The frequency of GJB2 mutations and the Δ (GJB6-D13S1830) deletion as a cause of autosomal recessive non-syndromic deafness in the Kurdish population

Role of GJB2 and GJB6 in Iranian Nonsyndromic Hearing Impairment: From Molecular Analysis to Literature Reviews

Background: Hearing impairment (HI) is a heterogeneous disorder. GJB2 and GJB6 genes are typically the first line of genetic screening before proceeding to any massive parallel sequencing. We evaluated the clinical utility of GJB2 and GJB6 testing in the Iranian population. Methods: GJB2 and GJB6 were sequenced. PubMed and Google Scholar were searched for Iranian publications on deletions in the DFNB1 locus. Results: We detected mutations of GJB2 in 16.5%, and no mutations of GJB6. Literature review revealed no reports of mutations of GJB6 in the Iranian population. Conclusion: This data and literature reviews indicate that GJB6 is not commonly responsible for Iranian nonsyndromic HI. Hence, the clinical utility of GJB6 genetic analysis as a first line for HI evaluation does not have the same utility as GJB2. The study is consistent with recent studies emphasizing the role of ethnicity in the selection of HI genetic testing strategy.

Genetic Epidemiology and Clinical Features of Hereditary Hearing Impairment in the Taiwanese Population

Hereditary hearing impairment (HHI) is a common but heterogeneous clinical entity caused by mutations in a plethora of deafness genes. Research over the past few decades has shown that the genetic epidemiology of HHI varies significantly across populations. In this study, we used different genetic examination strategies to address the genetic causes of HHI in a large Taiwanese cohort composed of >5000 hearing-impaired families. We also analyzed the clinical features associated with specific genetic mutations. Our results demonstrated that next-generation sequencing-based examination strategies could achieve genetic diagnosis in approximately half of the families. Common deafness-associated genes in the Taiwanese patients assessed, in the order of prevalence, included GJB2, SLC26A4, OTOF, MYO15A, and MTRNR1, which were similar to those found in other populations. However, the Taiwanese patients had some unique mutations in these genes. These findings may have important clinical implications for refining molecular diagnostics, facilitating genetic counseling, and enabling precision medicine for the management of HHI.

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.

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.

Unique spectra of deafness-associated mutations in Mongolians provide insights into the genetic relationships among Eurasian populations

Genetic factors are an important cause of idiopathic sensorineural hearing impairment (SNHI). From the epidemiological perspective, mutations of three deafness genes: GJB2, SLC26A4, and MT-RNR1, are much more prevalent than those of other genes worldwide. However, mutation spectra of common deafness genes differ remarkably across different populations. Here, we performed comprehensive genetic examination and haplotype analyses in 188 unrelated Mongolian families with idiopathic SNHI, and compared their mutation spectra and haplotypes to those of other European and Asian cohorts. We confirmed genetic diagnoses in 18 (9.6%) of the 188 families, including 13 with bi-allelic GJB2 mutations, three with bi-allelic SLC26A4 mutations, and two with homoplasmic MT-RNR1 m.1555A>G mutation. Moreover, mono-allelic mutations were identified in 17 families (9.0%), including 14 with mono-allelic GJB2 mutations and three with mono-allelic SLC26A4 mutations. Interestingly, three GJB2 mutations prevalent in other populations, including c.35delG in Caucasians, c.235delC in East Asians, and c.-23+1G>A in Southwest and South Asians, were simultaneously detected in Mongolian patients. Haplotype analyses further confirmed founder effects for each of the three mutations, indicating that each mutation derived from its ancestral origin independently. By demonstrating the unique spectra of deafness-associated mutations, our findings may have important clinical and scientific implications for refining the molecular diagnostics of SNHI in Mongolian patients, and for elucidating the genetic relationships among Eurasian populations.

Heterogeneity of Hereditary Hearing Loss in Iran: a Comprehensive Review

A significant contribution to the causes of hereditary hearing impairment comes from genetic factors. More than 120 genes and 160 loci have been identified to be involved in hearing impairment. Given that consanguine populations are more vulnerable to most inherited diseases, such as hereditary hearing loss (HHL), the genetic picture of HHL among the Iranian population, which consists of at least eight ethnic subgroups with a high rate of intermarriage, is expected to be highly heterogeneous. Using an electronic literature review through various databases such as PubMed, MEDLINE, and Scopus, we review the current picture of HHL in Iran. In this review, we present more than 39 deafness genes reported to cause non-syndromic HHL in Iran, of which the most prevalent causative genes include GJB2, SLC26A4, MYO15A, and MYO7A. In addition, we highlight some of the more common genetic causes of syndromic HHL in Iran. These results are of importance for further investigation and elucidation of the molecular basis of HHL in Iran and also for developing a national diagnostic tool tailored to the Iranian context enabling early and efficient diagnosis of hereditary hearing impairment.

