Platelet monoamine oxidase activity: relation to genetic load of schizophrenia.

Platelet monoamine oxidase (MAO) activity is significantly lower in chronic schizophrenic patients with a family history of schizophrenia compared to schizophrenics with no affected relatives and normal controls. These results are consistent with the concept of genetic and biologic heterogeneity in schizophrenia and suggest that the lack of uniformity across previous MAO studies of schizophrenia may be explained in part by the presence of biochemically normal phenocopies.