Mutation in gap and tight junctions in patients with non-syndromic hearing loss

Genetics and meta-analysis of recessive non-syndromic hearing impairment and Usher syndrome in Maghreb population: lessons from the past, contemporary actualities and future challenges

Hereditary hearing impairment (HI) is a heterogeneous condition with over 130 genes associated with genetic non-syndromic HI (NSHI) and Usher syndrome (USH). Approximately 80% of hereditary NSHI cases have autosomal recessive (AR) mode of inheritance. The high rate of consanguinity and endogamy in the Maghreb countries, including Tunisia, Algeria and Morocco, represents a major contributing factor to the development of ARHI. Since the 90s, those populations, with their particular large familiar structure, represented an effective key towards the discovery of the first HI loci and genes. In this study, we performed a deep literature database search to analyze the mutational spectrum and the distribution of pathogenic variants responsible of USH and the NSHI among those populations. To date, 124 pathogenic variants were identified in 32 genes of which over 70% represent population-specific variants. The particular variants' distribution is related to the high rate of consanguinity as well as the multiple shared features such as demographic history of migrations and social behavior that promoted the spreading of several founder mutations within those countries. This is the first study to report lessons from the past and current actualities of HI within the three Maghreb countries. However, despite the great impact placed by such population for the HI genetic studies, only a few next-generation sequencing platforms have so far been implemented with those countries. We, therefore, believe that those countries should be supported to implement this technology that would definitely be of great value in the discovery of additional novel HI genes/variants.

Connexin Genes Variants Associated with Non-Syndromic Hearing Impairment: A Systematic Review of the Global Burden

Mutations in connexins are the most common causes of hearing impairment (HI) in many populations. Our aim was to review the global burden of pathogenic and likely pathogenic (PLP) variants in connexin genes associated with HI. We conducted a systematic review of the literature based on targeted inclusion/exclusion criteria of publications from 1997 to 2020. The databases used were PubMed, Scopus, Africa-Wide Information, and Web of Science. The protocol was registered on PROSPERO, the International Prospective Register of Systematic Reviews, with the registration number “CRD42020169697”. The data extracted were analyzed using Microsoft Excel and SPSS version 25 (IBM, Armonk, New York, United States). A total of 571 independent studies were retrieved and considered for data extraction with the majority of studies (47.8% (n = 289)) done in Asia. Targeted sequencing was found to be the most common technique used in investigating connexin gene mutations. We identified seven connexin genes that were associated with HI, and GJB2 (520/571 publications) was the most studied among the seven. Excluding PLP in GJB2, GJB6, and GJA1 the other connexin gene variants (thus GJB3, GJB4, GJC3, and GJC1 variants) had conflicting association with HI. Biallelic GJB2 PLP variants were the most common and widespread variants associated with non-syndromic hearing impairment (NSHI) in different global populations but absent in most African populations. The most common GJB2 alleles found to be predominant in specific populations include; p.Gly12ValfsTer2 in Europeans, North Africans, Brazilians, and Americans; p.V37I and p.L79Cfs in Asians; p.W24X in Indians; p.L56Rfs in Americans; and the founder mutation p.R143W in Africans from Ghana, or with putative Ghanaian ancestry. The present review suggests that only GJB2 and GJB3 are recognized and validated HI genes. The findings call for an extensive investigation of the other connexin genes in many populations to elucidate their contributions to HI, in order to improve gene-disease pair curations, globally.

A Novel Nonsense Mutation (c.414G>A; p.Trp138*) in CLDN14 Causes Hearing Loss in Yemeni Families: A Case Report

Non-syndromic hearing loss (NSHL) is a hereditary disorder that affects many populations. Many genes are involved in NSHL and the mutational load of these genes often differs among ethnic groups. Claudin-14 (CLDN14), a tight junction protein, is known to be associated with NSHL in many populations. In this study, we aimed to identify the responsible variants in 3 different Yemeni families affected with NSHL. Firstly, clinical exome sequencing (CES) performed for 3 affected patients from these different families identified a new nonsense variant (c.414G > A) in CLDN14. This variant was then confirmed by Sanger sequencing and PCR-RFLP. Subsequently, four microsatellite markers were used to genotype these families, which revealed a founder effect for this variant. Overall, this study illustrates the implication of the CLDN14 gene in the Yemeni population with NSHL and identifies a new founder variant.

