Update of the spectrum of GJB2 gene mutations in 152 Moroccan families with autosomal recessive nonsyndromic hearing loss

First report of an Ivorian family with nonsyndromic hearing loss caused by GJB2 compound heterozygous variants

The primary etiology of congenital hearing loss is attributed to genetic factors, with GJB2 identified as a pivotal gene across diverse ethnic groups. Additionally, nonsyndromic hearing loss is predominantly inherited in an autosomal recessive manner. We used Sanger sequencing to analyze GJB2 in 17 deaf children from 13 unrelated Ivory Coast families. One family had two children born with severe congenital deafness and exhibited pathogenic compound heterozygous variants. These variants included a nonsense substitution (c.132G > A or p.Trp44Ter) and a newly discovered duplication of 7 base pairs (c.205_211dupTTCCCCA or p.Ser72ProfsTer32). Segregation testing confirmed these variants, marking the first identification of GJB2 in an Ivorian family with congenital hearing loss.

Homozygous Missense Variants in FOXI1 and TMPRSS3 Genes Associated with Non-syndromic Deafness in Moroccan Families

One of the most prevalent sensorineural disorders, autosomal recessive non-syndromic hearing loss (ARNSHL) which can affect all age groups, from the newborn (congenital) to the elderly (presbycusis). Important etiologic, phenotypic, and genotypic factors can cause deafness. So far, the high genetic variability that explains deafness makes molecular diagnosis challenging. In Morocco, the GJB2 gene is the primary cause of non-syndromic hereditary deafness, while the existence of a variant in the LRTOMT gene is the second cause of this condition. After excluding these two frequently occurring GJB2 and LRTOMT variants, whole-exome sequencing was carried out in two Moroccan consanguineous families with hearing loss. As a result, two novel variants in the TMPRSS3 (c.1078G>A, p. Ala 360Thr) and FOXI1 (c.6C>G, p. Ser 2Arg) genes have been discovered in deaf patients and the pathogenic effect has been anticipated by several bioinformatics and molecular modeling systems. For the first time, these variants are identified in the Moroccan population, showing the population heterogeneity and demonstrating the value of the WES in hearing loss diagnosis.

Novel pathogenic WHRN variant causing hearing loss in a moroccan family

OBJECTIVES

The most prevalent sensory disease in humans is deafness. A variety of genes have been linked to hearing loss, which can either be isolated (non-syndromic) or associated with lesions in other organs (syndromic). It has been discovered that WHRN variants are responsible for non-syndromic hearing loss and Usher syndrome type II.

METHODS AND RESULTS

Exome sequencing in a consanguineous Moroccan patient with severe hearing loss identified a single homozygous mutation c.619G > T; p.Ala207Ser in WHRN, encoding a cytoskeletal scaffold protein that binds membrane protein complexes to the cytoskeleton in ocular photoreceptors and ear hair cell stereocilia. Bioinformatics methods and molecular dynamic modeling were able to predict the pathogenic implications of this variation.

CONCLUSION

We used whole exome sequencing to find a homozygous WHRN gene variant in a Moroccan family. Numerous bioinformatics methods predict that this modification might result in a change in the WHRN protein's structure.

Molecular Mechanisms and Clinical Phenotypes of GJB2 Missense Variants

The GJB2 gene is the most common gene responsible for hearing loss (HL) worldwide, and missense variants are the most abundant type. GJB2 pathogenic missense variants cause nonsyndromic HL (autosomal recessive and dominant) and syndromic HL combined with skin diseases. However, the mechanism by which these different missense variants cause the different phenotypes is unknown. Over 2/3 of the GJB2 missense variants have yet to be functionally studied and are currently classified as variants of uncertain significance (VUS). Based on these functionally determined missense variants, we reviewed the clinical phenotypes and investigated the molecular mechanisms that affected hemichannel and gap junction functions, including connexin biosynthesis, trafficking, oligomerization into connexons, permeability, and interactions between other coexpressed connexins. We predict that all possible GJB2 missense variants will be described in the future by deep mutational scanning technology and optimizing computational models. Therefore, the mechanisms by which different missense variants cause different phenotypes will be fully elucidated.

