LOW PLASMA GABA IS A TRAIT-LIKE MARKER FOR BIPOLAR ILLNESS

Plasma gamma-aminobutyric acid (pGABA) is an index of brain GABA activ ity and a peripheral marker of mood disorder. Previous research has in dicated that pGABA is abnormally low in approximately 40% of patients symptomatic with primary unipolar depression. We have now measured pGA BA in a series of patients with bipolar disorder. Blood samples for GA BA determinations were collected soon after admission to hospital or c linic while patients were symptomatic. In both manic and depressed pha se bipolar patients, mean levels of pGABA were significantly lower tha n in healthy control subjects. The distribution of pGABA in bipolar pa tients, whether manic or depressed, was similar to that in symptomatic unipolar depression, with 30% to 40% having pGABA levels lower than t he control range. These data indicate that low pGABA is not specific t o the depressed state, as it is also found in the manic phase of bipol ar disorder. Low pGABA may represent a shared biologic correlate betwe en bipolar and unipolar illness.