Genetic secrets of left-handedness revealed as part of huge study

For the first time, researchers have identified genetic regions of the genome that lead to the development of left-handedness.

Despite making up approximately 10pc of the world’s population, there remains a number of genetic mysteries when it comes to left-handers. However, a new study led by researchers from the University of Oxford have discovered a wealth of new genetic information linked to left-handedness and their association with language regions of the brain.

Existing research on this percentage of the human population showed that 25pc of the variation in handedness can be attributed to genes, but not which ones.

Writing in Brain, the researchers identified some of these genetic variants by analysing the genomes of approximately 400,000 people based in the UK, including 38,332 left-handers.

Of a total of four genetic regions identified in the research, three were associated with proteins involved in brain development and structure. In particular, these proteins were related to microtubules important to cell scaffolding – called the cytoskeleton – guiding the construction and functioning of the cells in the body.

After taking detailed brain images of 10,000 of the study’s participants, the researchers found that genetic effects were associated with differences in brain structure in white matter tracts. This contains the cytoskeleton of the brain that plays a crucial role in languages.

Brain scans showing different genetic regions of the brain.

The language brain regions were more coordinated in left-handers between the two sides of the brain (green and orange) and were also connected by the white matter tracts influenced by one genetic region related to handedness (blue). Image: G Douaud, University of Oxford.

Potentially better verbal skills

“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,” said Dr Akira Wiberg who carried out the analyses.

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“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.”

Correlations were also found between these regions associated with left-handers as having a slightly a very slightly lower chance of having Parkinson’s disease, but a very slightly higher chance of having schizophrenia. As you would expect, the researchers also stressed that these correlations do not show cause-and-effect because they only relate to a very small difference in the number of people with these diseases.

Pointing to the treatment of left-handers throughout history, Prof Dominic Furniss, joint senior author of the study, said: “Throughout history, left-handedness has been considered unlucky, or even malicious.

“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.”

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