Many if not most putative endophenotypes have been identified through research that is atheoretical and empirically driven. This is not surprising given that we are searching for a biomarker that taps into genetic risk at a time when we have scant knowledge of genetic or biological mechanisms associated with psychopathology. As a consequence, articles listing requirements for endophenotype identification emphasize empirical criteria, not how to generate hypotheses regarding how best to specify their operational definition given existing theory because our theories are not refined enough to offer such precise specification (Vaidyanathan, Vrieze, & Iacono, 2015). Nevertheless, endophenotypes offer strong clues as to the pathophysiology of disorder; the utility of an endophenotype ultimately will derive from the insight it provides into underlying mechanisms. Once a candidate endophenotype has been shown to have demonstrable construct validity, the nomological net should be expanded to include the results of theory building research designed to identify the biological processes involved.
