GJB2 mutations: Passage through Iran

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.

Exome sequencing utility in defining the genetic landscape of hearing loss and novel-gene discovery in Iran

Hearing loss (HL) is one of the most common sensory defects affecting more than 466 million individuals worldwide. It is clinically and genetically heterogeneous with over 120 genes causing non-syndromic HL identified to date. Here, we performed exome sequencing (ES) on a cohort of Iranian families with no disease-causing variants in known deafness-associated genes after screening with a targeted gene panel. We identified likely causal variants in 20 out of 71 families screened. Fifteen families segregated variants in known deafness-associated genes. Eight families segregated variants in novel candidate genes for HL: DBH, TOP3A, COX18, USP31, TCF19, SCP2, TENM1, and CARMIL1. In the three of these families, intrafamilial locus heterogeneity was observed with variants in both known and novel candidate genes. In aggregate, we were able to identify the underlying genetic cause of HL in nearly 30% of our study cohort using ES. This study corroborates the observation that high-throughput DNA sequencing in populations with high rates of consanguineous marriages represents a more appropriate strategy to elucidate the genetic etiology of heterogeneous conditions such as HL.

Investigation of MYO15A and MYO7A Mutations in Iranian Patients with Nonsyndromic Hearing Loss

Hearing loss (HL) is the most common sensory disorder in humans, which affects individuals in both inherited and acquired forms. MYO15A and MYO7A gene mutations have a significant role in the development of deafness. In this study, we assessed the prevalence of MYO15A and MYO7A mutations in one hundred non-relative deaf Iranians. Materials and methods: The existence of MYO15A and MYO7A mutations were assessed using the tetra-primer ARMS-PCR method, High Resolution Melting (HRM) and sequencing method. Results: A heterozygote missense mutation, p.V2135L (c.6403G > T) in the MYO15A gene, was found in a patient using the sequencing method. Conclusion: These results explain the negligible prevalence of selected mutations among Iranian patients. Identifying common mutations in patients of an ethnic group can reduce the financial costs and time needed for identifying the causes of deafness.

Molecular diagnosis of SLC26A4-related hereditary hearing loss in a group of patients from two provinces of Iran

The SLC26A4 gene has been described as the second gene involved in most cases of autosomal recessive non-syndromic hearing loss (ARNSHL), after GJB2. Over 500 different SLC26A4 mutations have been reported, with each ethnic population having its own distinctive mutations. Here, we aimed to determine the frequency and mutation profile of the SLC26A4 gene from two different provinces (center and west) of Iran. This study included 50 nuclear families with two or more siblings segregating presumed ARNSHL. All affected tested negative for mutations in GJB2 at the DFNB1 locus and were therefore screened for autozygosity by descent using short tandem repeat polymorphisms (STRPs) of DFNB4. Sanger sequencing was performed to screen the 20 exons of the SLC26A4 gene for the families linked to this locus. In silico analyses were also performed using available software tools. Four out of 25 (16%) and 3 of 25 (12%) studied families of Isfahan and Hamedan provinces, respectively. were linked to DFNB4. Sanger sequencing led to the identification of six different mutations, one of which (c.919-2A>G) was recurrent and accounted for 31% of all mutant alleles. One out of 7 (14.3%) families with mutations were confirmed to be Pendred syndrome (PS). The SLC26A4 mutations have a high carrying rate in ARNSHL Iranian patients. The identification of a disease causing mutation can be used to establish a genotypic diagnosis and provide important information to the patients and their families.

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.

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.

The SLC26A4 c.706C>G (p.Leu236Val) Variant is a Frequent Cause of Hearing Impairment in Filipino Cochlear Implantees

HYPOTHESIS

Variants in SLC26A4 are an important cause of congenital hearing impairment in the Philippines.

BACKGROUND

Cochlear implantation is a standard rehabilitation option for congenital hearing impairment worldwide, but places a huge cost burden in lower-income countries. The study of risk factors such as genetic variants that may help determine genetic etiology of hearing loss and also predict cochlear implant outcomes is therefore beneficial.

METHODS

DNA samples from 29 GJB2-negative Filipino cochlear implantees were Sanger-sequenced for the coding exons of SLC26A4. Exome sequencing was performed to confirm results.

