Inclusion Criteria:  At the time of informed consent, participants must be ≤6 months and 0 days of age, corrected for gestation if necessary. Gestational age <40 weeks will be adjusted to a full-term gestational age of 40 weeks. Participants must have alglucosidase alfa enzyme replacement therapy (ERT) planned or initiated for IOPD treatment irrespective of study participation, according to the treating physician's decision regarding participants' routine disease management. Participants must have available and accessible medical records from the time of IOPD diagnosis and from subsequent follow-up. Participants must have a confirmed diagnosis of IOPD, defined as presence of 2 pathogenic GAA variants and documented GAA deficiency in blood (dried blood spot [DBS] accepted), skin, or muscle tissue, or presence of 1 pathogenic GAA variant and documented GAA deficiency in blood, skin, or muscle tissue from separate samples (either from 2 different tissues or from the same tissue but at 2 different sampling dates.) (DBS and leukocytes are acceptable as 2 different samples from blood). Participants must have established cross-reacting immunologic material (CRIM) status available prior to enrollment. CRIM status may be provided by historical CRIM testing results or prediction of CRIM status based on genotyping performed at a Clinical Laboratory Improvement Amendments (CLIA) or other appropriately certified genetic laboratory. Participants must have cardiomyopathy at the time of diagnosis (LVMI equivalent to mean age-specific LVMI): LVMI +1 standard deviation (SD) in participants diagnosed by newborn or sibling screening, LVMI +2 SD in participants diagnosed by clinical evaluation. Participants must have informed consent provided by parent(s)/legally acceptable representatives (LARs).  Exclusion criteria:  Participants with respiratory insufficiency, defined as: Oxygen saturation <90% on room air as determined by pulse oximetry, Venous partial pressure of carbon dioxide (pCO2) >55 mmHg or arterial pCO2 >40 mmHg on room air, Use of invasive (with intubation or tracheostomy) or noninvasive (no intubation or tracheostomy) ventilation at enrollment, for participants not having started ERT at enrollment, Use of invasive or noninvasive ventilation at the time of ERT initiation, for participants having started ERT before enrollment. Participants with major congenital abnormality including heart defect, neural tube defect, or Down syndrome that, in the opinion of the investigator, would preclude participation in the study or potentially decrease survival. Participants with clinically significant organic disease other than signs/symptoms related to Pompe disease, including clinically significant cardiovascular, hepatic, pulmonary, neurologic, or renal disease, or other medical condition, serious intercurrent illness, or circumstance that, in the opinion of the investigator, would preclude participation or potentially decrease survival. Previous or ongoing treatment in any clinical trial of, or managed access program for, avalglucosidase alfa or any other Pompe disease-specific therapy.  The above information is not intended to contain all considerations relevant to a patient's potential participation in a clinical trial.