Study: Rare gene could be source of left-handedness

(CN) — A vast majority of humanity uses their right hand to write and for other skills, but a good 10% of us are left hand dominant. But why do some people use one hand and not the other? According to researchers in the Netherlands, protein altering genetic variants and tubulin genes might be the answer.  

“This was really curiosity-driven research about a mystery in human biology: what is the genetic basis of the brain's left-right axis? We know that the two cerebral hemispheres already start to develop differently in the human embryo, but the mechanism is not known. Finding genes linked to asymmetries of the brain or behavior, like handedness, can give some clues,” said Clyde Francks, one of the authors and research group leaders of the study published Tuesday in Nature Communications, over email.  

Using data in a large biomedical database called UK Biobank, Francks and his colleagues trawled through the genetic data of 350,000 people looking for markers of left-handedness. They found a gene called TUBB4B — which gets integrated into microtubule proteins, which are filaments that acts as something akin to the internal skeleton of cells — which was 2.7 times more likely to show up in left-handed people than right-handed people.      

“It suggests that microtubules are involved in setting up the normal asymmetries of the brain, like left-hemisphere language dominance and hand control," Francks said. “In the embryonic brain, microtubules might help to create the left-right axis by giving some cells an asymmetrical twist at a certain stage.”

Francks and his colleagues also studied how genes that affect handedness, or which hand people use as the dominant one, are associated with aliments like schizophrenia, Parkinson’s disease, Alzheimer’s disease and autism.

They noted that analysis has indicated left-handedness tends to occur at increased rates for some neurodevelopmental disorders.

“These associations suggest that population-typical asymmetries are linked to neurotypical function," the authors wrote in the study. "Both autism and schizophrenia have shown genetic overlaps with structural brain asymmetry, in terms of common variant effects. Rare coding variants are also known to be involved in the genetic architecture of neurodevelopmental disorders.”

Most people who use their left hand as the dominant hand don’t have schizophrenia or autism, but they are more common in people who use their left hand than the general population, Francks wrote.

In the future, Francks wrote that he wants to "investigate the roles of microtubules in embryonic development of brain asymmetry."

"Mouse embryos might provide a way to do this. Like humans, mice show some left-right differences in their brains, for example in the functioning of the auditory cortex," he added.

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