Contribution of GJB2 mutations and Four common DFNB loci in autosomal recessive non-syndromic hearing impairment in Markazi and Qom provinces of Iran

This study aimed to investigate the contribution of four common DFNB ["DFN" for deafness and "B" for autosomal resessive locus] loci and GJB2 gene mutations [exon 2] in hearing impairment in individuals living in Markazi and Qom provinces of Iran. Forty consanguineous Iranian families with at least three affected individuals in family or pedigree who suffer from an autosomal recessive non-syndromic congenital hearing impairment were the subjects of this study. Blood samples were taken from both hearing and non-hearing individuals, DNA was extracted and amplified by using specific primers for the coding region of GJB2 gene [exon 2]. The PCR product of GJB2 gene was then sequenced. Also short tandem repeat [STR] markers amplified by using specific primers for loci DFNB2, DFNB3, DFNB4 and DFNB21. At least 2 microsatellite markers [STR] for each DFNB locus exceeding to 4-6 markers for the linked families were used. The amplified markers were analyzed by conventional Polyacrylamide Gel Electrophoresis followed by silver staining. Six families were homozygous or compound heterozygous for GJB2 mutations and were excluded from further studies. Linkage analysis was carried out for the remaining 34 families by genotyping the flanked STR markers of DFNB2, DFNB3, DFNB4 and DFNB21 loci. Six families showed linkage; including one family to DFNB2, two families to DFNB3 and three families to DFNB4 locus while no family showed linkage to DFNB21 locus. Undoubtedly, the best understanding of the genetic basis of hearing loss in Iranian population will be achieved by performing similar experiments in other provinces and also by analyzing more loci

Mutation analysis of connexin 26 gene and del[GJB6-D13S1830] in patients with hereditary deafness from two provinces in Iran

Mutations in the connexin 26 [Cx26] gene at the DFNB1 locus on chromosome 13q12 are associated with autosomal recessive non-syndromic hearing loss [ARNSHL]. There are many known mutations in this gene that cause hearing loss. A single frameshift, at position 35 [35delG] accounts for 50% of mutations in the Caucasian population with carrier frequencies of 1.5-2.5%. In this study we investigated the prevalence of Cx26 gene mutations by directly sequencing the coding exon of this gene belonging to ARNSHL individuals from 53 families in Qom and Markazi provinces of Iran. Seven different Cx26 variants were identified. Five Cx26 mutations including 35delG, 233delC, 176del16, W24X, L90P were found in 10 of 53 families [18.87%]. One polymorphism V153I was also found. One variant A171T with unknown effects was also detected. Six of the 53 families were observed to have GJB2 mutations in both alleles [11.32%]. The most common mutation was 35delG. Three out of 10 families [30%] with GJB2 variants contained 35delG mutation in both alleles and the frequency of 35delG allele was 0.50 among 10 out of 53 families. Also screening for the 342-kb GJB6 deletion mutant did not reveal any large deletion among families studied. Thus, in the two provinces, contribution of GJB2 [Gap Junction Protein Beta 2] mutations to familial deafness appears to be less significant. This necessitates further assessment of the other known genes regions as well as a search for new genetic factors in hereditary deafness in the Iranian population