Genetic causes of nonsyndromic hearing loss in Iran in comparison with other populations

Hearing loss (HL) is the most prevalent sensory defect affecting 1 in 500 neonates. Genetic factors are involved in half of the cases. The extreme heterogeneity of HL makes it difficult to analyze and determine the accurate genetic causes of the impairment. Up to now, 10 genes, namely, GJB2, GJB6, SLC26A4, TECTA, PJVK, Col11A2, Myo15A, TMC1, RDX and microRNA (miR-183), have been studied in an Iranian population. The prevalence of HL in Iran was estimated to be 2-3 times higher than that in other parts of the world. Here, the most common bases of congenital nonsyndromic hearing loss (NSHL) are discussed. We reviewed GJB2, GJB6 (large deletion), TECTA, SLC26A4 and PEJVK mutations, and studied their frequencies and distributions in different ethnic groups in 1934, 500, 121, 80 and 34 unrelated families throughout Iran, respectively. GJB2 mutation was the most common factor causing NSHL, with a mean frequency of 18.17% in the Iranian population. The importance of Iran's geographical location in the migration pathway from west to east through the silk route was also highlighted. SLC26A4 and TECTA mutations were the second and third main reasons of HL and accounted for up to 10 and 4% of prelingual HL in Iran, respectively. Mutations in GJB2, SLC26, TECTA and PJVK genes have an important role in HL in Iran and a screening test should be generated for better intervention and diagnosis programs.