⁃ Cohort 1:

• Male or female subjects who are aged 6 months to \< 18 years on Day 1

• Subject must have documentation of IOPD genotype

• Subject must have had hypertrophic cardiomyopathy at the time of diagnosis

• Subject must have received ERT for at least 6 months immediately before enrollment. For subjects whose ERT dosage has been modified, the subject must have been on the modified dosage and regimen for at least 3 months before enrollment

• Subjects aged ≥ 12 to \< 18 years must perform one valid 6-minute walk test (6MWT) (≥ 75 meters) at screening; Subjects aged ≥ 5 to \< 12 years must perform one valid 6MWT (≥ 40 meters) at screening; Subjects aged 18 months to \< 5 years must be ambulatory and assessed to be likely to be able to perform 6MWT (≥ 40 meters) when they turn 5 years old

• Subjects must have experienced a clinical decline on their current rhGAA dose and frequency

⁃ Cohort 2:

• Male or female subjects who are aged 0 to \<6 months at Day 1

• Subject must have documentation of IOPD genotype

• Subject must have had hypertrophic cardiomyopathy at the time of diagnosis

• Subject is ERT-naïve

⁃ Long-term Extension (Cohort 1 or Cohort 2):

⁃ 1\. Subject must have, in the opinion of the investigator, benefited from therapy with cipaglucosidase alfa/miglustat during the 104-week primary treatment period with no significant safety concerns.