• Participant must be ≥18 years of age and ≥40 kilograms (kg) of body weight at the time of signing the informed consent.

• Participant must have a diagnosis of LOPD based on documentation of 1 of the following:

‣ Deficiency of acid alpha-glucosidase (GAA) enzyme

⁃ GAA genotype

• Participant has a %FVC ≥30% and ≤80% in an upright position without mechanical ventilation at screening; or Participant has ≥10% %FVC drop from upright position to supine position and %FVC ≥20% in a supine position.

• Participant performs the 6MWT at screening, as determined by the clinical evaluator, and meets all of the following criteria:

‣ Screening values of 6-minute walk distance (6MWD) are ≥75 meters

⁃ Screening values of 6MWD are ≤90% of the predicted value for healthy adults

• Participants must be ERT-experienced, defined as currently receiving ERT and having been receiving ERT for ≥24 months, with no regimen change in the last 6 months.