The most commonly accepted criteria for a genetically influenced endophenotype include trait identification in an objective and quantitative manner in patients before onset of the disorder and/or periods of remission. State independence or longitudinal stability should be further established in longitudinal studies with repeated measures. Finally, epidemiological studies should be examined to determine whether the endophenotype co-segregates with SB in family members and is also found in non-affected family members at a higher rate than that in the general population. The endophenotype should therefore run in families and be associated with an increased risk of clinical illness. Such criteria are useful to distinguish endophenotypes from biological markers; the latter meet few of the above mentioned criteria and for this reason would likely not direct clinical research in psychiatry toward genetically meaningful conclusions. Our armamentarium used to assess endophenotypes includes, though is not limited to, neurophysiological, biochemical, endocrinological, neuroanatomical/imaging, cognitive and neuropsychological measures.17