RESULTS

Four cochlear implantees with bilaterally enlarged vestibular aqueducts (EVA) were homozygous for the pathogenic SLC26A4 c.706C>G (p.Leu236Val) variant, which has a minor allele frequency of 0.0015 in Filipino controls. In patients with the SLC26A4 variant there was no association between cochlear implant outcome and age at implantation or duration of implant. There was also no association between the occurrence of the SLC26A4 variant and postsurgical audiometric thresholds and parents' evaluation of aural/oral performance of children (PEACH) scores. On the other hand, the SLC26A4 variant increased presurgical median audiometric thresholds (p = 0.01), particularly at 500 to 2000 Hz.

CONCLUSION

The SLC26A4 c.706C>G (p.Leu236Val) variant is a frequent cause of congenital hearing impairment in Filipinos and is associated with bilateral EVA and increased presurgical audiometric thresholds, but does not adversely affect post-implant outcomes.

Distinct genetic variation and heterogeneity of the Iranian population

Iran, despite its size, geographic location and past cultural influence, has largely been a blind spot for human population genetic studies. With only sparse genetic information on the Iranian population available, we pursued its genome-wide and geographic characterization based on 1021 samples from eleven ethnic groups. We show that Iranians, while close to neighboring populations, present distinct genetic variation consistent with long-standing genetic continuity, harbor high heterogeneity and different levels of consanguinity, fall apart into a cluster of similar groups and several admixed ones and have experienced numerous language adoption events in the past. Our findings render Iran an important source for human genetic variation in Western and Central Asia, will guide adequate study sampling and assist the interpretation of putative disease-implicated genetic variation. Given Iran's internal genetic heterogeneity, future studies will have to consider ethnic affiliations and possible admixture.

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.

Next-generation sequencing reveals a novel pathological mutation in the TMC1 gene causing autosomal recessive non-syndromic hearing loss in an Iranian kindred

OBJECTIVES

Hearing loss (HL) is the most common sensory-neural disorder with excessive clinical and genetic heterogeneity, which negatively affects life quality. Autosomal recessive non-syndromic hearing loss (ARNSHL) is the most common form of the disease with no specific genotype-phenotype correlation in most of the cases. Whole exome sequencing (WES) is a powerful tool to overcome the problem of finding mutations in heterogeneous disorders.

METHODS

A comprehensive clinical and pedigree examination was performed on a multiplex family from Khuzestan province suffering from hereditary HL. Direct sequencing of GJB2 and genetic linkage analysis of DFNB1A/B was accomplished. WES was utilized to find possible genetic etiology of the disease. Co-segregation analysis of the candidate variant was done. High resolution melting analysis was applied to detect variant status in 50 healthy matched controls.

RESULTS

Clinical investigations suggested ARNSHL in the pedigree. The family was negative for DFNB1A/B. WES revealed a novel nonsense mutation, c.256G > T (p.Glu86*), in TMC1 segregating with the phenotype in the pedigree. The variant was absent in the controls.

CONCLUSION

Here, we report successful application of WES to identify the molecular pathogenesis of ARNSHL in a large family. The novel nonsense TMC1 variant meets the criteria of being pathogenic according to the ACMG-AMP variant interpretation guideline.

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.

Applying Two Different Bioinformatic Approaches to Discover Novel Genes Associated with Hereditary Hearing Loss via Whole-Exome Sequencing: ENDEAVOUR and HomozygosityMapper

BACKGROUND

Hearing loss (HL) is a highly prevalent heterogeneous deficiency of sensory-neural system with involvement of several dozen genes. Whole-exome sequencing (WES) is capable of discovering known and novel genes involved with HL.

MATERIALS AND METHODS

Two pedigrees with HL background from Khuzestan province of Iran were selected. Polymerase chain reaction-sequencing of GJB2 and homozygosity mapping of 16 DFNB loci were performed. One patient of the first and two affected individuals from the second pedigree were subjected to WES. The result files were analyzed using tools on Ubuntu 16.04. Short reads were mapped to reference genome (hg19, NCBI Build 37). Sorting and duplication removals were done. Variants were obtained and annotated by an online software tool. Variant filtration was performed. In the first family, ENDEAVOUR was applied to prioritize candidate genes. In the second family, a combination of shared variants, homozygosity mapping, and gene expression were implemented to launch the disease-causing gene.

