Scientists find gene variant linking handedness and dyslexia
New genetic mapping of children with dyslexia sheds light on the relationship between handedness and language-related disorders, adding weight to a much-hypothesised issue. Scientists in the UK discovered a variant of the so-called PCSK6 gene that is associated with handedness among children with dyslexia. Presented in the journal Human Molecular Genetics, the study was funded in part by the NEURODYS ('Dyslexia genes and neurobiological pathways') project, which clinched more than EUR 3 million under the 'Life sciences, genomics and biotechnology for health' Thematic area of the EU's Sixth Framework Programme (FP6) to investigate the biological basis of dyslexia. Right-handedness is much more prevalent than left-handedness. Experts say that because the left side of the brain controls the right side of the body, and vice versa, the left hemisphere of the brain generally controls our motor functions. The left hemisphere is also the dominant side for language function. Past studies have shown that people affected by damage to certain areas of the left side of their brain have some language impairment. 'This study provides the first genetic link between handedness, brain asymmetry and reading ability,' explains research leader Professor Tony Monaco of the Wellcome Trust Centre for Human Genetics at the University of Oxford in the UK, and one of the authors of the paper. 'Despite the known biological function of PCSK6, this is the first study implicating it with handedness. The fact that this association also seems to be apparent in people with dyslexia provides an interesting clue to explore whether there is a link between handedness and language-related disorders.' Until now, many researchers theorised that population bias towards right-handedness emerged because of language evolution, suggesting a connection between hand preference and language development disorders like specific language impairment (SLI) and autism. This latest study discovered a concrete link between a variant of the PCSK6 gene and relative hand skill in children with reading difficulties. Using a sample of 192 unrelated individuals with reading difficulties, the scientists found that those carrying the new variant in PCSK6 were usually more skilled with their right hand compared with people not carrying the variant. Researchers recognise that the protein product of the gene PCSK6 interacts with the NODAL protein, which helps establish left-right symmetry in the early stages of an embryo's development. The genetic variants of PCSK6, said the researchers, may contribute to the preliminary left-right patterning of the embryo which in turn impacts brain asymmetry development, and consequently handedness. 'Our closest relatives, the great apes, do not display the striking bias towards right-handedness seen in humans,' points out William Brandler, a researcher at the Wellcome Trust Centre for Human Genetics and one of the paper's authors. 'So understanding the genetic basis of handedness may offer us significant insights into our evolution.' The results of this study could be used for future research investigating the biology of language-related disorders and whether handedness and language evolved together.
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