The primary objective of this study is to evaluate potential biomarkers of GSD III.

Inclusion Criteria:

• Confirmed historical diagnosis of GSD III based on pathogenic mutations in the AGL gene on both alleles or GDE deficiency based on biopsy of liver, muscle, or fibroblasts
• Willing to comply with all study procedures
• Willing and able to provide written informed consent. If a minor, willing and able to provide written assent and have a legally authorized representative willing and able to provide written informed consent

Exclusion Criteria:

• Presence or history of any condition that, in the view of the Investigator, places the subject at high risk of poor study compliance, interferes with study participation, or interferes with the subject's ability to safely or reliably complete the study assessments
• Use of any IP within 30 days prior to informed consent/assent or at the time of enrollment

Subjects with a confirmed diagnosis of GSD III