Why am I Left Handed?

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As a left hander, all sorts of chaos has ensued throughout my life due to my awkward need to do everything backwards –from irritating elbow bumps at posh meals, the constant battle with ringed notebooks, to getting pen everywhere when I attempt to write anything neatly. Being lefty has changed my life in all sorts of ways, so recently I’ve started wondering, why AM I left handed, and how could this continue to reshape my life in the future?

Now, as around 90% of the population is right handed, it would be natural to assume that right-handedness would be a dominant trait. But actually if this were true, by now left-handedness would have been removed from the gene pool. It turns out there is actually an incredibly complex gene network which affects this handedness, and there has been a lot of research in recent years to locate the genes involved.

There have been many different theories about the genetics of left-handers and the specific genes involved in the development of handedness. The gene LRRTM1 was the first discovered to be linked to left-handedness and is thought to modify the development of asymmetry in the brain. The gene was discovered in 2007 by researchers from the university of Oxford. It’s a well known fact that the left side of the brain controls speech and language and the right side controls emotion, however in left-handers this is often reversed due to action of genes like LRRTM1.

Recently there have been more genes discovered. Researchers behind a paper published in 2013 claim to have found an entire network of genes, which have been linked to the development of asymmetry in the brain, specifically handedness.

The study began in dyslexia sufferers, where researchers found that those with a larger number of mutations in a gene called PCSK6 were more likely to be right handed. It has been known for a while that PCSK6 was related to left right asymmetry in the brain and so the study was expanded further to include those without dyslexia.

The results showed PCSK6 wasn’t the only culprit previously linked with left-right asymmetry in the brain that was found to affect handedness. The effect of the group of genes on handedness was based on the number of mutations in the alleles of each gene the people had. So, the more mutations these genes had on a person in either a left or right handed direction affected their likelihood to be left or right handed.

Unfortunately some of these genes are also linked to illnesses, for example LRRTM1 has been strongly linked to schizophrenia, meaning left-handers could be more likely to develop schizophrenia or schizoaffective disorders particularly if the gene is of paternal origin.

Other studies also link left-handed women to an increased likelihood of breast cancer. The common variable being that exposure to high levels of sex hormones like testosterone in the womb can induce left handedness, in the same way it can induce changes in breast tissue that can lead to cancer. Apparently being a lefty also means you’ll die several years earlier than right-handers and are twice as likely to develop Irritable Bowel Syndrome!

However it’s not all bad news for us left-handers! We’ve also got larger IQs than our right-handed counterparts according to the results from the BBCs ‘Test the Nation’ national IQ test. Left-handers were victorious in scoring an average of 109 compared to the right-handers measly 108. It may seem like the odds are stacked against the left handers but with several famous scientists, geniuses and world renowned musicians being lefties such as Marie Curie, Leonardo Da Vinci, and Jimi Hendrix us lefties must have something going for us!

Lucy

A note from the Antisense Science team- as the links between handedness and dyslexia are relatively new, research is ongoing in this area and requires more data before we can report it as fact.  It is always important to distinguish correlation and causation, as this post neatly points out.

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References:

Photo Credit: JFabra via photopin cc

Francks C1, Maegawa S, Laurén J, Abrahams BS, Velayos-Baeza A, Medland SE, Colella S, Groszer M, McAuley EZ, Caffrey TM, Timmusk T, Pruunsild P, Koppel I, Lind PA, Matsumoto-Itaba N, Nicod J, Xiong L, Joober R, Enard W, Krinsky B, Nanba E, Richardson AJ (2007). LRRTM1 on chromosome 2p12 is a maternally suppressed gene that is associated paternally with handedness and schizophrenia Mol Psychiatry DOI: PMC2990633

Brandler WM1, Morris AP, Evans DM, Scerri TS, Kemp JP, Timpson NJ, St Pourcain B, Smith GD, Ring SM, Stein J, Monaco AP, Talcott JB, Fisher SE, Webber C, Paracchini S. (2013). Common variants in left/right asymmetry genes and pathways are associated with relative hand skill PLoS Genet DOI: PMC3772043

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