A wealth of data suggests that common genetic pathways are involved in the development of alcohol and nicotine dependence. In addition to the large number of genes that likely contribute to these disorders, environmental factors, as well as interactions between genes or between genes and environmental factors, almost certainly also play a role. Indeed, several causal pathways may lead to either disorder or to both. Despite the complexity of these disorders, some findings regarding candidate genes have been replicated across studies and therefore appear robust. However, as advances in genetic technology have resulted in refined gene mapping techniques, it is equally important to identify refined phenotypes that distinguish the various pathways that lead to alcohol and nicotine dependence. The combination of clear distinctions among disease processes at the phenotypic level and the recent explosion in genetic technologies will dramatically increase researchers’ abilities to identify additional genetic factors as well as gene–environment interactions that contribute to alcohol and nicotine dependence.
