Genetic link to dyslexia

About five million Germans have serious learning difficulties when it comes to reading and writing. It is frequently the case that several members of the same family are affected. So hereditary disposition seems to play an important role in the occurrence of dyslexia.

Scientists at the universities of Marburg, Würzburg and Bonn have been working on this question together with Swedish colleagues from the Karolinska Institute in Stockholm. In examinations of German children with serious reading and writing difficulties they have now succeeded in demonstrating for the first time the contribution of a specific gene. Precisely how it contributes to the disorder remains unclear. It is thought that the genes may affect the migration of nerve cells in the brain as it evolves. The results will be published in the January edition of the American Journal of Human Genetics, but have already been made available online.

For several years child and youth psychologists at the universities of Marburg and Würzburg searched for families in which at least one child was considered dyslexic. "We then analysed blood samples taken from the families to identify candidate genes – and in the end we found the right one," explains the scientist who headed this part of the study from Marburg, Privatdozent Dr. Gerd Schulte-Körne.

The gene is located in the region of Chromosome 6, which had already been indicated by scientists from the USA and England in connection with reading and spelling disabilities. But the German-Swedish team has gone further and identified within this region a single gene which, as found among German children, is apparently an important factor in the emergence of dyslexia. "Known as the DCDC2 gene, it appears to affect the migration of nerve cells in the developing brain," says Professor Dr. Markus Nöthen from the Life and Brain Centre at Bonn University. Professor Nöthen and his team are in charge of the molecular work within the project.

Changes in the DCDC2 gene were frequently found among dyslexics. The altered gene variant often occurred among children with reading and writing difficulties. The gene appears to have a strong linkage with the processing of speech information when writing. The researchers now want to gain a better understanding of DCDC2 and discover in detail why children with this altered gene have a higher risk of dyslexia.

On the German side the project is funded by the German Research Foundation (Deutsche Forschungsgemeinschaft) and the Alfried Krupp von Bohlen and Halbach Foundation. The research group at the Karolinska Institute is supported by the Swedish Research Council, the Academy of Finland, the Sigrid Jusélius Foundation, and the Päivikki and Sakari Sohlberg Foundation. Professor Nöthen occupies the Alfried Krupp von Bohlen and Halbach Chair for Genetic Medicine. The Life & Brain Centre is a new research facility at the Bonn University Clinic which uses state-of-the-art technologies to conduct application-oriented aetiology.

About five per cent of all Germans are dyslexic. Despite good intelligence levels and regular school attendance they have great difficulties in reading texts and expressing themselves in writing. For many children the nature of their reading and spelling disability is not recognised until it is too late, i.e. when they are having psychological problems due to their learning difficulties. They can develop school-related anxieties and depression, even with thoughts of suicide.