period (PEAP), participants crossed over in a blinded manner for an additional 48-week blinded Crossover Period. Following randomization: 21 participants received DTX401; 25 received placebo. At Week 48, DTX401 treatment resulted in a statistically significant least squares (LS) mean (SE) daily cornstarch intake reduction of 41% (4.6) versus 10% (4.1) for Placebo (p < 0.0001). Clinical meaningfulness was evidenced by a mean desired percent reduction in daily cornstarch intake among those reporting in Baseline interviews (n = 33) of 45% (median = 41%). Greater and faster reductions in cornstarch were observed at Week 96 for the Crossover DTX401 group compared with the DTX401 group in the PEAP. The DTX401 safety profile was acceptable, and expected hepatic reactions consisting of transaminase elevations were managed with prophylactic corticosteroids. Treatment with DTX401 resulted in both a statistically significant and clinically meaningful reduction in cornstarch intake in the 48-week PEAP versus placebo, with greater cornstarch reductions in both groups at Week 96.

© 2026 Ultragenyx Pharmaceutical Inc. Journal of Inherited Metabolic Disease published by John Wiley & Sons Ltd on behalf of SSIEM.

Address: Montreal Children's Hospital, Montreal, Quebec, Canada.; Rady Children's Health, Orange, California, USA.; University of Groningen, University Medical Center Groningen, Beatrix Children's Hospital, Section of Metabolic Diseases, Groningen, the Netherlands.; UMCG Center of Expertise for Carbohydrate, Fatty Acid Oxidation and Ketone Bodies Disorders, University Medical Center Groningen, Groningen, the Netherlands.; Mount Sinai, New York, New York, USA.; Hospital Clínico Universitario de Santiago de Compostela, IDIS, CIBERER, Santiago de Compostela, Spain.; Children's Hospital of Philadelphia, Philadelphia, Pennsylvania, USA.; Duke University Medical Center, Durham, North Carolina, USA.; University of Connecticut, Farmington, Connecticut, USA.; University of Utah, Salt Lake City, Utah, USA.; Centre for Inherited Metabolic Diseases, Rigshospitalet, Copenhagen, Denmark.; Hospital Clínico Universitario de Santiago de Compostela, IDIS, CIBEROBN, Santiago de Compostela, Spain.; Children's Hospital Colorado, Aurora, Colorado, USA.; Hospital de Clinicas de Porto Alegre, Porto Alegre, Brazil.; University Medical Center Hamburg-Eppendorf, Hamburg, Germany.; Cleveland Clinic Childrens, Cleveland, Ohio, USA.; Department of Pediatrics, Division of Medical Genetics, McGovern Medical School at the University of Texas Health Science Center at Houston (UTHealth Houston) and Children's Memorial Hermann Hospital, Houston, Texas, USA.; Pediatric Clinic and Endocrinology Unit, IRCCS Istituto Giannina Gaslini, Genoa, Italy.; Department of Translational Medicine, University of Naples Federico II, Naples, Italy.; Department of Endocrinology, University of Groningen, University Medical Center Groningen, Groningen, the Netherlands.; Boston Children's Hospital, Boston, Massachusetts, USA.; Ultragenyx Pharmaceutical Inc., Novato, California, USA.

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