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Key points
- About 10% of people are left-handed.
- The reasons for left-handedness are not well understood.
- A new study found that rare genetic variants play a role in left-handedness.
Across the globe, most people are right-handed. On average, only around 10 percent of people are left-handed. Despite more than 100 years of research on the origins of left-handedness, it is still not very well understood why some are born left-handed while the vast majority are not.
Interestingly, left-handedness runs in families, and two left-handed parents have a higher chance of having a left-handed child than two right-handed parents. This finding led scientists to assume that there is a genetic component to handedness. Indeed, a large-scale study on so-called "common genetic variants" has shown that there were 41 locations in the genome associated with left-handedness and seven associated with ambidexterity (Cuellar-Partida and co-workers, 2021).
While these findings were certainly interesting, they left one question open. Altogether, the identified common genetic variants explained only a small amount of the variation in the handedness data. This suggests that the study does not give the whole picture and that further genetic factors influence left-handedness.
A new study on the role of rare variants for left-handedness
A new study, now published in the scientific journal Nature Communications (Schijven and colleagues, 2024), focused on the role of another form of genetic variants on left-handedness, so-called rare variants. Unlike the common genetic variants investigated in previous studies, these rare variants occur in less than 1 percent of people (hence the name “rare”). This makes it difficult to investigate them, since very large groups of volunteers are needed for studies focusing on rare variants.
Luckily, the scientists had access to a dataset of 38,043 left-handers and 313,271 right-handers from the U.K. Biobank, a large dataset used for neurogenetic research. They used a technique 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 may be especially relevant for left-handedness, as these proteins are important for forming the brain and the body.
Rare genetic variants play a role in left-handedness
So, what did the scientists find out?
For the first time, they could show that rare-protein-coding genetic variants play a role in left-handedness. Most importantly, significant effects were found for rare variants in a gene called TUBB4B. This gene is important for building microtubules, which play a role in giving cells stability. Interestingly, microtubules also play a role in very early developmental processes that decide about left and right in the body. Therefore, these research findings suggest a link 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)—certainly an intriguing finding.
So, if you are a lefty and wonder why, these findings suggest that there is a chance that the reason may be in your genes!
References
Cuellar-Partida G, Tung JY, Eriksson N, Albrecht E, Aliev F, Andreassen OA, Barroso I, Beckmann JS, Boks MP, Boomsma DI, Boyd HA, Breteler MMB, Campbell H, Chasman DI, Cherkas LF, Davies G, de Geus EJC, Deary IJ, Deloukas P, Dick DM, Duffy DL, Eriksson JG, Esko T, Feenstra B, Geller F, Gieger C, Giegling I, Gordon SD, Han J, Hansen TF, Hartmann AM, Hayward C, Heikkilä K, Hicks AA, Hirschhorn JN, Hottenga JJ, Huffman JE, Hwang LD, Ikram MA, Kaprio J, Kemp JP, Khaw KT, Klopp N, Konte B, Kutalik Z, Lahti J, Li X, Loos RJF, Luciano M, Magnusson SH, Mangino M, Marques-Vidal P, Martin NG, McArdle WL, McCarthy MI, Medina-Gomez C, Melbye M, Melville SA, Metspalu A, Milani L, Mooser V, Nelis M, Nyholt DR, O'Connell KS, Ophoff RA, Palmer C, Palotie A, Palviainen T, Pare G, Paternoster L, Peltonen L, Penninx BWJH, Polasek O, Pramstaller PP, Prokopenko I, Raikkonen K, Ripatti S, Rivadeneira F, Rudan I, Rujescu D, Smit JH, Smith GD, Smoller JW, Soranzo N, Spector TD, Pourcain BS, Starr JM, Stefánsson H, Steinberg S, Teder-Laving M, Thorleifsson G, Stefánsson K, Timpson NJ, Uitterlinden AG, van Duijn CM, van Rooij FJA, Vink JM, Vollenweider P, Vuoksimaa E, Waeber G, Wareham NJ, Warrington N, Waterworth D, Werge T, Wichmann HE, Widen E, Willemsen G, Wright AF, Wright MJ, Xu M, Zhao JH, Kraft P, Hinds DA, Lindgren CM, Mägi R, Neale BM, Evans DM, Medland SE. Genome-wide association study identifies 48 common genetic variants associated with handedness. Nat Hum Behav. 2021 Jan;5(1):59-70.
Ocklenburg S. Rare variants and handedness: spotlight on TUBB4B. Trends Genet. 2024 May 14:S0168-9525(24)00105-7.
Schijven D, Soheili-Nezhad S, Fisher SE, Francks C. Exome-wide analysis implicates rare protein-altering variants in human handedness. Nat Commun. 2024 Apr 2;15(1):2632.
