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Reproduced with kind permission from “Genes, Environment, and Dyslexia”, the 2005 Norman Geschwind Memorial Lecture by Richard K. Olson, Ph.D., Professor of Psychology, University of Colorado, Director, Colorado Learning Disabilities Research Center
Better prediction of children’s risk for dyslexia, prior to formal reading instruction in the schools, is an important long-term goal of our molecular genetic research. However, I believe that much more research will be needed before we can use cheek swabs and DNA analyses to significantly improve prediction of dyslexia beyond what we can glean from family history and pre-reading assessments of reading related skills. First, the results from recent molecular genetic association studies need to be replicated in other laboratories and with other independent samples. Second, the risk alleles identified to date are also present in many children who do not have dyslexia, so their effects may depend on complex interactions or additive influences from other genes and/or the environment. More research is needed to discover those genes and environmental risk factors before these risk alleles will be very useful for the prediction of dyslexia. Third, it appears that the specific alleles identified to date may account for only a modest proportion of the most severe cases of dyslexia and very few if any of the less severe cases. We have learned from our behavior genetic studies with twins that genetic influences are equally strong for less severe dyslexia, so there are likely to be other risk alleles that have yet to be discovered. These risk alleles are likely to be numerous and of small average effect in the population with dyslexia, since whole-genome linkage scans for dyslexia have often yielded inconsistent results. In conclusion, the evidence to date suggests a complex pattern of genetic influence on dyslexia that may involve many different genes of small effect, and the specific genes may vary across individuals. In view of its apparent complex genetic etiology, I do not believe we are close to having a useful DNA test of genetic risk for dyslexia at this time. But I also believe that this goal is one we should continue to vigorously pursue, along with the rapid advances in methods for efficiently mapping the human genome. I am sure there will be substantial benefits for many children when we can use DNA analyses to improve the early prediction of genetic risk for dyslexia and to achieve a better understanding of the interactions between genes, the developing brain, and reading.
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