RESULTS

GJB2 sequencing and linkage analysis established no homozygosity-by-descent at any DFNB loci. Utilizing ENDEAVOUR, BBX: C.C857G (P.A286G), and MYH15: C.C5557T (P.R1853C) were put forward, but none of the variants co-segregated with the phenotype. Two genes, UNC13B and TRAK1, were prioritized in the homozygous regions detected by HomozygosityMapper.

CONCLUSION

WES is regarded a powerful approach to discover molecular etiology of Mendelian inherited disorders, but as it fails to enrich GC-rich regions, incapability of capturing noncoding regulatory regions and limited specificity and accuracy of copy number variations detection tools from exome data, it is assumed an insufficient procedure.

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.

A Novel Pathologic Variant in OTOF in an Iranian Family Segregating Hereditary Hearing Loss

Objective Hearing loss (HL) is the most common sensory-neural defect and the most heterogeneous trait in humans, with the involvement of >100 genes, which make a molecular diagnosis problematic. Next-generation sequencing (NGS) is a new strategy that can overcome this problem. Study Design Descriptive experimental study. Setting Diagnostic laboratory. Subjects and Methods A comprehensive family history was obtained, and clinical evaluations and pedigree analysis were performed in a family with multiple individuals with HL. As the first tier, GJB2 was sequenced, and genetic linkage analysis of DFNB1A/B was performed to rule out the most common cause of the disease. Targeted NGS was used to unravel the molecular etiology of the disease in the HL-associated genes in the proband. Two homozygous variants remained in OTOF after proper filtration. Cosegregation and in silico analysis were done. Preimplantation genetic diagnosis (PGD) was accomplished via linkage analysis and direct sequencing of the pathogenic variant. Results Clinical evaluations suggested autosomal recessive nonsyndromic HL. Two homozygous variants, c.367G>A (p.Gly123Ser) and c.1392+1G>A, were identified in cis status. c.1392+1G>A met the criteria for being pathogenic according to the variant interpretation guideline of the American College of Medical Genetics and Genomics. PGD was successfully performed to prevent the recurrence of the disease in the related family. Conclusion A novel OTOF mutation causing HL was identified. Here, we report the effectiveness of the combined application of targeted NGS and PGD in diagnosis and prevention of hereditary HL.

An update of common autosomal recessive non-syndromic hearing loss genes in Iranian population

Autosomal-recessive genes are responsible for about 80% of the hereditary non-syndromic hearing loss (NSHL) cases. In Iran, due to consanguineous marriages, NSHL is the second most frequent disability after intellectual disability, occurring one in 16 individuals. Enormous heterogeneity in the genetic pathology of hearing loss causes a major challenge in identification of responsible genes. In Iran, GJB2 is responsible for the most cases of pre-lingual and non-syndromic hearing loss (with frequency of 16.7%) which followed by other genes with lower frequency. Although several studies have indicated that a large proportion of both syndromic and non-syndromic hearing loss in Iranian populations are caused by defects in just a few genes, new detection strategies such as NGS (Next-generation sequencing) have increased the spectrum of responsible mutations. However, by applying this technique in Iran patients screening, the role of lots of novel related genes have been reported. In this review, we aim to describe function of these genes and their contribution to non-syndromic genetic hearing loss in Iranian population and we classify the genes by their functions.

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.

Characterising the spectrum of autosomal recessive hereditary hearing loss in Iran

BACKGROUND

Countries with culturally accepted consanguinity provide a unique resource for the study of rare recessively inherited genetic diseases. Although hereditary hearing loss (HHL) is not uncommon, it is genetically heterogeneous, with over 85 genes causally implicated in non-syndromic hearing loss (NSHL). This heterogeneity makes many gene-specific types of NSHL exceedingly rare. We sought to define the spectrum of autosomal recessive HHL in Iran by investigating both common and rarely diagnosed deafness-causing genes.

DESIGN

Using a custom targeted genomic enrichment (TGE) panel, we simultaneously interrogated all known genetic causes of NSHL in a cohort of 302 GJB2-negative Iranian families.

