The purpose of this study is to obtain information pertaining to the occurrence of antibodies to investigational SPK-3006 capsid and GAA, GAA activity and GAA antigen levels in the usual care setting of Late-Onset Pompe Disease (LOPD) participants on an enzyme replacement regimen. Additionally, a careful evaluation of laboratory and functional testing in patients with LOPD may provide information to better understand the disease features and better drive the design of a future interventional investigational gene therapy trial. An understanding of the underlying status of liver and muscle health in individuals with LOPD may also inform best surveillance during the conduct of gene therapy trials.

Inclusion Criteria:

• Provide written informed consent and authorization to use protected health information in accordance with national and local privacy regulations
• Male or females ≥18 years of age
• Currently on ERT using regular recombinant human GAA infusions for at least 18 months prior to screening
• Documented history of clinically moderate late-onset Pompe disease.

Exclusion Criteria:

• History of HIV infection
• Requires any invasive ventilation (other than BiPAP at night) or noninvasive ventilation while awake and upright
• Previously received SPK-3006
• Previously dosed with any investigational or approved gene therapy product at any time or treated with an investigational drug within the last 12 weeks (vaccination studies are accepted)
• Any concurrent clinically significant condition that would not allow the potential participant to complete the Day 1 examinations, or other condition that, in the opinion of the Investigator and/or Sponsor, makes the subject unsuitable for participation in the study
• Unable or unwilling to comply with the schedule of visits and/or study assessments described in the clinical protocol.