Genomic architecture of deafness in Turkey reflects its rich past

More than 60% of prelingual deafness is genetic in origin, and of these up to 93% are monogenic autosomal recessive traits. Turkey has been continually inhabited since ancient times with traditional settlement of small and isolated villages. There is a high level of both parental consanguinity and assortative mating among the deaf and a long history of the use of sign language. All of these factors are known to have a profound influence on the survival, expression and spread of new mutations for deafness. Many of the identified deafness alleles are private in a single family or in an isolated village that reflect the effect of small population size or parental consanguinity. Single origins have been demonstrated for some mutations, including 35delG in GJB2 and R84W in TMIE, that are recurrently identified in unrelated families. Historic population movements in and around Turkey leading to gene flow and consequently founder effects are responsible for these mutations. Assortative mating among the deaf is likely to have contributed to contemporary high frequency of certain deafness loci.