unaffected relatives are presumably at elevated risk for developing a heritable disorder, they should score midway between probands and healthy comparison subjects. These patterns should be evident in all first-degree affected and unaffected relatives - parents, siblings and offspring. Given that the genetic liability for a clinical phenotype is shared by a candidate endophenotype, shared genetic influence should be evident. The same genetically informative samples that are used to establish the heritability of an endophenotype can often also be used to establish the degree to which genetic covariance is shared across the endophenotype and the clinical phenotype.