Genetic heterogeneity in GJB2, COL4A3, ATP6V1B1 and EDNRB variants detected among hearing impaired families in Morocco

BACKGROUND

Deafness is the most prevalent human sensorineural defect. It may occur as a result of an external auditory canal involvement, or a deficiency in the sound conduction mechanism, or an impairment of the cochlea, the cochlear nerve or central auditory perception. The genetic causes are the most common, as approximately 70% of hearing disorders are of hereditary origin, divided into two groups, syndromic (associated with other symptoms) and no syndromic (isolated deafness).

METHODS

A whole exome sequencing was performed to identify the genetic cause of hearing loss in six Moroccan families and Sanger sequencing was used to validate mutations in these genes.

THE RESULTS

The results of four out of the six families revealed four genetic variants in the genes GJB2, COL4A3, ATP6V1B1 and EDNRB responsible for non-syndromic and syndromic hearing loss. Multiple Bioinformatics programs and molecular modelling predicted the pathogenic effect of these mutations.

CONCLUSIONS

We identified in Moroccan deaf patients four homozygous mutations. These results show the importance of whole exome sequencing to identify pathogenic mutations in heterogeneous disorders with multiple genes responsible.

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.

Novel Mutation in AIFM1 Gene Associated with X-Linked Deafness in a Moroccan Family

INTRODUCTION

Auditory neuropathy is a hearing disorder where outer hair cell function within the cochlea is normal, but inner hair cell and/or the auditory nerve function is disrupted. It is a heterogeneous disorder, which can have either congenital or acquired causes.

METHODS

We found a disease-segregating mutation in the X-linked AIFM1 gene through whole-exome sequencing, encoding the apoptosis-inducing factor mitochondrion-associated 1.

RESULTS

The impact of the c.1045A>G; p.(Ser349Gly) mutation on the AIFM1 protein was predicted using different bioinformatics tools. The pedigree analysis in the examined family was consistent with X-linked dominant inheritance.

DISCUSSION/CONCLUSION

To our knowledge, this is the first study that identifies a mutation in the AIFM1 gene in Moroccan patients suffering from X-linked auditory neuropathy.

A homozygous MPZL2 deletion is associated with non syndromic hearing loss in a moroccan family

Adhesion glycoproteins are implicated in the pathophysiology of hearing loss, the most frequent inherited sensory disorder, affecting 1 in 1000 new-borns. Exome sequencing of a consanguineous Moroccan patient with mild hearing loss identified for the first time in a North African family a single homozygous mutation c.72delA in MPZL2 gene, encoding the Myelin Protein Zero-Like 2, reported as causing deafness in two other populations. Variable tandem repeat genotyping of this family revealed that the c.72delA MPZL2 allele shared a common haplotype with Turkish and Dutch families. These results confirm the pathogenicity of this MPZL2 mutation in recessive mild to moderate non-syndromic deafness.

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.

Whole exome sequencing identified mutations causing hearing loss in five consanguineous Pakistani families

Background

Hearing loss is the most common sensory defect, and it affects over 6% of the population worldwide. Approximately 50–60% of hearing loss patients are attributed to genetic causes. Currently, more than 100 genes have been reported to cause non-syndromic hearing loss. It is possible and efficient to screen all potential disease-causing genes for hereditary hearing loss by whole exome sequencing (WES).

Methods

We collected 5 consanguineous pedigrees from Pakistan with hearing loss and applied WES in selected patients for each pedigree, followed by bioinformatics analysis and Sanger validation to identify the causal genes.

Results

Variants in 7 genes were identified and validated in these pedigrees. We identified single candidate variant for 3 pedigrees: GIPC3 (c.937 T > C), LOXHD1 (c.6136G > A) and TMPRSS3 (c.941 T > C). The remaining 2 pedigrees each contained two candidate variants: TECTA (c.4045G > A) and MYO15A (c.3310G > T and c.9913G > C) for one pedigree and DFNB59 (c.494G > A) and TRIOBP (c.1952C > T) for the other pedigree. The candidate variants were validated in all available samples by Sanger sequencing.

Conclusion

The candidate variants in hearing-loss genes were validated to be co-segregated in the pedigrees, and they may indicate the aetiologies of hearing loss in such patients. We also suggest that WES may be a suitable strategy for hearing-loss gene screening in clinical detection.