RESULTS

We established a genetic diagnosis for 67% of probands and their families, with over half of all diagnoses attributable to variants in five genes: SLC26A4, MYO15A, MYO7A, CDH23 and PCDH15. As a reflection of the power of consanguinity mapping, 26 genes were identified as causative for NSHL in the Iranian population for the first time. In total, 179 deafness-causing variants were identified in 40 genes in 201 probands, including 110 novel single nucleotide or small insertion-deletion variants and three novel CNV. Several variants represent founder mutations.

CONCLUSION

This study attests to the power of TGE and massively parallel sequencing as a diagnostic tool for the evaluation of hearing loss in Iran, and expands on our understanding of the genetics of HHL in this country. Families negative for variants in the genes represented on this panel represent an excellent cohort for novel gene discovery.

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.

Ethnic-specific spectrum of GJB2 and SLC26A4 mutations: their origin and a literature review

OBJECTIVE

The mutation spectrum of the GJB2 and SLC26A4 genes, the 2 most common genes causing deafness, are known to be ethnic specific. In this study, the spectrum of the reported GJB2 and SLC26A4 mutations in different populations are reviewed and considered from a human migration perspective.

METHODS

Fifty-two and 17 articles on GJB2 and SLC26A4 mutations, respectively, were reviewed through the PubMed database from April 1996 to September 2014. The 4 most prevalent mutations were selected and compared. A cluster analysis was subsequently performed for these selected mutations.

RESULTS

The present review of frequent mutations shows the ethnic-specific GJB2 and SLC26A4 gene mutation spectrum. A cluster analysis of the GJB2 and SLC26A4 genes revealed similarities between ethnic populations.

CONCLUSION

The mutation spectrum reviewed in this study clearly indicated that the frequent mutations in the GJB2 and SLC26A4 genes are consistent with the founder mutation hypothesis. A comparison with the Y-chromosome phylogenetic tree indicated that these mutations may have occurred during human migration.

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.

The role and spectrum of SLC26A4 mutations in Iranian patients with autosomal recessive hereditary deafness

OBJECTIVE

To determine the prevalence and types of SLC26A4 mutations and the relevant phenotypes in a series of Iranian deaf patients.

DESIGN

A descriptive laboratory study.

STUDY SAMPLE

One hundred and twenty-one families including 60 unrelated patients and 61 unrelated multiplex families with autosomal recessive deafness were included. In the 61 multiplex families, linkage was conducted for short tandem repeats (STRs) of the DFNB4. Selected individuals from the linked families and all of the 60 deaf individuals were subjected to sequencing of SLC26A4.

RESULTS

Seven out of the 61 (11.5%) families were linked to the locus which upon further inquiry led to identification of eight different mutations. Also, five out of the 60 (8.3%) patients were positive for the mutations. The SLC26A4 mutations clarified in 9.1% (12 families) of total investigated alleles included: c.2106delG, c.65-66insT, c.881-882delAC, c.863-864insT, c.1226G> A, c.1238A> G, c.1334T> G, c.1790T> C, c.1489G> A, c.919-2A> G (IVS7-2A> G), c.1412delT, and c.1197delT. Six out of 12 (50%) families with mutations were confirmed to be Pendred syndrome (PS).

CONCLUSIONS

The results probably suggest a high prevalence and specificity of SLC26A4 mutations among Iranian deaf patients. Molecular study of SLC26A4 may lead to elucidation of the population-specific mutation profile which is of importance in diagnostics of deafness.

Spectrum and frequency of GJB2 mutations causing deafness in the northwest of Iran

OBJECTIVE

Mutations in GJB2 and GJB6 which comprise DFNB1 locus cause up to half of all cases of the prelingual autosomal recessive non-syndromic hearing loss (ARNSHL) worldwide. This study has intended to assess the spectrum and frequency of GJB2/GJB6 mutations in northwest of Iran.

