Schizophrenia is actually eight genetically distinct disorders, study reveals

Scientists have identified eight separate clusters of genetic variations that, together, carry a 70 to 100 percent risk of a patient developing a certain type of schizophrenia.

The discovery could revolutionise diagnosis and treatment for the debilitating psychiatric illness. Scientists already knew that around 80 percent of the risk of schizophrenia is inherited, but have struggled for decades to identify specific genes linked to the condition. 

But a new approach has analysed the DNA of more than 4,000 people with the illness, and have identified that there are actually eight different classes of schizophrenia, each influenced by distinct gene clusters.

The research was led by scientists from the Washington University School of Medicine in St Louis in the US.

“Genes don’t operate by themselves,” said C. Robert Cloninger, one of the senior investigators, in a press release. “They function in concert much like an orchestra, and to understand how they’re working, you have to know not just who the members of the orchestra are but how they interact.”

To unravel these interactions, the scientists analysed the DNA variations between 4,200 people with schizophrenia and 3,800 people without the disease. They also matched these DNA variations to specific symptoms in individual patients.

After looking at 700,000 small changes in DNA, known as single nucleotide polymorphism (SNP), the scientists mapped which changes influenced which symptoms, and patterns began to emerge.

For example, in patients with hallucinations or delusions, they identified specific genetic variations that led to a 95 percent certainty of schizophrenia. And for patients who have disorganised speech and behaviour, they found a separate group of DNA variations that carried a 100 percent schizophrenia risk.

Overall, despite no single genetic changes being strongly linked to the disease on their own, the eight clusters the scientists identified all carried a 70 to 100 percent risk of developing schizophrenia. The results are published in The American Journal of Psychiatry.

As the press release explains, this makes it almost impossible for people with these genetic clusters to avoid the condition.

“What we’ve done here, after a decade of frustration in the field of psychiatric genetics, is identify the way genes interact with each other, how the ‘orchestra’ is either harmonious and leads to health, or disorganised in ways that lead to distinct classes of schizophrenia,” said Cloninger.

The scientists also went a step further and replicated their findings in two additional DNA databases of people with schizophrenia.

This work could now help researchers find targets for new drugs that could treat specific schizophrenia symptoms. And their DNA mapping technique could also be applied to help scientists find gene clusters that influence other diseases, such as cardiovascular disease and cancer.