What makes some people left-handed? A study tries to unravel the reasons

How some people can use their left hand to perform all major tasks of the day, including writing, has always intrigued the right-handed lot. This inquisitiveness has also made many scientists scratch their heads, as there is no proven theory of how some people acquire left-handedness, and whether their brain wiring is somewhat different than their rivals, right-handed people.

Now a new study suggests that left-handedness is associated with some rare variants of specific genes.

Researchers at the Max Planck Institute for Psycholinguistics in the Netherlands conducted a study on genetic data from more than 350,000 people. They got the data from UK Biobank, which included 38, 043 left-handed and 313, 271 right-handed people.

The team came across some potential similarities and differences between brain-related disorders that contribute to left-handedness.

Study found certain genes are related to left-handedness

The team searched for specific genes that might have a link to left-handedness and observed whether these rare genes have any say in influencing it. The team found that the inheritability of left-handedness with these rare coding variants was only about 1 per cent.

The team deducedthat left-handed people are 2.7 times more likely to have rare coding variants in a gene called TUBB4B that codes for tubulins that make microtubules. These microtubules are responsible for forming the major part of the cytoskeleton which gives cells their shape. The microtubules are also important for neuron development, migration and plasticity.

"It is not known how microtubules affect inter-individual variation in human handedness," write the authors, "but it has been suggested that they may contribute to cellular chirality early in brain development, and thereby to organ-intrinsic formation of the brain's left-right axis."

Researchers did not find any link between left-handedness and any nine genes implicated in neurogenerative diseases by large-scale exome studies.

However, what they found during the study came as a surprise to the team as well. They discovered that people with two variations in genes previously are related to autism, DSCAM and FOXP1; potentially also having higher chances of being left-handed.

"This study reveals a role for rare, protein-altering variants in left-handedness, providing further evidence for the involvement of microtubules and disorder-relevant genes," the authors write.

In other words, most left-handed people do not have autism, but the higher rate of left-handedness may be due to the presence of these rare gene changes. The authors suggest that when DSCAM or FOXP1 mutations contribute to autism, changes in the left-right axis development of the brain may be also affected by these mutations.

The research was published in Nature Communications.

(With inputs from agencies)