描述
GABA-Transaminase Deficiency (Gamma-amino butyric acid transaminase deficiency; GABA-T) is caused by a defect in the gene coding for gamma-aminobutyrate transaminase, which is responsible for catabolism of gamma-aminobutyric acid (GABA), an important, mostly inhibitory neurotransmitter in the central nervous system, into succinic semialdehyde. The active enzyme is a homodimer of 50-kD subunits complexed to pyridoxal-5-phosphate. GABAT is present in several tissues in addition to brain and is most active in liver. GABA-T catalyzes the conversion of gamma-aminobutyrate and L-beta-aminoisobutyrate to succinate semialdehyde and methylmalonate semialdehyde, respectively. This enzyme can also convert delta-aminovalerate and beta-alanine. Defects in GABA-T cause accumulation of beta-alanine and gamma aminobutyric acid in plasma and spinal fluid, as well as accumulation of homocarnosine in spinal fluid. Symptoms include hyperreflexia, hypotonia, lethargia, macrosomia, mental retardation, and seizures.