Prevalence of GJB2 (CX26) gene mutations in south Iranian patients with autosomal recessive nonsyndromic sensorineural hearing loss

Analysis of GJB2 Gene Mutations in 1330 Deafness Cases of Major Ethnic Groups in Northwest China

Background: The GJB2 gene is the most common deafness gene, and epidemic characteristics have obvious racial specificity. Our study aimed to investigate the prevalence and ethnic specificity of the GJB2 gene in deafness in major ethnic groups in Northwest China, evaluate the value of molecular screening for deafness in minority populations, and explore the strategies and methods for genetic diagnosis. Methods: Ethics approval was obtained to collect 1330 cases of moderate to very severe nonsyndromic sensorineural deafness in northwestern China. The mutation characteristics of ethnic minorities were analyzed and compared with those of 464 patients with nonsyndromic sensorineural deafness among ethnic Han in the northwestern from research group by Sequence Scanner V25.0. Then, we analyzed the ethnic specificity of the mutations. Results: A total of 15 GJB2 sequence changes were detected in 1330 minority patients. The study showed that the allele frequency in Tibetan patients was significantly lower than that in Hui and Dongxiang patients, that in Uygur patients was significantly lower than that in Han and Hui patients, and that in Kazak and Tibetan patients was significantly lower than that in Han patients, and the differences between other ethnic groups were not statistically significant. Each ethnic group has a unique GJB2 gene mutation spectrum, and its hotspot mutation distribution has its own characteristics, with c.235delC, c.109 G > A, c.299-300delAT, and c.35delG being common. Conclusions: It has been confirmed that GJB2 gene mutation has a high prevalence in patients with nonsyndromic sensorineural hearing loss in Northwest China. Each ethnic group has a unique mutation spectrum for the GJB2 gene, which is related to its genetic background. It is necessary to develop a corresponding gene diagnosis strategy according to the hotspot mutations and mutation spectrum of each ethnic group.

GJB2 mutations in Iranian Azeri population with autosomal recessive nonsyndromic hearing loss (ARNSHL): First report of c.238 C>A mutation in Iran

Objective

Autosomal‐recessive nonsyndromic hearing loss (ARNSHL) is a heterogeneous genetic disorder. Mutations in the gap junction protein beta 2 (GJB2) gene, encoding connexin 26, are a significant cause of ARNSHL in different ethnic groups. This study aimed to identify the frequency and type of GJB2 mutations in the Iranian Azeri population.

Methods

Fifty unrelated families presenting ARNSHL in Ardabil Province, the northwest of Iran, were studied to determine the frequency and type of GJB2 mutations leading to ARNSHL. ARMS‐PCR screened all DNA samples to detect c.35delG; p. Gly12Val mutation. In addition, normal samples for c.35delG; p. Gly12Val were analyzed by direct sequencing for other GJB2 mutations.

Result

Of the fifty families, 13 (26%) showed a GJB2 gene mutation, with c.35delG; p. Gly12Val mutation was the most prevalent one that occurred in eight (61.5%) out of the 13 families. Of the families, two were homozygous for c.358‐360delGAC; p. Glu120del mutation, and one was homozygous for c.290dupA; p. Tyr97Ter and c.299–300delAT; p. His100Arg mutations. Also, we detected a novel mutation, c.238C>A; p. Gln80lys, in one of the families.

Conclusion

Our findings are comparable to previous studies, indicating c.35d3lG; p. Gly12Val mutation in the GJB2 gene is the most common cause of GJB2‐related hearing loss in the Iranian Azeri population. Furthermore, our study highlights the significance of ARNSHL screening programs of live births based on local population data in Iran.

Identification of homozygous mutations for hearing loss

BACKGROUND

Hearing loss is the most common sensory disorder worldwide, affecting about 1 out of every 1000 newborns. The disease has major genetic components, and can be inherited as a single gene disorder either in autosomal dominant or recessive fashions. Due to the high rate of consanguineous unions, Iran has one of the highest prevalence of autosomal recessive nonsyndromic deafness (ARNSD) in the world.

