Genetic cause of dyslexia traced

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SCIENTISTS HAVE identified the location of a gene for dyslexia, creating the possibility of screening tests and early treatment for the learning disorder. The discovery means that at least four genes are now implicated in causing dyslexia.

An international team in Norway, Belgium and the United States has narrowed the new gene's location to a short stretch of DNA on chromosome 2. Chromosomes are sets of thousands of genes: each parent contributes 22 of them, plus a sex chromosome, to the child.

Identifying the gene's location but not its exact DNA sequence is like knowing its road, but not its house number. Previous research has also pointed to locations, but not specific genes, on chromosomes 1, 6 and 15. Dyslexia is estimated to affect about 1 child in 20. Other research has suggested which regions of the brain may be responsible - perhaps because their development is linked to those genes' activity.

The team that found the new location, by studying a large Norwegian family, hopes to sieve through the 100-odd genes in the stretch of DNA to identify the specific gene. That, said Dr Toril Fagerheim of University Hospital of Tromsoe, Norway, who led the research, "will provide us with insight into the nature and frequency of at least one gene that is involved in reading and spelling". The work is reported today in the Journal of Medical Genetics.

But a leading British researcher on dyslexia, Professor John Stein at Oxford University's Laboratory of Physiology, pointed out that dyslexia iscaused by both genetic and environmental factors. Studies have shown 60 per cent of the variance in reading ability is explained by inheritance, he said. "That means 40 per cent is due to environmental factors."