A recent study highlights the role of rare genetic variations in left-handedness. Globally, most people are right-handed. On average, about 10% of people are left-handed. Despite over a century of research on the origins of left-handedness, it is still not well understood why some individuals are born left-handed while the vast majority are not.
Interestingly, left-handedness tends to run in families, and two left-handed parents are more likely to have a left-handed child than two right-handed parents. This finding led scientists to believe that there is a genetic component to handedness. Indeed, a large-scale study on so-called "common genetic variations" has shown that there are 41 regions in the genome associated with left-handedness and seven associated with ambidexterity (Cuellar-Partida and colleagues, 2021).
While these findings were certainly intriguing, they left one question open. Overall, the identified common genetic variations explained only a small amount of the variation in the handedness data. This suggests that the study does not provide the whole picture and that additional genetic factors influence left-handedness.
A New Study on the Role of Rare Variations in Left-Handedness
A new study, now published in the scientific journal Nature Communications (Schijven and colleagues, 2024), focused on the role of another type of genetic variations in left-handedness, called rare variations. Unlike the common genetic variations explored in previous studies, these rare variations occur in less than 1% of people (hence the name "rare"). This makes it challenging to study them, since very large groups of participants are needed for studies focusing on rare variations.
Fortunately, the scientists had access to a dataset of 38,043 left-handers and 313,271 right-handers from the U.K. A biobank is a huge collection of data used for studying genetic factors in brain research. They used a method called exome sequencing, in which information on genetic variation in all areas of the genome that encode proteins is collected (see Ocklenburg, 2024 for a more detailed description). These genes could be crucial for left-handedness because the proteins they produce are vital for brain and body development.
Rare Genetic Variations Play a Role in Left-Handedness
So, what did the researchers discover?
For the first time, they could show that rare protein-coding genetic variations play a role in left-handedness. Specifically, significant effects were found for rare variations in a gene called TUBB4B. This gene is important for building microtubules, which play a role in providing cell structure. Interestingly, microtubules also play a role in early developmental processes that determine left and right in the body. Therefore, these research findings suggest a connection between left-handedness and left-right differentiation of the body (e.g., that the heart is on the left side and the liver on the right) indeed a fascinating finding.
So, if you are a lefty and wonder why, these findings suggest that one of the reasons might be in your genes!