A Prospective, Observational Study in Patients With Late-Onset Pompe Disease

Inclusion Criteria: * The patient must provide signed, informed consent prior to performing any study-related procedures. * The patient must have a diagnosis of Pompe disease based upon: a) documented marked deficiency of GAA activity by muscle biopsy, skin fibroblasts, or leukocytes OR b) documented GAA gene mutation by deoxyribonucleic acid (DNA) analysis * The patient must be greater than 8 years of age if enrolled at a site in the U.S. and greater than 18 years of age if enrolled at a site in Europe * The patient must have documented onset of symptoms of Pompe disease after 12 months of age * The patient must have at least 3 testable muscle groups in the arms and 3 testable muscle groups in the legs using quantitative muscle testing * The patient must be able to perform pulmonary and muscle function testing in the supine position * The patient must be able to provide reproducible muscle and pulmonary function test results within 10% of each other performed on Day 1 and Day 2 of the Screening/Baseline visit and forced vital capacity measurements within 10% of each other performed in the upright position on Day 1 and Day 2 of the Screening/Baseline visit * The patient must have the ability to comply with the clinical protocol Exclusion Criteria: * The patient is unable to ambulate (use of assistive devices, such as walker, cane, crutches, is permitted); * The patient requires the use of invasive ventilatory support. * The patient requires the use of noninvasive ventilatory support during waking hours. * The patient has received enzyme replacement therapy with acid alpha-glucosidase from any source * The patient has received an investigational drug within 30 days prior to study enrollment, or is currently enrolled in another study which involves clinical evaluations * The patient has a medical condition, serious intercurrent illness, or other extenuating circumstance that, in the opinion of the Investigator, may significantly interfere with study compliance including all prescribed evaluations and follow-up activities * The patient has a major congenital abnormality * For female patients only, the patient is pregnant or lactating, or is unwilling to practice birth control methods during the course of the study