What do Jimi Hendrix, Judy Garland, David Bowie, Lady Gaga, Barack Obama, Bill Gates, Paul McCartney, and Justin Bieber have in common with each other? They are all left-handed, which is a characteristic that about 10% of people have.

However, why do most people have right hands while some have left? Research is ongoing in that area, and a recent study provides insight into the genetic component of left-handedness in certain individuals. Researchers discovered that left-handed people have uncommon variations of a gene that controls cell shape 2.7 times more frequently than right-handed ones.

Although left-handedness is only partially explained by these genetic polymorphisms (about 0.1%), the study’s findings suggest that the TUBB4B gene may be involved in the formation of the brain asymmetry that underpins the identification of a dominant hand.

The two parts of the brain, known as the hemispheres, are prominent for various functions and have slightly different anatomy in most people.

“For example, most people have left-hemisphere dominance for language, and right-hemisphere dominance for tasks that require directing visual attention to a location in space,” said neurobiologist Clyde Francks of the Max Planck Institute for Psycholinguistics in the Netherlands, senior author of the study published on Tuesday in the journal Nature Communications.

“In most people, the left hemisphere also controls the dominant right hand. The relevant nerve fibers cross from left-to-right in the lower part of the brain. In left-handers, the right hemisphere is in control of the dominant hand. The question is: what causes the asymmetry of the brain to develop differently in left-handers?”

TUBB4B regulates a protein that integrates into microtubules, which are filaments that give cells their internal structure. According to Francks, the discovery of uncommon mutations in this gene that are more prevalent in left-handed people raises the possibility that microtubules play a role in establishing the normal asymmetries of the brain.

In the human embryo, the two cerebral hemispheres begin to grow differently, albeit the exact mechanism is yet unknown.

“Rare genetic variants in just a handful of people can pinpoint genes that give clues to developmental mechanisms of brain asymmetry in everyone. TUBB4B could be a good example of this,” Francks added.

The results were based on genetic information from the UK Biobank, a dataset that included over 350,000 middle-aged and older persons in Britain. Eleven percent were left-handed.

Which hand is dominant for most people might just be determined by coincidence.

“We think that most instances of left-handedness occur simply due to random variation during development of the embryonic brain, without specific genetic or environmental influences. For example, random fluctuations in the concentrations of certain molecules during key stages of brain formation,” Francks said.

Many societies have denigrated left-handedness over the ages and attempted to convert lefties to right-handedness. The word “right” in English also denotes “correct” or “proper.” The Latin root of the term “sinister” means “on the left side.” Furthermore, a “left-handed compliment” is an insult that appears to be flattering.

According to Francks, the prevalence of left-handedness varies throughout the world, being lower in the Middle East, Africa, and Asia than in Europe and North America.

“This likely reflects suppression of left-handedness in some cultures – making left-handed kids switch to right-handedness, which also used to happen in Europe and North America,” Francks added.

The discipline of psychiatry may find use for the new results. According to Francks, those with autism are almost three times more likely to be left-handed or ambidextrous than those with schizophrenia, even though the vast majority of left-handed persons do not have either of these disorders.

“Some of the genes that function in the developing brain during early life might be involved in both brain asymmetry and psychiatric traits. Our study found suggestive evidence of this, and we have also seen it in previous studies where we looked at more common genetic variants in the population,” Francks added.

(Adapted from Reuters.com)