Contrary to what was previously thought, schizophrenia is not a single disease but a group of eight genetically distinct disorders, each with its own set of symptoms, according to new research.
Experts hope the finding is a first step toward better diagnosis and treatment of psychiatric illness.
It is known that 80% of the risk of suffering from schizophrenia is inherited, but scientists have not been able to identify the specific genes for this condition.
In the latest research from Washington University School of Medicine in St. Louis, which analyzed the genetic influences of 4,000 people with schizophrenia, scientists identified distinct genes that contribute to eight different classes of the condition.
«Genes don’t act on their own,» said C. Robert Cloninger, one of the study’s principal investigators.
«They work like an orchestra at a concert, and to understand how they work you have to know not only who the members of the orchestra are but also how they interact.»
stronger in group
Cloninger and his colleagues matched precise DNA variations in people with and without schizophrenia with symptoms in individual patients.
In some patients with hallucinations or delusions, for example, the researchers matched genetic characteristics with the patients’ symptoms, showing that specific genetic variations interacted to create a 95% chance of suffering from schizophrenia.
In another group, disorganized language and behavior were found to be specifically associated with a set of DNA variations that resulted in 100% disease development.
Although individual genes have only weak and inconsistent associations with schizophrenia, groups of groups of interacting genes create an extremely high and consistent risk of the disease, on the order of 70% to 100%, the study concluded.
That makes it nearly impossible for people with those genetic variations to avoid the disease.
In all, the researchers identified 42 clusters of genetic variations that increase with schizophrenia risk.
«In the past, scientists have been looking for associations between individual genes and schizophrenia,» said Dragan Svrakic, co-investigator and professor of psychiatry at the University of Washington.
«When one study identified an association, no one else could replicate it.»
«What was missing was the insight that these genes don’t act independently. They work together to perturb the structure and function of the brain, and that leads to disease,» he explained.
Svrakic said that it was only when the research team was able to organize the genetic variations and symptoms of patients into groups that they realized how particular groups of DNA variations acted together to cause specific types of symptoms.
The researchers divided the patients according to the type and severity of their symptoms, such as different types of hallucinations or delusions, and other symptoms, such as a lack of initiative, trouble organizing thoughts, or a disconnect between emotions and thoughts.
The results indicated that the symptom profiles describe eight qualitatively distinct disorders based on genetic conditions.
The scientists say it could also change the approach to understanding the causes of other complex diseases such as heart disease, hypertension and diabetes.