Schizophrenia might in fact be a group of related but distinct genetic disorders - a study has identified specific gene clusters that can be linked to eight clinically different types of the psychiatric illness.
The findings could have implications for better targeted diagnosis and treatment for the condition.
'Genes don't operate by themselves', said Professor Robert Cloninger, one of the study's senior investigators. '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'.
The researchers at Washington University School of Medicine in the USA compared the DNA of 4,200 people with and 3,800 people without schizophrenia. They looked at areas of the genome where the DNA differed by one simple unit, these changes being known as single nucleotide polymorphisms (SNPs).
Taking a new approach, the researchers first identified sets of interacting SNPs that occur within individuals, not taking clinical status into account. They then looked at the risk of schizophrenia associated with each of these SNP sets and replicated their findings using two independent samples. Ultimately, they were able to test whether specific SNP sets were associated with distinct sets of clinical symptoms.
Surprisingly, they found that the symptom groups they created consisted of eight distinct schizophrenic disorders that were characterised by specific underlying genetic conditions.
For example, patients who displayed disorganised speech and behaviour were specifically associated with a set of genetic variations that carry, the researchers claim, 'a 100 percent risk of schizophrenia'.
'In the past, scientists had been looking for associations between individual genes and schizophrenia', said Dr Dragan Svrakic, who co-authored the study. 'When one study would identify an association, no one else could replicate it. What was missing was the idea that these genes don't act independently. They work in concert to disrupt the brain's structure and function, and that results in the illness'.
The idea that schizophrenia is a wholly or even predominantly genetic condition does not have universal support among psychiatrists. All the same, the researchers hope that one day schizophrenia will be regarded in much the same way as breast cancer is today - as not one disease but several, driven by different genes.
'Doctors today have tests to predict a woman's risk of some types of breast cancer, and other tests that help them select the most effective drugs', said a report in USA Today, paraphrasing Professor Cloninger.
'Those sorts of tests could be extremely helpful for people with schizophrenia, who often try two or three drugs before finding one that's effective'.
The study was published in The American Journal of Psychiatry.