Can Epigenetics Explain the Mystery of Right and Left Handedness?

Are you among the 90% of people who are right-handed or the 10% who are lefties? Have you ever wondered why you naturally favor a certain hand over the other? Now, researchers are suggesting that epigenetics could be the explanation.

They are finding that handedness may not be dictated by the brain, as previously thought, but by the environment and epigenetic marks in the spinal cord. “These results fundamentally change our understanding of the cause of hemispheric asymmetries,” the authors concluded in their paper published in eLife.

Hemispheric asymmetries refer to anatomical and functional differences between the two sides of the brain, such as the size of a certain area or its purpose. A team of international researchers showed that gene activity in the spinal cord is asymmetrical as early as when a child is still in the womb, which might also be the reason for their particular handedness as they grow older.

In light of this new research, we might wonder if epigenetics could even play a part in the interesting personality traits that are often reflected in lefties or righties. For instance, people who are left-handed have a slightly higher chance of psychosis, are more likely to pursue art, more prone to experiencing negative emotions, and have been shown to drink more alcohol than righties.

It has been thought that discrepancies in gene activity of the two hemispheres were likely responsible for whether someone was a lefty or a righty. After about a month of pregnancy, unborn children prefer sucking on either their left or right thumb. Even earlier than that, they prefer to move either their left or right hand as they grow in the womb.

The researchers believe the cause of left or right preference is linked to the epigenetic marks in the spinal cord and not the brain. This is because the motor cortex, which initiates hand and arm movements by communicating to the spinal cord, isn’t even connected to the spinal cord at this time.

The group set out to analyze asymmetries in genome-wide mRNA expression, miRNA expression and DNA methylation patterns in the spinal cord during the eighth to twelfth week of pregnancy. They found significant right-left differences in the parts of the spinal cord linked to the movements of the legs and arms. Essentially, epigenetic factors were at the root of the asymmetric gene activity.

They uncovered that DNA methylation played a key role in the difference to the activity of genes. This mechanism occurs when a methyl group is attached to the DNA by a particular epigenetic enzyme and is associated with a reduction in gene expression.

It’s interesting to think that we may have been destined to be left or right-handed since before we were born. It’s clear that epigenetics has a significant influence on our life and it’s revealing itself in even the smallest aspects.

Source: Ocklenburg, S., et al. (2017). Epigenetic regulation of lateralized fetal spinal gene expression underlies hemispheric asymmetries. eLife, 6:e22784.

Reference: Weiler, J. The reasons for our left or right-handedness. Ruhr-University Bochum. 17 Feb 2017. Web.