Low IQ Increases Genetic Risk for Schizophrenia

First Posted: May 16, 2013 11:27 AM EDT

A new study gives an in-depth look into clues that may actually link a schizophrenia to a reduced IQ. As previous studies have shown that it is commonly associated with cognitive impairments that may cause functional disability, reduced cognitive ability may not necessarily be an indicator of the problem.

The study, led by Dr. Andrew McIntosh and colleagues at the University of Edinburgh, provides new evidence that there may be a genetic risk for schizophrenia that is associated with lower IQ among people who do not develop the 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. 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 McIntosh.

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," 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."

However, researchers also note that more studies need to be conducted in order to determine and understand how the gene variants contribute to the development of the disorder.

The findings for the study are published in the journal Biological Psychiatry

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