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Abstract
Introduction: Congenital hearing loss is the most common sensory deficit in the world and mutations in GJB2 gene are the most common cause of deafness in many populations. Frequency of GJB2 mutations is estimated about 16% in Iran and varies among different provinces with a decreasing trend from north to south. The aim of this study was to investigate the frequency of GJB2 mutations in Mazandaran province, north of Iran, among non-syndromic hearing loss patients. Methods: 262 patients from 204 families participated in this study. After genomic DNA extraction, GJB2 gene analysis was carried out using DNA sequencing of both coding and non-coding regions by ABI 3130XL genetic analyzer. Results: 30.15% of all subjects showed mutations in GJB2 gene. Four mutations, including c.35delG (Gly12Valfs*), IVSI-1 + 1G > A, c.95G > A (Arg32His) and c.224 G > A (Arg75Gln) comprises 69.89% of all mutations in this study c.35delG and IVSI-1 were the most common mutations among patients respectively. Codon 75 mutation (c.224G > A. p: Arg75Gln) with autosomal dominant inheritance was seen in 7 cases from 3 families. 22 patients showed only one mutation in GJB2 gene and in 126 (48.09%) individuals, parents had a consanguineous marriage. Discussion: Frequency of GJB2 gene related hearing loss among patients was higher than average (16%) in this province. This study also showed a dominant inheritance pattern of GJB2 gene in this area. Consanguineous marriage also showed highly frequent among parents. More investigation needs to clarify cause of hearing loss in those 22 patients with one mutation in GJB2 gene, either two gene inheritance or another gene may be responsible for hearing loss.
Highlights
Congenital hearing loss is the most common sensory deficit in the world and mutations in GJB2 gene are the most common cause of deafness in many populations
262 patients from 204 families with hearing loss, including 154 severe were screened for GJB2 gene. 79 individuals (30.15%) showed mutations in GJB2 gene, which 72 individuals (27.48%) had two mutations with autosomal recessive inheritance and 7 individuals (2.67%) showed one mutation with autosomal dominant inheritance in GJB2 gene (Figure 1)
The GJB2 gene related hearing loss in Iran varies between 35% to zero, shows a decreasing trend from north to south of the country with average about 16% according to the previous studies [21] [22] [23] [24]
Summary
Congenital hearing loss is the most common sensory deficit in the world and mutations in GJB2 gene are the most common cause of deafness in many populations. The aim of this study was to investigate the frequency of GJB2 mutations in Mazandaran province, north of Iran, among non-syndromic hearing loss patients. 22 patients showed only one mutation in GJB2 gene and in 126 (48.09%) individuals, parents had a consanguineous marriage. The prevalence of deafness in Iran is higher due to the high rate of consanguineous marriages, approximately 3 per 1000 [7] [8]. This disorder is extremely heterogeneous and more than 150 genes are identified causing deafness to date. 121 genes responsible for non-syndromic deafness have been identified, of wich genes have autosomal recessive inheritance, others have autosomal dominant (54 genes) and X-linked (5 genes) inheritance (http://hereditaryhearingloss.org)
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