results, to study additional questions not answered in those previous meta-analyses; and e) found strong evidence of association with both alcohol dependence and the alcohol-induced medical diseases. In addition, the procedure of ‘extended-quality score’ suggested in our previous study (Li et al. 2006) was also applied to assist the assessment of quality of the association studies. However, the limitations were that the majority of studies included were predominately from Asian populations, because of the protective 504lys allele was barely detected in the European-ancestry populations. The studies of both English and Chinese languages were included in this meta-analysis, and those of other Asian languages were not considered. In addition, it is possible that some negative results tend to be not published, which is hard to measure.
