The pattern of illness in pairs of psychotic siblings.

The authors describe the results of a blind rediagnosis, with DSM-III criteria, of psychotic siblings who were originally diagnosed as schizophrenic when reported by Zehnder in 1940. The distribution in sibling pairs of patients meeting criteria for affective illness and schizophrenia differed significantly from chance expectation, suggesting that, from a familial perspective, the two disorders were not closely related. However, the distribution of patients diagnosed as having schizoaffective disorder resembled that found for schizophrenia and not affective illness. Using several sets of diagnostic criteria, the authors found a moderate degree of familial independence for paranoid and nonparanoid schizophrenia.