Candidate gene approaches, as well as family-based linkage studies together with genome-wide association studies (GWAS), have implicated many variants in and around the seven ADH genes that contribute to alcohol dependence or alcohol-related traits, including alleles of ADH1A, ADH1B, ADH1C, ADH2 and ADH4. While there are 18 genes encoding members of the ALDH enzyme family, only ALDH2 plays a major role in oxidizing acetaldehyde in the liver (Edenberg 2013). Here, ADH4 is linked to alcohol dependence.