METHODS

508 Patients with presumed ARNSHL were analyzed by applying ARMS-PCR, SSCP, PCR-RFLP and sequencing assays.

RESULTS

Seventy-five (14.7%) different homozygous and eighty-seven (17.1%) different compound heterozygous genotypes were detected in this cohort. Concerning the GJB2 gene, c.35delG was the most prevalent mutation, accounting for 16.4% of the samples. In addition 29 sequence variations other than c.35delG mutation were distinguished in GJB2; namely, delE120, Ins A 290-291, R143Q, V37I, R32H, Y155X, V27I + T123N, F154F, 167delT, 312del14, 299-300delA, T8M, W24X, E114G + V27I, 235delC, R184P, V153I, S139N, A171T, M163V (unknown mutation), G127V, E147X, R127H, 35insG, R143W, V27I, G160S, E114G and IVS1 + 1G > A. Moreover, the IVS1 + 1G > A was accounted as a second common mutation.

CONCLUSIONS

Overall, the frequency of GJB2 mutations (≥31%) is in agreement with other white population. These findings highlight the importance of the study of GJB2 gene in the diagnosis to provide early treatment and genetic counseling.

Compound Heterozygosity for Two Novel SLC26A4 Mutations in a Large Iranian Pedigree with Pendred Syndrome

Objectives

The aim of this study was to detect the genetic cause of deafness in a large Iranian family. Due to the importance of SLC26A4 in causing hearing loss, information about the gene mutations can be beneficial in molecular detection and management of deaf patients.

Methods

We investigated the genetic etiology in a large consanguineous family with 9 deaf patients from Fars province of Iran with no GJB2 mutations. Initially, linkage analysis was performed by four DFNB4 short tandem repeat markers. The result showed linkage to DFNB4 locus. Following that, DNA sequencing of all 21 exons, their adjacent intronic sequences and the promoter of SLC26A4 was carried out for mutation detection.

Results

Two novel mutations (c.863-864insT and c.881-882delAC) were identified in exon 7 of the gene, in both homozygous and compound heterozygous state in patients.

Conclusion

Our results supported the importance of the SLC26A4 mutations in the etiology of hearing loss among the Iranian patients and therefore its mutation screening should be considered after GJB2 in the molecular diagnostics of hearing loss, especially when enlarged vestibular aqueduct or goiter is detected.

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

Hereditary hearing loss is a genetically heterogeneous disorder. Mutations in connexin 26 (CX26), are a major cause in many countries and are largely dependent on ethnic groups. The purpose of our study was to evaluate the prevalence of GJB2 mutations among affected individuals from south of Iran. Fifty patients presenting with autosomal recessive non-syndromic hearing loss from Fars, province in south of Iran, were studied for mutations in GJB2 gene and screened by direct sequencing. Mutations were detected in 15 out of 50 patients (30 %). Eight different mutations were identified; six of them were previously identified (35delG, V27I M34V, V153I, A149T, V198M). The remaining two alleles, L28I and N169T, were novel variants. The most common mutations were 35delG followed by V153I with an allele frequency of 7 and 6 %, respectively. In this study, 30 % of our subjects were found to have the causative variants or polymorphisms in GJB2 and the c.35delG mutation was the most common cause in our patients. However, more study with larger sample size as well as in vitro functional study for these new variants in Xenopus oocytes is required.

A comprehensive study to determine heterogeneity of autosomal recessive nonsyndromic hearing loss in Iran

Hearing loss is the most common sensory disorder worldwide and affects 1 of every 500 newborns. In developed countries, at least 50% of cases are genetic, most often resulting in nonsyndromic deafness (70%), which is usually autosomal recessive (∼80%). Although the cause of hearing loss is heterogeneous, mutations in GJB2 gene at DFNB1 locus are the major cause of autosomal recessive nonsyndromic hearing loss (ARNSHL) in many populations. Our previous study showed that mutations of GJB2 gene do not contribute to the major genetic load of deafness in the Iranian population (∼16%). Therefore, to define the importance of other genes in contributing to an ARNSHL phenotype in the Iranian population, we used homozygosity mapping to identify regions of autozygosity-by-descent in 144 families which two or more progeny had ARNSHL but were negative for GJB2 gene mutations. Using flanking or intragenic short-tandem repeat markers for 33 loci we identified 33 different homozygous variations in 10 genes, of which 9 are novel. In aggregate, these data explain ∼40% of genetic background of ARNHSL in the Iranian population.

