Significant progress has been made in identifying susceptibility loci and genes for addictions. Comparison of linkage peaks for addictions to various substances confirms what we have learned from genetic epidemiological studies, namely that genetic vulnerability to different substances in part overlaps. Variants in several genes, including aldehyde dehydrogenases, GABRA2, ANKK1, and neurexins 1 and 3, have been associated with addictions to multiple drugs. Most recently, variants of the CHRNA5/A3/B4 cluster on chromosome 15 were found by GWAS, as well as by targeted studies, to be associated not only with addictions to tobacco, alcohol, and cocaine, but with lung cancer as well. These genes have effects on nicotine responses in animal models and can thus be considered established targets for these studies. Nevertheless, the exact nature of the variants and their functions are still unknown. Functional studies as well as studies in other ethnic populations with different LD structure may be revealing. GWAS confirmation of candidate gene findings is reassuring, and similar to the robust findings in type II diabetes85 but in sharp contrast to GWAS results in other psychiatric disorders,
