More recently, several genome-wide association studies (GWASs) using 500,000 to 1 million SNPs spanning the entire genome have provided unbiased screens for variants affecting alcohol-related behaviors [23-32] (Table 1; Additional file 1). Many of these studies have used samples from large consortia, such as the Collaborative Studies of Genetics of Alcoholism (COGA), the Study of Addiction: Genetics and Environment (SAGE) and the Australian Twin Registry. Consistent with GWAS for other traits [33], many novel loci have been implicated in alcohol dependence and alcohol consumption, but these loci have small effects and are thus difficult to detect with the available sample sizes, especially given the high significance threshold required to control for multiple tests. In one GWAS study, the gene encoding ACN9 homolog (ACN9), which is involved in gluconeogenesis and required for the assimilation of ethanol or acetate into carbohydrate [34], has been associated with susceptibility to alcohol dependence [35]. Two SNPs in the 3' flanking region of the gene encoding peroxisomal trans-2-enoyl-CoA reductase, which is a key enzyme for the peroxisomal fatty acid chain elongation pathway, achieved genome-wide significance for
