Etiology of Hearing Loss and Genetic Hearing Loss

Hearing loss is one of the most common sensory disorders and has numerous environmental and genetic factors that influence its onset and development. Hearing loss can be classified by either the affected anatomic or functional lesion of hearing loss, or as conductive or sensorineural hearing loss (SNHL). Genetic factors account for about 50% of congenital SNHL, and are therefore the most common cause. Molecular genetics research has identified more than 100 genes related to hearing and hearing loss, and shown that the risk of hearing loss caused by non-genetic factor is modified by genetic susceptibility. About 30% of genetic hearing loss is syndromic related and has affected phenotypic markers in other organs that make it easier to correctly diagnose the etiology of the hearing loss. In some cases, hearing loss can precede the pathologies of other organs and in these cases, hearing loss acts as a predictor of the syndrome associated pathologies of other organs. Inheritance of nonsyndromic hearing loss follows common inheritance patterns such as autosomal dominant, autosomal recessive, sex chromosome related, and mitochondrial inheritances. The paucity of predominant phenotypes and ethnic specificity of the prevalence and types of mutations may hinder the genetic diagnosis in nonsyndromic hearing loss. However, progress in elucidating the causal mutations is going forward using stratified genetic diagnostic strategies of candidate genes identified by hearing phenotypes and patterns of inheritance.