In your daily life, you may have seen some of your relatives or friends or colleagues that are left-handed and have wondered what makes them left-handed while the vast majority of the people around us are right-handed. Researchers from the University of Oxford also wondered about the same issue and conducted a research study, published in Brain, to see if there is an association between the genetic characteristics and left-handedness. To conduct this study, the researchers used the data from the UK Biobank. Brain imaging phenotypes were identified after analyzing about 9,000 brain imaging data, which included 721 left-handers. Genome-wide association studies were performed in approximately 400,000 individuals that included 38,332 left-handers. Each individual was genotyped across 547,011 single nucleotide polymorphisms (SNPs). SNP-based enrichment analyses were performed to determine the biological pathways. Average expression analyses of mapped genes were performed in 53 tissue types. Estimation of heritability of SNPs according to the right-handed versus left-handed individuals was completed to find out if there is any correlation between genotypes and the neurological and psychiatric diseases.
The analysis of brain images according to the handedness resulted in increased functional connectivity between left and right language networks within the brain in left-handers than in the right-handers. This increased connectivity suggests that left-handers have an advantage in verbal ability over right-handers. The genome-wide analysis of handedness revealed four significant loci (rs199512, rs45608532, rs13017199, and rs3094128). Out of the four loci, three are linked to proteins that are responsible for brain structure and development. One of the four loci (rs1199512) mentioned above was associated with handedness and neurological diseases such as Parkinson’s disease, schizophrenia. The study revealed that left-handers have a lower chance of developing Parkinson's disease than the right-handers. In contrast, left-handers have a higher chance of developing schizophrenia compared to right-handers. The author also concludes that a larger sample size is needed to get a better understanding of the aforementioned associations.