GAD2, also named as GAD65, belongs to the group II decarboxylase family. GAD2 catalyzes the production of GABA. It is responsible for the synthesis of the essential neurotransmitter gamma-aminobutyric acid (GABA) from L-glutamic acid. GAD2 is expressed in nervous and endocrine systems and are thought to be involved in synaptic transmission and insulin secretion. Autoantibodies against GAD2 may serve as markers for type I diabetes. Many individuals suffering from an adult onset disorder known as Stiff Person Syndrome (SPS) also express autoantibodies to GAD2. The antibody is specific to GAD2.