Key Inclusion Criteria:  Confirmed diagnosis of GSD III by gene sequencing or enzymatic testing History of significant hypoglycemia or elevation in liver enzyme (alanine aminotransferase) in the past year Alanine aminotransferase at or below 5 times normal during the three months prior to dosing Willing and able to comply with standard dietary management of GSD III  Key Exclusion Criteria:  History of liver transplant or currently awaiting liver transplant History of cirrhosis Active Hepatitis B or C Severe kidney impairment History of liver cancer or large liver tumors History of any cancer within the past 3 years Known history of HIV infection Known severe allergy to polyethylene glycol (PEG), polysorbate, or mRNA vaccine Heart failure that causes marked limitation in physical activity Poorly controlled diabetes Poorly controlled hypothyroidism Treatment with immunosuppressive medications such as those used to treat chronic autoimmune conditions and solid organ transplants Pregnant or nursing, or planning to become pregnant during the study  Note: Additional inclusion/exclusion criteria may apply, per protocol