Analysis of p.Gly12Valfs*2, p.Trp24* and p.Trp77Arg mutations in GJB2 and p.Arg81Gln variant in LRTOMT among non syndromic hearing loss Egyptian patients: implications for genetic diagnosis

Hearing loss (HL) is a global sensory disorder that affects children and deprives them from their rights to enjoy standard social and educational levels. Although hundreds of genetic mutations across several genes have been linked to HL, very limited studies are available on Egyptian population which has high rate of consanguinity and HL. The frequency of the p.Gly12Valfs*2, p.Trp24* and p.Trp77Arg mutations in GJB2 along with the p.Arg81Gln variant in LRTOMT gene was investigated in Egyptian patients. 103 non-syndromic HL (NSHL) Egyptian patients and 100 control subjects were recruited in this study. PCR-RFLP and Direct sequencing were performed to screen and confirm presence/absence of those mutations in Egyptian population. The p.Gly12Valfs*2 mutation was found in eight patients (7.8%) (six homozygous and two heterozygous) with an allele frequency of 6.8%. The p.Trp24* and p.Trp77Arg were absent in both HL patients and controls. Another one patient had the heterozygous variant for p.Arg81Gln in LRTOMT gene. This study reports, for the first time, the presence of a heterozygous change for the p.Arg81Gln in LRTOMT gene in one Egyptian patient. The p.Gly12Valfs*2 mutation, but not the p.Trp24* nor the p.Trp77Arg, in GJB2 is the most frequent variant among Egyptian patients and would therefore be recommended for genetic counseling and diagnosis.

Genetic analysis of CLDN14 in the Chinese population affected with non-syndromic hearing loss

OBJECTIVE

The CLDN14 gene, encoding the tight junction protein Claudin-14, has been proposed as a candidate causative gene affecting autosomal recessive non-syndromic hearing loss (ARNSHL). Genetic analysis of nonsynonymous single-nucleotide variations (nsSNVs) in CLDN14 has been performed in different populations. The role of CLDN14 nsSNVs in contributing to hearing loss in Chinese populations would be investigated in this study.

METHODS

Target screening for CLDN14 variations were conducted in 500 unrelated patients diagnosed with non-syndromic hearing loss (NSHL).

RESULTS

No reported pathogenic CLDN14 nsSNVs in heterozygote or homozygote were detected in this study, however, we identified 4 heterozygous nsSNVs [c.11C > T, p.(Thr4Met); c.16G > A, p.(Val6Met); c.68T > C, p.(Ile23Thr); c.367A > C, p.(Thr123Pro)] in CLDN14. The 4 nsSNVs are located at claudin-14 transmembrane domains, but assessed to be poorly conservative and non-pathogenic via multiple in silico algorithms. The structure-based analysis also suggested that the 4 nsSNVs had less structural and functional impact on claudin-14.

CONCLUSION

Our findings indicated that CLDN14 might not be a major causative gene for NSHL in Chinese populations, which would contribute to fully understanding the genetic cause of NSHL in the East Asian populations.

Etiology and associated GJB2 mutations in Mauritanian children with non-syndromic hearing loss

Origins of all hearing impairment forms may be divided into genetic mutations and acquired influence. Both carry damage to the inner ear structure resulting in a mild to profound dysfunction of the auditory system. The purpose of this study was to assess the different etiologies of deafness in two reference centers for hearing-impaired children in Nouakchott/Mauritania. Data on gender, age, consanguinity, etiology and family history of deafness were gathered by interviewing the custodians of 139 children with hearing loss. DNA of pupils with hereditary non-syndromic deafness was then screened for GJB2 mutations by sequencing methods. Postnatal hearing loss was found in 36 (25.8 %) out of the 139 children surveyed. The main etiologies of this group were infections caused by meningitis (12.9 %) and measles (2.8 %). Unknown and ototoxic origins accounted for, respectively, 5.7 and 3.5 %. In 103 (74.1 %) children, deafness was identified near after the time of birth and, therefore, presumed as congenital. 56.8 % of deaf children had consanguineous parents. Two GJB2 mutations, c.del35G with an allele frequency of 4.7 % and R32C (3.7 %) were detected. Infections such as meningitis and measles were the most prevalent causes of postnatal deafness. In cases of congenital hearing impairment, two GJB2 allele variants, i.e., del35G and R32C (3.7 %) were detected. Extended genetic testing is recommended for a more comprehensive determination of congenital causes.

