The largest study ever undertaken into the genetic basis of mental illnesses has found more than 100 genes that play some kind of role in the development of schizophrenia – one of the most common of the serious psychiatric disorders.

Scientists believe they are closer than they have ever been to understanding the complex interplay between genes and upbringing that can result in some people being at high risk of developing schizophrenia, which usually strikes in late adolescence or early adulthood.

Schizophrenia affects about one in every 100 people and is marked by hallucinations and delusions where patients hear voices or believe that other people are trying to control or read their minds, causing fearfulness, withdrawal and extreme agitation.

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The identification of the precise locations in the human genome that are involved with the illness could lead to both a fundamental understanding of its causes as well aid the development of new treatments or drugs, the researchers said.

The huge international study by the Schizophrenia Working Group of the Psychiatric Genomics Consortium analysed the DNA of about 37,000 schizophrenia patients and compared the smallest mutations to those found in about 113,000 healthy people.

The scientists identified about 128 independent genetic variants at 108 locations on the human chromosomes that contribute significantly to susceptibility to schizophrenia – 83 of these sites have never before been linked to the illness, the scientists said.

“By studying the genome, we are getting a better handle on the genetic variations that are making people vulnerable to psychiatric disease,” said Tom Insel, director of the US National Institute of Mental Health, which co-funded the study.

It is estimated that schizophrenia costs the UK taxpayer about £2bn a year in care and treatment, with further unquantified personal costs for patients and family members. The global drugs bill alone is estimated to be £12.5bn a year, not including hospital stays.

Michael O’Donovan, professor of psychiatric genetics at the Medical Research Council’s neurogenetics centre at Cardiff University said after years of resistance by some medical professionals to the idea of a genetic basis for schizophrenia, the latest study proves it beyond doubt.

“It is absolutely crystal clear now that genetics is involved in schizophrenia and although the biological implications of the genetics are not yet clear, we’re beginning to see patterns emerging from the data,” Professor O’Donovan said.

“The big picture is that large collaborations like this into schizophrenia has the capacity to crack the illness open in the same way that similar studies have done to other diseases with a genetic basis,” he said.

Some of the genes identified by the study, which is published in the journal Nature, are known to be involved with controlling the production of dopamine, a neurotransmitter in the brain that was long suspected of playing a role in the illness.

Other genes are involved with glutamate, another important neurotransmitter, while a few of the newly identified genes play a role in acquiring immunity to infections, which fits with the idea that exposure to viruses in early life may increase a person’s susceptibility to the illness.

Professor O’Donovan said that genes contribute to between about a third and one half of the risk of developing schizophrenia and he would not be surprised if further research involving genome-wide studies reveals up to 1,000 genes that are linked to disease susceptibility.

“The wealth of new findings has the potential to kick-start the development of new treatments in schizophrenia, a process which has stalled for the last 60 years,” he said.