Frequency of W24X Gene Polymorphism among the Students from Hearing Impaired Schools of Shimoga District

Introduction An important accompaniment of Non-syndromic sensorineural hearing loss is family history and consanguinity. One of the widely studied single nucleotide polymorphism is the gap junction protein beta-2 (GJB2) gene which encodes the protein connexin26. This study aims to detect the frequency of W24X mutation in a population with non-syndromic sensorineural hearing loss concerning the degree of consanguinity. Materials and Methods The study includes 76 subjects with Non-syndromic sensorineural hearing loss. These subjects had congenital sensorineural hearing loss and other causes for the same had been ruled out. The SNP rs 104894396 was identified by the PCR-RFLP method. Results The frequency of the wild allele was 0.84% and the mutant allele was 0.15%. The frequency of wild allele and mutant allele did not differ much between patients with and without consanguinity. The association between consanguineous marriage and allele frequency was not significant. Gene polymorphism was not present in 77 percent of our NSHL subjects, though 79 percent of our study population were a result of consanguineous marriage. Conclusion Though the role of consanguineous marriages in congenital sensorineural hearing loss is well established, the association between allele frequency and consanguineous marriage was not seen. We assume that other genes responsible for deafness may be involved in the population.

Whole-Genome Sequencing Improves the Diagnosis of DFNB1 Monoallelic Patients

Hearing loss is the most common sensory defect, due in most cases to a genetic origin. Variants in the GJB2 gene are responsible for up to 30% of non-syndromic hearing loss. Today, several deafness genotypes remain incomplete, confronting us with a diagnostic deadlock. In this study, whole-genome sequencing (WGS) was performed on 10 DFNB1 patients with incomplete genotypes. New variations on GJB2 were identified for four patients. Functional assays were realized to explore the function of one of them in the GJB2 promoter and confirm its impact on GJB2 expression. Thus, in this study WGS resolved patient genotypes, thus unlocking diagnosis. WGS afforded progress and bridged some gaps in our research.

Spectrum and frequency of GJB2 (Cx26) gene mutations in patients with hearing impairments in the Republic of Buryatia

В диагностике наследственной несиндромальной потери слуха высокую информативность обеспечивают методы молекулярно-генетического анализа мутаций гена GJB2 (Cx26). Впервые в Республике Бурятия (Восточная Сибирь) путем прямого секвенирования были определены спектр и частота мутаций гена GJB2 у 165 индивидов с нарушениями слуха. В обследованной выборке было обнаружено 13 известных аллельных вариантов гена GJB2 (c.-254C>T, c.-49G>A, c.-23+1G>A, c.35delG, c.79G>A, c.101T>C, c.109G>A, c.235delC, c.299_300delАТ, c.327_328delinsA, c.341A>G, c.457G>A и c.516G>C). У пациентов бурятов мутационный спектр был представлен пятью патогенными GJB2-вариантами: c.-23+1G>A (4,1%), c.109G>A (0,6%), c.235delC (1,4%), c.327_328delGGinsA (0,6%), c.516G>C (0,6%). Среди русских пациентов было обнаружено пять мутаций: c.35delG (25,7%), c.-23+1G>A (3,3%), c.101Т>С (0,6%), c.109G>A (1,9%), c.299_300delАТ (0,6%). Вклад биаллельных мутаций гена GJB2 в этиологию потери слуха в общей выборке пациентов из Бурятии составил 15,8% (26/165). При распределении пациентов по этнической принадлежности вклад биаллельных мутаций гена GJB2 в этиологию потери слуха у русских составил 28,9% (22/76), в то время как у бурятов лишь 5,1% (4/79). Таким образом, результаты нашего исследования свидетельствуют о том, что мутации гена GJB2 не являются основной причиной потери слуха у бурятов. Вероятно, у большей части GJB2-негативных пациентов потеря слуха может быть обусловлена мутациями в других генах, ответственных за развитие наследственных нарушений слуха. In the diagnosis of hereditary non-syndromic hearing loss (HL), the methods of molecular genetic analysis of the GJB2 (Cx26) gene mutations provide high valuable information. For the first time, in the Republic of Buryatia (Eastern Siberia), the spectrum and frequency of GJB2 gene mutations were determined in a sample of 165 individuals with HL using sequencing of significant regions of the GJB2 gene. A total of 13 known allelic variants were found (c.-254C>T, c.-49G>A, c.-23+1G>A, c.35delG, c.79G>A, c.101T>C, c.109G>A, c.235delC, c.299_300delAT, c.327_328delinsA, c.341A>G, c.457G>A u c.516G>C). In the sample of Buryat patients, the mutation spectrum was represented by five GJB2 variants: c.-23+1G>A (4.1%), c.109G>A (0.6%), c.235delC (1.4%), c.327_328delGGinsA (0.6%), c.516G>C (0.6%). Five mutations were found among Russian patients: c.35delG (25.7%), c.-23+1G>A (3.3%), c.109G>A (1.9%), c.101T>C (0.6%), c.299_300delAT (0.6%). In general, the contribution of biallelic mutations of the GJB2 gene to the etiology of HL in the total sample of patients in Buryatia was 15.8% (26/165). When the total sample of patients was divided by ethnicity the contribution of biallelic mutations of the GJB2 gene to the etiology of HL in Buryat patients was 5.1% (4/79), and in Russian patients - 28.9% (22/76). Thus, the results of our study indicate that the mutations in the GJB2 gene are not the main cause of HL in Buryats. Probably, in some GJB2-negative patients (84.2% in our study), HL may be due to the mutations in other genes responsible for the development of hereditary hearing impairments.

