February 26, 2013
2 min read
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Schizophrenia genes increased odds of IQ loss later in life

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Researchers reported that healthy people who are at greater genetic risk for schizophrenia are more likely to experience a decline in IQ as they age, even if they never develop the disorder.

“Retaining our thinking skills as we grow older is important for living well and independently,” study researcher Ian J. Deary, PhD, director of the University of Edinburgh’s Centre for Cognitive Ageing and Cognitive Epidemiology, said in a press release. “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 functions as they age.”

Deary and colleagues compared the IQ scores of 937 participants who were enrolled in the Lothian Birth Cohort in 1936. The cohort was tested for IQ when they were aged 11 years and again at 70 years using the Moray House Test. When the study participants were aged 70 years, they also completed an additional cognitive battery that included tests from the Wechsler Adult Intelligence Scale-Third Edition. None of the study participants were known to have schizophrenia.

The researchers also examined the cohort’s genes to calculate their likelihood of developing schizophrenia. An independent birth cohort from 1921 also was included in the analyses.

Comparing low- vs. high-risk participants, Deary and colleagues found that there was no significant difference in IQ at age 11 years, but those with a greater genetic risk for schizophrenia had slightly lower IQs at the age of 70 years. Those at greater risk also had a greater estimated decline in IQ over their lifetime vs. low-risk participants. The significant association between schizophrenia risk and change in cognitive ability was not fully replicated in the 1921 cohort.

The researchers noted that one limitation of the study is that the Moray House Test is not in common use today, and contemporary measures of cognitive ability have proved more accurate. Failure to replicate the findings in the 1921 cohort was another limitation, they wrote.

However, Deary and colleagues said the link between schizophrenia risk and IQ loss was found in a predominantly healthy population and was therefore not simply due to psychosis or its subsequent treatment.

“Cognitive aging is growing in importance as a personal, social, and economic burden on societies,” the researchers wrote. “It appears to be partly heritable; yet, the specific genes are elusive. This new clue to the location of some of the genetic variation in cognitive aging could aid the mechanistic understanding of both cognitive ability and schizophrenia and the link between them.”

Disclosure: The researchers report no relevant financial disclosures.