Mutation detection in GJB2 gene among Malays with non-syndromic hearing loss

OBJECTIVES

To identify the mutations in the GJB2 gene and to determine its association with non-syndromic hearing loss in Malays.

METHODS

A comparative cross sectional study was conducted on a group of children from the deaf schools and the normal schools. A total of 91 buccal cell samples of non-syndromic hearing loss and 91 normal hearing children were taken. Polymerase chain reaction was used to amplify the coding region of GJB2 gene. The PCR product of GJB2 coding region was preceded with screening for mutations using denaturing high performance liquid chromatography (dHPLC) and mutations detected were confirmed by DNA sequencing.

RESULTS

Twelve sequence variations including mutations and polymorphisms were found in 32 patients and 37 control subjects. The variations were G4D, V27I, E114G, T123N, V37I and R127H in both groups, W24X, R32H, 257_259 del CGC and M34L in patients only and I203T and V153I in control subjects only. There were no association between homozygous (P=0.368) or heterozygous (P=0.164) GJB2 gene and non-syndromic hearing loss.

CONCLUSIONS

The types of GJB2 gene mutation were different and vary in Malay non-syndromic hearing loss as compared to the other races. Furthermore, the mutation did not associate with hearing loss in the population. Other related genes are believed to be involved and need to be sought in this group of patients.

The spectrum of GJB2 mutations in the Iranian population with non-syndromic hearing loss--a twelve year study

OBJECTIVE

Mutations in GJB2, encoding connexin 26 (CX26), are causally related to autosomal recessive form of non-syndromic hearing loss (NSHL) at the DFNB1 locus and autosomal dominant NSHL at the DFNA3 locus. In this study, we investigated the prevalence of GJB2 mutations in the Iranian deaf population.

METHODS

A total of 2322 deaf probands presenting the ethnically diverse Iranian population were screened for variants in GJB2. All persons were first screened for the c.35delG mutation, as this variant is the most prevalent GJB2-deafness causing mutation in the Iranian population. In all persons carrying zero or one c.35delG allele, exons 1 and 2 were then sequenced.

RESULTS

In total, 374 (~16%) families segregated GJB2-related deafness caused by 45 different mutations and 5 novel variants. The c.35delG mutation was most commonly identified and accounts for ~65% of the GJB2 mutations found in population studied.

CONCLUSION

Our data also show that there is a gradual decrease in the frequency of the c.35delG mutation and of GJB2-related deafness in general in a cline across Iran extending from the northwest to southeast.

Spectrum of GJB2 (Cx26) gene mutations in Iranian Azeri patients with nonsyndromic autosomal recessive hearing loss

OBJECTIVE

Hereditary hearing impairment is a genetically heterogeneous disorder. In spite of this, mutations in the GJB2 gene, encoding connexin 26 (Cx26), are a major cause of nonsyndromic recessive hearing loss in many countries and are largely dependent on ethnic groups. The purpose of our study was to characterize the type and prevalence of GJB2 mutations among Azeri population of Iran.

METHODS

Fifty families presenting autosomal recessive nonsyndromic hearing loss from Ardabil province of Iran were studied for mutations in GJB2 gene. All DNA samples were screened for c.35delG mutation by ARMS PCR. Samples from patients who were normal for c.35delG were analyzed for the other variations in GJB2 by direct sequencing. In the absence of mutation detection, GJB6 was screened for the del(GJB6-D13S1830) and del(GJB6-D13S1854).

RESULT

Thirteen families demonstrated alteration in the Cx26 (26%). The 35delG mutation was the most common one, accounting for 69.2% (9 out of 13 families). All the detected families were homozygous for this mutation. Two families were homozygous for delE120 and 299-300delAT mutations. We also identified a novel mutation: c.463-464 delTA in 2 families resulting in a frame shift mutation.

CONCLUSION

Our results suggest that c.35delG mutation in the GJB2 gene is the most important cause of GJB2 related deafness in Iranian Azeri population.

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.

