People with schizophrenia have high rates of rare genetic mutations which appear to disrupt the developing brain, according to a study released Thursday.
Individuals with the devastating mental condition have three and sometimes four times the number of rare genetic abnormalities that healthy individuals do, and more of them affect genes regulating brain function.
The abnormalities consist of duplicated or deleted strands of DNA and differ from person to person, so much so that the genetic fingerprint of the disease is unique for every individual.
"We speculate that most people with schizophrenia have a different genetic cause," said Mary-Claire King, professor of genome sciences at the University of Washington in Seattle, who collaborated on the study.
"The mutations are individually rare, but share consequences downstream."
Schizophrenia is a chronic psychiatric disorder that afflicts about one percent of the population. People with the illness suffer from hallucinations, delusions, feelings of persecution and disorganized thinking.
Some of the symptoms can be managed with anti-psychotic medications, but there is no cure.
Prior to the publication of this study in Science, it was assumed that genetic studies like this one would trace the origins of the illness back to a cluster of common, or high frequency, genetic mutations.
But this paper suggests the genetic signature of schizophrenia, much like autism, is more complicated than that, involving dozens or even hundreds of genes, whose function has been disrupted by duplications or deletions of DNA.
For this paper, the researchers from University of Washington, Cold Spring Harbor Laboratory in New York and the National Institutes of Health studied a relatively modest number of people: 150 individuals with schizophrenia and 268 healthy patients.
The study implicated 24 different genes in the disease, and yet virtually every single mutation or copy number variation was different, which suggests that studies of larger populations will implicate even larger number of genes.
Many copy number variations are benign, but the researchers looked only at rare abnormalities, and not only were they much more abundant in the people with the disorder, but a preponderance of them were in genes that affect communication between brain cells.
Specifically, 15 percent of schizophrenia patients who developed the illness as adults had these rare DNA errors versus just five percent of healthy controls.
The rate jumped to 20 percent among patients who had a more severe form of the illness that began in childhood or adolescence.
"This is an important new finding in the genetics of schizophrenia," said Thomas Insel, director of the National Institute of Mental Health.
"Identifying genes prone to harbouring these mutations in brain development pathways holds promise for treatment and prevention of schizophrenia, as well as a wide range of other neurodevelopmental brain disorders."