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Congenital hearing loss has been documented to occur in 1 of 1000 live births, with over half of these cases predicted to be hereditary in nature.1,2 Most hereditary hearing loss is inherited in a recessive manner, accounting for approximately 85% of non-syndromic hearing loss (NSHL). Deafness is an extremely genetically heterogeneous disorder, shown by the fact that 33 loci for recessive NSHL and 39 loci for dominant NSHL have been mapped to date (updated regularly on the Hereditary Hearing Loss Homepage: http://dnalab-www.uia.ac.be/dnalab/hhh/index.html). In populations with increased levels of consanguinity, such as India,3 congenital hearing loss is even higher. According to the 47th Round of the National Sample Survey Organisation (NSSO) taken in 1991 (http://www.healthlibrary.com/), 3 242 000 subjects over the age of 5 have a hearing disability, which is defined as a hearing impairment of 60 decibels and above in the better ear to total loss of hearing in both ears. Prelingual recessively inherited deafness has long been recognised in India. A significant number of the deafness loci have been discovered or found in the Indian population, facilitated by the large extended families and high rates of consanguinity. Seven deafness loci are currently known to be associated with deafness in India. These include DFNB3,4 DFNB5,5 DFNB6,6 DFNB7/B11,7 DFNB15,8 DFNB17,9 and DFNB18.10 In four of these seven cases, the associated gene has been cloned: transmembrane cochlear expressed gene 1 (TMC1) for DFNB7/B11,11 myosin XVA (MYO15A) for DFNB3,4,12 transmembrane inner ear expressed gene (TMIE) for DFNB6,13 and harmonin for DFNB18.14
In many parts of the world, deafness associated with the DFNB1 locus on chromosome 13q11 is the most prevalent. Two genes localised to this chromosomal region have been implicated in deafness, including connexin26 (Cx26, gene symbol GJB2 …