• Males and females ≥18 years of age
• Documented GSDIa with confirmation by molecular testing
• Documented history of ≥1 hypoglycemic event with blood glucose <60 mg/dL (<3.33 mmol/L)
• Patient's GSDIa disease is stable as evidenced by no hospitalization for severe hypoglycemia during the 4-week period preceding the screening visit

• Anti-AAV8 neutralizing antibody titer ≥1:5
• Screening or Baseline (Day 0) blood glucose level <60 mg/dL (<3.33 mmol/L)
• Liver transplant, including hepatocyte cell therapy/transplant
• Presence of liver adenoma >5 cm in size
• Presence of liver adenoma >3 cm and ≤5 cm in size that has a documented annual growth rate of ≥0.5 cm per year
• Significant hepatic inflammation or cirrhosis as evidenced by imaging or any of the following laboratory abnormalities: alanine aminotransferase (ALT) or aspartate aminotransferase (AST) > upper limit of normal (ULN), total bilirubin >1.5 × ULN, alkaline phosphatase >2.5 × ULN

Note additional inclusion/exclusion criteria may apply, per protocol.