New research has allowed investigators to assess the individual risk of developing a mental disorder if a brother or sister has been hospitalized for the same condition.
Researchers completed a large survey using data from all patients hospitalized in psychiatric wards in Israel, and matched the information to their siblings.
Investigators discovered similar risk profiles among siblings of patients with bipolar disorder.
Researchers explain that this is the first study to assess risk of developing any psychiatric diagnosis in siblings of all patients hospitalized for any type of mental disorder in an entire population.
The study finding were presented at the European College of Neuropsychopharmacology (ECNP) Congress in Vienna.
The lifetime chance of suffering a mental disorder is extremely high. It is estimated that each year 38.2 percent of the population suffers from a mental disorder, corresponding to 164.8 million persons affected in Europe, alone.
Experts have known that siblings of patients with major mental disorders have an increased risk of suffering from the same disorder, but until now the risks have not been quantified
In the new study, an international team examined the rates of mental disorders in the families of 6111 Israeli patients who had been hospitalized with schizophrenia, bipolar disorder, or depression.
They compared them to over 74,000 controls, age-and gender matched controls, taken from the Israeli Population Registry, which records all births, deaths, marriages, and divorces in the country.
By comparing the relative rates of mental disorders, they were able to show just how much more siblings are at risk of the same, and also other mental health conditions.
If a brother or sister has schizophrenia, a sibling has 10 times greater chance of themselves suffering from schizophrenia.
They also have six to eight fold increased chance of suffering from schizoaffective disorder, and seven to 20 times greater risk of suffering from bipolar disorder than the general population.
If a brother or sister suffers from bipolar disorder, then their siblings have four times greater chance of suffering from bipolar disorder, schizophrenia, and other psychiatric disorders.
“This is a large study which allows us to put meaningful figures on the risks of developing mental disorders after they have arisen in a brother or sister. The figures are quite striking, with 10-fold risk of developing schizophrenia, and similar risks once a sibling has developed bipolar disorder,” said lead researcher Mark Weiser, M.D.