A Study of mRNA-3745 in Adult and Pediatric Participants With Glycogen Storage Disease Type 1a (GSD1a)

Inclusion Criteria: * Documented GSD1a with confirmation of biallelic gene encoding glucose-6-phosphatase-α (G6PC) mutations by genetic testing. * Absence of hospitalization for hypoglycemia in the 4 weeks prior to Screening Exclusion Criteria: * Solid organ transplant * Received gene therapy for GSD1a * Presence of liver adenoma \>5 centimeters (cm) in size * Diagnosis of type 1 or type 2 diabetes mellitus * Presence of liver adenoma with growth of \>2 cm or \>5 newly diagnosed liver adenomas, in the previous 2 years Note: Additional inclusion/exclusion criteria may apply, per protocol.