Additionally, gene–gene and gene–environment interactions are two pieces of information missing from the current map because of the small number of reported studies. We expect more results in these two areas will be published with the development of efficient algorithms and become important parts of the susceptibility map. It also is worth noting that half of the 48 ND loci were significantly associated with alcohol-related phenotypes, and ~30% were involved in illicit drug dependence (Supplementary Table 2), suggesting that the 60 genes on the ND map are good candidates for addiction studies of other drugs as well.
