GAD65 is one of the two isoforms of glutamate decarboxylase (GAD), an enzyme that catalyzes the decarboxylation of glutamate to produce gamma-aminobutyric acid (GABA). This enzyme is primarily expressed in the brain but can also be found in the insulin-producing beta cells of the pancreas. Although the function of GAD65 in the pancreas is not well understood, it is believed to help modulate the secretion of glucagon in alpha cells. GAD65 is a target of autoantibodies in people who later develop type 1 diabetes or latent autoimmune diabetes. Because of this, GAD autoantibodies are often used as a biomarker for these conditions.