Finding mutation within non-coding region of GJB2 reveals its importance in genetic testing of hearing loss in Iranian population

OBJECTIVE

Hereditary hearing loss is the most common neurosensory disorder in humans. Half of the cases have genetic etiology with extraordinary genetic heterogeneity. Mutations in one gene, GJB2, are the most common cause for autosomal recessive non-syndromic hearing loss (ARNSHL) in many different populations. GJB2 encodes a gap junction channel protein (connexin 26), and is located on DFNB1 locus on chromosome 13q12.11 which also involve another connexin gene, GJB6. Mutation screening of GJB2 revealed that a high number of patients with deaf phenotype have heterozygous genotype and carry only one mutant allele. As the first comprehensive study in Iran, we have targeted GJB2-related Iranian heterozygotes, looking for second mutant allele which leads to hearing impairment. They bear first mutation in their coding exon of GJB2.

METHOD

Using PCR-based direct sequencing, we assessed 103 patients with ARNSHL for variants in non-coding exon and promoter region of this gene, for the first time in Iran.

RESULT

We have identified the second mutant allele in splice site of exon-1 of GJB2 which is known as IVS1+1G>A in 17 probands. We found no mutation in promoter region of GJB2.

CONCLUSION

Our findings reveal that IVS1+1G>A mutation in noncoding exon of GJB2 is the most common mutation after 35delG within multi ethnical Iranian heterozygote samples. It emphasizes to approach exon1 of GJB2 in case of ARNSHL genetic diagnosis.

Connexin 26 gene mutations in non-syndromic hearing loss among Kuwaiti patients

OBJECTIVE

To study connexin 26 (Cx26) gene mutations among autosomal recessive non-syndromal hearing loss in Kuwaiti patients and evaluate their effect on phenotypes.

SUBJECTS AND METHODS

This cross sectional study included 100 patients aged between 6 months and 18 years, who were referred to the Sheikh Salem Al-Ali Centre for audiology and speech evaluation of autosomal recessive non-syndromic sensorineural hearing loss confirmed by clinico-genetic evaluation and a battery of diagnostic tests. Gene profiling and sequencing were performed to detect the presence and nature of Cx26 mutation.

RESULTS

Of the 100 patients, mutation of Cx26 gene was detected in 15 patients (15%) of which 9 (60%) cases were heterozygous and 6 cases (40%) were homozygous. Eighty per cent of the 15 Cx26 positive cases resulted from the 35delG mutation. Among the heterozygous cases, 6 (66.6%) were positive for 35delG. All 6 homozygous patients were positive for the 35delG mutation. A significant correlation was found between genetic findings (p = 0.013) and family history (p = 0.029), as well as the onset (p = 0.015), course (p = 0.033), degree and configuration of hearing loss (p = 0.001).

CONCLUSION

Among the selected Kuwaiti population sample, the Cx26 gene mutation was responsible for 15% of autosomal recessive non-syndromic sensorineural hearing loss. We recommend that screening for Cx26 gene mutation be considered in the screening strategy of patients with non-syndromic childhood hearing loss for counselling and management purposes. .

A novel splice-site mutation in the GJB2 gene causing mild postlingual hearing impairment

The DFNB1 subtype of autosomal recessive, nonsyndromic hearing impairment, caused by mutations affecting the GJB2 (connection-26) gene, is highly prevalent in most populations worldwide. DFNB1 hearing impairment is mostly severe or profound and usually appears before the acquisition of speech (prelingual onset), though a small number of hypomorphic missense mutations result in mild or moderate deafness of postlingual onset. We identified a novel GJB2 splice-site mutation, c. -22-2A>C, in three siblings with mild postlingual hearing impairment that were compound heterozygous for c. -22-2A>C and c.35delG. Reverse transcriptase-PCR experiments performed on total RNA extracted from saliva samples from one of these siblings confirmed that c. -22-2A>C abolished the acceptor splice site of the single GJB2 intron, resulting in the absence of normally processed transcripts from this allele. However, we did isolate transcripts from the c. -22-2A>C allele that keep an intact GJB2 coding region and that were generated by use of an alternative acceptor splice site previously unknown. The residual expression of wild-type connection-26 encoded by these transcripts probably underlies the mild severity and late onset of the hearing impairment of these subjects.

