The purpose of this study is to assess anti-recombinant human acid α-glucosidase (anti-rhGAA) antibody titers after treatment with immune modulation therapy in patients of Pompe disease.

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 blood samples or 2 GAA gene mutations;
• The patient (and/or legal guardian) must have ability to comply with clinical protocol;
• Regimen A only: The patient is receiving enzyme replacement therapy, exhibits clinical decline, and has persistent high anti-recombinant human acid α-glucosidase (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 cross-reactive immune material (CRIM) -negative AND have not received Myozyme infusion prior to enrollment

Exclusion Criteria:

• The patient is at risk of reactivation or is a carrier of Hepatitis B or Hepatitis C;
• 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 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.