Gene may offer clues on why some are left-handed, study says

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 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.”

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.

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.