Anti-glutamic acid decarboxylase (GAD) antibodies
Anti-GAD antibodies target an enzyme called Glutamic Acid Decarboxylase. This enzyme is responsible for converting glutamic acid to GABA,a chemical found in high concentrations in the cerebellum. It is believed that the lack of GABA results in cerebellar ataxia. Patients with cerebellar ataxia of an unknown cause should have an anti-GAD test. The anti-GAD antibodies have also been associated with a disease characterized by stiffness of the muscles, called "stiff person syndrome". The stiff person syndrome and cerebellar ataxia do not necessarily occur together in patients with anti-GAD antibodies. Anti-GAD antibodies are particularly common in diabetes mellitus and autoimmune diseases such as thyroid disease and rheumatoid arthritis. The treatment for anti-GAD antibodies is corticosteroids or prednisone to reduce the abnormal immune response. If this is ineffective infusion of immunoglobulin intravenously (IVIG) or a procedure called plasma exchange can be used.