Screening of OTOF mutations in Iran: a novel mutation and review

OBJECTIVE

Mutations in OTOF have been reported to cause nonsyndromic hearing loss in different populations. The purpose of this study is screening of OTOF mutations in Iranian population.

METHODS

Thirty-eight consanguineous families affected with autosomal recessive nonsyndromic hearing loss (ARNSHL) and negative for GJB2 or GJB6 mutations were screened by autozygosity mapping and Sanger sequencing to find OTOF mutations.

RESULTS

A novel homozygous frameshift mutation (c.1981dupG) was found to cause hearing loss in one family and no other OTOF variants were detected in the remaining families. The affected individuals were homozygous forp. D661GfsX2 causing defect in long isoform of otoferlin.

CONCLUSIONS

We conclude that OTOF mutations are not the major cause of ARNSHL in the Iranian population but still may play an important role in HL; therefore evaluation the OTOF gene is of concern.

Prevalence of IVS1+1G>A mutation among Iranian Azeri Turkish patients with autosomal recessive non-syndromic hearing loss (ARNSHL)

OBJECTIVE

Mutations in the GJB2 gene has been reported as a main cause for autosomal recessive non-syndromic hearing loss (ARNSHL) all over the world. IVS1+1G>A which is splice site mutation have been detected in several populations as disruptive mutation. This study has intended to assess the significance of this mutation, IVS1+1G>A, to the autosomal recessive non-syndromic genetic load among Iranian Azeri Turkish patients.

METHODS

Following our previous study, one hundred and seventy four unrelated patients with prelingual ARNSL were included in this study. Thirty nine patients had only one identified mutated allele, whereas hundred and thirty five patients were negative for coding region of GJB2. All these patients were screened for IVS1+1G>A by applying PCR-RFLP assay.

RESULTS

Among studied patients nine compound heterozygote with 35delG, delE120, 235delC were identified. Additionally, six patients were detected with only one IVS1+1G>A mutated allele. In these patients, the other mutated allele was left unidentified. One patient was identified to be homozygous for IVS1+1G>A. Further studies carried out on parents of positive cases, showed that one of the healthy parents (mother) to be homozygous for IVS1+1G>A mutation. By self-report, this person had no hearing impairment, although it is possible that she has mild or moderate hearing loss, which she is unable to detect. Her child was compound heterozygous (IVS1+1G>A/35delG) with profound deafness. The frequency of IVS1+1G>A was found to be about 4.9%, however the parental consanguinity was observed in 37.5% of IVS1+1G>A-mutated families.

CONCLUSIONS

Our results support founder effect regarding these mutations and the presence of an ancient ancestor is strengthened in comparison to hot spot hypothesis. Also the results suggest variable expressivity of IVS1+1G>A mutation with respect to hearing loss.

Prevalence of the GJB2 IVS1+1G >A mutation in Chinese hearing loss patients with monoallelic pathogenic mutation in the coding region of GJB2

Background

Mutations in the GJB2 gene are the most common cause of nonsyndromic recessive hearing loss in China. In about 6% of Chinese patients with severe to profound sensorineural hearing impairment, only monoallelic GJB2 mutations known to be either recessive or of unclear pathogenicity have been identified. This paper reports the prevalence of the GJB2 IVS1+1G>A mutation in a population of Chinese hearing loss patients with monoallelic pathogenic mutation in the coding region of GJB2.

Methods

Two hundred and twelve patients, screened from 7133 cases of nonsyndromic hearing loss in China, with monoallelic mutation (mainly frameshift and nonsense mutation) in the coding region of GJB2 were examined for the GJB2 IVS1+1G>A mutation and mutations in the promoter region of this gene. Two hundred and sixty-two nonsyndromic hearing loss patients without GJB2 mutation and 105 controls with normal hearing were also tested for the GJB2 IVS1+1G>A mutation by sequencing.

