Further analyses can also benefit from the apparent overlap in the genetic determinants of multiple traits. For example, our observations can guide downstream multivariate analysis as well as the construction of composite traits. Combining traits with a shared genetic component can result in composite traits with higher heritability than their component phenotypes [50], increasing power. Combining other trait groupings will likely be less helpful. In some cases, observed overlaps are persuasive, such as, for example, overlap in the genetic components related to the metabolic syndrome. For personality traits, our analyses imply that the facets defining each factor share major genetic determinants, and that the phenotypic organization of the facets into higher order factors is genetically rooted, an inference supported by direct analysis of genetic factor structure (see Table S3). Interestingly, we found no evidence for the simple notion that a shared genetic determinant can be responsible for both personality and cardiovascular traits. To account for the association, more complex hypotheses must thus be entertained, possibly involving shared environmental factors or gene–environment interactions.
