Connexin 26 and autosomal recessive non-syndromic hearing loss

It has long been recognized that heredity plays a major role in hearing impairment. Although the facts about the genetic basis of hearing loss have fascinated both clinicians and geneticists for a long time, it is only within the last few years that the genes and molecular mechanisms underlying deafness have begun to be discovered. There is a great deal of genetic heterogeneity in deafness. This reflects many different loci for deafness involved in orchestrating the hearing process. Hearing loss can be conductive, sensor ineural or mixed in nature. Genetic heterogeneity makes the identification of causative mutation necessary for accurate diagnosis of the cause of deafness. Hearing loss is also caused by environmental factors adding complexities to identification of etiology. Genetic form of hearing loss can be syndromic or non-syndromic. The syndromic disorders are those where hear ing loss is accompanied by involvement of one or several other organ systems and non-syndromic disorders, where the inner ear appears to be the only affected organ. Hundreds of syndromic forms of deafness have been described and the underlying genetic defects have been identified for many of the more common forms. Thirty percent of genetic cases are estimated to be part of a heritable syndrome. Thus, the vast majority of genetic deafness is isolated or non-syndromic. This review focuses primarily on non-syndromic autosomal recessive type of hearing loss (ARNSHL).