People at greater genetic risk of schizophrenia could see a fall in IQ as they age, study shows.
Scientists at the University say IQ decline in those at risk could happen even if they do not develop schizophrenia.
The findings could lead to new research into how different genes for schizophrenia affect brain function over time. Schizophrenia -- a severe mental disorder characterised by delusions and by hallucinations -- is in part caused by genetic factors.
The researchers used the latest genetic analysis techniques to reach their conclusion on how thinking skills change with age.
"Retaining our thinking skills as we grow older is important for living well and independently. If nature has loaded a person's genes towards schizophrenia, then there is a slight but detectable worsening in cognitive functions between childhood and old age," said Professor Ian Deary, Director of the University of Edinburgh's Centre for Cognitive Ageing and Cognitive Epidemiology.
They compared the IQ scores of more than 1,000 people from Edinburgh.
The people were tested for general cognitive functions in 1947, aged 11, and again when they were around 70 years old.
The researchers were able to examine people's genes and calculate each subject's genetic likelihood of developing schizophrenia, even though none of the group had ever developed the illness.
They then compared the IQ scores of people with a high and low risk of developing schizophrenia.
Scientists found that there was no difference at age 11, but people with a greater genetic risk of schizophrenia had slightly lower IQs at age 70.
Those people who had more genes linked to schizophrenia also had a greater estimated fall in IQ over their lifetime than those at lower risk.
"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," said Professor Andrew McIntosh, Centre for Clinical Brain Sciences.
Schizophrenia affects around 1 per cent of the population, often in the teenage or early adult years, and is associated with problems in mental ability and memory.
The study, which was funded by the BBSRC, Age UK, and the Chief Scientist Office, is published in the journal Biological Psychiatry.
The University's Centre for Cognitive Ageing and Cognitive Epidemiology is funded by the Cross Council Lifelong Health and Wellbeing initiative.
- Andrew M. McIntosh, Alan Gow, Michelle Luciano, Gail Davies, David C. Liewald, Sarah E. Harris, Janie Corley, Jeremy Hall, John M. Starr, David J. Porteous, Albert Tenesa, Peter M. Visscher, Ian J. Deary. Polygenic Risk for Schizophrenia Is Associated with Cognitive Change Between Childhood and Old Age. Biological Psychiatry, 2013; DOI: 10.1016/j.biopsych.2013.01.011
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