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.