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

Inclusion Criteria:

1. Documented GSD1a with confirmation by genetic testing
2. Documented history of ≥1 hypoglycemic event with blood glucose <60 mg/dL (<3.3 mmol/L) and symptoms of hypoglycemia in the absence of acute illness, with at least one such event in the 4 weeks before starting run in (Day -14)

Exclusion Criteria:

1. Liver transplant, including hepatocyte cell therapy/transplant
2. Received gene therapy for GSD1a
3. Presence of liver adenoma >5 centimeters (cm) (±10%) in size
4. Participant has a diagnosis of type 1 or type 2 diabetes mellitus
5. Presence of liver adenoma with growth of >2 cm or >5 newly diagnosed liver adenomas, in the previous 2 years
6. Participants with known allergy to magnetic resonance imaging (MRI) contrast can be enrolled and receive MRI without contrast. Participants for whom MRI is contraindicated could be enrolled if an alternative imaging technique can be performed.

Note: Additional inclusion/exclusion criteria may apply, per protocol.