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)

Abstract

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.

Keywords: GJB2; Russia; Southern Siberia; Tuvinians; hearing loss; nonsyndromic autosomal recessive deafness 1A (DFNB1A).

Figure 1

(A) Identification of the c.516G>C (p.Trp172Cys) mutation by Sanger sequencing. (B) The 3D structure of normal protein connexin 26 (Cx26-WT). Two adjacent Cx26-WT hemichannel subunits with designation of Trp (tryptophan) on position 172. The extracellular loop of Cx26 (E2, 155-192 amino acid residues) where variant p.Trp172Cys located is marked by blue. (C) Close-up view of Cx26-WT (Trp172) and mutant Cx26-p.Trp172Cys (Cys172) connexin 26.

Figure 2

The pedigrees of Tuvinian families demonstrating the segregation of variant c.516G>C (p.Trp172Cys) in a homozygous state or in compound with other recessive GJB2 mutations (c.235delC, c.-23+1G>A, and c.299_300delAT) with HL in affected family members. Deaf individuals are shown by black symbols. The variant c.516G>C (p.Trp172Cys) is shown by red.