• Family studies have played a central role in the controversy over the nosologic status of paranoid psychosis or delusional disorder (DD). In this study, 12 cases of DD were blindly rediagnosed from a cohort of 146 schizophrenics. The prevalence of schizophrenia in the relatives of the DD probands was significantly less than that found in the relatives of the schizophrenics. Affective illness was equally uncommon in both groups of relatives. Inferiority feelings clustered significantly in the relatives of the DD probands. From a familial perspective, DD is not closely related to schizophrenia or affective illness but does have a familial link to inferiority feelings. Investigators should take cognizance of the entity of DD as one possible source of heterogeneity within "schizophrenia."
Kendler KS, Hays P. Paranoid Psychosis (Delusional Disorder) and SchizophreniaA Family History Study. Arch Gen Psychiatry. 1981;38(5):547-551. doi:10.1001/archpsyc.1980.01780300059007