The major limitation of our study is the lack of knowledge on the different types of alcohol dependence in the subjects analyzed. Namely, alcohol dependence can be divided into several clinically and etiologically different subgroups, the main divisions being the Type 1 alcoholism characterized with later onset and little or no antisocial behavior, and Type 2 alcoholism, illustrated by an early onset, and a more severe course with higher levels of alcohol-related problems (Cloninger, 1987). In a Swedish case–control study analyzing Cloninger type 1 and type 2 alcoholics, the OPRM1 118G allele was associated with alcohol dependence, but no difference was observed in A118G genotype distribution between type 1 and type 2 alcoholics (Bart et al., 2005). However, further research is warranted to clarify the possible association between A118G polymorphism with the specific alcohol dependence subgroups.
