Seeing sounds: a genetic link to synaesthesia

A scientist who has synaesthesia and is leading research into the neurological condition has found a link to genetic regions in chromosomes. It is hoped that the work, published in the American Journal of Human Genetics last week, will help to improve understanding into cognitive development.

Synaesthesia is defined as a cross wiring of senses, when stimulation of one sensory pathway leads to involuntary experiences in a second sensory pathway, for example sound synaesthesia - when a person perceives sounds as colours. Another form is the stimulation of one sensory pathway being experienced as another facet of the same pathway, for example colour synaesthesia - when a person sees letters or numbers as colours. The condition is seen in less than one per cent of the population, and is known to run in families, although the genetics are not well understood.

Dr Julian Asher says that when he hears a violin, he sees 'something like a rich red wine' and that 'a cello is more like honey'. He designed the research as part of his PhD in Professor Anthony Monaco's laboratory at the Wellcome Trust Centre for Human Genetics at the University of Oxford, along with Professor Simon Baron-Cohen at the Department of Psychiatry at the University of Cambridge. The study comprised a genetic analysis that tracked markers in the genes of 121 individuals from 43 families who have the condition. Comparison with individuals from the same families who do not exhibit symptoms allowed the identification of four regions of chromosomes linked to the syndrome.

The most interesting of these was on chromosome 2, as this region has previously been linked to autism. Sensory and perceptual abnormalities have also been described as part of the autism spectrum disorders. The other candidate regions were also intriguing, as they were known to be involved in regulating neuronal activity and brain structure, as well as epilepsy, dyslexia, learning and memory.

The findings will not only help the understanding of the complicated genetics of synaesthesia, but also help develop simple diagnoses of the condition in children. Synaesthesia can be distracting for children in a learning environment, so a genetic test to allow its early identification could facilitate their academic success.

Dr Asher concludes: 'This study comprises a significant step towards identifying the genetic substrates underlying synaesthesia, with important implications for our understanding of the role of genes in human cognition and perception'.