Dyslexia gene associated with reading difficulties in general population
1 October 2008
Dyslexia is a learning difficulty that affects the development of literacy and language-related skills such as reading and spelling, but does not affect overall IQ. It is believed that as many as one in ten people are affected by dyslexia to some degree.
Previous research has identified at least six candidate genes that appear to affect susceptibility to developing dyslexia. However, scientists have often failed to replicate these findings, suggesting that their role in causing dyslexia is debatable.
The most promising of the candidates is the gene KIAA0319, which lies on chromosome 6. This gene has been reported in at least three independent studies. Researchers at the Wellcome Trust Centre of Human Genetics, University of Oxford, have previously identified a haplotype - a particular DNA sequence, which spans part of this gene - associated with dyslexia in both a large sample of UK families and a sample of twins in the US. This association was also identified independently by researchers at Cardiff University.
Now, working with a cohort of over 6000 seven to nine-year old children from Children of the 90s, also know as the Avon Longitudinal Study of Parents and Children (ALSPAC), researchers have looked at the association between this particular haplotype, which is carried by 15 per cent of the population, and general reading ability.
"On average, people carrying this common genetic variant tended to perform poorly on tests of reading ability," says Dr Silvia Paracchini from the Wellcome Trust Centre for Human Genetics, lead author of the study. "However, it's important to note that this is only true for reading ability and not for IQ, so it doesn't appear to be connected to cognitive impairment."
Dr Paracchini and colleagues have previously shown that the same haplotype is associated with reduced expression of the KIAA0319 gene during development of the foetus - in other words, it acts like a dimmer switch, reducing the power of the gene to do its normal job as the foetus grows. This affects development of the cerebral cortex, the area of the brain responsible for thought processes. In animal studies, switching off KIAA0319 affects neuronal migration, the process that enables nerve cells created in the inner layer of the cerebral cortex area to migrate outwards to their destination.
"This is clearly only part of the jigsaw puzzle that explains why some people have poorer reading ability than others or develop dyslexia," says Dr Paracchini. "There are likely to be many other contributing factors, but our research provides some valuable clues. We need to carry out studies into the exact role that this gene plays in brain development and how this affects people's reading ability."
Professor Margaret Snowling, Vice President of the British Dyslexia Association comments: "The finding of a gene associated with reading ability in the general population as well as in dyslexia is in line with our observation that there are degrees of dyslexia from mild to severe. It also implies that other genes or environmental experiences must be involved in determining reading ability. This ties in with what we have known for many years - some individuals are able to compensate and go on to successful careers even though they carry this gene variation.
"Another exciting finding is that this gene seems associated with slow brain growth in certain regions. From a practical perspective this research underlines the need for the early identification of dyslexia and suggests that intervention at a time when the brain is still developing could lead to positive outcomes for literacy and other skills."
Image: Anthea Sieveking; Wellcome Images
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Notes for editors
1. Paracchini, S et al. The KIAA0319 dyslexia susceptibility gene is associated with reading skills in the general population. Am J Psychiatry. 2008 Oct 1. [Epub ahead of print]
2. The Wellcome Trust is the largest charity in the UK. It funds innovative biomedical research, in the UK and internationally, spending over £600 million each year to support the brightest scientists with the best ideas. The Wellcome Trust supports public debate about biomedical research and its impact on health and wellbeing.
3. Oxford University's Medical Sciences Division is one of the largest biomedical research centres in Europe. It represents almost one-third of Oxford University's income and expenditure, and two-thirds of its external research income. Oxford's world-renowned global health programme is a leader in the fight against infectious diseases (such as malaria, HIV/AIDS, tuberculosis and avian flu) and other prevalent diseases (such as cancer, stroke, heart disease and diabetes). Key to its success is a long-standing network of dedicated Wellcome Trust-funded research units in Asia (Thailand, Laos and Vietnam) and Kenya, and work at the MRC Unit in The Gambia. Long-term studies of patients around the world are supported by basic science at Oxford and have led to many exciting developments, including potential vaccines for TB, malaria and HIV, which are in clinical trials.
4. The Wellcome Trust Centre for Human Genetics was established to undertake research into the genetic basis of common diseases. The scientific objective of the Centre is to explore all aspects of the genetic susceptibility of disease. The Centre houses multidisciplinary research teams in human genetics, functional genomics, bioinformatics, statistical genetics and structural biology.
5. ALSPAC is the Avon Longitudinal Study of Parents and Children (also known as Children of the 90s). It is a unique ongoing research project based in the University of Bristol. It enrolled 14 000 mothers during pregnancy in 1991-2 and has followed most of the children and parents in minute detail ever since. The ALSPAC study could not have been undertaken without the continuing financial support of the Medical Research Council, the Wellcome Trust, and the University of Bristol among many others.