“I crashed the flight simulator because I started to hear with my eyes.” (5) It’s not one of the most conventional introduction lines that you’ll ever hear. But really, as many as 1% of the population actually has this form of synaesthesia; that is, auditory-visual synaesthesia. This neurological condition is characterised by the mixing of senses. This is caused by the crossing of sensory stimuli and the resulting combinations formed. For example, people with synaesthesia may see music – usually in the form of a colour – instead of just hearing it. The picture on the left is an example of how someone with synthaesthesia might view letters and colours.
It has been noted since the first description of synaesthesia, by Sir Francis Galton, that this condition tends to run in families, suggesting a genetic link. In fact, “40% of synaesthetes (sufferers of synaesthesia) have a first-degree relative.”(2) This, coupled with the fact that females seem statistically more likely to inherit this disease than males(1), has long since suggested to researchers that synaesthesia is linked to the X chromosome.
However, a recent study headed by Dr. Julien Asher (Department of Genomic Medicine, Imperial College, London), in collaboration with Professor Simon Baren-Cohen (Department of Psychiatry, University of Cambridge), indicates that this may not be the case. Using a “genome wide screen to search for susceptibility genes linked to auditory-visual synaesthesia”(1), they managed to identify four regions that could be linked to synaesthesia: on chromosomes 2, 5, 6 and 12. This suggests that the condition is multigenic. There was no evidence to suggest X-linkage.
Interestingly, the region on chromosome 2, which is most strongly linked to synaesthesia, has also previously been linked to autism. While this does not mean that the two conditions are related, it does suggest that this gene is “involved in how the brain gets built” [Hubbard 2009](3) In addition, the region on chromosome 6 is also linked to dyslexia.
All scientists involved are extremely optimistic that this identification of the genetic factors involved in this condition will be extremely useful. “Once we start to identify genes that are involved, we can start to look at what function they play in a mouse or monkey brain," he said, and then "come up with ways of studying what they do experimentally" Hubbard, a cognitive neuroscientist at Vanderbilt University in Tennessee said.
1 Science Daily 2009, Seeing Sounds or Hearing Colours: Scientists Narrow Search For Genes Associated With Synaesthesia, accessed 26 March 2009, http://www.sciencedaily.com/releases/2009/02/090205133728.htm.
2 Science Blogs LLC 2009, The Genetics of Synaesthesia, accessed 26 March 2009, http://scienceblogs.com/neurophilosophy/2009/02/synaesthesia_the_neurological_condition_in.php.
3 The Genes That Turn ‘Three’ Red 2009, American Scientist, accessed 26 March 2009, http://www.americanscientist.org/science/pub/the-genes-that-turn-three-red.
4 Synthesthesia 2009, Wikipedia Foundation, accessed 26 March 2009, http://en.wikipedia.org/wiki/Synaesthesia.
5 Egan, D. & Dick, L. 2007, 'The Right Stuff', House M.D., Fox, America.
