Despite ample evidence that psychiatric disorders involve dysfunctional brain systems, there are no biomarkers that can be used clinically to confirm a diagnosis or identify a given individual as at risk, and it is not clear that the candidate biomarkers that exist do a better job identifying cases than existing interview methods (although see (Clementz et al., 2015)). In addition, our understanding of the pathophysiology of psychiatric disorders remains fairly primitive. In the absence of a good theoretical framework regarding the mechanisms that give rise to abnormal behavior, it is difficult to develop hypotheses that generate new biomarker candidates, so much of the research conducted to date has involved an atheoretical empirical approach to biomarker discovery. Although this is true for endophenotypes as well as other biomarkers, the construct validity of a putative endophenotype is enhanced by the knowledge that psychopathology is heritable. Unlike other types of biomarkers which need only show an association to psychopathology to be elevated to candidate status, endophenotypes must show such association plus evidence that they are under genetic influence. As Table 1 indicates, these two criteria must be met for a biomarker to receive provisional consideration as an endophenotype.
