Gene Transfer Study in Patients With Late Onset Pompe Disease

Inclusion Criteria: * Participant is aged ≥ 18 years. * Participant has a documented clinical diagnosis of Pompe disease by genetic testing. * Participant has received enzyme replacement therapy (ERT) with rhGAA for the previous ≥ 2 years. * Participant has been on a stable standard dose (at least 20 mg/kg every 2 weeks) of ERT with rhGAA for at least the previous 6 months. * Participant or legally authorized representative(s) (LAR) (if applicable) provides written informed consent. * Participant and LAR(s) are willing and able to comply with study visits and study procedures. * Participant must agree to refrain from blood or blood products donation and sperm or egg donation from the time of AT845 administration until the later of 90 days or 3 consecutive negative viral shedding samples * Participants enrolled in previous protocol versions 1 through 9: Participant has upright FVC ≥ 30% of predicted normal value. Participants enrolled starting with protocol version 10 and subsequent amendments: Participant has upright FVC ≥ 30% and ≤ 85% of predicted normal value. * Participants enrolled starting with protocol version 10 and subsequent amendments: Participant who is able to ambulate ≥ 40 m without stopping and without the use of an assistive device. The use of an assistive device for community ambulation is acceptable. (Participants enrolled under previous protocol versions 1 through 9 will not be excluded if they do not meet this criterion during Rescreening visit). Exclusi…