Familial Overlap between Bipolar Disorder and Psychotic Symptoms in a Canadian Cohort

Background: Although they were once considered separate nosologic entities, there is current interest in the etiologic overlap between bipolar disorder (BD) and schizophrenia. A critical issue concerns the familial basis of the overlap, specifically, the possibility of a distinct familial subtype of BD with psychotic features. Methods: We recruited individuals with BD from the community and compared them with a matched group diagnosed with no mental disorder to confirm familial aggregation for BD, schizophrenia, and psychotic symptoms. We then compared BD probands both with and without first-degree relatives with psychotic symptoms on several clinical indicators to determine the specificity of the familial aggregation. Results: As expected, there was evidence for familial aggregation of schizophrenia and psychotic symptoms in families having probands with BD. Familial loading for schizophrenia and psychotic symptoms was especially notable in male relatives of female probands with BD. We found no differences in the clinical profile of probands with BD stratified for familial loading for psychotic symptoms. Conclusions: Findings from this sample support etiologic theories arguing for a shared but nonspecific genetic etiology for BD and schizophrenia, with psychotic symptoms being a potential key indicator for genetic studies.