Evidence for the segregation of a major gene for human plasma GABA levels.

Gamma-aminobutryic acid (GABA) is a major neurotransmitter in the central nervous system, and plasma levels of GABA may reflect brain GABA activity. In 35-40% of patients with mood disorders, plasma GABA levels are low compared to psychiatrically normal controls. Low plasma GABA in this subgroup of patients has characteristics of a biological trait marker for mood disorders. Low plasma GABA is also found in a subset of patients with alcohol dependence, but not in schizophrenia, anxiety, or eating disorders, suggesting some diagnostic specificity. Previous data from a small study of monozygotic twins are consistent with the hypothesis that plasma GABA levels are under genetic control. To better understand these mechanisms, we conducted a segregation analysis of plasma GABA levels in a sample of 157 individuals from 50 nuclear families. Analysis using the Class D regressive model indicated that the familial transmission of plasma GABA levels is compatible with the segregation of a recessive major gene. Our results suggest that plasma GABA levels are under single gene control. Future research should address the precise mechanisms which may account for the abnormality in GABA levels seen in a subset of patients with mood disorders.