Glutamic acid decarboxylase (GAD) is an enzyme that plays a crucial role in the synthesis of gamma-aminobutyric acid (GABA), a key neurotransmitter in the brain. It catalyzes the conversion of glutamic acid into GABA by removing a carboxyl group. This process is essential for regulating neuronal excitability and maintaining a balance between excitation and inhibition in the nervous system. GAD exists in two main isoforms, GAD65 and GAD67, which are found in different tissues and have distinct functions. Dysregulation of GAD activity has been linked to various neurological disorders, including epilepsy and anxiety disorders, highlighting its importance in brain health and function.