Objective: We sought to clarify the familial relationship between the nonschizophrenic, nonaffective psychoses (schizoaffective disorder [SAD], schizophreniform disorder, delusional disorder, and atypical psychosis) and schizophrenia and affective illness (AI).
Design: A case-controlled epidemiologic family study using DSM-III-R criteria.
Results: Compared with relatives of unscreened controls, the risk of nonschizophrenic, nonaffective psychoses was significantly elevated in relatives of probands with schizophrenia, SAD, schizotypal personality disorder, and psychotic AI. No significant elevation in risk to these disorders was seen in relatives of probands with nonpsychotic AI. The risk for SAD alone was significantly increased in relatives of probands with psychotic or bipolar AI.
Conclusions: The nonschizophrenic, nonaffective psychoses have a significant familial relationship with both schizophrenia and schizotypical personality disorder. Schizoaffective disorder, as defined by DSM-III-R, shares familial etiologic factors with at least some forms of AI.