Genetic Linkage of DFNB4, DFNB28, DFNB93 Loci in Autosomal Recessive Non-syndromic Hearing Loss: Evidence for Digenic Inheritance in GJB2 and GJB3 Mutations

Background: Autosomal recessive non-syndromic hearing loss (ARNSHL) a most frequent hereditary type ofhearing impairment, exhibit tremendous genetic heterogeneity. We aimed to determine the contribution of threecommon DFNB loci (DFNB4, DFNB28, and DFNB93), and mutation analysis of Gap Junction Beta-2 gene(GJB2) and GJB3 genes in ARNSHL subjects in southern Iran.Methods: Thirty-six large ARNSHL pedigrees (167 individuals) with at least two affected subjects (72 patients)were included in this descriptive study from Hormozgan Province of Iran, during 2014 - 2015. The variation ofGJB2 and GJB3 genes were screened using direct sequencing method. The negative samples for GJB2 and GJB3genes mutations were analyzed for the linkage to DFNB4, DFNB28, and DFNB93 loci by genotyping thecorresponding short tandem repeat (STR) markers using polymerase chain reaction (PCR) and polyacrylamide gelelectrophoresis (PAGE) methods.Results: DNA sequencing of GJB2 were identified heterozygous mutation (964 C/T) in 13.88% of the studiedfamilies. Three missense mutations (788G/A, 284C/T and 973G/C) were also detected in coding region of theGJB3 gene. The 284C/T mutation in the GJB3 occurs in compound heterozygosity along with the 964T/Cmutation in the GJB2 in one family. Finally, we found no evidence of linkage to either of DFNB4, DFNB93 andDFNB28 loci.Conclusion: Highlighting the hypothesis that a genetic interaction between GJB2 and GJB3 genes could be lead toARNSHL, however, no evidence of linkage to the DFNB loci was found. 284C/T variant in GJB3 gene might bepathogenic when accompanied by variant in GJB2 in a digenic pattern. However, further large-scale familial andfunctional studies are required to challenge this hypothesis.

Keywords:

ARNSHL , GJB2 , GJB3 , DFNB loci , Linkage analysis