Platelet MAO activity in patients with affective psychosis and their first-degree relatives

26 patients with affective psychoses, 11 with the unipolar and 15 with the bipolar form of the disease, 102 first-degree relatives and healthy controls matched for age and sex were examined for their platelet MAO activity. For evaluation of enzyme activity kinetic parameters as well as activities under saturation conditions were determined. The degree of depression was estimated by two standard self-rating depression scales. Intrafamilial correlation of MAO was found. MAO activities of patients did not differ from controls, and there was no consistent difference in MAO between the relatives and their controls. Neither among patients nor among relatives or controls were there indications for a relationship between MAO and the degree of depression. Reduced MAO activity cannot be regarded as a genetic marker of vulnerability to affective psychosis.