Genes associated with left-handedness identified and linked with language regions in the brain

If you're fed up with scissors designed for right-handed people, spare a thought for the long-suffering lefties who, in the not-so-distant past, were forced to learn to write with their non-dominant hand. Thankfully we now live in more enlightened times, and it's been known for a while that genetics plays a part in determining which hand someone will favor. Now, for the first time, researchers have identified regions of the genome related to this trait in the general population.

The study was led by researchers at the University of Oxford who analyzed the genomes of around 400,000 people from UK Biobank. The cohort included 38,332 left-handers, which gels with estimates that around 90 percent of the world's population is right-handed.

The team identified four genetic regions that are associated with handedness, three of which were associated with proteins involved in brain development and structure. Specifically, these proteins were related to microtubules that form part of the cytoskeleton inside cells, which provides structure and shape to guide the construction and function of cells in the body.

Around 10,000 of the study participants had their brains imaged, revealing that the genetic variants associated with left-handedness were also associated with differences in brain structure. Namely, the researchers found differences in white matter tracts that link language-related regions in the brain.

"We discovered that, in left-handed participants, the language areas of the left and right sides of the brain communicate with each other in a more coordinated way," says Dr Akira Wiberg, a Medical Research Council fellow at the University of Oxford, who carried out the analyses. "This raises the intriguing possibility for future research that left-handers might have an advantage when it comes to performing verbal tasks, but it must be remembered that these differences were only seen as averages over very large numbers of people and not all left-handers will be similar."

Additionally, the researchers found correlations between the genetic regions associated with left-handedness and slightly higher chance of having schizophrenia, but a slightly lower chance of having Parkinson's disease. However, they are at pains to point out the correlations are extremely slight and should not be construed as causational. But they do say that examining these genetic links could provide new insights into how those conditions develop.

Throughout history, left-handedness has been considered unlucky, or even malicious," says Professor Dominic Furniss, joint senior author on the study. "Indeed, this is reflected in the words for left and right in many languages. For example, in English 'right' also means correct or proper; in French 'gauche' means both left and clumsy. Here we have demonstrated that left-handedness is a consequence of the developmental biology of the brain, in part driven by the complex interplay of many genes. It is part of the rich tapestry of what makes us human."

The team's study appears in the journal Brain, a Journal of Neurology.

Source: University of Oxford