Further Evidence for the Implication of the MET Gene in Non-Syndromic Autosomal Recessive Deafness

Mutations in the mesenchymal epithelial transition factor (MET) gene are frequently associated with multiple human cancers but can also lead to human non-syndromic autosomal recessive deafness (DFNB97). In the present study, we identified a novel homozygous missense mutation in the METgene causing a non-syndromic hearing impairment DFNB97 form. Whole-exome sequencing was performed to determine the genetic causes of hearing loss in a Moroccan consanguineous family with an affected daughter. The structural analysis of native and mutant in the SEMA domain of the MET receptor was investigated using a molecular dynamics simulation (MDS) approach. We identified a novel pathogenic homozygous c.948A>G (p.Ile316Met) mutation in the MET gene in one deaf Moroccan young girl carrying a total bilateral non-syndromic hearing impairment. The results of the MDS approach show that an Ile316Met mutation in the SEMA domain leads to protein flexibility loss. This may produce a major impact on the structural conformation of the MET receptor, which also affects the function and binding site of the receptor. This is the first time that a mutation in the MET gene is described in a Moroccan family. Moreover, this study reports the second family in the world associating deafness and mutation in the MET gene.

GJB2-related hearing loss in central Iran: Review of the spectrum and frequency of gene mutations

Mutations in the GJB2 gene are a main cause of autosomal-recessive nonsyndromic hearing loss (ARNSHL) in many populations. Previous studies have estimated the average frequency of GJB2 mutations to be ∼16% in Iran, but would vary among different ethnic groups. Here, we have taken together and reviewed results from our two previous publications and data from searching other published mutation reports to provide a comprehensive collection of data for GJB2 mutations and HL in central Iran. In all, 332 unrelated families were included and analyzed for the prevalence and type of the GJB2 gene mutations. In total, the frequency of GJB2 mutations was found to be 16% in the central provinces, which is significantly higher than those identified in southern populations of Iran. Also, c.35delG was the most frequent mutation in the related population. The present study suggests that mutations in the GJB2 gene, especially c.35delG, are important causes of HL in central Iran and can be used as a basis of genetic counseling and clinical guidelines in this region.

The spectrum of GJB2 gene mutations in Algerian families with nonsyndromic hearing loss from Sahara and Kabylie regions

INTRODUCTION

DFNB1, caused by mutations of GJB2 or GJB6, is the most prevalent genetic form of nonsyndromic (i.e., isolated) congenital deafness in countries located around the Mediterranean Sea. Because some mutations are restricted to specific ethnic-geographic groups, we studied the prevalence and spectrum of GJB2/GJB6 mutations in deaf patients originating from two different Algerian regions, Kabylie and Sahara.

PATIENTS AND METHODS

Among 91 reportedly unrelated Algerian patients affected by prelingual deafness, 80 patients (41 from Kabylie and 39 from Sahara) were diagnosed with isolated deafness. All had profound deafness, except one patient with mild deafness. They were screened for the presence of GJB2 mutations by direct sequencing of the single coding exon of GJB2. Patients without mutations were then screened for the presence of the most frequent two deletions of GJB6: del(GJB6-D13S1854) and del(GJB6-D13S1830).

RESULTS

Causative mutations were found in 13 and 8 patients from Kabylie and Sahara, respectively, accounting for more than a quarter of the cohort. The c.35delG, p.Gly12Valfs*2 mutation remains the most important mutation both in Kabylie (10 patients) and Sahara (7 patients). All detected patients were homozygous for this mutation. In addition, two other mutations (c.139G > T, p.Glu47* and c.167delT, p.Leu56Argfs*26) were found homozygous in one family each, and two patients were compound heterozygotes for (c.35delG p.Gly12Valfs*2/c.139G > T, p.Glu47*). No deletion of GJB6 was detected.

CONCLUSION

We confirm that mutations in GJB2, mainly c.35delG, are one of the most prevalent causes of nonsyndromic congenital deafness in Algeria, whereas the del (GJB6-D13S1854) and del (GJB6-D13S1830) deletions of GJB6 contribute little, if any. Further investigation is needed to identify the cause of deafness in other patients without diagnostic.

