In summary, COGA was the first study to screen the genome for regions involved in both alcohol dependence and habitual smoking. The findings provide evidence that some chromosomal regions are linked to both disorders, whereas other regions are specific to one of the disorders (see Table). Such linkage studies, however, can only examine markers that signal the proximity of genes contributing to a given disorder. Additional studies have already identified specific candidate genes that may contribute to alcohol and/or nicotine dependence. Such candidate gene studies are described in the following section.
