SINGAPORE - Researchers trying to find a breakthrough in treating schizophrenia can now better narrow down the areas to work on.

A global team that includes researchers from the Institute of Mental Health (IMH) and the Agency for Science, Technology and Research (A*Star) here has identified 287 regions of the human DNA that harbour genes which predispose one to schizophrenia.

The genomic study is the largest of its kind, said IMH and A*Star's Genome Institute of Singapore in a joint release on Thursday (April 7).

This paves the way for more targeted research in the ongoing quest to find a novel treatment that would allow more people with the severe and highly complex mental illness to live a normal life, said the researchers at IMH.

Schizophrenia is characterised by not just psychotic symptoms like hallucinations and delusions, but also by cognitive impairments and other symptoms.

In Singapore, a nationwide study found last year that schizophrenia is most common among the psychotic disorders here, affecting one in 116 people (it is one in 100 globally). The illness is associated with an elevated risk of suicide, serious physical illnesses and a reduced life expectancy.

Epidemiological studies have shown that schizophrenia tends to run in families, but scientists do not really understand the exact cause of the disorder, which has affected efforts to find more effective treatments.

In the global study, scheduled to be published in journal Nature, the researchers at the global Psychiatric Genomics Consortium showed that apart from the genomic regions, the genes associated with schizophrenia risk tend to be concentrated in brain cells called neurons, suggesting that it is the biological role of these brain cells that is key to understanding the illness.

They also discovered that two rare variants that significantly increase schizophrenia risk were linked to autism and other neuro developmental disorders, which shows the shared genetic risk among these psychiatric disorders.

In a sister paper, researchers discovered 10 genes with rare mutations that increase a person's chance of developing schizophrenia by 10 to 50 per cent, when the general lifetime risk is under 1 per cent.

"These biological processes have previously been speculated to be theoretically related to schizophrenia - this study is seminal in the sense that the DNA data analyses provided real evidence from real data to show it," said Dr Max Lam, a research fellow at IMH.

"The ultimate goal of conducting genomic research is in fact the hope that we can administer the right treatment to the right patient at the right time."

The findings stem from the work of hundreds of researchers across 45 countries. Over 13 years, they collected and analysed DNA samples from 76,755 people with schizophrenia and 243,649 without it.

Singapore contributed 3,741 samples, including 1,752 from people with schizophrenia.

Dr Jimmy Lee, a senior consultant at IMH's department of psychosis and research division, said the absence of living brain tissues has made it hard for clinicians and scientists to advance their understanding of mental illnesses.

This feat of a study was made possible only with the rise of human genomics technology more than a decade ago, when researchers realised that they could study brain function indirectly via the human DNA.

"Deciphering DNA codes for the structure of neurons and how they "talk" to each other in the brain is equivalent to putting together a jigsaw puzzle to understand behaviour," he added in the release.

Speaking to The Straits Times, he said antipsychotic drugs, which are the mainstay of treatment for schizophrenia, are effective in alleviating the so-called positive symptoms such as delusions and hallucinations.

"We just don't know, out of more than 70 different medications, who will respond to which medications," he added.

And about one-third of patients do not respond to treatments.

"Additionally, cognitive impairment and negative symptoms (such as social withdrawal), also core symptoms in schizophrenia, to date have no efficacious medical treatments and exact significant burden on patients and their caregivers," he noted.

Understanding the biology of the illness will allow scientists to develop different kinds of treatments, he added.

Most people with schizophrenia exhibit symptoms when they are below age 30, and they require long-term treatment.