Platelet MAO activity in hallucinating and paranoid schizophrenics: a review and meta-analysis.

Published studies of platelet monoamine oxidase (MAO) activity of paranoid (P) and nonparanoid (NP) schizophrenics and normal controls, and of hallucinating (H) and nonhallucinating (NH) schizophrenics and normal controls were critically reviewed, and summary analyses were conducted on the original published data. Methods of comparing results across studies are discussed. Meta-analysis of the results of 11 analyses from 9 studies, examining a total of 165 P and 152 NP schizophrenics and 985 normal controls, indicated that the typical P schizophrenic studied had platelet MAO activity lower than that of 61% of NP schizophrenics and 79% of normal controls. Meta-analysis of the results of 8 separate analyses from 6 studies comprising 130 H, 81 NH schizophrenics, and 186 normal controls indicated that the average H schizophrenic studied had platelet MAO activity lower than that of 84% of NH schizophrenics and 80% of normal controls. In comparison with normal control values, P schizophrenics had the greatest mean percentage decrease in platelet MAO activity (30%), followed by NP schizophrenics (24%), and H schizophrenics (24%). These findings could not readily be attributed to diagnostic, demographic, or methodological factors, nor to the effects of alcohol or neuroleptics.

Relationship of auditory hallucinations and paranoia to platelet MAO activity in schizophrenics: sex and race interactions.

Platelet monoamine oxidase (MAO) activity was determined in 37 female and 64 male patients with Research Diagnostic Criteria diagnoses of paranoid or undifferentiated schizophrenia, or schizoaffective disorder, mainly schizophrenic, and for 71 female and 65 male normal controls (NCs). Female NCs had significantly higher adjusted mean platelet MAO activity than male NCs and female, paranoid, nonhallucinating schizophrenics. Male NCs had significantly higher adjusted mean platelet MAO activity than male, paranoid, hallucinating schizophrenics. Examination of main and interactive effects of diagnostic subtype, presence/absence of auditory hallucinations, gender, and race within the group of schizophrenic patients revealed no statistically significant main effect but, rather, significant interactive effects of auditory hallucinations with gender, with diagnostic group and gender, and with diagnostic group and race in the prediction of platelet MAO activity. The interaction of diagnostic subtype with race and gender in the prediction of platelet MAO activity was also statistically significant. In general, significantly decreased platelet MAO activity was associated with both paranoid subtype and presence of auditory hallucinations in male and in black schizophrenics; and with paranoid subtype alone in white male schizophrenics. These interactive relationships with platelet MAO activity in schizophrenics may account for discrepancies in previous reports of the activity of this enzyme in schizophrenics, and are consistent with reduced platelet MAO activity in subgroups of schizophrenics.