[Etiologic profile of severe and profound sensorineural hearing loss in children in the region of north-central Morocco]

Introduction

Le diagnostic d'une surdité profonde est possible dès les premiers jours de vie. Or, le développement du langage et l'intégration scolaire et professionnelle ne sont pas possible que si la surdité est prise en charge précocement. L’établissement d'un diagnostc étiologique a des implications pronostiques et thérapeutiques.

Méthodes

C'est une étude rétrospective allant de Juin 2009 au mois de Janvier 2012 ayant recensé 250 cas d'enfants porteurs d'une surdité sévère et profonde.

Résultats

La moyenne d’âge au moment de l'annonce du diagnostic est de 3.7 ans. Les étiologies prédominantes sont les surdités génétiques dans 35.6% suivies des surdités acquises dans 30.8% des cas. Dans 34.4% des cas aucune étiologie n'a pu être retrouvée.

Conclusion

Cette étude met en évidence la prédominance éventuelle de causes génétiques de la surdité neurosensorielle de l'enfant au Maroc, et souligne la nécessité d'améliorer les politiques de prévention des maladies infectieuses et de dépistage de la surdité néonatale. Cependant, des analyses moléculaires plus ciblées et la réalisation d'un scanner des rochers systématiques sont nécessaires pour évaluer plus précisément la contribution des étiologies génétiques.

Genetic and molecular analysis of the CLDN14 gene in Moroccan family with non-syndromic hearing loss

BACKGROUND:

Hearing loss is the most prevalent human genetic sensorineural defect. Mutations in the CLDN14 gene, encoding the tight junction claudin 14 protein expressed in the inner ear, have been shown to cause non-syndromic recessive hearing loss DFNB29.

AIM:

We describe a Moroccan SF7 family with non-syndromic hearing loss. We performed linkage analysis in this family and sequencing to identify the mutation causing deafness.

MATERIALS AND METHODS:

Genetic linkage analysis, suggested the involvement of CLDN14 and KCNE1 gene in deafness in this family. Mutation screening was performed using direct sequencing of the CLDN14 and KCNE1 coding exon gene.

RESULTS:

Our results show the presence of c.11C>T mutation in the CLDN14 gene. Transmission analysis of this mutation in the family showed that the three affected individuals are homozygous, whereas parents and three healthy individuals are heterozygous. This mutation induces a substitution of threonine to methionine at position 4.

CONCLUSION:

These data show that CLDN14 gene can be i mplicated in the development of hearing loss in SF7 family; however, the pathogenicity of c.11C>T mutation remains to be determined.

Stromal Claudin14-heterozygosity, but not deletion, increases tumour blood leakage without affecting tumour growth

The maintenance of endothelial cell-cell junctions is vital for the control of blood vessel leakage and is known to be important in the growth and maturation of new blood vessels during angiogenesis. Here we have investigated the role of a tight junction molecule, Claudin 14, in tumour blood vessel leakage, angiogenesis and tumour growth. Using syngeneic tumour models our results showed that genetic ablation of Claudin 14 was not sufficient to affect tumour blood vessel morphology or function. However, and surprisingly, Claudin 14-heterozygous mice displayed several blood vessel-related phenotypes including: disruption of ZO-1-positive cell-cell junctions in tumour blood vessels; abnormal distribution of basement membrane laminin around tumour blood vessels; increased intratumoural leakage and decreased intratumoural hypoxia. Additionally, although total numbers of tumour blood vessels were increased in Claudin 14-heterozygous mice, and in VEGF-stimulated angiogenesis ex vivo, the number of lumenated vessels was not changed between genotypes and this correlated with no difference in syngeneic tumour growth between wild-type, Claudin 14-heterozygous and Claudin 14-null mice. Lastly, Claudin 14-heterozygosity, but not complete deficiency, also enhanced endothelial cell proliferation significantly. These data establish a new role for Claudin 14 in the regulation of tumour blood vessel integrity and angiogenesis that is evident only after the partial loss of this molecule in Claudin 14-heterozyous mice but not in Claudin 14-null mice.

