WASHINGTON, Sept. 19 (Xinhua) -- A team of over 250 researchers from more than 20 countries have discovered that common genetic variations contribute to a person's risk of schizophrenia and bipolar disorder.
The study of more than 50,000 adults aged 18 and older provides new molecular evidence that 11 DNA regions in the human genome have strong association with these diseases, including six regions not previously observed. The researchers also found that many of these DNA variants contribute to both diseases.
The findings, reported by the Psychiatric Genome-Wide Association Study Consortium (PGC) and published this week in two papers in the journal Nature Genetics, represent significant advances in understanding the causes of these chronic, severe, and debilitating disorders.
"This is the largest study of its kind by far," said Patrick Sullivan, a PGC coordinator and professor of genetics at the University of North Carolina at Chapel Hill.
The study that focused on schizophrenia identified "strong evidence for seven different places in the human genome, five of which were new and two previously implicated, that contain DNA changes that are significantly associated with schizophrenia," Sullivan said in a statement.
In a joint analysis of a schizophrenia and bipolar disorder sample, the Consortium found three different DNA regions, or loci, in which both disorders reached genome-wide statistical significance. "This tells us that these disorders, which many of us have considered to be separate things, actually share fundamental similarity," Sullivan said.
Schizophrenia and bipolar disorder are common and often devastating brain disorders. Some of the most prominent symptoms in schizophrenia are persistent delusions, hallucinations and cognitive problems. Bipolar disorder (or manic-depressive illness) is characterized by episodes of severe mood problems including mania and depression. Both affect about one percent of the world's population and usually strike in late adolescence or early adulthood.
Despite the availability of treatments, these illnesses are usually chronic, and response to treatment is often incomplete leading to prolonged disability and personal suffering. Family history, which reflects genetic inheritance, is a strong risk factor for both schizophrenia and bipolar disorder, and it has generally been assumed that dozens of genes, along with environmental factors, contribute to disease risk.