Genetics of hereditary hearing loss in east Iran population: A systematic review of GJB2 mutations

Mutations in the GJB2 gene are the most common cause of pre-lingual hearing loss (HL) worldwide. Previous studies have shown the frequency of GJB2 mutations to be 16% in Iran, but varies among different ethnic groups. Here, we have reviewed results from previous published mutation reports to provide a comprehensive collection of data for GJB2 mutations and HL in eastern Iran. We conducted a systematic literature review of PubMed, Google Scholar, Web of Science, and Science Direct databases for articles published before March, 2019. The literature search was performed by 2 independent researchers. The primary data of these studies including the number of samples, allelic frequency, and so on were extracted. Six studies involving 812 unrelated families from four different eastern provinces were included and analyzed for the type and prevalence of GJB2 mutations. A total of 19 different genetic variants were detected. GJB2 mutations were 8.8% in the studied eastern provinces, which was lower than that reported in northern populations of Iran. Moreover, a gradient in the frequency of GJB2 mutations from north to south Iran was observed. c.35delG was the most frequent mutation, accounting for 48.5% % of the populations studied. However, this mutation was absent in the Baluchi population. This review shows that particular rare mutations are frequent in some Iranian ethnic groups, and should be considered for genetic counselling.

Genetics of Hearing Loss in North Iran Population: An Update of Spectrum and Frequency of GJB2 Mutations

Diagnosis of pre-lingual hearing loss (HL) is difficult owing to the high number of genes responsible. The most frequent cause of HL is DFNB1 due to mutations in the GJB2 gene. It represents up to 40% of HL cases in some populations. In Iran, it has previously been shown that DFNB1 accounts for 16-18% of cases but varies among different ethnic groups. Here, we reviewed results from our three previous publications and data from other published mutation reports to provide a comprehensive collection of data for GJB2 mutations and HL in northern Iran. In total, 903 unrelated families from six different provinces, viz., Gilan, Mazandaran, Golestan, Ghazvin, Semnan, and Tehran, were included and analyzed for the type and prevalence of GJB2 mutations. A total of 23 different genetic variants were detected from which 18 GJB2 mutations were identified. GJB2 mutations were 20.7% in the studied northern provinces, which was significantly higher than that reported in southern populations of Iran. Moreover, a gradient in the frequency of GJB2 mutations from north to south Iran was observed. c.35delG was the most common mutation, accounting for 58.4% of the cases studied. This study suggests that c.35delG mutation in GJB2 is the most important cause of HL in northern Iran.

An update of spectrum and frequency of GJB2 mutations causing hearing loss in the south of Iran: A literature review

OBJECTIVE

Mutations in the GJB2 gene are a major cause of autosomal recessive non-syndromic HL (ARNSHL) in many populations. Previous studies have estimated the average frequency of GJB2 mutations to be between 16 and 18% in Iran, but would vary among different ethnic groups. Here, we have taken together and reviewed results from our three previous publications and data from search other published mutation reports to provide a comprehensive collection of data for GJB2 mutations and HL in the south of Iran.

METHODS

In all, 447 unrelated families were included and analyzed for the prevalence and type of the GJB2 gene mutations.

RESULTS

Totally, the frequency of GJB2 mutations was found to be 11.5% in the southern provinces studied which is significantly lower than that identified in Northern populations of Iran, and also a southwest to southeast Iranian gradient in the frequency of GJB2 mutations is suggested.

CONCLUSIONS

This study highlights the importance of establishing prevalence, based on the local population for screening and diagnostic programs of live births in Iran.

Mitochondrial tRNAIle A4317G mutation may be associated with hearing impairment in a Han Chinese family

Mutations in the mitochondrial genome have been identified to be associated with hearing loss. The aim of the present study was to investigate the role of mitochondrial DNA (mtDNA) variants in a Chinese family with hearing loss. Polymerase chain reaction (PCR)‑Sanger sequencing was used to screen the mtDNA variants and nuclear genes [gap junction protein β2 (GJB2) and transfer (t)RNA 5‑methylaminomethyle‑2‑thiouridylate methyltransferase (TRMU)]; in addition, the mtDNA copy number was determined by quantitative PCR. The present study characterized the molecular features of a Chinese family with maternally‑inherited hearing loss and identified mtDNA A1555G and tRNAIle A4317G mutations. The A4317G mutation was localized at the TΨC arm of tRNAIle (position 59) and created a novel base‑pairing (G59‑C54), which may alter the secondary structure of the tRNA. In addition, patients carrying the A4317G mutation exhibited a lower mtDNA copy number compared with the controls, suggesting that this mutation may cause mitochondrial dysfunction that is responsible for the deafness. However, no functional variants in the GJB2 and TRMU genes were detected. mtDNA A1555G and A4317G mutations may contribute to the clinical manifestation of hearing loss in this family.

