Objectives: This report seeks to evaluate the specificity of the familial liability to schizophrenia by examining in the relatives of the various proband groups the risk for affective illness (AI), anxiety disorders, and alcoholism.
Design: A case-controlled epidemiologic family study using DSM-III-R criteria.
Participants: Three hundred eighty-four index probands from a psychiatric case register, 150 unselected control probands from an electoral register and 2043 of their living and traceable relatives, of whom 1753 were personally interviewed.
Results: In personally interviewed relatives of schizophrenic probands, the lifetime risk for all AI (24.9% +/- 3.8%) or just bipolar AI (1.2% +/- 0.7%) was very similar to that found in interviewed relatives of controls (22.8% +/- 4.0% and 1.4% +/- 0.7%, respectively). However, the risk for all AI (49.7% +/- 12.9%) or bipolar AI (4.8% +/- 3.2%) was substantially increased in relatives of schizoaffective probands. A substantially higher proportion of relatives of schizophrenic vs control probands who had AI demonstrated psychotic--and specially mood-incongruent psychotic--symptoms when affectively ill. Neither the risk for anxiety disorders nor that for alcoholism was increased in relatives of schizophrenic vs control probands.
Conclusions: The familial liability to schizophrenia possesses some specificity and does not substantially increase the risk to AI, anxiety disorders, or alcoholism. Even when narrowly defined, schizoaffective disorder has a substantial familial link to classic AI. The familial liability to schizophrenia predisposes to psychosis, and especially mood-incongruent psychosis, when affectively ill. Finally, these results do not support the hypothesis that, from a familial perspective, schizophrenia and AI are on a single etiologic continuum.