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Does dyslexia really exist?

Ian Sample The Guardian

Are children who cannot read properly being called ‘dyslexic’ to avoid embarrassment? ‘No’, say researchers.

Not according to some education experts. Instead, they argue, dyslexia is an emotional construct used, in many cases, to save children who are poor readers from embarrassment.

Unsurprisingly, scientists studying the biological basis of dyslexia beg to differ. "To say it's a myth is pretty far-fetched," says Tony Monaco, head of neurogenetics at Oxford University and an expert on the condition.

According to the professor, children who are simply poor readers may mistakenly be diagnosed with dyslexia if their reading ability is not assessed alongside their general intelligence. The sign of real dyslexia is a reading ability far below that for a child's age and intelligence.

The role of heredity

Research is gradually teasing out the developmental glitches that give rise to dyslexia. "From studies of twins in UK and Colorado, we know that around 50-60% of the variance in reading ability is due to genetic influences," says Monaco. The condition is highly hereditary with around half of children born to people with dyslexia also developing the condition.

In a study of 300 families, his group identified a gene on chromosome six they suspect is strongly linked to dyslexia. The gene is thought to help neurons in the developing brains of babies move to their correct positions. "When you knock the gene out in rats, you get no movement of the neurons," says Monaco. The finding was bolstered by researchers at Cardiff University who independently identified the same gene as a potential factor in dyslexia. "In the developing brain, neurons have to move to the right level and it appears that a variant of this gene impairs that movement," says Monaco.

Underactive brains

Brain scans carried out by another Oxford University researcher, John Stein of the Dyslexia Research Trust, have shown that people with dyslexia have underactive brains in several key areas associated with reading and vocal word formation.

"The evidence so far points strongly to dyslexics inheriting a genetic trait that means they have impaired neuronal migration," he says.

Experts believe other genes will be discovered that also contribute to a person's susceptibility to being dyslexic. Already, a Finnish group has found a gene on chromosome 15 that impairs neuronal movement in developing humans. And Monaco's group believes another contributing gene lies on chromosome 18.

Other research supports the notion that it is a real neurological condition: post mortem examination of brains of people with dyslexia revealed many neurons were in the wrong place.