Inclusion Criteria:

• patient's legally authorized guardian(s) must provide signed, informed consent prior to performing any study-related procedures; patient's signature required if patient understands informed consent
• patient must have a diagnosis of Pompe disease based on deficient endogenous GAA activity or GAA gene mutations
• patient must have demonstrable muscle weakness
• patient must be greater than or equal to five years of age and younger than eighteen years of age
• patient must be able to provide 3 reproducible FVC tests in sitting position during screening
• patient must perform muscle function testing
• patient must ambulate 10 meters (assistive devices permitted)
• patient and legal guardian must comply with the clinical protocol

Exclusion Criteria:

• patient requires the use of invasive ventilatory support
• patient requires the use of noninvasive ventilatory support while awake and in an upright position
• patient has received enzyme replacement therapy with GAA from any source
• patient has used an investigational product within 30 days prior to study enrollment, or is currently enrolled in another clinical or observational study
• patient has a medical condition, serious intercurrent illness, or other extenuating circumstance that, may significantly interfere with study compliance, including all prescribed evaluations and follow-up activities
• Female patients pregnant, lactating or unwilling to practice birth control methods during study
• Male patients unwilling to use barrier contraceptives during study