Glutamic Acid Decarboxylase Autoantibodies in Stiff-Man Syndrome

This chapter describes glutamic acid decarboxylase (GAD) autoantibodies in stiff-man syndrome (SMS). The isolation and characterization of GAD has led to the diagnostic tests for SMS and insulin dependent diabetes mellitus (IDDM), based on the detection of GAD autoantibodies. Analysis of GAD-reactive T cells has lead to a better understanding of autoimmune mechanisms and potential immunotherapeutics. GAD catalyzes the conversion of glutamate to gamma amino butyric acid (GABA), a widely used neurotransmitter throughout the central and peripheral nervous systems. Differences in the properties of GAD autoantibodies in SMS and IDDM patients might arise from differences in the presentation of GAD to the immune system by β cells vs. neurons.