This gene encodes one of several forms of glutamic acid decarboxylase, identified as a major autoantigen in insulin-dependent diabetes. The enzyme encoded is responsible for catalyzing the production of gamma-aminobutyric acid from L-glutamic acid. A pathogenic role for this enzyme has been identified in the human pancreas since it has been identified as an autoantibody and an autoreactive T cell target in insulin-dependent diabetes. This gene may also play a role in the stiff man syndrome.Alternative splicing of this gene results in two products, the predominant 67-kD form and a less-frequent 25-kD form.An important paralog of this gene is GAD2.GAD2 (Glutamate Decarboxylase 2) is a Protein Coding gene. Diseases associated with GAD2 include Stiff-Person Syndrome and Autoimmune Polyendocrine Syndrome, Type Ii. GO annotations related to this gene include protein heterodimerization activity and carboxy-lyase activity.