Differences in platelet monoamine oxidase activity in subgroups of schizophrenic and depressive disorders.

Platelet monoamine oxidase (MAO) activity was measured in patients with nonaffective schizophrenic disorders (i.e., without prominent symptoms of depressions or manias), and in patients with schizophrenia-related depressions. MAO activity was significantly lower than control values in a subgroup of 16 patients with nonaffective schizophrenic disorders (most of whom were paranoid) characterized by the presence of auditory hallucinations and delusions. Platelet MAO activity was not reduced in 16 other nonaffective schizophrenic patients without auditory hallucinations. Platelet MAO activity was significantly higher than control values in a group of 8 depressed patients with schizophrenia-related depressions characterized by the presence of chronic asocial, eccentric, or bizarre behavior. These findings of differences in platelet MAO activity in clinically defined subgroups of nonaffective schizophrenic disorders and the schizophrenia-related depressive disorders may help to account for some of the discrepancies in findings among the various studies of platelet MAO activity in schizophrenic and affective disorders.