Assessing Noncoding Sequence Variants of GJB2 for Hearing Loss Association

The noncoding genome and hearing loss

The age of sequencing has provided unprecedented insights into the human genome. The coding region of the genome comprises nearly 20,000 genes, of which approximately 4000 are associated with human disease. Beyond the protein-coding genome, which accounts for only 3% of the genome, lies a vast pool of regulatory elements in the form of promoters, enhancers, RNA species, and other intricate elements. These features undoubtably influence human health and disease, and as a result, a great deal of effort is currently being invested in deciphering their identity and mechanism. While a paucity of material has caused a lag in identifying these elements in the inner ear, the emergence of technologies for dealing with a minimal number of cells now has the field working overtime to catch up. Studies on microRNAs (miRNAs), long non-coding RNAs (lncRNAs), methylation, histone modifications, and more are ongoing. A number of microRNAs and other noncoding elements are known to be associated with hearing impairment and there is promise that regulatory elements will serve as future tools and targets of therapeutics and diagnostics. This review covers the current state of the field and considers future directions for the noncoding genome and implications for hearing loss.

Evaluation of the GJB2 and GJB6 Polymorphisms with Autosomal Recessive Nonsyndromic Hearing Loss in Iranian Population

INTRODUCTION

Hearing loss (HL), with more than 100 gene loci, is the most common sensorineural defects in humans. The mutations in two GJB2 and GJB6 (Gap Junction Protein Beta 2, 6) genes are responsible for nearly 50% of autosomal recessive nonsyndromic hearing loss. The aim of the present study was to evaluate polymorphisms of 111C>T (rs7329857) and 337G>T (rs7333214) in GJB2 (encoding connexin 26) and GJB6 (encoding connexin 32) genes, respectively.

MATERIALS AND METHODS

In this study, 32 blood samples were obtained from Iranian patients with HL defect and 32 normal blood samples were prepared. After genomic deoxyribonucleic acid extraction, genotyping in rs7333214 and rs7329857 polymorphisms was conducted using tetra-amplification refractory mutation system-polymerase chain reaction and the obtained data were analyzed.

RESULTS

In this study, the prevalence rates of CC, CT, and TT genotypes in GJB2 gene were reported as 84.4%, 68.7%, and 0% in the affected subjects and 0%, 15.6%, and 31.3% in the control samples, respectively, which were statistically significant (P=0.004). In relation to GJB6 gene, the prevalence rates of GG, GT, and TT genotypes were 65.2%, 78.1%, and 25% in the control subjects and 21.9%, 9.4%, and 0% in the affected samples, respectively, which were not statistically significant (P>0.05).

CONCLUSION

The results of this study revealed that 111C>T polymorphism in GJB2 gene was involved in the incidence of HL in the studied population and could be suggested as a prognostic factor in genetic counseling before marriage and pregnancy.

Unique Mutational Spectrum of the GJB2 Gene and its Pathogenic Contribution to Deafness in Tuvinians (Southern Siberia, Russia): A High Prevalence of Rare Variant c.516G>C (p.Trp172Cys)

Mutations in the GJB2 gene are the main cause for nonsyndromic autosomal recessive deafness 1A (DFNB1A) in many populations. GJB2 mutational spectrum and pathogenic contribution are widely varying in different populations. Significant efforts have been made worldwide to define DFNB1A molecular epidemiology, but this issue still remains open for some populations. The main aim of study is to estimate the DFNB1A prevalence and GJB2 mutational spectrum in Tuvinians-an indigenous population of the Tyva Republic (Southern Siberia, Russia). Sanger sequencing was applied to analysis of coding (exon 2) and non-coding regions of GJB2 in a cohort of Tuvinian patients with hearing impairments (n = 220) and ethnically matched controls (n = 157). Diagnosis of DFNB1A was established for 22.3% patients (28.8% of familial vs 18.6% of sporadic cases). Our results support that patients with monoallelic GJB2 mutations (8.2%) are coincidental carriers. Recessive mutations p.Trp172Cys, c.-23+1G>A, c.235delC, c.299_300delAT, p.Val37Ile and several benign variants were found in examined patients. A striking finding was a high prevalence of rare variant p.Trp172Cys (c.516G>C) in Tuvinians accounting for 62.9% of all mutant GJB2 alleles and a carrier frequency of 3.8% in controls. All obtained data provide important targeted information for genetic counseling of affected Tuvinian families and enrich current information on variability of GJB2 worldwide.

Novel deleterious mutation in MYO7A, TH and EVC2 in two Pakistani brothers with familial deafness

Objective

In Pakistan, 74% of consanguineous marriages are among the first cousins. Continuity of consanguineous marriages over generations increases the risk of recessive diseases such as deafness. The objective of this study was to investigate genetic origin of Pakistani deaf brothers with parents of consanguineous marriage.

Methods

DNA was extracted from the blood through Qiagen kit. Paired-end sequencing library was prepared according to protocol of Illumina's TruSight Rapid Capture kit and TruSight Inherited Disease Panel. Library was normalized and used for Next Generation Sequencing through MiSeq. NGS data were analyzed using various bioinformatics tools.

Results

Both brothers were found to have novel deleterious mutation in MYO7A (c.2476G>A) while the younger brother had additional novel deleterious mutation in TH (c.43C>T) and EVC2 (c.2614C>T) genes.

Conclusion

It is concluded that in addition to novel mutations in MYO7A, TH and EVC2, the CDH23 and GJB2 can also be responsible for deafness in the family with consanguineous marriages.