New data from researchers at the University of Oxford has shown that a modified form of the dyslexia susceptibility gene, KIAA0319—found in many dyslexic individuals—is also a common biological factor among those who suffer from reading difficulties within the general public.
The Wellcome Trust’s Dr Silva Paracchini, lead author of the report published in The American Journal of Psychiatry this month said that the new findings are, “clearly only part of the jigsaw puzzle that explains why some people have poorer reading ability than others or develop dyslexia.
“There are likely to be many other factors, but our research provides some valuable clues.”
Dyslexia is characterized by difficulties with phonological recognition, rapid naming, operational memory, processing speed, and the mechanical growth of skills that effect an individual’s development of literacy and language recognition.
Variations in the dyslexia susceptibility gene, which is found on the sixth human chromosome, have been identified in three separate studies as major factors in the disorder. Dr Paracchini's team has now found a link between one such variant, which is carried by 15 per cent of the population, and general reading facility.
It has previously been demonstated that this variant, or haplotype, includes an inhibitor that limits the expression of the KIAA0319 gene and slows its maturation in foetuses. As a result, the area of the brain responsible for thought processes, the cerebral cortex, is affected during the stages of development within a mother’s womb.
Dr Paracchini said: “On average, people carrying this common genetic variant tended to perform poorly on tests of reading ability.
“However, it’s important to note that this is only true for reading ability and not for IQ, so it doesn’t appear to be connected to cognitive impairment.”
Over the past three years, six genes have been identified and linked to the development of dyslexia and reading issues. In 2005, paediatric researchers at Yale School of Medicine identified a link between variations in the DCDC2 gene of chromosome six and problems with letter and word recognition.
The Vice President of the British Dyslexia Association, Professor Margaret Snowling, was enthusiastic about Dr Paracchini's findings, saying: “The discovery of a genetic association with reading ability in the general population as well as in dyslexia is in line with our observation that there are degrees of dyslexia from mild to severe.
“It also implies that other genes or environmental experiences must be involved in determining reading ability. This ties in with what we have known for many years – many individuals are able to compensate and go on to successful careers even though they carry this gene variation”.