The genetic analyses demonstrated evidence for linkage of the AorD phenotype with a region on chromosome 1, and the same region also showed evidence, though less substantial, of linkage with the ALC phenotype. This chromosome 1 region also showed possible linkage with mania and depression among the participants in the NIMH Genetics Initiative Bipolar Study (Rice et al. 1997). Preliminary results suggested that this finding may be accounted for by families in which the probands have both alcoholism and mania. Thus, although the interpretation of linkage results in complex diseases is the subject of ongoing controversy and must be done cautiously, it appears likely that a locus on chromosome 1 accounts for some of the familial aggregation of alcoholism and depression in the COGA study. The findings suggest that this region contains one or more genes associated with different clinical phenotypes (e.g., alcoholism, depression, and mania), a phenomenon called pleiotropy.
