Platelet GABA-transaminase in affective illness.

Platelet gamma-aminobutyric acid (GABA)-transaminase was measured in 18 bipolar patients, 59 normal volunteers, and 9 pairs of monozygotic twins. A significantly lower mean activity was observed in the bipolar group, although lower female bipolar values may account for most of the difference. Enzyme activity was correlated in monozygotic twins, suggesting genetic influences on enzyme activity. Values obtained in the postprandial state were significantly lower than values in the fasting state. These data are discussed in light of other evidence of altered GABA metabolism in affective illness.