Pompe disease (Glycogen storage disease type II or GSD-II), is a rare autosomal recessive disease caused by the deficiency of acid á-glucosidase (GAA), which is needed for the degradation of lysosomal glycogen. Other names for Pompe disease include acid maltase deficiency (AMD) and glycogenosis type II. Pompe disease is characterized by organelle-bound (lysosomal) accumulation of glycogen in many body tissues, as opposed to the exclusive cytoplasmic accumulation of glycogen that occurs in most other glycogen storage disorders.

The objective of the observational study is to collect prospective, observational data on patients with late-onset Pompe disease. It is expected that data from this study will be used to optimize the design of future clinical studies to evaluate the safety and efficacy of enzyme replacement therapy with recombinant human acid alpha-glucosidase (rhGAA) in this patient population.
This information will serve the following purposes: (1) characterize the clinical presentation of late-onset Pompe disease; (2) determine the intra- and inter-patient variability for the planned study assessments in late-onset Pompe disease; (3) assist in determining clinical efficacy endpoints for future clinical studies; and (4) evaluate oligosaccharides as a biochemical marker of disease severity.