The risk for developing schizophrenia may be signalled through tell-tale signs in IQ deficiency which could be picked up through intelligence tests, Irish researchers have discovered.

Researchers at NUI Galway and TCD have found that genetic variants associated with risk for schizophrenia and other psychotic disorders are also associated with performance on measures of IQ, memory and social cognition.

Professor of Psychology Gary Donohue of NUI Galway, who who was one of the researchers, said the findings supported the view that the genetics of schizophrenia and brain functioning overlap.

"The findings also raise the possibility that the risk of developing schizophrenia may be identified by changes in cognitive ability - tell-tale signs found in IQ, memory or social intelligence tests."

These cognitive defects, he said, often appear before the emergence of  symptoms of schizophrenia and can predict individual levels of disability.

"Understanding how genetic variants contribute to this aspect of disability is an important step towards understanding the underlying biology and developing better and more personalized treatments," Prof Donohue said.

Schizophrenia affects about one in 50 Irish adults. Treatments are available for this condition, but their success rates vary.

It is as yet unknown what causes schizophrenia.

The study, which was funded by Science Foundation Ireland and the Health Research Board, tested performance on a number of cognitive functions known to be affected in people with psychosis.

A total of 424 patients took part in the research, including 340 with schizophrenia or schizoaffective disorder, and 83 with bipolar or major depressive disorder with features of psychosis.

Patients were given individual scores based on their loading for genetic variants interacting with ZNF804A, a genetic variant identified with schizophrenia.

It was found that higher scores on this ZNF804A interaction pathway were linked to poorer performance on cognitive measurements, including both general cognitive ability and social intelligence.

The findings are published in the journal JAMA Psychiatry.