GJB2 and GJB6 genes and the A1555G mitochondrial mutation are only minor causes of nonsyndromic hearing loss in the Qatari population

OBJECTIVE

This study reports results from the first survey of the genetic causes of nonsyndromic sensorineural hearing loss (NSHHL) in the Qatari population. DESIGN AND STUDY SAMPLES: Data were collected from 126 Qatari patients (58 males and 68 females) belonging to inbred families (56%), showing an autosomal recessive pattern of inheritance (96%). Fifty-three patients were less than 10 years old, 55 in the age range of 10 to 20 years, while 18 were aged between 20 and 30 years. All subjects had moderate to severe sensorineural hearing loss and were screened for GJB2 mutations, GJB6 deletion, and for A1555G mitochondrial mutation.

RESULTS

Four patients were homozygous and one was heterozygous for c.35delG; five were homozygous for the IVS1 + 1G < A, and two were heterozygous for c.229 T > C. Only 8.3% of the pathogenic alleles were detected. No patients were positive for GJB6 deletion or for A1555G .

CONCLUSIONS

These findings: (1) demonstrate that GJB2, GJB6 deletion and A1555G mutation account for a minor proportion of NSHHL in the Qatari population, (2) further strengthen the need to search for causative genes, (3) clearly contribute to establishing preventive strategies for NSHHL in Qatar and in the Gulf area.

Large-scale screening of mitochondrial DNA mutations among Iranian patients with prelingual nonsyndromic hearing impairment

Hereditary hearing impairment (HI) is a genetically heterogeneous disorder caused by mutations either in nuclear DNA (nDNA) or in mitochondrial DNA (mtDNA). The nDNA mutations account for the majority of prelingual nonsyndromic HI (NSHI). The present survey was conducted to screen for known pathogenic mtDNA mutations including A1555G, A3243G, C1494T, and A7445G to provide an accurate estimate of their prevalence in prelingual NSHI for the first time in the Iranian subpopulations. One thousand unrelated probands with NSHI (including both GJB2-negative and GJB2 heterozygote cases) and 1000 healthy matched controls were investigated using the PCR/RFLP method followed by DNA sequencing to confirm the observed mtDNA mutations. Two of the studied mutations, namely A3243G and A7445G, were each found in a single family (a frequency of 0.1% for each). Mutation screening for A3243G followed by DNA sequencing led to the identification of G3316A substitution, with no prior link to HI. Surprisingly, screening for A3243G in the studied population identified 6 cases (0.6%) in probands and 10 (1%) in normal subjects. A1555G, the most common mtDNA mutation associated with deafness in other populations, was not found in the studied samples. To conclude, our findings indicate G3316A as a nonpathogenic variant in the prelingual NSHI subpopulations of Iran and suggest that mtDNA mutations do not play a major role in the etiology of NSHI in Iran.

Did the GJB2 35delG mutation originate in Iran?

Mutations in GJB2 are a major cause of autosomal recessive non-syndromic hearing loss (ARNSHL) in many populations. A single mutation of this gene (35delG) accounts for approximately 70% of GJB2 mutations that are associated with ARNSHL in Caucasians in many European countries and also in Iranian. In this study, we used PCR and restriction digestion to genotype five single nucleotide polymorphisms (SNPs) that define the genetic background of the 35delG mutation over an interval of 98 Kbp that includes the coding and flanking regions of GJB2. Two microsatellite markers, D13S175 and D13S141, were also analyzed in patients and controls. These data suggest that the 35delG mutation originated in northern Iran.

Prenatal screening for the 35delG GJB2, del (GJB6-D13S1830), and del (GJB6-D13S1854) mutations in the Romanian population

OBJECTIVE

In this study, the aim of prenatal screening was to estimate the carrier frequency of the three mutations 35delG, del (GJB6-D13S1830), and del (GJB6-D13S1854), which are known to be the leading mutations of hereditary hearing loss in European populations.

METHODS

We performed a prenatal screening to assess the carrier frequency of the most common mutations at the DFNB1 gene locus in the general population. Samples of amniotic fluid (n=339) and chorionic villi (n=11) were taken from an unselected group of 350 unrelated pregnant women with normal hearing. Genomic fetal DNA was extracted and analyzed by PCR multiplex assays.

RESULTS

The rate of carriers for the 35delG GJB2 mutation was 3.14%, comparable to that of most Southeastern European populations. All samples were negative for GJB6-D13S1830 and GJB6-D13S1854 deletions. The genetic tests were considered for carrier detection and early diagnosis rather than termination of pregnancy.

