Gene involved in cell shape offers clues on left-handedness
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[April 03, 2024]
By Will Dunham
WASHINGTON (Reuters) - What do Lady Gaga, Barack Obama, Bill Gates, Paul
McCartney and Justin Bieber have in common with Jimi Hendrix, Judy
Garland and David Bowie? They are all left-handed, a trait shared by
roughly 10% of people.
But why are some people left-handed while most are righties? That is an
area of active research, and a new study sheds light on a genetic
component of left-handedness in some people. Researchers identified rare
variants of a gene involved in controlling the shape of cells and found
them to be 2.7 times more common in left-handed people.
While these genetic variants account for only a tiny fraction - perhaps
0.1% - of left-handedness, the researchers said the study shows that
this gene, called TUBB4B, may play a role in the development of the
brain asymmetry that underlies the determination of a dominant hand.
In most people, the two halves, or hemispheres, of the brain have
slightly different anatomies 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 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?"
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TUBB4B controls a protein that gets integrated into filaments called
microtubules that provide internal structure for cells. The
identification of rare mutations in this gene that are more common in
left-handers suggests that microtubules are involved in setting up the
brain's normal asymmetries, Francks said.
The two cerebral hemispheres start to develop differently in the human
embryo, though the mechanism has remained unclear.
"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.
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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% were left-handed.
For most people, the determination of which hand is dominant may
come down to chance.
"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.
Over the centuries, many cultures disparaged left-handedness and
tried to force lefties to become right-handed. In English, the word
"right" also means "correct" or "proper." The word "sinister"
derives from a Latin word meaning "on the left side." And a
"left-handed compliment" means an insult masquerading as praise.
The prevalence of left-handedness varies in different parts of the
world, with lower rates in Africa, Asia and the Middle East compared
to Europe and North America, Francks said.
"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 new findings might have relevance in the field of psychiatry.
While the overwhelming majority of left-handed people have neither
of these conditions, people with schizophrenia are around twice as
likely to be left-handed or ambidextrous and people with autism are
around three times as likely, Francks said.
"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.
(Reporting by Will Dunham, Editing by Rosalba O'Brien)
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