First genetic clues to synaesthesia revealed

17 February 2009

Trust-funded researchers have found the first genetic regions with links to synaesthesia, the brain condition that leads some people to see sounds and hear written words.

The research, the first genome-wide association study of the condition, brings us closer to identifying the genes that play a key role in its development. This could also shed light on how genetics affects our cognition and perception.

Synaesthesia affects about one per cent of the population. Researchers from the Wellcome Trust Centre for Human Genetics and colleagues examined the genomes of 43 families with synaesthesia for genetic variations.

They found four regions with links to the condition, the strongest in a region on chromosome 2. This houses a number of genes, one of which is important in the development of the cerebral cortex - the part of the brain that deals with memory and language. Other genes are associated with nervous system problems that cause epilepsy.

Separate regions contain genes linked to other neurological and psychiatric disorders, such as dyslexia and autism, or code for receptors involved in learning and memory.

"Our study shows clearly that there is not a single gene involved in this disorder, so it is probably several gene variants acting together to increase susceptibility or many major genes involved, but each contributing strongly to individual cases," said Professor Anthony Monaco, Head of the Neurodevelopmental and Neurological Disorders Group at the Wellcome Trust Centre, and a co-author on the study.

Contrary to previous suggestions, the study found no evidence of links to the X chromosome, indicating that the condition is not simply inherited from the mother. In fact, two of the families were the first confirmed cases of father-to-son transmission of synaesthesia.

"The lack of evidence for a major gene involved from the X chromosome indicates that there are probably multiple genes involved, and that there must be other explanations besides X linkage to explain the preponderance of females affected," said Professor Monaco.

Image credit: schaaflicht, Flickr (licensed under Creative Commons)

Reference

Asher JE et al. A Whole-Genome Scan and Fine-Mapping Linkage Study of Auditory-Visual Synesthesia Reveals Evidence of Linkage to Chromosomes 2q24, 5q33, 6p12, and 12p12. The American Journal of Human Genetics, published online before print 5 February 2009.