GADs catalyze the formation of gamma-aminobutyric acid (GABA), a major inhibitory neurotransmitter in the brain. Two forms, GAD1/GAD67 and GAD2/GAD65, have been identified in human. They are expressed in the brain, pancreas, ovary, and oviduct. Abnormalities in GADs are related to several neurological disorders including epilepsy and schizophrenia. GAD2/GAD65 is an autoimmune target in insulin-dependent diabetes mellitus.