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.