Glycogen Storage Disease Type Ia (GSDIa) Disease Monitoring Program

Inclusion Criteria: * Patient who had: * DTX401 (full or partial dose) administered in a parent clinical study (Group 1) or * Prescribed DTX401(full or partial dose) administered in a post-marketing setting (Group 2) * Patient is willing and able to provide informed consent after the nature of the study has been explained, and prior to any research-related assessments or procedures. If a minor or an adult with cognitive limitations, the patient is willing and able (if possible) to provide assent and have a legally authorized representative provide informed consent after the nature of the study has been explained, and prior to any research-related assessments or procedures. Exclusion Criteria: * Presence of any condition that would interfere with study participation, interpretation of results or affect patient's safety in the opinion of the Investigator