GJB2 and GJB6 screening in Tunisian patients with autosomal recessive deafness

Autosomal recessive nonsyndromic deafness (ARNSD or DFNB) is a very common genetically heterogenous disorder. Although DFNB1 mutations are known to be the most frequent cause of this disorder, they are largely dependent on ethnic groups. The aims of our study are to specify the prevalence and the spectrum of GJB2 mutations as well as the prevalence of GJB6 large deletion in Tunisian population.

PATIENTS AND METHODS

95 unrelated patients with moderate to severe sensorineural hearing loss have been tested. The GJB2 coding region has been studied by PCR/Sequencing and the del(GJB6-D13S1830) mutation has been screened by fluorescent PCR multiplex.

RESULTS

27.36% of patients present mutations on both alleles of GJB2 gene and no one has the del(GJB6-D13S1830) mutation. The c.35delG mutation represents 86.5% of GJB2 deafness alleles and is found in homozygous state in 22 patients and in heterozygous state in one patient. Four other mutations are detected in four probands: two are compound heterozygous for the p.V37I/p.E47X and the c.35delG/p.R184P mutations, and two are homozygous for the p.E47X and the c.333-334delAA mutations.

CONCLUSION

Our results showed that c.35delG is the most common but not the only GJB2 mutation and that the del(GJB6-del D13S1830) is absent in our cohort. Consequently, we propose a systematic sequencing of GJB2 coding region for ARNSD Tunisian patients and we suggest additional studies to specify the real prevalence of del(GJB6-D13S1830) in our population.

Digenic inheritance in autosomal recessive non-syndromic hearing loss cases carrying GJB2 heterozygote mutations: assessment of GJB4, GJA1, and GJC3

OBJECTIVE

Autosomal recessive non-syndromic hearing loss (ARNSHL) can be caused by many genes. However, mutations in the GJB2 gene, which encodes the gap-junction (GJ) protein connexin (Cx) 26, constitute a considerable proportion differing among population. Between 10 and 42 percent of patients with recessive GJB2 mutations carry only one mutant allele. Mutations in GJB4, GJA1, and GJC3 encoding Cx30.3, Cx43, and Cx29, respectively, can lead to HL. Combination of different connexins in heteromeric and heterotypic GJ assemblies is possible. This study aims to determine whether variations in any of the genes GJB4, GJA1 or GJC3 can be the second mutant allele causing the disease in the digenic mode of inheritance in the studied GJB2 heterozygous cases.

METHODS

We examined 34 unrelated GJB2 heterozygous ARNSHL subjects from different geographic and ethnic areas in Iran, using polymerase chain reaction (PCR) followed by direct DNA sequencing to identify any sequence variations in these genes. Restriction fragment length polymorphism (RFLP) assays were performed on 400 normal hearing individuals.

RESULTS

Sequence analysis of GJB4 showed five heterozygous variations including c.451C>A, c.219C>T, c.507C>G, c.155_158delTCTG and c.542C>T, with only the latter variation not being detected in any of control samples. There were three heterozygous variations including c.758C>T, c.717G>A and c.3*dupA in GJA1 in four cases. We found no variations in GJC3 gene sequence.

CONCLUSION

Our data suggest that GJB4 c.542C>T variant and less likely some variations of GJB4 and GJA1, but not possibly GJC3, can be assigned to ARNSHL in GJB2 heterozygous mutation carriers providing clues of the digenic pattern.

Mutations in CLDN14 are associated with different hearing thresholds

Mutations in CLDN14, encoding tight junction protein claudin 14, cause profound deafness in mice and humans. We identified a Pakistani family, in which the affected individuals were homozygous for a known pathogenic mutation c.254 T>A resulting in p.V85D substitution in CLDN14; however, in contrast to the previously reported families with mutations in CLDN14, most of the affected individuals in this family exhibit only a severe hearing loss. In order to identify the contribution of CLDN14 to less than profound deafness, we screened for mutations of CLDN14 in 30 multiplex and 57 sporadic cases with moderately severe to severe hearing loss from Pakistan. We identified one other affected individual homozygous for p.V85D substitution. Comparison of audiometric data from all patients indicates that mutations in CLND14 cause varying degrees of hearing loss, which may be enhanced at high frequencies. This suggests that a modifier can reduce the severity of hearing loss associated with mutations of CLDN14. Our data indicates that mutations in CLDN14 should be explored when considering the etiology of less severe hearing loss.