Results

Four patients with monoallelic mutation in the coding region of GJB2 were found carrying the GJB2 IVS1+1G>A mutation on the opposite allele. One patient with the GJB2 c.235delC mutation carried one variant, -3175 C>T, in exon 1 of GJB2. Neither GJB2 IVS1+1G>A mutation nor any variant in exon 1 of GJB2 was found in the 262 nonsyndromic hearing loss patients without GJB2 mutation or in the 105 normal hearing controls.

Conclusion

Testing for the GJB2 IVS 1+1 G to A mutation explained deafness in 1.89% of Chinese GJB2 monoallelic patients, and it should be included in routine testing of patients with GJB2 monoallelic pathogenic mutation.

High level of intrafamilial phenotypic variability of non-syndromic hearing loss in a Lur family due to delE120 mutation in GJB2 gene

Hearing loss is the most common sensory defect in the world. The genetic basis of this condition is very complex. Molecular variations in GJB2 gene are the common cause of hearing impairment in Caucasians. One expects that affected members of a family with same mutation have similar phenotype. Here, we report phenotypic variability in hearing loss among the members of a Lur family. Two brothers from a Lur family from Lurestan province in western Iran with variable degrees of nonsyndromic sensorineural hearing loss were evaluated for genetic counseling. Clinical examinations, audiological tests and molecular studies including GJB2 gene sequencing and detection of Delta(GJB6-D13S1830) deletion were performed. Sequencing analysis of GJB2 gene revealed delE120 mutation in both brothers in homozygous form. Since one of them was profoundly deaf and the other was mild hearing loss and had normal conversation, we were expecting different genotypes or other causative effects. Delta(GJB6-D13S1830) was not found. Phenotypic variability between members of different families with the same type of mutation can be expected which may be due to the role of different modifying factors, unrecognized gap junction isoforms, or polymorphism effects.

Novel syndrome of cataracts, retinitis pigmentosa, late onset deafness and sperm abnormalities: a new Usher syndrome subtype with X-linked inheritance?

Tissues of the auditory, ocular and reproductive systems have some similarities in their protein families and structures. Consequently, syndromes comprising these systems are described. Hearing loss alone is a component of more than 400 known syndromes and is a common nonsyndromic congenital disorder. Here we describe a syndrome in five brothers with the distinctive presentation of late-onset progressive hearing loss, cataracts, retinitis pigmentosa, sperm motility and shape problems in a family from the Kurdish population in Iran. The clinical findings of these patients are presented in detail and compared to the classical Usher syndromes.

High carrier frequency of the GJB2 mutation (35delG) in the north of Iran

OBJECTIVE

Mutations in the GJB2 gene are a major cause of autosomal recessive and sporadic non-syndromic hearing loss in many populations. A single mutation of this gene (35delG) accounts for approximately 70% of mutations in Caucasians with a carrier frequency of 2-4% in Europe. This study aims to determine the rate of 35delG carrier frequency in Iran.

METHODS

Genomic DNA was extracted from a total of 550 unaffected unrelated subjects from 4 provinces of Iran following the standard phenol chloroform procedure. The one base pair deletion (35delG) was analysed using a nested PCR procedure; 35delG mutation carriers were subsequently confirmed by sequence analysis. Moreover, using the Binomial probability distribution, we compared the 35delG carrier frequency of Iranian population with the various Middle Eastern and overall European populations.

RESULTS

Of the four populations studied, we found a high carrier frequency of 2.8% in Gilan province in the north of Iran. The overall 35delG carrier frequency was found to be 1.25% in the populations studied (our present and previous data) which is similar to the overall 35delG carrier frequency detected in Middle Eastern populations, but Significantly lower than that identified in European populations.

Prevalence and Etiology of Hearing Loss in Rural Nicaraguan Children

OBJECTIVE/HYPOTHESIS

The prevalence and causes of pediatric hearing loss (HL) in the developing world are largely unknown. Infectious sequelae, ototoxic medications, and genetic causes may play a larger role in developing countries. In addition, the significance of GJB2 mutation gene in poorly developed areas remains unclear. The intent of this study is to investigate the prevalence and etiology of HL in children living in a remote, impoverished region of northern Nicaragua.

STUDY DESIGN

Cross-sectional study.

METHODS

Clinical data from two sources were analyzed: data from screening examinations performed in rural schools in the Department of Jinotega, Nicaragua (group A) and pediatric HL patients seen at the Otolaryngology and Audiology Clinic in Jinotega, Nicaragua (group B). Patients with congenital HL were offered a genetic test for GJB2 mutations. Comparisons were made using parametric (analysis of variance) and nonparametric (Kruskal-Wallis) tests.

