> A genetic analysis has identified a possible origin of this perceptual phenomenon in a set of genes that determine a hyper-interconnection between brain areas, thus supporting the hypothesis that synaesthesia has a hereditary component.

Synesthesia is a perceptual phenomenon in which inputs from different senses are associated with each other. In particular, a stimulation of a sense automatically provokes a secondary perception in another sense. It is a peculiarity that only some people experience, who can see colors associated with sounds, or a geometric shape associated with a flavor. So far this phenomenon has remained without a plausible organic explanation. Not only because the different senses refer to different physical phenomena, but also because in the most commonly accepted neurobiological model the different sensory information is elaborated in separate regions of the cerebral cortex.

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However, the research carried out in this field highlighted important data. Synesthesia is structured in childhood, occurs in some families and concerns generations. It is very likely therefore that it has a hereditary component. [A study published in the "Proceedings of the National Academy of Sciences"](http://www.pnas.org/content/early/2018/02/27/1715492115) by a collaboration between the Max-Planck-Institute for Psycholinguistics in Nijmegen, in the Netherlands, and the University of Cambridge in the United Kingdom, has now thoroughly analyzed genetics of synaesthesia. 

>"Brain imaging studies indicate that the brains of adults who are able to experience synaesthesia have circuits that are slightly different from those of normal people," said Amanda Tilot, a Max-Planck-Institut geneticist and co-author of the study. "Hence the confirmation that part of the answers on the origin of this phenomenon is to be found in the genetic heritage". 




Thanks to advanced sequencing techniques, the group has studied gene variants that occur in three synaesthetic families, whose members have a specific tendency to associate sounds and images; the authors, in particular, have traced the passage of these variations from generation to generation. 
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The analysis of the data confirmed that the genetics of synaesthesia is complex, ie it does not depend on a few genes valid for all cases. The researchers have identified a first set of 37 genes, some of which, in each family, are co-segregated, ie they are transmitted together from generation to generation. There are then seven genes that are particularly active during the neurocerebral development phase, which in children marks the beginning of manifestations of visuo-auditory synaesthesia. 

These are the COL4A1 , ITGA2 , MYO10 , ROBO3 , SLC9A6 and SLIT2 genes , which code for proteins involved in various ways in neuronal differentiation, in the migration of nerve cells and especially in the atherogenesis, ie in the formation and growth of axons. These are offshoots that ensure the connection between different neurons both within the brain regions and between one region and another. 

Overall, therefore, the results corroborate the hypothesis that at the origin of the synaesthesia, at least for the visual-auditory type analyzed, there is an interconnection between different populations of neurons and probably between different brain regions.


### References For Further Reading 

[Reliawire](https://reliawire.com/axonogenesis-variants-synesthesia/)

[Science Daily](https://www.sciencedaily.com/releases/2018/03/180305150549.htm)

[Medical Xpress](https://medicalxpress.com/news/2018-03-uncover-molecular-clues-synesthesia.amp)


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