Researchers have identified rare variants of a gene related to cell shape control and found that the number of these gene variants is 2.7 times higher in left-handed individuals.
What do singer Lady Gaga, former U.S. President Barack Obama, billionaire Bill Gates, musician Paul McCartney, and “the Prince of Pop” Justin Bieber have in common with musician Jimi Hendrix, actress Judy Garland, and music legend David Bowie? They are all left-handed, a trait found in only about 10% of the world’s population.
But why are some people left-handed while most are right-handed? This is the question that scientists are actively researching to find answers.
About 10% of the world’s population is left-handed. (Image source: Reuters)
A study published in the journal Nature Communications on April 2 has shed light on the genetic makeup of left-handed individuals.
The researchers identified rare variants of a gene involved in controlling cell shape and found that the prevalence of these gene variants is 2.7 times higher among left-handed individuals.
Although these genetic variants represent a very small fraction—about 0.1%—in left-handed individuals, the researchers indicated that the gene called TUBB4B may play a role in the asymmetric development of the brain, which underlies the determination of handedness.
In most people, the two hemispheres of the brain have slightly different anatomical structures and are responsible for different functions.
Neuroscientist Clyde Francks from the Max Planck Institute for Psycholinguistics in the Netherlands, who led the study, stated that for most people, the left hemisphere is dominant for language functions and the right hemisphere is dominant for spatial orientation functions.
He emphasized: “In most individuals, the left hemisphere controls the right hand. The associated nerve fibers cross from left to right at the lower part of the brain. In left-handed individuals, the right hemisphere controls the dominant hand.” The question arises: what causes the asymmetry of the brain to develop differently in left-handed individuals?
The TUBB4B gene controls a protein that is integrated into structures called microtubules that provide the internal structure for cells.
Francks noted that the identification of rare mutations in this gene being more common in left-handed individuals suggests that microtubules are involved in establishing the normal asymmetry of the brain. The two hemispheres begin to develop differently during human embryonic development, although the exact mechanisms remain unclear.
He further added: “Rare genetic variants in a small number of individuals may accurately identify genes that provide clues about the mechanisms of asymmetric brain development. TUBB4B could be a prime example.”
These findings are based on genetic data collected from over 350,000 middle-aged to elderly individuals in the UK within a dataset known as the UK Biobank. Among them, about 11% are left-handed.
For most people, determining handedness may depend on specific actions. Francks mentioned that most cases of left-handedness occur simply due to random variation during the development of the embryonic brain, with no specific genetic or environmental influences.
For example, random fluctuations in the concentration of certain molecules during critical stages of brain formation.
According to the expert, these new findings may indicate a link to the field of psychiatry. The majority of left-handed individuals do not have mental health issues; however, those with schizophrenia are twice as likely to be left-handed or ambidextrous, and individuals with autism are three times more likely.
Francks explained: “Some genes that are active in the developing brain during early life may be related to both brain asymmetry and psychiatric traits. Our research has found evidence suggesting this, and we have also seen it in previous studies when examining more common genetic variants in the population.”
