Inclusion Criteria:

• The patient (and/or patient's legal guardian if patient is < 18years) must provide written informed consent prior to any study-related procedures that are performed;
• The patient must have a confirmed diagnosis of Pompe disease defined as a documented acid α-glucosidase (GAA) enzyme deficiency from any tissue source or 2 GAA gene mutations;
• The patient (and/or legal guardian) must have ability to comply with clinical protocol;
• The patient has received Myozyme therapy (20mg/kg qow) for at least 6 months immediately prior to enrollment;
• Regimen A only: The patient exhibits clinical decline; The patient has persistent high anti-rhGAA antibody titers and/or tested positive for antibodies that inhibit enzymatic activity and/or uptake of Myozyme;
• Regimen B only: The patient is CRIM-negative AND The patient does not exhibit clinical decline; OR ALL OF THE FOLLOWING: The patient is CRIM-negative AND The patient exhibits clinical decline AND The patient does NOT exhibit high anti-rhGAA antibody titers and has NOT tested positive for antibodies that inhibit enzymatic activity and/or uptake of Myozyme.

Exclusion Criteria:

• The patient has a clinical condition unrelated to Pompe disease that would interfere with program assessments;
• The patient is at risk of reactivation or is a carrier of Hepatitis B or Hepatitis C;
• The patient is at risk of reactivation or has positive serology suggestive of active infection cytomegalovirus, Herpes simplex, JC virus, parvovirus and Epstein Barr virus;
• The patient is at risk of reactivation of tuberculosis or has regular contact with individuals who are being actively treated for tuberculosis;
• The patient has low serum albumin;
• The patient has a major congenital abnormality;
• The patient has used any investigational product (other than alglucosidase alfa) within 30 days prior to study enrollment;
• The patient is pregnant or lactating;
• The patient has had or is required to have any live vaccination within one month prior to enrollment.