RESULTS

School-based screening examinations (group A) revealed a high prevalence of significant HL (>30 dB) of 18%. The majority of these children had normal otoscopic examinations (58%). A family history of HL was seen in 24% of children who failed screening exams. Positive family history was more common in patients with HL (P < .01) and in specific schools (P < .05). Clinic-based evaluations (group B) reveal a population with predominantly severe-profound HL. Physical dysmorphism was common, yet identifiable syndromic HL was rare. Although familial HL was common (33%), there were no pathologic GJB2 mutations. Other common risk factors in this population were maternal infection during pregnancy, neonatal distress, low birth weight or prematurity, and gentamicin exposure.

CONCLUSIONS

HL in this rural, third world environment is more prevalent, and the etiologies responsible in this study group are different from those encountered in industrialized nations. Poor perinatal health care, infectious causes, gentamicin exposure, and hereditary HL are potentially preventable causes that play a major role in this population.

Non-syndromic, autosomal-recessive deafness

Non-syndromic deafness is a paradigm of genetic heterogeneity with 85 loci and 39 nuclear disease genes reported so far. Autosomal-recessive genes are responsible for about 80% of the cases of hereditary non-syndromic deafness of pre-lingual onset with 23 different genes identified to date. In the present article, we review these 23 genes, their function, and their contribution to genetic deafness in different populations. The wide range of functions of these DFNB genes reflects the heterogeneity of the genes involved in hearing and hearing loss. Several of these genes are involved in both recessive and dominant deafness, or in both non-syndromic and syndromic deafness. Mutations in the GJB2 gene encoding connexin 26 are responsible for as much as 50% of pre-lingual, recessive deafness. By contrast, mutations in most of the other DFNB genes have so far been detected in only a small number of families, and their contribution to deafness on a population scale might therefore be limited. Identification of all genes involved in hereditary hearing loss will help in our understanding of the basic mechanisms underlying normal hearing, in early diagnosis and therapy.

Ethnicity and mutations in GJB2 (connexin 26) and GJB6 (connexin 30) in a multi-cultural Canadian paediatric Cochlear Implant Program

OBJECTIVE

To determine the relationship between ethnicity and mutations in the GJB2 and GJB6 genes in multi-cultural patients enrolled in a Canadian paediatric Cochlear Implant Program.

METHODS

Blood was analyzed from 65 paediatric cochlear implant users by direct sequencing of the coding region and intron/exon boundaries of the GBJ2 gene. Individuals heterozygous for one mutation in GJB2 or in whom mutations in GJB2 were not detected were analyzed for the common 342 kb deletion mutation D13S1830 in the GJB6 gene. Information regarding ethnicity of patients' families was obtained from patient records and/or interview.

RESULTS

GJB2 mutations were found in 36.9% of paediatric cochlear implant users tested. Nine different GJB2 mutations were identified among individuals from 14 different countries of origin. Seventy-eight percent of all identified pathogenic GJB2 mutations were 35delG. Biallelic GJB2 mutations were found in 16 cochlear implant users (66.7% of GJB2 mutations). Three novel GJB2 sequence changes were identified: (1) a missense mutation T107C (L36P) in an individual of African decent; (2) a missense mutation G475T (D159Y) in an individual of Caribbean decent; (3) a regulatory region change 1-34C to T in an individual of African decent. GJB6-D13S1830 mutations were not found in any of the patients tested. Individuals of African, Caribbean and East Indian decent had different GJB2 mutations than the remainder of individuals tested. Patients of Asian, Italian, Spanish, Polish and Armenian decent were not found to carry mutations in GJB2 or the common GJB6-D13S1830 mutation.

CONCLUSIONS

This study represents the largest number of biallelic GJB2 mutations isolated in a group of paediatric cochlear implant users to date. Numerous and diverse GJB2 mutations were found in this multi-cultural group of children. Even though GJB2 mutations have been widely reported in the literature, this discussion represents the first report of GJB2 mutations in a multi-ethnic population (Canadian), as compared with previous studies that investigated fairly homogeneous populations. The diversity of GJB2 mutations identified reinforces the importance of testing for changes in GJB2 by direct sequencing of the entire coding region rather than testing only for common mutations.