Another approach that can be applied following the initial identification of a susceptibility gene is reverse phenotyping (Schulze et al., 2005; Rietschel et al., 2008). Reverse phenotyping systematically identifies the phenotypic features that show the strongest association with the genetic risk factor identified in genetic studies. It is of great interest to understand the spectrum (or cluster) of phenotypes that are associated with a specific genetic risk factor since this means that they are causally linked and that shared biological pathways contribute to their development. In the future, the genetic data may also be used to improve the definition of the phenotype in the clinical setting.
