Although the results to date have been somewhat disappointing, they underscore the prior observations from linkage studies and support the hypothesis that alcohol dependence is a genetically heterogeneous disorder influenced by many genes of small effect. The power to detect statistically significant association is also an important consideration. The sample sizes (n < 5,000) in GWAS of alcohol dependence to date are much smaller than those of successful GWAS of other diseases such as type 2 diabetes and breast cancer, which used >30,000 subjects (140a).
