A genetic familial study of monoamine oxidase B activity and concentration in alcoholics.

Platelet monoamine oxidase B (MAO B) activity and concentration were studied in a small sample of alcoholic families (n = 8) and in 20 unrelated, nonalcoholic controls. Complex segregation analyses of familial data indicated that both activity and concentration are controlled by a single major gene locus with a multifactorial background effect accounting for 0-50% of the variance. When the alcoholic family members (n = 24) were compared with the controls, all determinations of activity display significant differences, whereas MAO B concentration levels showed no difference. These results indicated that the lowered MAO B activities frequently reported among alcoholics do not reflect a change in the number of MAO B macromolecules expressed in platelets, but could be caused by the presence of an inhibitor or by a polymorphic or variant form of the enzyme.