• 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