Pompe disease (also known as glycogen storage disease Type II) is caused by a deficiency of a critical enzyme in the body called acid alpha-glucosidase (GAA). Normally, GAA is used by the body's cells to break down glycogen (a stored form of sugar) within specialized structures called lysosomes. In patients with Pompe disease, an excessive amount of glycogen accumulates and is stored in various tissues, especially heart and skeletal muscle, which prevents their normal function. The objective of this protocol is to provide enzyme replacement therapy with rhGAA on an expanded access basis, to severely affected patients with infantile-onset Pompe disease for whom there is no alternative treatment and who do not meet the clinical characteristics described in the inclusion criteria for participation in other Genzyme Corporation-sponsored study currently enrolling patients with infantile-onset Pompe disease.