LONDON The common genetic variation linked to dyslexia may also help explain why some people without the learning difficulty are not good readers, researchers said on Wednesday.
The finding also points to the gene most likely to be involved in dyslexia among a handful of candidates, said Silvia Paracchini of the Wellcome Trust Center for Human Genetics in Oxford, who led the study.
She stressed the variation does not appear to impair cognitive development and is related to reading ability, not intelligence.
"This is the first time this same genetic variant has been shown to be important to dyslexia and to reading ability in general," Paracchini said in a telephone interview. "It looks like this gene is involved in determining whether a person is a good reader or a bad reader."
Dyslexia is a learning difficulty affecting the development of literacy and language-related skills such as reading and spelling. It does not affect intelligence and affects as many as an estimated one in 10 people.
The researchers looked at the gene called KIAA0319 involved in development of the area of the brain responsible for thought processes. Previous research has identified it as a possible
genetic link to dyslexia.
They studied more than 6,000 seven- to nine-year-old children and determined through tests that the 15 percent who carried the mutated version of the gene tended to have problems reading, including those who were not dyslexic.
"Even if they were defined as not dyslexic, they still had problems reading," Paracchini said.
Previously the team had shown that the variation acts like a dimmer switch which reduces the gene's power to do its normal job as a fetus grows.
The findings, published in the American Journal of Psychiatry, give researchers a target as they try to understand better why some people develop dyslexia and others are less good at reading than the general population, Paracchini said.
"There are likely to be many other contributing factors, but our research provides some valuable clues," she added in a statement. "We need to carry out studies into the exact role that this gene plays in brain development and how this affects people's reading ability."
(Reporting by Michael Kahn; Editing by Maggie Fox and Tim Pearce)