Background: Gamma -aminobutyric acid (GABA), a non-protein amino acid acts as an inhibitory neurotransmitter in the central nervous system of mammalians. The glutamate decarboxylase (GAD) is responsible for the conversion of L-glutamate to GABA. The human brain has two isoforms of this enzyme, GAD65 and GAD67 that differ in molecular weight, amino acid sequence, antigenicity, cellular location ...