Schizophrenia: Brotherly Divided

29. November 2016
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Genetic factors play an important role in mental illnesses such as schizophrenia. A major study has now investigated the risk of disease for siblings of those affected. Conclusion: physicians should be more aware of the increased risk.

The risk of developing a mental disorder is high: a recent study estimates that each year 38 percent of the population in the European Union is affected by a mental illness – this adds up to 164.8 million people. The most common disorders are anxiety disorders, sleep disorders, depression, somatoform disorders and alcohol or drug addiction. This relatively high number is also due to the fact that for the first time the study took into account instances of these medical conditions during childhood and adolescence, as well as those during advanced age.

In order to estimate the influence of genetic factors in a disease, the risk of disease is investigated among direct relatives – in particular among parents and children or monozygotic and dizygotic twins. However among siblings of patients with severe mental disorders the risk of disease is found to be elevated as well. Hence the relatives of schizophrenic patients have higher risk for the disease itself, as well as for schizophrenia-related disorders.

Nevertheless, there exist hardly any comprehensive studies which have estimated the level of disease risk among siblings. Now a research team has for the first time taken all patients who had been in treatment due to a severe mental disorder in one country into one study* and examined the siblings’ risk of also developing some form of mental illness.

Data of patients from all over Israel

The research team led by Mark Weiser from Sheba Medical Center in Ramat Gan (Israel) examined the rate of mental illness among the siblings of 6,111 Israeli patients treated for schizophrenia, bipolar disorder or depression in a psychiatric hospital or outpatient clinic. They compared these with about 74,900 control subjects who in terms of age and gender distribution were comparable to the study group. The data from the control group came from the Israeli Population Registry in which all births, deaths, marriages and divorces in the country are recorded.

Researchers from King’s College London and from the Hospital Clinic in Barcelona also participated in the study. The results were presented by the research team at the Congress of the European College of Neuropsychopharmacology in Vienna.

Elevated risk among siblings with schizophrenia and bipolar disorder

If a brother or sister suffers from schizophrenia, the siblings in the general population had a 10-fold increased risk of also developing schizophrenia. They also had a 6 to 8-fold increased risk of developing a schizoaffective disorder, and a 7 to 20-fold increased risk of developing bipolar disorder.

What’s more if a patient has been treated for bipolar disorder, the siblings also had an increased risk: their risk of developing bipolar disorder, schizophrenia or some other psychiatric disorder was four times as high as in the general population. Siblings of patients who underwent depression treatment also had an increased risk of schizophrenia and other psychiatric disorders. Among the other mental disorders that were recorded in the study were anxiety disorders, adjustment disorders, post-traumatic stress disorder (PTSD), eating disorder, dissociative disorders, developmental and personality disorders.

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The risk of developing a particular mental disorder among siblings of patients with schizophrenia compared with the general population (matched by age and gender). © Mark Weiser, Sheba Medical Center, Israel

Results are important for clinical practice

“This is a large, representative study which provides meaningful figures about the risk of mental illness in siblings when their brothers or sisters suffer from certain mental disorders”, says Weiser. “The numbers are pretty impressive, with a 10-fold increased risk for schizophrenia if a sibling has been diagnosed with the disorder”.

The results are also important for clinical practice, Weiser emphasises. “They encourage healthcare professionals working with psychiatric patients to be more aware of the risk of mental disorders for patients’ siblings”. Doctors might, for example, be able to recognise early warning symptoms in relatives of patients sooner and to react to them more promptly.

Furthermore, the results could also be beneficial for researchers who are occupied with finding the genetic causes of mental illness, according to Weiser. “It [the data] suggests that the same genes are associated with an increased risk for several mental illnesses”.

Mental disorders are often genetic “relatives”

Specialists assume that most mental illnesses originate from the interaction of genetic susceptibility and environmental stressors – such as a severe trauma in childhood or a strong stress. That a significant genetic influence plays a part in major psychiatric disorders is something already known from previous studies. Thus the risk of developing schizophrenia amounts to 13 percent when one parent is affected by the condition – compared to one percent in the general population. First-degree relatives of bipolar patients when compared to the general population have a ten-fold increased risk of developing the condition themselves, and a three-fold increased risk of developing depression. And in the case of depression, heredity is estimated at 35 percent.

It seems the same risk genes play a role with diverse mental disorders: there are significant genetic overlaps between schizophrenia, bipolar disorder and depression. Recent studies additionally show that genetic risk factors with both schizophrenia and bipolar disorders are related to anatomical differences in the brain, which could in turn favour the occurrence of diseases.

* on the accessed page provide the abstract title “Risk of psychiatric disorders in siblings of patients diagnosed with schizophrenia or affective disorders”

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