A long-term study provides evidence that the genetic risk for schizophrenia is associated with lower IQ among people who do not develop this disorder.
Schizophrenia is a rare but serious psychiatric disorder, usually beginning in late adolescence, and is characterized by hallucinations, delusions, paranoia, cognitive impairment, social withdrawal, self-neglect and loss of motivation and initiative.
The study, published in Biological Psychiatry, involved data from 937 individuals in Scotland who first completed IQ testing in 1947, at age 11.
At age 70, their IQ was tested again, and their DNA was analyzed to estimate their genetic risk for schizophrenia.
The findings show that those 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 linked to 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.
“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,” said Andrew McIntosh, M.D., from the University of Edinburgh.
These findings suggest that common genetic variants may underlie both cognitive aging and the 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,” commented Dr. John Krystal, editor of Biological Psychiatry.
“However, we have yet to understand the development of cognitive impairments that produce disability in young adulthood, the period when schizophrenia develops for many affected people.”
More research is needed, but these new findings add to the growing and extensive effort to figure out how the gene variants that contribute to the development of schizophrenia give rise to the cognitive problems often associated with it.
Source: Biological Psychiatry