Researchers from the University of Edinburgh claim they have found a genetic link between people who inherit schizophrenia and those with low intelligence quotient scores (IQ).
"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," explained the study's lead researcher Dr. Andrew McIntosh, M.D.
Schizophrenia is considered a chronic brain disorder, in which the sufferer is unable to perceive reality as it is. In most cases it is accompanied by hallucinations, delusional thinking, and erratic behavior.
In 1911, psychiatrists Eugen Bleuler and Emil Kraepelin released Dementia Praecox or the Group of Schizophrenias, where the term schizophrenia was coined. The book is touted as the first comprehensive assessment of a schizophrenic mind.
Since Blueler and Kraepelin's preliminary analysis of schizophrenia, the dysfunction of cognitive abilities has always been considered a possible indicator of the psychiatric disorder. In fact, improving cognitive functions was the most promising form of treatment for schizophrenia in the 1990s.
The research team headed up by Mcintosh analyzed data from 937 people from Scotland who were around the age of 70. All participants had taken an initial IQ test when they were 11. DNA samples were drawn to establish each individual's current genetic risk of developing schizophrenia.
Study participants who recorded the lowest IQ scores were all shown to be genetically predisposed to developing schizophrenia. Researchers also noticed the presence of schizophrenia risk-related gene variants that could affect cognitive function.
"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," Dr. Macintosh added.
The study's findings were published in the Society of Biological Psychiatry's journal Biological Psychiatry.
"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, M.D., 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."
Source: McIntosh AM. Polygenic Risk for Schizophrenia Is Associated with Cognitive Change Between Childhood and Old Age. Biological Psychiatry. 2013