A Study to Assess Safety and Efficacy of Avalglucosidase Alfa Administered Every Other Week in Pediatric Patients With Infantile-onset Pompe Disease Previously Treated With Alglucosidase Alfa

This is a multi-stage, phase 2, open-label, multicenter, multinational, ascending dose cohort, repeated intravenous (IV) infusion study of avalglucosidase alfa in pediatric patients with Infantile-Onset Pompe Disease (IOPD) who have been previously treated with alglucosidase alfa for a minimum of 6 months immediately prior to study entry and have demonstrated clinical decline or unsatisfactory clinical response.

The duration of the study for each participant will be up to 8 years and 9 months that will consist of a 14-day screening period, that may be extended to up to 4 weeks in pre-specified situations. This is followed by a 25-week treatment period and an up to a 430-week treatment extension period and a 4-week post-treatment observation period. Cohort 1 and 2 (Cohort 1: avalglucosidase alfa 20 milligrams per kilogram \[mg/kg\], Cohort 2: avalglucosidase alfa 40 mg/kg) will be non-randomized and Cohort 3 (Cohort 3a: avalglucosidase alfa 40 mg/kg \[maximum tolerated dose\] and Cohort 3b: alglucosidase alfa) will be randomized.

Eligibility Criteria:
Inclusion criteria:

* The participants has confirmed acid alpha-glucosidase (GAA) enzyme deficiency from any tissue source.
* The participants who has reached legal age of majority as defined by local regulation, or the participant's legal guardian(s) must provide signed informed consent prior to performing any study-related procedures. If the participant is legally minor per local regulations, assent shall be obtained from participants, if applicable.
* The participants (and participant's legal guardian if participant is legally minor as defined by local regulation) must have the ability to comply with the clinical protocol.
* The participants is less than 18 years old.
* The participants, if female and of childbearing potential, must have a negative serum pregnancy test (beta-human chorionic gonadotropin) and must not breastfeeding at screening/Baseline.
* The participant has cardiomyopathy at the time of diagnosis: i.e., left ventricular mass index (LVMI) equivalent to mean age specific LVMI plus 2 standard deviations.
* The participant has been receiving a stable dose of alglucosidase alfa regularly for a minimum of 6 months immediately prior to study entry.
* For participants in Stage 1: The participant has documented evidence of clinical decline in at least 1 of the following parameters related to Pompe Disease and not related to intercurrent illness as assessed by the Investigator: respiratory function, motor skills, and/or cardiac parameters.
* For participants in Stage 2: The participant has documented evidence of suboptimal clinical response in at least 1 of the following parameters related to Pompe Disease and not related to intercurrent illness as assessed by the Investigator: respiratory function, motor skills, and/or new onset of ptosis.

Exclusion criteria:

Participants are excluded from the study if any of the following criteria apply:

* The participant has high antibody titer to alglucosidase alfa.
* The participant has a high risk for a severe allergic reaction to neoGAA (avalglucosidase alfa).
* The participant requires any prohibited concomitant medications (e.g., immune modulatory treatment) for the duration of the study.
* The participant has previously participated in any ACT14132 study cohort.
* Female participant of childbearing potential not protected by highly effective contraceptive method of birth control and/or who is unwilling or unable to tested for pregnancy.

The above information is not intended to contain all considerations relevant to a participant's potential participation in a clinical trial.