The significance of ammonia/gamma-aminobutyric acid (GABA) ratio for normality and liver disorders

Cohen (1,2) has illustrated that extremely high Gamma-aminobutyric acid (GABA) levels in the urine and blood and high plasma ammonia were observed for an autistic male child diagnosed with infantile autism. GABA is a major inhibitory neurotransmitter of the mammalian brain and the enzyme responsible for catabolism is GABA-Transaminase (GABA-T). Elevated levels of ammonia in the plasma results in a decrease in the efficiency for the GABA-T enzyme and this results in higher GABA concentrations after regulation in the liver. It is postulated that a link between plasma ammonia and plasma GABA exists where the concentration of GABA in the plasma is directly related to the ammonia plasma concentration. A ratio of approximately 0.30 (plasma ammonia/GABA) is a consistent finding for normal subjects and for subjects with infantile autism and liver diseases such as hepatic encephalopathy. (C) 2002 Elsevier Science Ltd. All rights reserved.