Intraindividual stability and extent of genetic determination of platelet monoamine oxidase activity.

Intraindividual stability and extent of genetic determination of platelet MAO activity with tryptamine as substrate was evaluated. Repeated determinations on the same days as well as during an interval of 1-30 days show a high intraindividual stability of MAO. Reexamination of subjects who had formerly been selected because of either low or high MAO activity led to a "regression to the mean", thus pointing to a certain influence of environmental factors on the enzyme values. Twin and family studies, however, show a remarkable influence of genetic factors.