Cause of dyslexia narrowed down to single chromosome

A pre-school test to identify children with a predisposition to dyslexia has become more likely with the discovery of a genetic link to the disorder, scientists said yesterday.

A study of more than 200 families of children who are dyslexic has revealed that a region of chromosome 18 – one of the 23 pairs of human chromosomes – is strongly associated with the condition.

Scientists from the Wellcome Trust Centre for Human Genetics in Oxford say that the biggest dyslexia study of its kind has identified what could turn out to be the most important gene involved in causing "word blindness".

Professor Tony Monaco, the director of the centre, said that chromosome 18 was identified using a scan of the full complement of genetic material that makes up the human genome, the first time this has been done for dyslexia. Previous studies had identified other possible genes involved in predisposing children to the disorder – notably one on chromosome 6 – but the latest study, published in the journal Nature Genetics, produced the most unambiguous link yet, Professor Monaco said.

"The strength of the signal is pretty sound. There are several genes involved in dyslexia and this is not going to be a single-gene disorder," he said. "So far we have only mapped the gene to a chromosome region. We have yet to find the gene and determine what it does. Over the next few years, we will be looking at the genes most likely to be associated with the disorder," he said.

The researchers measured the severity of reading and spelling problems in each of the 208 families in the study. They correlated this with the pattern of inheritance and looked for links with specific regions of each of the 23 pairs of chromosomes, leading them to a region of chromosome 18.

"It is rare to find such a strong link between a genetic region and complex disorders. This is the first time the whole genome has been scanned in a large number of families with dyslexia from different parts of the world, which is why the results are so interesting," Professor Monaco said.

Once the gene itself was located, and defects identified, a test could be used to identify children at risk of the condition so they could receive special tuition earlier in life. "At the moment it is very difficult in a large classroom to pick up dyslexia and many children have suffered as a result," he said.