Two novel homozygous missense mutations identified in the BSND gene in Moroccan patients with Bartter's syndrome

OBJECTIVES

Hearing loss (HL) is one of the most common sensorineural disorders. In the present study, we identified two novel missense mutations in BSND gene causing Bartter syndrome type IV which is a genetic disease with an autosomal recessive transmission, characterized by hypokalaemia, metabolic alkalosis, an elevation in plasma renin activity and hyperaldosteronism as well as sensorineural deafness.

METHODS

Whole-exome sequencing was performed to study the genetic causes of Hearing loss in two unrelated patients from two Moroccan families.

RESULTS

The two novel homozygous mutations p.Arg8Gly (c.22C > G), p.Thr36Asn (c.107C > A) in exon 1 of BSND gene which encodes barttin were identified in 7 patients belonging to two unrelated families originated from central region of Morocco.

CONCLUSION

We identified two novel missense mutations p.Arg8Gly and p.Thr36Asn in exon 1 of BSND gene; both mutations were described for the first time in Moroccan patients with Bartter syndrome type IV.

Novel compound heterozygous MYO7A mutations in Moroccan families with autosomal recessive non-syndromic hearing loss

The MYO7A gene encodes a protein belonging to the unconventional myosin super family. Mutations within MYO7A can lead to either non syndromic hearing loss or to the Usher syndrome type 1B (USH1B). Here, we report the results of genetic analyses performed on Moroccan families with autosomal recessive non syndromic hearing loss that identified two families with compound heterozygous MYO7A mutations. Five mutations (c.6025delG, c.6229T>A, c.3500T>A, c.5617C>T and c.4487C>A) were identified in these families, the latter presenting two differently affected branches. Multiple bioinformatics programs and molecular modelling predicted the pathogenic effect of these mutations. In conclusion, the absence of vestibular and retinal symptom in the affected patients suggests that these families have the isolated non-syndromic hearing loss DFNB2 (nonsyndromic autosomal recessive hearing loss) presentation, instead of USH1B.

Analysis of p.V37I compound heterozygous mutations in the GJB2 gene in Chinese infants and young children

The p.V37I (c.109G>A) mutation in the GJB2 gene is the common frequent cause of congenital deafness; however, its pathogenicity is debated. The present study investigated the prevalence of p.V37I in Chinese infants and young children and associated clinical characteristics. The subjects of the present study were screened for mutations in GJB2 (235delC, 299delAT, 176dell6, 35delG), SLC26A4 (IVS7-2A>G, 2168A>G), GJB3 (538C>T), and in the mitochondrial 12S rRNA gene (1555A>G, 1494C>T). Subjects with p.V37I underwent an audiological evaluation. GJB2 exon sequencing revealed that 20 subjects had p.V37I compound heterozygous mutations, one of whom had a family history; the mutations included c.235delC/p.V37I (n = 12), c.299AT/p.V37I (n = 7), and c.176del16/p.V37I (n = 1). Of the 20 subjects, 12 were referred for Universal Newborn Hearing Screening (UNHS). Nine of the 20 subjects had mild hearing loss in the better ear and 5 had moderate hearing loss in the better ear while 4 had normal hearing. Among subjects with the c.235delC/p.V37I mutation, 5 had mild hearing loss and 2 had moderate hearing loss while 3 had normal hearing. Among subjects with the c.299AT/p.V37I mutation, 3 had mld hearing loss and 3 had moderate hearing loss while 1 had normal hearing. One subject with the c.176del16/p.V37I mutation had mild hearing loss. Few studies have reported on the clinical characteristics of Chinese infants with p.V37I compound heterozygous mutations identified via screening for deafness genes and GJB2 sequencing. The c.235delC/p.V37I mutation was the most prevalent mutation found in subjects. The degree of hearing loss associated with p.V37I compound heterozygous mutations was mainly mild to moderate.