A person who is at greater risk for developing schizophrenia is more likely to experience a decline in IQ with age.
This may happen even if the person does not go on to develop the disorder, say scientists at the University of Edinburgh.
Schizophrenia is a rare but serious psychiatric disorder, usually beginning in late adolescence, and is characterized by hallucinations, delusions, paranoia, cognitive impairment, social withdrawal, self-neglect and loss of motivation and initiative.
It has been shown that genetic factors influence the development of the disorder.
“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 Aging and Cognitive Epidemiology.
Using genetic analysis techniques, the researchers compared the IQ scores of more than 1,000 people from Edinburgh. The participants were tested for general cognitive functions in 1947, at age 11, and again when they were about 70 years old.
The scientists analyzed the genes of the participants and calculated each person’s genetic likelihood of developing schizophrenia — even though none of the group had ever developed the illness.
Then the researchers compared the IQ scores of people with a high risk of developing schizophrenia to the scores of those with a low risk for the disorder.
The researchers found that there was no significant difference between IQ scores at age 11. However, they found that those with a stronger genetic risk of schizophrenia had slightly lower IQs at the age of 70.
Furthermore, the participants who had more genes linked to schizophrenia also had a greater estimated fall in IQ over their lifetime than those at lower risk for the disorder.
“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. It typically strikes in the teenage or early adult years and is associated with problems in mental ability and memory.
The study is published in the journal Biological Psychiatry.
Source: University of Edinburgh