VIENNA – The brothers and sisters of patients hospitalized for schizophrenia, bipolar disorder, or unipolar depression are themselves at strikingly high risk of subsequently developing not only the same disorder as their sibling, but other forms of major mental illness as well, Mark Weiser, MD, reported at the annual congress of the European College of Neuropsychopharmacology.
He presented the results of the first comprehensive national population-based study to examine in this fashion the extent to which heritability contributes to schizophrenia and affective disorders. This nested case-control study included all siblings of 6,111 Israeli patients hospitalized for schizophrenia, schizoaffective disorder, bipolar disorder, or unipolar depression. The siblings’ rates of and reasons for subsequent psychiatric hospitalization were compared with those of 74,988 age- and gender-matched Israeli controls. All admission and discharge diagnoses were made by board-certified psychiatrists.
Siblings of individuals with schizophrenia were at 9.4-fold increased risk of subsequent hospitalization for schizophrenia, 8.5-fold relative risk for schizoaffective disorder, and 7.7-fold increased risk for bipolar disorder, compared with controls.
Moreover, siblings of patients with bipolar disorder were not only at 8.4-fold increased risk of subsequent hospitalization for that disease, they also were at 4.2-fold greater risk than controls for schizophrenia and 7.6-fold increased risk for hospitalization for other psychiatric disorders, a grab bag category that included anxiety disorders, dissociative disorder, post-traumatic stress disorder, eating disorders, pervasive developmental disorders, and personality disorders, according to Dr. Weiser, professor of psychiatry at Tel Aviv University.
Siblings of patients hospitalized for unipolar depression were at 6.2-fold relative risk of subsequent hospitalization for schizophrenia and 9.7-fold increased risk of hospitalization of other psychiatric disorders. “The bottom line of our study is it’s not a one gene/one disorder model. There’s not a gene for schizophrenia and a different gene for bipolar disorder. There are probably a bunch of different genes that increase the risk for schizophrenia but also increase risk for bipolar disorder, and the other way around,” the psychiatrist explained in an interview.
“Clinically it’s well known from the literature that if I have schizophrenia, there’s an increased chance that my brother will have it as well, so when my brother comes in having trouble, you obviously suggest that he might be developing schizophrenia. What these data imply is that if the brother of a schizophrenia patient comes in seeking help, it might not be schizophrenia, because he’s also at increased risk for bipolar disorder. So your index of suspicion should be much broader, not only for the one specific illness but for the whole idea of psychopathology in general. It’s a challenge. It demands for clinicians to be more broad-minded and to understand that these genes we’re looking for in large studies are not specific for one particular illness,” Dr. Weiser said.
This study was made possible because Israel, like Denmark, maintains multiple comprehensive national registries in which health care researchers are able to tap into and connect.
“A study like this can’t be done in the United States,” he said. “No how, no way.”
Dr. Weiser reported having no financial conflicts of interest regarding this study, which was conducted without external funding.