PEOPLE who carry genes which put them at greater risk of suffering from schizophrenia are also more likely to see their IQ drop as they get older, Scottish research suggests.
Research published by the University of Edinburgh reveals the increased genetic risk of the condition seemed to affect a person’s intelligence, even if they did not go on to develop the condition.
The researchers hope that the results could lead to new research into how different genes for schizophrenia affect how the brain works over a lifetime.
The scientists said the results also showed that genes associated with the condition influenced people in other important ways besides causing the illness itself.
The latest genetic analysis techniques were used by the Edinburgh team to reach its conclusion on how thinking skills change with age.
The researchers compared the IQ scores of more than 1,000 people from Edinburgh who were tested for general cognitive functions in 1947, when the subjects were aged 11, and again when they were around 70 years old.
They 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.
The researchers, writing in the journal Biological Psychiatry, then compared the IQ scores of people with a high and those with a low risk of developing schizophrenia.
They found that there was no difference in the scores at the age of 11.
But the researchers did find that people with a greater genetic risk of schizophrenia had slightly lower IQs at age 70.
Those people who had numerically more genes linked to schizophrenia also had a greater estimated fall in IQ over their lifetime than those at lower risk.
Ian Deary, director of the University of Edinburgh’s Centre for Cognitive Ageing and Cognitive Epidemiology, and the man who led the research team, said: “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.”
Andrew McIntosh, of the University of Edinburgh’s Centre for Clinical Brain Sciences, added: “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.”
Schizophrenia – a severe mental disorder characterised by delusions and by hallucinations – is in part caused by genetic factors.
Other factors which trigger the condition could include brain damage at birth or in pregnancy, childhood abuse and the use of street drugs
The condition 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 Edinburgh study received funding from a number of bodies, including the charity Age UK and the Chief Scientist Office.
The University of Edinburgh’s Centre for Cognitive Ageing and Cognitive Epidemiology is funded by the Cross Council Lifelong Health and Wellbeing initiative.