A Review on Autosomal Recessive Non-syndromic Hearing Impairment

Hearing impairment (HI) or deafness is the most common sensory disorder in humans. The prevalence of bilateral hearing loss is 1.6 in 1,000 in Pakistan. HHI may be syndromic or non-syndromic, prelingual or postlingual, and conductive or sensorineural. Non-syndromic HHI results in sensorineural hearing loss. About 40 genes are identified to cause non-syndromic autosomal recessive deafness of 120 cloned genes of deafness. HHI is 75-80% transmitted through an autosomal recessive trait. Total 95 autosomal recessive non-syndromic deafness loci (DFNB) have been identified. Up till now, 28 loci and 15 genes involved in deafness have been mapped in Pakistan. Different mutations in the same gene may cause different phenotypes. Most cases of recessive HHI involve mutation in a single locus. But cases are found in which mutation in two different genes (GJB2/GJB6) or two different mutations in a single allele (GJB2) are involved. The GJB2 is the most important gene responsible for 50% of the cases of prelingual, non-syndromic autosomal recessive hearing loss. Others include SLC26A4, MYO15A, OTOF, CDH23 and TMC1. These genes are the most frequent cause of autosomal recessive non-syndromic hearing impairment. In the present report, we have reviewed these genes, their functions, mutations, and their contribution to genetic deafness. Cochlear implant is one of the solutions for cure of congenital sensorineural deafness. Gene therapy is under clinical trials to treat the defective gene involved in hearing impairment.