This Specific Gene Could Be the Reason You’re Left-Handed

Lefties, take note: We know a little more about the genetic basis for your dominant hand. Researchers have identified a rare genetic variant coding for a protein that may be partially responsible for this trait.

The hand you’re more inclined to use is an expression of brain asymmetry. If your left hemisphere is dominant, then you’re a righty; if your right hemisphere is dominant, you’re a lefty. This asymmetry starts to appear during fetal development, which indicates there may be a genetic cause. In particular, the genetic variants involved code for cylindrical, cellular structures called microtubules.

Now, neuroscientists in the Netherlands used the human exome, the sequence of all the protein-coded portions of a genome, to delve into this mystery. They used a dataset from the U.K. Biobank that included the genomes of over 300,000 righties and 30,000 lefties, searching for rare, protein-altering genetic variants associated with hand dominance. They identified the potential culprit as the TUBB4B gene. They published their findings today in the journal Nature Communications.

The TUBB4B gene codes for a type of protein called tubulin, which builds the cylindrical microtubules. Across the entire exome, this gene had the most significant association with left-handedness, which indicates that microtubules may be crucial to the human brain asymmetry involved in hand dominance.

Even though microtubules are infinitesimally small cellular structures, they could still factor into hand dominance. Microtubules, for example, help build cilia, or the cell organelles that allow movement. The paper details that cilia could offer a mechanism for whole-cell asymmetry, which can ultimately influence brain development. The gene variants modify the tubulin created, which affects how microtubules come together. In other words: the way a gene codes for the proteins that build these tiny structures biases the cells’ shape and movement.

The team found that TUBB4B is 2.7 times more likely to possess rare coding variants in lefties, meaning that left-handed folks are more than twice as likely to have a rare coding variant of this gene that produces varied tubulin. In other words, how a gene codes for the protein that builds microtubules correlates with hand dominance. Carriers of this coding variant have significantly higher chances of being lefties than non-carriers. However, not all lefties have this rare coding variant; they’re simply more likely to have it than righties. Less than 1 percent of the total population analyzed in this dataset had this rare protein-altering genetic variant of TUBB4B.

While the connection between genes coding for microtubule proteins and hand dominance remains unclear, these researchers have found a clue in this particular gene and its variants. Their work furthers evidence that microtubules nonetheless play a role in influencing what eventually becomes hand dominance. Now, we’ve spotted the genetic coding variant and its corresponding protein involved in this trait.