In the remarkable new study, Dr. Andrew McIntosh and his colleagues at the University of Edinburgh provide new evidence that the genetic risk for schizophrenia is associated with lower IQ among people who do not develop this disorder.
The authors analyzed data from 937 individuals in Scotland who first completed IQ testing in 1947, at age 11.
Around age 70, they were retested and their DNA was analyzed to estimate their genetic risk for schizophrenia.
The researchers found that individuals with a higher genetic risk for schizophrenia had a lower IQ at age 70 but not at age 11.
Having more schizophrenia risk-related gene variants was also associated with a greater decline in lifelong cognitive ability.
"If nature has loaded a person's genes towards schizophrenia, then there is a slight but detectable worsening in cognitive function between childhood and old age," McIntosh said.
"With further research into how these genes affect the brain, it could become possible to understand how genes linked to schizophrenia affect people's cognitive function," he said.
These findings suggest that common genetic variants may underlie both cognitive aging and risk of schizophrenia.
"While this study does not show that these common gene variants produce schizophrenia per se, it elegantly suggests that these variants may contribute to declines in intelligence, a clinical feature associated with schizophrenia," Dr. John Krystal, Editor of Biological Psychiatry said.