Glycogen storage disease type Ia (GSDIa) is a rare, life-threatening, inherited carbohydrate metabolism disorder caused by glucose-6-phosphatase (G6Pase) deficiency, which is essential for glycogenolysis and gluconeogenesis. GSDIa management includes a strict medically prescribed diet that typically includes daily uncooked cornstarch doses, including overnight, to maintain euglycemia. DTX401 is an investigational adeno-associated virus serotype 8 vector expressing the human G6PC1 gene that encodes G6Pase. This open-label, phase 1/2, dose-escalation, 52-week gene therapy trial evaluated the safety and efficacy of a single DTX401 infusion in 12 adults with GSDIa (ClinicalTrials.gov Identifier: NCT03517085). Three participants in Cohort 1 received DTX401 2.0 × 10