Increased morbid risk for schizophrenia in families of in-patients with bipolar illness

Background. It has been reported that relatives of probands with severe, ps ychotic forms of bipolar illness have increased rates of schizophrenia but not the relatives of individuals with milder, non-psychotic forms of disord er. In this study, we examined the prevalence of psychiatric disorders in t he first degree relatives of a sample of 103 inpatients with bipolar disord er and in a matched control sample of 84 healthy individuals. Method. Relat ives of cases and controls were interviewed using the FH-RDC to determine f amilial morbid risk for schizophrenia and bipolar disorder. Age- and sex-ad justed morbidity risks were calculated in both samples according to the met hod of Stromgren. Results. The morbid risks for both bipolar disorder (4.9% ) and schizophrenia (2.8%) were higher in relatives of patients than in rel atives of controls (0.3% and 0.6% respectively). The relative risks were 14 .2 [95% confidence interval (CI) = 3.1-64.2] for bipolar disorder and 4.9 ( 95% CI = 1.3-18.8) for schizophrenia. Relatives of women with early onset o f bipolar illness had the highest morbid risks for both bipolar illness and schizophrenia. The presence of more than one patient with bipolar disorder in a family increased the risk for schizophrenia nearly fourfold (RR = 3.5 , 95% CI = 1.2-10.2). There was no additional effect of presence of psychot ic features. Conclusion. Our results suggest that the transmission of psych osis is not disorder-specific, Bipolar illness characterised by a high fami lial loading is associated with increased risk of schizophrenia in the rela tives. (C) 2000 Elsevier Science B.V. All rights reserved.