OAT and ornithine aminotransferase deficiency: GACR is caused by homozygous or compound heterozygous mutations in the OAT gene.[5] The OAT gene, which consists of 11 exons, encodes the mitochondrial enzyme ornithine aminotransferase which is a key enzyme in the pathway that converts arginine and ornithine into the neurotransmitters glutamate and Gamma-aminobutyric acid (GABA); where vitamin B6 works as a co-factor for the enzyme.[6]