Most people are right-handed and use their right hand to perform tasks such as writing or eating, but around 10-12% of the world’s population is left-handed and their dominant hand is the left. Laterality is the preference for using one side of the body more than the other and is not limited to just the hands, but can extend to other parts such as the dominant foot, eye or ear, although the term left-handed is mainly used in the context of the dominant hand.
In left-handed individuals the right cerebral hemisphere is more dominant for the control of that hand, while in the case of right-handed people the left hemisphere is more dominant. The reasons why some people are left-handed and others are right-handed are not fully understood, but genetic, biological and environmental factors are believed to be involved. Now, a team of scientists from the Netherlands has analyzed genome data from 350,000 people from the UK Biobank – approximately 11% of whom were left-handed – to investigate the genetic basis of this handedness.
The researchers identified rare variants of a gene involved in determining cell shape. Their findings have been published in Nature Communications and suggest that the TUBB4B gene is 2.7 times more likely to contain rare coding variants in left-handed people.
Although these genetic variants only explain a minimal percentage – perhaps only 0.1% – of left-handedness, the researchers have indicated that the study demonstrates that the TUBB4B gene could play a role in the development of the cerebral asymmetry that determines which is the dominant hand.
In most people, the two halves or hemispheres of the brain have slightly different anatomies and master different functions. “For example, most people have a left hemisphere dominance for language and a right hemisphere dominance for tasks that require directing visual attention to a place in space,” explained neurobiologist Clyde Francs of the Max Planck Institute. of Psycholinguistics in the Netherlands, lead author of the study, in statements to the Reuters agency.
Genetic bases of left-handedness and its relationship with psychiatric problems
TUBB4B controls a protein that integrates into filaments called microtubules, which provide internal structure to cells. The identification of rare mutations in this gene, which are more common in left-handed people, suggests that microtubules are involved in establishing normal brain asymmetries, says Francks.
The two cerebral hemispheres begin to develop differently in the human embryo, although the mechanism is not well understood. “Rare genetic variants in just a handful of people may point to genes that offer clues to the developmental mechanisms of brain asymmetry in everyone. TUBB4B could be a good example of this,” adds Francks.
For most people, determining which hand is dominant can be a matter of chance. “We believe that most cases of left-handedness occur simply due to random variation during embryonic brain development, without specific genetic or environmental influences. For example, random fluctuations in the concentrations of certain molecules during key stages of brain formation,” says Francks.
“People with schizophrenia are about twice as likely to be left-handed or ambidextrous and people with autism are about three times as likely.”
The new findings could have relevance in the field of psychiatry. Although the vast majority of left-handed people do not have either of these conditions, people with schizophrenia are about twice as likely to be left-handed or ambidextrous and people with autism are about three times as likely, Francks said. “Some of the genes that function in the developing brain during early life could 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.
“I don’t think it can be concluded that the gene for left-handedness has been found,” says Gemma Marfany, professor of Genetics at the University of Barcelona and group leader at CIBERER, who has not participated in the research, as she told SMC Spain. where he explains why he thinks this way: “In the European population the percentage of left-handed people is around 10% of the population. Researchers have tried to find a gene involved in this characteristic. After analyzing and comparing the coding regions of more than 38,000 left-handed and more than 300,000 right-handed people from the UK Biobank, they have only been able to detect very rare (rare) genetic variants in heterozygosity in one gene, TUBB4, in less than 29 people left-handed (that is, less than one per thousand left-handed individuals). These identified variants have not been found in right-handed people, although other similar variants have been found in the same gene in 89 right-handed people.”
“Although the sequencing and analysis work is correct, the interpretation of the results seems overrated to me. The statistical predictive value, with these very, very low numbers, is irrelevant, since it cannot be demonstrated that this gene is decisive for this characteristic, particularly considering that being left-handed is very common in the population.”
Amaia Carrión, scientist at the Basque Center on Cognition, Brain and Language (BCBL) and Marie Skłodowska-Curie and Ikerbasque research fellow, for her part, points out in statements to the same medium that: “this study complements previous studies and indicates that the variation Rare genetics involving changes at the protein level also play a role in left-handedness. Furthermore, the identified gene is closely related to those indicated by other genetic studies, highlighting the possible role of microtubules.”
“Right or left hand dominance is established early in development and, for most people, the right hand is the most dominant. “This suggests to us that there is probably a genetic basis and is the motivation for these studies on the genetic basis of left-handedness.”
“However, it should be noted that the studies carried out to date, including this one, have very low heritability estimates (proportion of variance explained by genetic variation): 0.9-5% depending on the study. Twin studies, which tend to give higher heritability estimates, have estimates as high as 25%. Therefore, most of the variation we observe in the phenotype (being right- or left-handed) is not explained by variation at the genetic level.”
“This study tells us that, in addition to the common variation studied so far, rare genetic variation is also involved, but the effects observed are very small and, therefore, are only detectable in this type of studies with very large samples” .
