Additional follow-up of the linkage signals observed across the three phenotypes in COGA suggested that it was not simply the same individuals contributing to the results across the phenotypes; for example, only half of the individuals who had attempted suicide also had alcohol dependence, and only 25% of the individuals with alcohol dependence have childhood conduct disorder. To the extent that these phenotypes represent an underlying liability to behavioral disinhibition, considering these phenotypes jointly in linkage analyses, rather than analyzing each individually, should enhance the power to detect linkage if there is a gene (or genes) in the region that is predisposing to this broad constellation of psychiatric outcomes. Further, to the extent that AD characterized by suicide attempts and conduct disorder may represent a more homogeneous and heritable form of the disorder, considering a combined phenotype would also increase our power to detect linkage.