METHODS

We carried out a genetic screening of ten Iranian kindreds with more than one offspring affected by ARNSD caused by consanguineous unions. Sanger sequencing and whole exome sequencing together with in silico 3D structure modeling and protein stability prediction were used to identify the underlying disease causing genes.

CONCLUSION

We identified the causes of deafness in all 10 kindred. In six kindreds homozygous mutations were identified in GJB2 gene by Sanger sequencing. By using whole exome sequencing (WES), a homozygous missense mutation was identified in ESRRB gene as the first ever reported disease gene in Iran. Also two novel homozygous frameshift and missense mutations were identified in MYO15A gene and one previously reported mutation in TMC1 gene in three independent kindred. Our study shows the efficacy of WES for unraveling new pathogenic mutations in ARNSD patients and expands the spectrum of genes contributing to ARNSD in the Iranian population. The findings of our study can facilitate future genetic screening of patients with ARNSD , early screening and optimal design of novel therapeutics.

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.

GJB2 mutations causing autosomal recessive non-syndromic hearing loss (ARNSHL) in two Iranian populations: Report of two novel variants

OBJECTIVE

Hereditary hearing loss (HL) is a noticeable concern in medicine all over the world. On average, 1 in 166 babies born are diagnosed with HL in Iran, which makes it a major public health issue. Autosomal recessive non-syndromic HL (ARNSHL) is the most prevalent form of HL. Although over 60 genes have been identified for ARNSHL, GJB2 mutations are the most prevalent causes of 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. In the present study, we aimed to determine the frequency and mutation profile of 70 deaf patients from two different provinces (center and west) of Iran.

METHODS

We enrolled 70 Iranian deaf patients with ARNSHL from Isfahan (40 family) and Hamedan (30 family) provinces. After extraction of genomic DNA, the entire coding region of GJB2 was directly sequenced in all patients. Multiplex PCR was used for detection of del(GJB6-D13S1830) and del(GJB6-D13S1854) in the GJB6 gene. In silico analyses were also performed by available software tools.

RESULTS

A total of eleven different mutations were detected, nine of which were previously reported and the other two (c.130T > G and c.178T > G) were novel. Homozygous GJB2 mutations were observed in 22.5% and 20% of all the subjects from Isfahan and Hamedan provinces, respectively. c.35delG was the most frequent mutation. One compound heterozygous genotype (c.358_360delGAG/c.35delG) was observed for c.35delG. Screening for the two GJB6 deletions did not reveal any positive sample among heterozygous or GJB2 negative samples.

CONCLUSIONS

The present study suggests that mutations in the GJB2 gene specially c.35delG are important causes of ARNSHL in the center and west of Iran. Totally, 15% of the patients were heterozygous carriers. Further investigation is needed to detect the genetic cause of HL in the patients with monoallelic GJB2 mutations.

Mutation spectrum of autosomal recessive non-syndromic hearing loss in central Iran

OBJECTIVE

To identify the spectrum of mutations in connexin 26 gene and frequency of two deletions in connexin 30 gene in central Iran.

METHODS

After extraction of DNA from 300 blood samples, connexin 26 gene coding region was amplified using specific primers. PCR products were used for bidirectional sequencing. Multiplex PCR was used for detection of del(GJB6-D13S1830) and del(GJB6-D13S1854) in the GJB6 gene.

RESULTS

Eighteen different mutations including two novel variants in GJB2 gene were detected. The GJB2 mutations were observed in 23.3% of all the subjects. In addition, none of the deaf patients carried the del(GJB6-D13S1830) and del(GJB6-D13S1854) in the GJB6 gene. The 35delG mutation was the most common mutation, accounting for 32.65% of the mutant alleles.

