Platelet monoamine-oxidase activity in schizophrenia. Relation to genetic load of the illness and treatment with antipsychotic drugs.

A significant decrease of mean platelet monoamine-oxidase (MAO) activity was observed in a sample of haloperidol-treated schizophrenic patients as compared with normal control subjects. The enzyme activity was not significantly reduced in drug-free schizophrenics. No significant difference was found between drug-free schizophrenics with and without a family history of the illness and between healthy relatives of schizophrenics and normal subjects without a family history of schizophrenia. MAO activity was significantly reduced after 14 and 21 days of treatment with haloperidol, in comparison with baseline values. It is suggested that neuroleptic intake may at least in part explain low MAO values repeatedly reported in schizophrenics.