Genetic Linkage Analysis of the DFNB21 Locus in Autosomal Recessive Hearing Loss in Large Families from Khuzestan Province

Background: Hearing loss (HL) is the most common congenital defect in humans. One or two in thousand newborn babies have prelingual hearing loss. Autosomal recessive non-syndromic hearing loss (ARNSHL) is the most common form of hereditary deafness. Hearing loss is more common in the developing countries which is due to genetic and environmental (cultural -health factors) reasons. HL has a wide range of clinical demonstrations including: congenital or late onset, conductive or sensoryneural, syndromic or non-syndromic hearing loss. The goal of this project is to determine the portion of the DFNB21 (TECTA) in ARNSHL in families with negative GJB2 gene in Khuzestan province. Materials and Methods: We studied 21 families with ARNSHL with at least 4 patients and negative for GJB2 mutations from Khuzestan province. Genetic linkage analysis was performed using STR markers linked to DFNB21 locus. Results: Following genetic linkage analysis and haplotyping, out of 21 families with ARNSHL, one family showed linkage to the DFNB21 (TECTA) locus. Conclusion: The results of this project confirm other studies in Iran and give insight into the most common loci causing ARNSHL in Iran which could be helpful in research and clinic

Applying Two Different Bioinformatic Approaches to Discover Novel Genes Associated with Hereditary Hearing Loss via Whole-Exome Sequencing: ENDEAVOUR and HomozygosityMapper

Background: Hearing loss (HL) is a highly prevalent heterogeneous deficiency of sensory-neural system with involvement of several dozen genes. Whole-exome sequencing (WES) is capable of discovering known and novel genes involved with HL. Materials and Methods: Two pedigrees with HL background from Khuzestan province of Iran were selected. Polymerase chain reaction-sequencing of GJB2 and homozygosity mapping of 16 DFNB loci were performed. One patient of the first and two affected individuals from the second pedigree were subjected to WES. The result files were analyzed using tools on Ubuntu 16.04. Short reads were mapped to reference genome (hg19, NCBI Build 37). Sorting and duplication removals were done. Variants were obtained and annotated by an online software tool. Variant filtration was performed. In the first family, ENDEAVOUR was applied to prioritize candidate genes. In the second family, a combination of shared variants, homozygosity mapping, and gene expression were implemented to launch the disease-causing gene. Results: GJB2 sequencing and linkage analysis established no homozygosity-by-descent at any DFNB loci. Utilizing ENDEAVOUR, BBX: C.C857G (P.A286G), and MYH15: C.C5557T (P.R1853C) were put forward, but none of the variants co-segregated with the phenotype. Two genes, UNC13B and TRAK1, were prioritized in the homozygous regions detected by HomozygosityMapper. Conclusion: WES is regarded a powerful approach to discover molecular etiology of Mendelian inherited disorders, but as it fails to enrich GC-rich regions, incapability of capturing noncoding regulatory regions and limited specificity and accuracy of copy number variations detection tools from exome data, it is assumed an insufficient procedure