Low IQ may signal schizophrenia risk

Scientists have found evidence that the genetic risk for schizophrenia is associated with lower IQ among people who do not develop this disorder.
The relationship between the heritable risk for schizophrenia and low intelligence quotient(IQ) has not been clear.
Schizophrenia is commonly associated with cognitive impairments that may cause functional disability.
There are clues that reduced IQ may be linked to the risk for developing schizophrenia. For example, reduced cognitive ability may precede the onset of schizophrenia symptoms.
Also, these deficits may be present in healthy relatives of people diagnosed with schizophrenia.
In a new study by the University of Edinburgh, published in journal Biological Psychiatry, the authors analysed 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 analysed 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," said study author Dr Andrew McIntosh.
"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," McIntosh added.

These findings suggest that common genetic variants may underlie both cognitive ageing 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," Krystal said.