Monoamine Oxidase: Research Strategies

The most widely replicated neurochemical finding in schizo-phrenia is that of lower levels of monoamine oxidase (MAO) in the platelets of chronic schizophrenics than in normal controls. Yet, the etiological role of MAO in schizo-phrenia remains to be demonstrated. The incidence of low MAO in other psychiatric disorders, effects of diet, hormones and drugs, and relation-ships of platelet MAO to brain levels and genetic mechanisms re-main unclear. This article examines factors which make any biological indicator suitable for use as a diag-nostic test for schizophrenia and in-quires into the methodological pit-falls and unexamined assumptions of various research strategies which use this measure. The finding of lower levels of monoamine oxidase (MAO) in platelets of chronic schizophrenics than in platelets of normal controls, first reported by Murphy and Wyatt in 1972, has now received more widespread replication than any other neurochemical finding in schizophrenia. Combining prob-abilities across 14 (Buchsbaum and Rieder 1979) or 31 (Wyatt, Potkin, and Murphy 1979) published studies drawing patients from multidiscipli-nary research hospitals on three con-tinents yields far less than 1 in 106 that such distributions arise by chance. In this special issue of the Schizophrenia Bulletin devoted to MAO, Wyatt and co-authors (p. 199) present an overview of the extent of this research. Has the elusive etiol-ogy of schizophrenia now been dem-onstrated? Are the results the prod-uct of some pervasive but occult ar-tifact? Is the crucial yes or no investi-gation still needed? The purpose of this review of the Proceedings of the Natonal Institute of Mental Health (NIMH) Confer