New research shows that schizophrenia is not a single disease, but a group of eight distinct disorders, each caused by changes in clusters of genes that lead to different sets of symptoms.
The finding sets the stage for scientists to develop better ways to diagnose and treat schizophrenia, a mental illness that can be devastating when not adequately managed, says C. Robert Cloninger, co-author of the study published today in the American Journal of Psychiatry.
"We are really opening a new era of psychiatric diagnosis," says Cloninger, professor of psychiatry and genetics at the Washington University School of Medicine in St. Louis. Cloninger says he hopes his work will "allow for the development of a personalized diagnosis, opening the door to treating the cause, rather than just the symptoms, of schizophrenia."
Clonginger and colleagues found that certain genetic profiles matched particular symptoms. While people with one genetic cluster have odd and disorganized speech – what is sometimes called "word salad" – people with another genetic profile hear voices, according to the study, funded by the National Institutes of Health.
Some genetic clusters gave people higher risks of the disease than others, according to the study, which compared the DNA of 4,200 people with schizophrenia to that of 3,800 healthy people.
One set of genetic changes, for example, confers a 95% chance of developing schizophrenia. In the new study, researchers describe a woman with this genetic profile who developed signs of the disorder by age 5, when she taped over the mouths of her dolls to make them stop whispering to her and calling her name. Another patient – whose genetic profile gave her a 71% risk of schizophrenia – experienced a more typical disease course and began hearing voices at age 17.
The average person has less than a 1% risk of developing schizophrenia, Cloninger says.