Genes for Hearing Colours and Seeing Sounds

Synaesthesia is a neurological condition that is characterized by a visual response to sounds and other images. It affects less than 1% of the population and is known to run in families. In those affected, the stimulation of one sensory pathway results in experiences in another. A person with colour synaesthesia reading black text may see the individual letters or words as vibrantly colorful. In ordinal linguistic personification, numbers, days of the week and months of the year evoke personalities. In spatial sequence or number form synaesthesia, they can elicit precise locations in space; a year could be viewed as a three dimensional map.

How a synaesthete might perceive letters and numbers

Dr. Julian E. Asher from the Department of Genomic Medicine at the Imperial College London designed a study to look for genes linked to auditory visual synaesthesia. The research involved a sophisticated genome-wide screening to search for the genes linked to the condition. Four candidate regions linked with susceptibility were found. Initially, a theory of the condition being linked to the X chromosome was prevalent due to there being no verified reports of father to son transmission. In the study it was found that synaesthesia may depend on interactions between several genes, including genetic loci associated with synesthesia on the long arm of chromosome 2 (2q24), the long arm of chromosome 5 (5q33), the short arm of chromosome 6 (6p12) and the short arm of chromosome 12 (12p12). The region on chromosome 2 was particularly interesting as previously it has been linked to autism. Those who suffer from autism often report sensory and perceptual abnormalities and synaesthesia is sometimes reported as a symptom. Genes associated with dyslexia and epilepsy are also located in the candidate regions.

The findings of the study indicate the genetic basis of the condition as far more complex than previously believed. Inheritance may depend upon a combination of multiple genes and modes of inheritance. "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," Dr. Asher concluded.