Baysian approaches to these analyses suggest that the stronger the evidence for coheritabilities of substance dependence and these “related” phenotypes, the higher the likelihood that molecular genetic studies will demonstrate true overlaps [145]. We focus on phenotypes that display good evidence for heritability from classical genetic studies, including evidence that complex genetics plays substantial etiologic roles. We focus first on heritable phenotypes that co-occur with addictions at frequencies much greater than those that we would expect if they were independent of each other. For example, even though substance dependence and bipolar disorder are each common, the product of their population frequencies does not nearly explain the ca. 2/3 of bipolar individuals who report abuse of or dependence on an addictive substance [146, 147].
