Glutamate decarboxylase

Glutamate decarboxylase (GAD) is an enzyme that catalyzes the decarboxylation of glutamate to GABA. GAD uses PLP as a cofactor.

In mammals, GAD exists in two isoforms encoded by two different genes - Gad1 and Gad2. These isoforms are GAD67 and GAD65 with molecular weights of 67 and 65 kDa, respectively. GAD1 and GAD2 are expressed in the brain where GABA is used as a neurotransmitter, GAD2 is also expressed in the pancreas.

Diabetes
Both GAD67 and GAD65 are targets of autoantibodies in people who later develop insulin-dependent diabetes mellitus FT, FT.

Schizophrenia and Bipolar disorder
Substantial dysregulation of GAD mRNA expression is observed in schizophrenia and bipolar disorder.