Paris: Schizophrenia is caused by a large number of rare genetic mutations rather than a few, easily-identifiable faulty genes, said scientists who compiled the world's largest database on the debilitating disorder.
Two studies published Wednesday in the journal Nature said the genetic triggers for the mental illness that affects about one in 100 people were far more complex than previously thought.
Gathering data from nearly 7,000 people in Bulgaria and Sweden, two teams of scientists said genes implicated in schizophrenia worked in clusters to disrupt specific proteins.
They tend to be part of gene networks that govern signalling between brain cells, or deal with learning and memory, the researchers said.
The "finding is sobering but also revealing: it suggests that many genes underlie risk for schizophrenia and so any two patients are unlikely to share the same profile of risk genes," said Shaun Purcell of the Broad Institute in Massachusetts.
"These types of studies should provide a firm base from which we can chart a course toward the ultimate goal of subtyping patients and offering a more personalised treatment path than the one-size-fits-all approach currently used."
One of the studies compared the genetic sequences of 2,500 schizophrenia patients in Sweden with the same number of healthy individuals, looking for sites and patterns of mutations.
The other compared the gene sequences of more than 600 sufferers and their parents in
"Both studies yielded further evidence that the disorder arises from the combined effects of many genes -- a condition known as 'polygenicity'," said a Broad Institute statement.
"The studies also suggest that genetic alterations tended to cluster in a few networks of functionally-related genes."
Schizophrenia is a chronic, often debilitating illness, afflicting about 2.4 million adults in the United States alone.
Symptoms include hallucinations, delusions and paranoia.