The impact of the sociodemographic structure of deaf people communities on the prevalence of hereditary hearing loss

Abstract

Hearing loss caused by environmental or genetic factors concerns more than 10% of the world’s population, leading to disability and considerable deterioration of the quality of life for deaf people. On the average, one in 1000 children is born deaf with 50–60% of the cases having a genetic cause. Nonsyndromic hereditary deafness is a monogenic disease with uniquely high genetic heterogeneity. The prevalence of some forms of genetic deafness varies in different regions of the world and is determined, as for many other monogenic diseases, by the ethnic composition, isolation, founder and bottleneck effects, rate of consanguineous marriages, and potential heterozygote selective advantage. It is assumed that some social factors (a longstanding tradition of assortative marriages between deaf people combined with an increase in their social adaptation and genetic fitness) have contributed to a high prevalence of hearing loss caused by mutations in the GJB2 (C×26) gene. The breach of deep social isolation of the deaf some 300 years ago in Europe (and later in the United States) with the establishment of schools for the deaf teaching sign language as a common communication tool (linguistic homogamy) triggered these events. Computer simulation and comparative retrospective studies have shown that these social processes could have doubled the rate of GJB2 deafness in the United States over two centuries. The information about the sociodemographic structure of deaf communities in the past is extremely limited by the almost complete lack of the relevant archival data. Nevertheless, studies of the sociodemographic and medical genetic characteristics of deaf communities are now important for both predicting the prevalence of various hereditary deafness forms and understanding the impact of social factors on evolutionary processes in human populations.