The Genetic Role of Left-Handedness

Ellie Teng ’21

lefthandwriting
Figure 1. Genetics are significant in the development of handedness.

90% of the population are right- handed, so what is different about individuals who are left- handed? Handedness was previously known to be partially affected by the genome; twin studies showed that genes account for about 25% of the variation in handedness. Researchers at the University of Oxford sought to connect the genetic difference to areas of the brain that control language. Brain images were taken from 9,000 subjects and scientists performed a genome- wide association study that included 400,000 subjects. 

Three genetic regions were found to code for proteins that aid in brain development. These proteins affected microtubules which are components of the cytoskeleton. Genetic differences found in the genome of left- handers were associated with differences in white matter tracts containing the cytoskeleton of the brain that connects to language regions. The white matter connects the grey matter which is a component of the functional language networks that vary between left- and right- handers. In left-handers the language areas on either side of the brain communicate in a more coordinated way. 

Genes related to the cytoskeleton are responsible for left-right asymmetry displayed in animals. For example, this is demonstrated in snail shells that coil to the left or to the right. In humans, the cytoskeletal difference is visible in the brain.  Because these phenotypes begin to show during the early stages of development in animals, scientists speculate that the development of handedness would begin to appear in the womb. 

On a different topic, correlations have been made between the genetic regions in left-handers and a slightly lower risk of developing Parkinson’s disease, a neurological disease that affects movement. However, left- handers have a slightly higher risk of developing schizophrenia. Researchers stressed that this was only a correlation and that correlation does not equal causation. Regardless, studying the genetic variance in left- handers may be helpful in understanding these diseases. 

 

References

  1. A. Wiberg, et al., Handedness, language areas and neuropsychiatric diseases: insights from brain imaging and genetics. Brain (2019). Doi: 10.1093/brain/awz257
  2. Image retrieved from: https://pixnio.com/objects/books/table-hands-person-text-writing-book-ink

 

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