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 alglucosidase alfa on an expanded access basis, to severely affected patients with late-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 studies currently enrolling patients with late-onset Pompe disease.

Inclusion Criteria:

• The patient or the patient's legal guardian(s) must provide written informed consent prior to any study-related procedures being performed.
• The patient has/had onset of symptoms compatible with Pompe disease after 12 months of age. Age at onset of symptoms must be documented in the patient's medical record(s).
• The patient has documented GAA deficiency consistent with a diagnosis of Pompe disease, or the patient has a confirmed diagnosis of Pompe disease by documented genotype. Tissues used for determination of GAA deficiency may include blood, muscle or skin fibroblasts.
• The patient must have the following conditions: a. The patient must be wheelchair bound (unable to ambulate with the use of assistive devices, such as walker, cane, or crutches) AND b. The patient requires the use of invasive ventilation (defined as the use of any form of ventilatory support applied through an endotracheal tube).
• Female patients of childbearing potential must have a documented negative pregnancy test prior to dosing each month. In addition, all female patients of childbearing potential must use a medically accepted method of contraception throughout the program. Male patients who are sexually active must use a barrier method of contraception.

Exclusion Criteria:

• Use of any investigational product within 30 days prior to program enrollment.
• Major congenital abnormality;
• Clinically significant organic disease (with the exception of symptoms relating to late-onset Pompe disease), including clinically significant cardiovascular, hepatic, pulmonary, neurologic, or renal disease, or other medical condition, serious intercurrent illness, or extenuating circumstance that, in the opinion of the Investigator, would preclude participation in the study or potentially decrease survival.
• The patient meets the clinical characteristics described in the inclusion criteria for participation in other Genzyme Corporation-sponsored treatment study currently enrolling patients with late-onset Pompe disease.