A Common Founder Effect of the Splice Site Variant c.-23+1G>A in GJB2 Gene Causing Autosomal Recessive Deafness 1A (DFNB1A) in Eurasia

The mutations in the GJB2 gene are known to be a major cause of autosomal recessive deafness 1A (OMIM 220290). The most common pathogenic variants of the GJB2 gene have high ethno-geographic specificity in their distribution that being attributed to a founder effect related with Neolithic migration routes of Homo sapiens. Curiously, the c.-23+1G>A splice site variant is frequently found among deaf patients of both Caucasian and Asian origin. It is currently unknown whether this mutation did spread across Eurasia as a result of the founder effect or it could have multiple local centers of origin. To determine the origin of the c.-23+1G>A we reconstructed 𝑓2-haplotypes by genotyping SNPs on the Illumina OmniExpress 730K platform in 23 deaf individuals homozygous for this variant from different populations of Eurasia (Yakuts, Tuvinians, Evenk, Kumyk, Armenian, Russians and Slovak). The analysis revealed that the homozygosity regions in different individuals overlapped in one short region with the length of ~5.2 kb. These data support the hypothesis of the common founder effect in distribution of the c.-23+1G>A variant of GJB2 gene. Based on the published data on the c.-23+1G>A prevalence among 16,177 deaf people and calculation of TMRCA of the 𝑓2-haplotypes carrying this variant we reconstructed the potential migration routes of the c.-23+1G>A carriers around the world. This analysis indicates that the c.-23+1G>A variant may have originated approximately 6,000 years ago in the territory of the Caucasus or Middle East, followed by spread throughout Europe, South and Central Asia and other regions of the world.

GJB2: Frequency of the Less Common Variants in a Sample of the Portuguese Population

Introduction: Sequence variants in the GJB2 gene account for up to 50% of cases of non-syndromic sensorineural hearing loss in the Caucasian population. In this study, we report the frequency of the less common variants of the GJB2 gene in a Portuguese sample and compare these frequencies with those of a group of hearing-impaired patients.Material and Methods: In order to select the less common GJB2 variants, 147 hearing-impaired patients followed in Centro Hospitalar Universitário de São João were evaluated. Afterwards, the presence of those variants was tested in 360 individuals from Generation 21.Results: The patient assessment enabled the selection of 11 GJB2 variants. Of those, 10 were investigated in Generation 21 participants, with only four being detected, in heterozygosity: p.Phe83Leu, p.Arg127His, p.Val153Ile and p.Asn206Ser, with the allelic frequencies (95% confidence interval) of 0.14% (0.01% - 0.87%), 0.28% (0.01% - 1.08%), 0.97% (0.43% - 2.04%) and 0.14% (0.01% - 0.88%), respectively. Two variants, p.Val37Ile and p.Val95Met, were more frequent in the patients’ group with statistical significance.Discussion: Our results allow for the p.Arg127His and p.Val153Ile variants to comply with polymorphism criteria and support the pathogenicity of p.Val37Ile and p.Val95Met variants. Moreover, two cases of moderate hearing loss were explained by the p.Val37Ile/p. Asn206Ser genotype, substantiating both the pathogenicity of such variants and the hypothesis that compound heterozygosity with p.Ans206Ser is associated with mild-moderate genotypes.Conclusion: Understanding the role of the variants is essential in order to provide genetic counselling to patients and their families. We explored a set of uncommon GJB2 variants that comprised 12% of the hearing-impaired patients in this study, supporting the relevance of their description.

Connexin 26 (GJB2) Gene Mutations Linked With Autosomal Recessive Nonsyndromic Sensorineural Hearing Loss in Iraqi Population.

Objectives: The ARNSHL wasn’t been studied enough in Iraq, this study aimed to detect the prevalence of the three most common mutations of Connexin 26 gene in Iraqi population. This study was conducted in order to detect c.35delG, c.235delC and c.167delT mutations in GJB2 gene, we were employed PCR-RFLP assays.Results: The current case-control study was conducted from January 2018 to January 2020, The study was included 95 deaf patients (55 males and 40 females) their age range between 11-40 years and 21.5 ± 6.3 year (mean ± SD) and 110 healthy control group, their ages range between 10-40 years and 20.1 ± 5.9 year (mean ± SD), these two groups were matched in age and gender. From 95 deaf patients with ARNSHL who were participated in this study, c.35delG was the main frequent mutation encountered with GJB2 gene, The second frequent mutation was c.235delC, None of 95 deaf patients were showed the c.167delT mutation, these variants were not detected in healthy control group which was studied parallel with patients group. Our data conclude that GJB2 c.35delG and c.235delC gene mutations were the main cause of ARNSHL in Iraqi deaf population.