Scientists believe they have discovered for the first time, evidence that dyslexia is caused by faulty wiring in the brain.

Experts have become increasingly convinced that the reading and writing disorder has a biological and genetic origin but this theory did not equate with the fact that the incidence of dyslexia is much higher in some countries.

For example it is ten times more common in the US as in Italy - suggesting it was a cultural problem rather than a medical one.

But now a study, published in Science magazine of dyslexics from different countries has found the neurological basis for the disorder that crosses national boundaries and suggests that in countries such as Italy, there may be high numbers of undiagnosed dyslexic people.

The national differences in the numbers of diagnosed dyslexics is being explained by the fact that dyslexic people find certain languages are easier for dyslexic people to read and therefore their problems are less pronounced and more likely to go undetected.

Languages which are most difficult for dyslexics to read are those where there are many ambiguous ways of pronouncing the spelling of particular words, including English and French. An example would be words such as mint and pint.

But in Italian there is no such ambiguity which is why dyslexic people find the language easier to read. However Italian dyslexics proved just as bad as dyslexics from other countries at other language tests for diagnosing the condition.