CONCLUSIONS

Our study suggests a need for detecting the carriers. This is the first step for the construction of a national database and provides information for health planners and policy makers to help them in planning programs and allocation resources. The molecular testing was well received by pregnant women and appears to be feasible and highly acceptable.

Detection of the GJB2 Mutation in Iranian Children with Hearing Loss Treated with Cochlear Implantation

The 35delG mutation in the gap junction protein, β2, 26kDa (GJB2) gene is the most common mutation that has been found in children with non syndromic hearing loss. Testing for the GJB2 gene mutation is simple and can directly answer the concerns of the parents about cause of the disorder and prognosis for their children. Cochlear implantation (CI) is one of the methods of hearing rehabilitation in patients with complete hearing loss. The present study was designed for genetic assessment of children who were referred for CI. Connexin 26 (Cx26) gene analyses were performed on 42 children with non syndromic hearing loss who were referred to the Baqiyatallah Hospital, Tehran, Iran for genetic consultation and CI. Clinical history was obtained and an examination conducted on each individual. Genomic DNA was extracted from peripheral blood and mutation identification of the Cx26 gene was performed by polymerase chain reaction (PCR) amplification and direct sequencing of the coding sequence of the gene. Cochlear implantation was performed for all patients and treatment response was assessed for all of them based on speech intelligibility rating (SIR) before and after CI. We found six patients (14.3%) with the 35delG mutation on the Cx26 gene, two homozygotes and four heterozygotes. No other mutation was detected. Treatment response in children with the homozygous 35delG mutation was better than in heterozygous patients, and treatment response in children with the mutation was better than in children with no mutation. Mutation screening for finding deafness causing mutations in the GJB2 gene is a useful predictor of post-implantation speech perception. We suggest microarray or other advanced mutation detection methods for assessment of other genes that might be responsible for non syndromic deafness.

Prevalence of GJB2-associated deafness and outcomes of cochlear implantation in Iran

OBJECTIVES

To investigate the prevalence of mutations in the coding exon of the GJB2 gene in Iranian children with cochlear implants, and to compare the outcomes of auditory perception and speech production in cochlear-implanted children with and without GJB2 mutation.

MATERIALS AND METHODS

One hundred and sixty-six prelingually deaf children who had undergone cochlear implantation at the Iranian Cochlear Implant Center, Tehran, were selected from a pool of 428 implanted children. The prevalence of GJB2 gene mutations was assessed using nested polymerase chain reaction and direct sequencing. To enable comparisons, we also identified 36 implanted children with non-GJB2 deafness. Patients' speech perception and speech production were assessed using the Categorization of Auditory Performance and Speech Intelligibility Rating scales.

RESULTS

Thirty-three of 166 probands (19.9 per cent) were found to have GJB2 deafness-causing allele variants and were diagnosed with DFNB1 deafness. Results also indicated a significant improvement in speech perception and production scores in both GJB2 and non-GJB2 patients over time.

CONCLUSION

Children with GJB2-related deafness benefit from cochlear implantation to the same extent as those with non-GJB2-related deafness.

Clinical Application of Screening for GJB2 Mutations before Cochlear Implantation in a Heterogeneous Population with High Rate of Autosomal Recessive Nonsyndromic Hearing Loss

Clinical application of mutation screening and its effect on the outcome of cochlear implantation is widely debated. We investigated the effect of mutations in GJB2 gene on the outcome of cochlear implantation in a population with a high rate of consanguineous marriage and autosomal recessive nonsyndromic hearing loss. Two hundred and one children with profound prelingual sensorineural hearing loss were included. Forty-six patients had 35delG in GJB2. Speech awareness thresholds (SATs) and speech recognition thresholds (SRTs) improved following implantation, but there was no difference in performance between patients with GJB2-related deafness versus control (all P > 0.10). Both groups had produced their first comprehensible words within the same period of time following implantation (2.27 months in GJB2-related deaf versus 2.62 months in controls, P = 0.22). Although our findings demonstrate the need to uncover unidentified genetic causes of hereditary deafness, they do not support the current policy for genetic screening before cochlear implantation, nor prove a prognostic value.

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.