These regions are known to contain genes associated with a variety of disorders, including autism, dyslexia and epilepsy.

Rather than identifying specific genes, this analysis identified four distinct chromosomal regions located on three different chromosomes, all containing genes of interest. In this case, however, the researchers searched for evidence of genetic linkage.Д«y comparing the DNA samples from different generations of synaesthetes from the same family, they identified the microsatellites which are inherited together. These sequences are therefore often used to identify genetic variation in humans, as different alleles of the same gene can be distinguished from one another. Microsatellites consist of very short sequences which are repeated multiple times each allele, or variant, of a given gene contains a unique number of repeats, and this number often varies between individuals. The researchers obtained DNA samples from each participant, and analysed more than 400 microsatellites dispersed across all the chromosomes. They recruited a total of 196 individuals, of which 121 were synaesthetes as confirmed by a questionnaire designed to test for the intensity and genuinesness of the synaesthetic experience. The study reveals also that synaesthesia is not X-linked, and that the genetics of this form of synaesthesia - and probably that of other forms - is far more complex than previously thought.ДЄ group led by Julian Asher of the Wellcome Trust Centre for Human Genetics, in collaboration with Simon Baron-Cohen's group at Cambridge, studied 43 large families, all of which include multiple members with auditory-visual synaesthesia. In the American Journal of Human Genetics, they report the identification of a number of genes that are likely to be involved in auditory-visual synaesthesia, in which sounds are perceived as colours. Researchers from the University of Oxford have now conducted the first genome-wide search for genes linked to the condition.

A number of genetic studies also support the theory that a single gene is responsible for synaesthesia, and that it is inherited in a dominant manner (in other words, just one copy of the gene, inherited from either parent, is sufficient to cause it). Synaesthesia is known to affect females more than males, and although the female predominance of the condition is now known to have been exaggerated, the condition is presumed to be linked to the X chromosome.

Modern techniques have confirmed that the condition does indeed have a strong genetic component - more than 40% of synaesthetes have a first-degree relative - a parent, sibling or offspring - who also has synaesthesia, and families often contain multiple synaesthetes. When Sir Francis Galton first described the 'peculiar habit of mind' we now call synaesthesia, he noted that it often runs in families.

Synthesia condition