The largest genome wide association study (GWAS) to date on handedness has identified nearly 50 new variants and provided interesting insights into disease predispositions including bipolar disorder and schizophrenia. Left-handedness which accounts around 10% of the population, showed increased predispositions to a number of neurological conditions.

Schizophrenia is a highly polygenic trait with an undetermined number of causal factors and genes involved. With a 1% lifetime risk, identifying associated predispositions may help our understanding of the disorder. Left-handed individuals are over-represented in several neurodevelopmental diseases including autism and depression. Luckily there are positive associations of being left-handed, such as higher educational attainment and increased ability in music and maths.

The international team pre-published in BioRxiv and used publicly available data to find the variants from the UK Biobank, 23andMe, and the International Handedness Consortium. Handedness is defined as the preferential usage of one hand over another, which can first be observed in embryos when they begin single arm movements.

Combining the publicly available data sources yielded 1.5 million right-handed and 194,198 left-handed individuals. From this GWAS 41 loci were identified, 28 of which had been previously associated with other complex traits – 3 with schizophrenia.

In addition, 8 of the loci identified were close to microtubule-associated genes. These structures form part of the cytoskeleton and are essential for cell division, and consequentially neuronal development. Given their role in the control of neuron migration, microtubule-associated genes provide a potential link between left handedness and neurodevelopmental disorders.

The research concludes that handedness is a neurological trait that is not born in the hands. The trait is a highly polygenic one with many small contributing genetic variants. By using such a large sample size, the researchers were able to identify variants previously overlooked. These variants provide guidance of where in the genome warrants further exploration, hopefully facilitating greater understanding of the complex links between hand preference and neurological disorders.

FYI: International Left Handers Day is on August 13th for any fellow lefties who feel slightly disadvantaged by this research!

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