Clinical Study for Treatment-naïve IOPD Babies to Evaluate Efficacy and Safety of ERT With Avalglucosidase Alfa

This is a single group, treatment, Phase 3, open-label study to assess efficacy, safety, pharmacokinetic (PK), pharmacodynamics (PD) of avalglucosidase alfa in treatment-naïve male and female participants with IOPD. Study details include: * Study duration: Screening - up to 4 weeks; * Primary Analysis Period (PAP) - 52 weeks; * Extended Treatment Period (ETP) - 52 weeks; * Extended Long term Treatment Period (ELTP) - 104 weeks; 4-week follow-up period for a total study duration - up to 4.08 years. * Treatment duration: Up to 4 years * Visit frequency: every other week and potentially every week