CONCLUSION

The present study indicates that mutations in the GJB2 gene particularly 35delG are important causes for ARNSHL. 60% of the patients were heterozygous carriers. Thus, further investigation is needed to detect the genetic cause of hearing loss in patients with mono allelic mutations in the coding region of GJB2.

Analysis of common deafness gene mutations in deaf people from unique ethnic groups in Gansu Province, China

CONCLUSIONS

The GJB2 gene mutation characteristic of Dongxiang was the interaction result of ethnic background and geographical environment, and Yugur exhibited the typical founder effect. The SLC26A4 gene mutation characteristic of Dongxiang was related to caucasian backgrounds and selection of purpose exons, i.e. ethnic background and the penetrance of ethnic specificity caused the low mtDNA1555A>G mutation frequency in Dongxiang.

OBJECTIVES

To determine the prevalence of GJB2 and SLC26A4 genes and mtDNA1555A>G mutations and analyze the ethnic specificity in the non-syndromic sensorineural hearing loss (NSHL) of unique ethnic groups in Gansu Province.

METHODS

Peripheral blood samples were obtained from Dongxiang, Yugur, Bonan, and ethnic Han groups with moderately severe to profound NSHL in Gansu Province. Bidirectional sequencing (or enzyme digestion) was applied to identify the sequence variations.

RESULTS

The pathogenic allele frequency of the three gene mutations was different. The frequency of the GJB2 gene among the Dongxiang, Yugur, Bonan, and ethnic Han groups was 9.03%, 12.5%, 5.88%, and 12.17%, respectively. No difference was found between the ethnic groups. The frequencies of the SLC26A4 genes were 3.23%, 8.33%, 0%, and 9.81%, respectively. The mutation frequency of mtDNA1555A>G was 0%, 0%, 0%, and 6.03%, respectively. No difference was found between the ethnic groups, except for the Dongxiang and ethnic Han groups, both in SLC26A4 gene and mtDNA1555A>G.

Analysis of trafficking, stability and function of human connexin 26 gap junction channels with deafness-causing mutations in the fourth transmembrane helix

Human Connexin26 gene mutations cause hearing loss. These hereditary mutations are the leading cause of childhood deafness worldwide. Mutations in gap junction proteins (connexins) can impair intercellular communication by eliminating protein synthesis, mis-trafficking, or inducing channels that fail to dock or have aberrant function. We previously identified a new class of mutants that form non-functional gap junction channels and hemichannels (connexons) by disrupting packing and inter-helix interactions. Here we analyzed fourteen point mutations in the fourth transmembrane helix of connexin26 (Cx26) that cause non-syndromic hearing loss. Eight mutations caused mis-trafficking (K188R, F191L, V198M, S199F, G200R, I203K, L205P, T208P). Of the remaining six that formed gap junctions in mammalian cells, M195T and A197S formed stable hemichannels after isolation with a baculovirus/Sf9 protein purification system, while C202F, I203T, L205V and N206S formed hemichannels with varying degrees of instability. The function of all six gap junction-forming mutants was further assessed through measurement of dye coupling in mammalian cells and junctional conductance in paired Xenopus oocytes. Dye coupling between cell pairs was reduced by varying degrees for all six mutants. In homotypic oocyte pairings, only A197S induced measurable conductance. In heterotypic pairings with wild-type Cx26, five of the six mutants formed functional gap junction channels, albeit with reduced efficiency. None of the mutants displayed significant alterations in sensitivity to transjunctional voltage or induced conductive hemichannels in single oocytes. Intra-hemichannel interactions between mutant and wild-type proteins were assessed in rescue experiments using baculovirus expression in Sf9 insect cells. Of the four unstable mutations (C202F, I203T, L205V, N206S) only C202F and N206S formed stable hemichannels when co-expressed with wild-type Cx26. Stable M195T hemichannels displayed an increased tendency to aggregate. Thus, mutations in TM4 cause a range of phenotypes of dysfunctional gap junction channels that are discussed within the context of the X-ray crystallographic structure.