Because the data presented in the previous section suggested some interaction of vulnerability factors for alcoholism and depression, the COGA investigators performed genetic linkage analyses using DNA samples from sibling pairs with the AAD, AorD, and DEP phenotypes in order to identify chromosomal regions linked to these phenotypes. In the sibling pairs, both siblings had the phenotype under investigation. This analysis included 224 AAD pairs (57 percent male), 1,359 AorD pairs (56 percent male), and 440 DEP pairs (49 percent male). The AorD phenotype is the most inclusive because it refers to people with either the ALC or DEP phenotypes. Most of the sibling pairs added to the ALC data set to generate the AorD data set (59 percent of all added pairs and 94 percent of the mixed gender pairs) consisted of an alcoholic brother with a depressed sister.
