Analysis of monoamine oxidase A (MAOA) promoter polymorphism in Finnish male alcoholics

Alterations in monoamine oxidase A (MAOA) expression and enzyme activity may be associated with alcoholism and impulsive behavior. Therefore, functional polymorphisms in the MAOA gene would be good candidates to consider in the interindividual differences that exist in the susceptibility to alcoholism. One variant that has been considered as a candidate in alcoholism is a repeat polymorphism in the MAOA gene promoter. We analyzed a cohort of Finnish males with either type 1 or type 2 alcoholism, as well as controls, for differences in the distribution of MAOA promoter alleles. Based on other studies, we postulated that type 2 alcoholism, which is associated with antisocial behavior, but not type 1 alcoholism, would be correlated with the inheritance of the low promoter activity allele. However, we failed to find a difference in allele distribution in type 1 and type 2 alcoholics. In addition, there was no difference in the allele distribution when each group of alcoholics was compared with controls. However, when both groups of alcoholics were pooled and compared with controls, the difference in allele distribution reached a trend towards significance. Our results suggest a minimal association between the MAOA low activity promoter alleles and alcoholism, regardless of the presence or absence of antisocial behavior. Interestingly, approximately 3% of type 2 alcoholics were found to be heterozygous for the MAOA promoter polymorphism. Since MAOA is X-linked, the heterozygotes are probable cases of Klinefelter's syndrome (47,XXY) suggesting that X-chromosome aneuploidy may increase the risk for developing type 2 alcoholism.