This study is a prospective active comparator study to assess the immune response elicited by human recombinant agalsidase therapy in subjects who are switching from agalsidase alfa to agalsidase beta with Fabry disease. Fabry disease is an X-linked lysosomal storage disorder, due to deficient alpha-galactosidase A activity. The progressive accumulation of globotriaosylceramide (GL-3) in the lysosomes of the vascular endothelial cells of multiple organ systems like the kidneys, heart, skin, and brain, leads to a microvascular disease. In Fabry disease, nephropathy dominates and renal function impairment occurs as a result of accumulation of GL-3 in renal cells

Clinically, the development of an immune response is anticipated in a number of patients treated with any recombinant human proteins and suggested to be more common especially when the native protein is deficient or absent as many male patients with Fabry disease.

The immune response that results in the development of antibodies against the infused proteins may affect the clinical outcome of enzyme replacement therapy by the development of hypersensitivity, anaphylactoid, or febrile reactions, or may lead to the development of cytokine release and a generalized inflammatory response or immune complex formation. Furthermore, the mounted immune response may lead to inactivation or degradation of the recombinant enzyme or may change the pharmacokinetic and pharmacodynamic properties of the therapeutic protein.

The different rates of antibody formation with agalsidase alfa and agalsidases beta are often attributed to differences in techniques used to measure antibody formation. However, other factors such as host, structural similarity of the infused protein and tertiary structural difference such as glycosylation may lead to differences in the immune response. Among the factors that may affect host response are also the dose and the infusion frequency. Although agalsidase alfa and beta are derived from the same complementary DNA sequence there are minor differences in glycosylation patterns, and different dosing is used, 0.2 mg per kg every other week for agalsidase alfa, 1.0 mg per kg for agalsidase beta.

The investigator hypothesize that although the observation that the antibodies exhibit in vitro neutralizing capacity may suggest the presence of a single immunogenic epitope for both human recombinant alpha-galactosidases, the immunogenicity may not be similar for both agalsidase alfa and beta, and thus the differences in immune response will be determined by the host factors and the escalating dose of infused protein.

Inclusion Criteria:

• Confirmed diagnosis of Fabry disease
• Have been treated with ERT using recombinant human agalsidase A.

Exclusion Criteria:

• If the diagnosis of Fabry disease is not confirmed
• If the subject or guardian is not able to provide consent
• Any chronic immunosuppressive state or therapy such as patients on dialysis or post-transplantation immunosuppressive therapy.

30 subjects of (7 and above) who meet eligibility criteria.