Scientists at the Wellcome Trust Centre for Human Genetics, University of Oxford, have found a genotype which influences whether a person with dyslexia is a lefty or not. They’ve found a new gene for handedness and the first genetic evidence to shed light on the mystery link between handedness and a language-related disorder.
Most people are right-handed. Since the left side of the brain controls the right side, and the right, left, this means that for most people, the left hemisphere of the brain is the dominant side for motor functions, such as handedness. In addition to this, family studies show that genetics strongly influence handedness.
Most individuals also keep language function to the left, proven each time injury to the left side of the brain results in language impairment.
Some say that the dominance of right-handedness in humans shows that language evolution took a left at the brain hemisphere. So scientists have thought that there may be a link between hand preference and disorders that affect language development, such as autism and specific language impairment (SLI). So far, no proof.
In the current study funded by the Wellcome Trust, the Medical Research Council and the European Union, scientists scanned the genomes of 192 children with reading difficulties. These children also had their left- and right-hand skill measured. The results of the study were published in the journal Human Molecular Genetics.
The scientists found a strong link between a variant of a gene called PCSK6 and relative hand skill in these children with reading difficulties. Specifically, while most people are better at using their right hand, those who carried the variant in PCSK6 were, on average, more skilled with their right hand compared to the left than those not carrying the variant. This result was also seen in two independent groups of children with reading difficulties.
William Brandler, one of the study’s authors, explains: “Our closest relatives, the great apes, do not display the striking bias towards right-handedness seen in humans. So understanding the genetic basis of handedness may offer us significant insights into our evolution.”
“This study provides the first genetic link between handedness, brain asymmetry and reading ability,” says Professor Tony Monaco, leader of the group that made this discovery. “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.”
One of the aims of this study was to understand the genetics of handedness, and the results should open up new avenues into exploring the biology of language-related disorders, and help identify whether language and handedness did indeed evolve hand-in-hand.