What is the risk of developing a mental illness if a brother or sister is living with the condition? A recent study conducted in Israel is one of the first of its kind to quantify a potential genetic link for psychoses. It suggests that people who have a sibling with schizophrenia are up to 10 times more likely to develop the chronic mental illness themselves, Medical Daily reports.

Nearly 3.5 million Americans—or 1 percent of the total U.S. population—are currently diagnosed with schizophrenia, a long-term mental disorder characterized by a breakdown of thought processes and emotional responses to outside stimuli. Symptoms of the mental illness include hallucinations, delusions, disorganized speech and thinking, and significant social and workplace dysfunction. Although a lot of recent research has explored the science behind the schizophrenic brain, mental health experts still aren’t sure what exactly causes the condition.

For this latest study, researchers at Sheba Medical Center in Tel Aviv examined the siblings of more than 6,000 Israelis who were diagnosed and hospitalized with schizophrenia, bipolar disorder or depression. Researchers compared these individuals with almost 75,000 others who served as controls matched by age and gender. By comparing the relative rates of mental disorders in this select population, scientists were able to show the risk siblings shared of developing schizophrenia or other mental health conditions.

Ultimately, scientists found that people faced a 10-fold greater chance of suffering from schizophrenia if a brother or sister developed the mental illness. In addition, siblings included in the study were also 6 to 8 times more likely to suffer from schizoaffective disorder and 20 times more likely to develop bipolar disorder if their brother or sister had these illnesses.

“These results are important clinically, as they encourage mental health workers to be aware of the increased risk of psychiatric disorders in siblings of patients,” said lead study author Mark Weiser, PhD, MD, chairman of the department of psychiatry at Tel Aviv University. “These results can also be used by researchers studying the genetic underpinnings of mental disorders.”

The study supports other recent research that suggests chronic mental illnesses, such as schizophrenia, bipolar disorder and depression, may share a common genetic link.

To learn more about these studies, click here.