RESUMO
BACKGROUND: It has been reported that relatives of probands with severe, psychotic forms of bipolar illness have increased rates of schizophrenia but not the relatives of individuals with milder, non-psychotic forms of disorder. In this study, we examined the prevalence of psychiatric disorders in the first degree relatives of a sample of 103 inpatients with bipolar disorder and in a matched control sample of 84 healthy individuals. METHOD: Relatives of cases and controls were interviewed using the FH-RDC to determine familial morbid risk for schizophrenia and bipolar disorder. Age- and sex-adjusted morbidity risks were calculated in both samples according to the method of Strömgren. RESULTS: The morbid risks for both bipolar disorder (4.9%) and schizophrenia (2.8%) were higher in relatives of patients than in relatives 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 of 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 psychotic features. CONCLUSION: Our results suggest that the transmission of psychosis is not disorder-specific. Bipolar illness characterised by a high familial loading is associated with increased risk of schizophrenia in the relatives.
