Because genetic factors had been implicated in the development of both alcoholism and smoking, and because some of these genetic factors were expected to overlap, COGA investigators performed a genomic screen for both disorders in families of alcoholics (Bierut et al, 2004). In these analyses, the degree of sharing between siblings was examined for 336 genetic markers from throughout the genome. The genomic screen identified several chromosomal regions that may contain genes influencing the development of habitual smoking but not of alcohol dependence. For example, two regions on chromosome 9 exhibited increased allele sharing among sibling pairs who were both habitual smokers; therefore, these regions may play a role in the development of this disorder. However, these regions showed no significant evidence of a genetic contribution to alcohol dependence—that is, they were not shared at rates greater than chance among pairs of alcohol-dependent siblings. Therefore, these regions likely contain genes that specifically influence the susceptibility to habitual smoking.
