In order to be considered as an endophenotype, several criteria must be met [43]: 1) the endophenotype must be associated with illness in the population, 2) the endophenotype must be heritable, 3) the endophenotype must be primarily state-independent (manifests in an individual whether or not illness is active), 4) within families, endophenotype and illness co-segregate, and 5) the endophenotype must be found in affected family members, and must also be found in non-affected family members at a higher rate than in the general population. Endophenotype-based strategies have successfully identified genes associated with many psychiatric disorders.
