Monoamine oxidase (MAO) catalyzes the oxidative deamination of a number of neurotransmitters in the brain and peripheral tissues.80,81 Two MAO enzymes, type A and B, were discovered and characterized on the basis of their substrate selectivity and inhibitor sensitivity.82,83 The biochemistry and molecular biology of MAO have been studied extensively.80 The finding of MAO activity differences in platelets of alcohol-dependent individuals versus controls was first reported approximately 40 years ago.84 It was subsequently found that human platelets contained exclusively the B-type of MAO.85 Early studies also suggested that low platelet MAO activity was associated with certain personality traits, such as impulsiveness, risk-taking behaviors, aggressiveness, and, in particular, predisposition to alcohol and drug dependence.80,86 It has been hypothesized that low levels of platelet MAO activity may be an endophenotype for predisposition to alcohol and drug abuse; however, the results from several studies have not been consistent, and this discrepancy has been primarily attributed to the confounding effect of tobacco use.80,86 Snell et al87 examined the relationship between differences in platelet MAOB activity associated with alcohol dependence, cigarette smoking, and gender. The
