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Gene involved in cell shape offers clues to left-handedness

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WASHINGTON: What do Lady Gaga, Barack Obama, Bill Gates, Paul McCartney and Justin Bieber have in common with Ronald Reagan, Jimi Hendrix, Judy Garland, Fidel Castro and David Bowie? They are all left-handed, a characteristic shared by about 10% of people.

But why are some people left-handed while most are right-handed? This is an active area of ​​research, and a new study highlights a genetic component to left-handedness in some people. Researchers identified rare variants of a gene involved in controlling cell shape and found that they were 2.7 times more common in left-handed people.

Although these genetic variants represent only a tiny fraction – perhaps 0.1 percent – of left-handers, the researchers said the study shows that this gene, called TUBB4B, could play a role in the development of left-handed people. The cerebral asymmetry that underlies the determination of a dominant hand.

In most people, the two halves, or hemispheres, of the brain have slightly different analyses and are dominant for different functions.

“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 the neurobiologist Clyde Francks of the Max Planck Institute for Psycholinguistics in the Netherlands, lead author. of the study published Tuesday in the journal Nature Communications.

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

TUBB4B controls a protein that fits into filaments called microtubules that provide the internal structure of cells. The identification of rare mutations in this gene, more common in left-handed people, suggests that microtubules are involved in setting up normal brain asymmetries, Francks said.

The two cerebral hemispheres begin to develop differently in the human embryo, although the mechanism remains unclear.

“Rare genetic variants in only a handful of people can identify genes that give clues about the mechanisms by which brain asymmetry develops in everyone. TUBB4B could be a good example,” Francks added.

The findings were based on genetic data covering more than 350,000 middle-aged to older adults in Britain, in a dataset called the UK Biobank. About 11 percent were left-handed.

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 variations during embryonic brain development, without specific genetic or environmental influences. For example, random fluctuations in the concentrations of certain molecules during key stages of the formation of the brain”, explains Francks. said.

Over the centuries, many cultures have denigrated left-handedness and attempted to force left-handers to become right-handed. In English, the word “right” also means “correct” or “appropriate”. The word “sinister” derives from a Latin word meaning “on the left side.” And a “left-handed compliment” means an insult disguised as praise.

The prevalence of left-handedness varies across regions of the world, with lower rates in Africa, Asia and the Middle East than in Europe and North America, Francks said.

“This likely reflects the suppression of left-handedness in some cultures – forcing left-handed children to become right-handed, which was also happening in Europe and North America,” Francks added.

The new findings could be relevant in the field of psychiatry. While the overwhelming majority of left-handers suffer from neither condition, 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 early in life might be involved in both brain asymmetry and psychiatric traits. Our study found suggestive evidence for this, and we also saw it in previous studies where we looked at more common genetic variants in the population,” Francks added.

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