Monoamine Oxidase Activity: A Genetic Marker of Schizophrenia?

Platelet monoamine oxidase activity in first-degree relatives of schizophrenic patients

Platelet monoamine oxidase (MAO) is under genetic control. A lower MAO activity in chronic schizophrenia has repeatedly been reported, and it has been suggested that reduced activity of this enzyme reflects an increased vulnerability to schizophrenia. To test this hypothesis platelet MAO was determined in 65 first-degree relatives of 22 schizophrenic index patients and in matched healthy controls. No difference in mean activity between the two samples could be detected, suggesting that reduced MAO activity in schizophrenia is more likely to be a phenomenon secondary to the disease. A significant parent-offspring correlation of MAO activities was obtained.

Comparison of platelet count and platelet protein methods for determination of platelet MAO activity

Platelet monoamine oxidase (MAO) activity in 10 normal volunteers was studied as a function of platelet protein or electronically-determined platelet counts. Comparisons of the two methods were made for samples assayed on the same day as well as one week later. The MAO activities resulting from both methods were significantly correlated and reproducible but the results of the platelet count method were, in most instances, slightly but significantly more reliable than the platelet protein method. The relevance of these results to the controversy concerning platelet MAO activity in schizophrenia is discussed.

Monoamine oxidase (MAO) of platelets, plasma, lymphocytes and granulocytes in schizophrenia

Monoamine oxidase (MAO) levels in plasma, platelets, lymphocytes and granulocytes have been compared in schizophrenics and controls using three substrates. No significant difference was found between MAO levels in controls and the schizophrenic group as a whole, but platelets and lymphocytes of the latter (tyramine or benzylamine substrate) showed greater variation and in some cases higher values than controls, irrespective of treatment. Schizophrenics who experienced auditory hallucinations had significantly lower MAO levels in lymphocytes and platelets than those who did not.

Substrate-typic changes of platelet monoamine oxidase activity in sub-types of schizophrenia

Monoamine oxidase (MAO) activity has been measured in the platelets of controls (n = 42) and schizophrenic patients (n = 49) of three subtypes, using beta-phenylethylamine, p-tyramine, and tryptamine as substrates. Characteristic differences of MAO activity were observed between platelets of patients and controls; the differences were substrate-typic: decreased enzyme activity was found with all three substrates in platelets of the parnaoid subtype. With tryptamine, MAO activity was decreased in the platelets of all three sub-types of schizophrenia. With p-tyramine, MAO was low in patients with affective psychoses and paranoid schizophrenia. The value of MAO activity measurements as a means for distinguishing sub-types of schizophrenic disorders is improved by using two substrates; tryptamine and p-tyramine. Possible mechanisms of the substrate-typic changes of platelet MAO activity in schizophrenia are discussed.