Genetic Control of Platelet and Plasma Monoamine Oxidase Activity

Monoamine oxidase (MAO) activity of platelets and plasma from nine pairs of identical (MZ) twins, 11 pairs of fraternal (DZ) twins, and 20 age and sex matched control pairs was measured. Mean intrapair difference in platelet and plasma MAO activity and the variability of intrapair differences increase in the rank order MZ<DZ<controls. Intraclass correlation coefficients follow the rank order MZ>DZ>controls for platelet and plasma enzyme activity, and the heritability of the platelet and plasma enzyme activities are respectively 0.83 and 0.86. The distribution of platelet MAO activity is nonunimodal, indicating the possibility of genetic heterogeneity. Results indicate that genetic factors influence the activity of MAO, an enzyme which influences biogenic amine metabolism and may play a role in depression and other neuropsychiatric illnesses.