ZIP Study-OL Study of Safety, PK, Efficacy, PD, Immunogenicity of ATB200/AT2221 in Pediatrics Aged 0 to < 18 y.o. w/LOPD

Prior treatment

• Subject has received any investigational/experimental drug, oral anabolic steroid or derivative, biologic, or device within 30 days or 5 half-lives of the therapy or treatment, whichever is longer, before screening
• Subject has received treatment with prohibited medications within 30 days of screening
• Subject has received any gene therapy at any time

Other illness

• Subject has any intercurrent illness or condition at screening or baseline that may preclude the subject from fulfilling the protocol requirements or suggests to the investigator and/or the medical monitor that the potential subject may have an unacceptable risk by participating in this study
• Subject has a hypersensitivity to any of the excipients in ATB200, approved rhGAA, or AT2221
• Subject has any prior history of illness or condition known to affect motor function, such as, but not limited to, Guillain-Barre syndrome, cerebral palsy, etc
• Subject who is diagnosed with Pompe disease via newborn screening and is asymptomatic (ie, showing no signs and symptoms of Pompe disease (Cohort 2 Only)

Other

• Female subject is pregnant or breast-feeding at screening
• Subject requires the use of ventilation support for \> 6 hours per day while awake
• Subject has evidence of moderate to severe hypertrophic cardiomyopathy aligning with classic IOPD
• In the opinion of the investigator, the parent or legally authorized representative is unlikely or unable to comply with the study requirements

• Male or female subjects (ERT-naïve \[have never received a dose of rhGAA\] or ERT-experienced \[have received rhGAA every 2 weeks for at least 6 months immediately before enrollment, and if ERT dosage has been modified, must have been on the modified dosage for at least 3 months before enrollment\]) diagnosed with LOPD who are aged 12 to \<18 years at screening (Cohort 1 only) or aged 0 months to \< 12 years at screening (Cohort 2 only)
• Subject weighs ≤ 115 kg. (Cohort 1 Only)
• Subject must have a diagnosis of LOPD based on documentation as defined in study protocol
• If of reproductive potential and if sexually active, female and male subjects agree to use a highly effective method of contraception throughout the duration of the study and for up to 90 days after their last dose of Cipaglucosidase Alfa/Miglustat
• Subject has a sitting forced vital capacity (FVC) ≥ 30% of the predicted value for healthy Adolescents at screening (Cohort 1 only)
• Subject (aged 12 to \<18 years; Cohort 1) performs one 6-Minute Walk Test (6MWT) (≥ 75 meters) at screening that is valid, as determined by the clinical evaluator, or subject (aged ≥ 5 to \< 12 years; Cohort 2) performs one 6MWT (≥ 40 meters) at screening that is valid, as determined by the clinical evaluator