Importance of genetic effects for monoamine oxidase activity in thrombocytes in twins reared apart and twins reared together.

The relative importance of shared genes, shared environments, and individual specific environmental effects for monoamine oxidase (MAO) activity in thrombocytes was assessed in the Swedish Adoption/Twin Study of Aging. The sample consists of identical twins separated at an early age and reared apart (30 pairs), identical twins reared together (60 pairs), fraternal twins reared apart (66 pairs), and fraternal twins reared together (68 pairs), whose average age was 63.5 years; 49% were female. Consistent with the literature, the heritability of MAO activity was 0.77 and did not differ across cohort (under or over 63 years of age) or gender. Sharing rearing environments or similar experiences later in life does not result in familial similarity for MAO activity.