THE FREQUENCY and type of psychiatric abnormality in the relatives of schizophrenic patients is of critical importance in testing both genetic and psychogenic theories of the etiology of schizophrenia. A large number of studies over the years have found the prevalence of schizophrenia in the siblings of schizophrenic patients (index cases) to be many times greater than it is in the general population (the most common figure, uncorrected for risk age, is 8%, which is about eight times greater than the general population).
Lidz et al1 have concluded that schizophrenia in the index case is but the extreme of a spectrum of personality disorders found in the children of parents who have created a malignant psychotoxic developmental environment. In a study of 24 sibs of 18 adolescent or young adult hospitalized schizophrenic patients from upper-class socially intact families, these authors found
Pollack M, Woerner MG, Goldberg P, Klein DF. Siblings of Schizophrenic andPsychopathology and Gender Concordance. Arch Gen Psychiatry. 1969;20(6):652-658. doi:10.1001/archpsyc.1969.01740180036004