Pompe Disease / Glycogen Storage Disease II (GSDII) or is a rare lysosomal storage disease. Patients have been classified as infantile, juvenile or adult onset types. More recently, it has been recognized that there is a continuum of phenotypes between the classical infantile onset and the adult form. Infantile GSDII presents during the first weeks or months of life with poor feeding, failure to thrive, macroglossia, severe hypotonia, cardiomegaly, mild hepatomegaly, and respiratory insufficiency. There is often a rapid progression to cardiac failure and death typically occurs within the first year. Later onset forms are characterized by skeletal muscle weakness, respiratory insufficiency and hepatomegaly. Cardiac involvement is usually absent or mild. The adult onset form presents in the third to sixth decade and is similar to the juvenile form but with a slower progression of skeletal muscle weakness.