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

Hearing loss is the most frequent sensory disorder. It affects 3 in 1000 newborns. It is genetically heterogeneous with 60 causally-related genes identified to date. Mutations in GJB2 gene account for half of all cases of non-syndromic deafness. The aim of this study was to determine the relative frequency of GJB2 allele variants in Tunisia. In this study, we screened 138 patients with congenital hearing loss belonging to 131 families originating from different parts of Tunisia for mutations in GJB2 gene. GJB2 mutations were found in 39% of families (51/131). The most common mutation was c.35delG accounting for 35% of all cases (46/131). The second most frequent mutation was p.E47X present in 3.8% of families. Four identified mutations in our cohort have not been reported in Tunisia; p.V37I, c.235delC, p.G130A and the splice site mutation IVS1+1G>A (0.76%). These previously described mutations were detected only in families originating from Northern and not from other geographical regions in Tunisia. In conclusion we have confirmed the high frequency of c.35delG in Tunisia which represents 85.4% of all GJB2 mutant alleles. We have also extended the mutational spectrum of GJB2 gene in Tunisia and revealed a more pronounced allelic heterogeneity in the North compared to the rest of the country.     

Newborn genetic screening for hearing impairment: a preliminary study at a tertiary center

Universal newborn hearing screening (UNHS) is of paramount importance for early identification and management of hearing impairment in children. However, infants with slight/mild, progressive, or late-onset hearing impairment might be missed in conventional UNHS. To investigate whether genetic screening for common deafness-associated mutations could assist in identifying these infants, 1017 consecutive newborns in a tertiary hospital were subjected to both newborn hearing screening using a two-step distortion-product otoacoustic emissions (DPOAE) screening and newborn genetic screening (NGS) for deafness. The NGS targeted 4 deafness-associated mutations commonly found in the Taiwanese population, including p.V37I (c.109G>A) and c.235delC of the GJB2 gene, c.919-2A>G of the SLC26A4 gene, and mitochondrial m.1555A>G of the 12S rRNA gene. The results of the NGS were then correlated to the results of the NHS. Of the 1017 newborns, 16 (1.6%) had unilateral DPOAE screening failure, and 22 (2.2%) had bilateral DPOAE screening failure. A total of 199 (19.6%) babies were found to have at least 1 mutated allele on the NGS for deafness, 11 (1.1%) of whom were homozygous for GJB2 p.V37I, 6 (0.6%) compound heterozygous for GJB2 p.V37I and c.235delC, and 1 (0.1%) homoplasmic for m.1555A>G, who may potentially have hearing loss. Among them, 3 babies, 5 babies, and 1 baby, respectively, passed the NHS at birth. Comprehensive audiological assessments in the 9 babies at 3 months identified 1 with slight hearing loss and 2 with mild hearing loss. NGS for common deafness-associated mutations may identify infants with slight/mild or potentially progressive hearing impairment, thus compensating for the inherent limitations of the conventional UNHS.     

Residual Hearing in DFNB1 Deafness and Its Clinical Implication in a Korean Population

Introduction

The contribution of Gap junction beta-2 protein (GJB2) to the genetic load of deafness and its mutation spectra vary among different ethnic groups.

Objective

In this study, the mutation spectrum and audiologic features of patients with GJB2 mutations were evaluated with a specific focus on residual hearing.

Methods

An initial cohort of 588 subjects from 304 families with varying degrees of hearing loss were collected at the otolaryngology clinics of Seoul National University Hospital and Seoul National University Bundang Hospital from September 2010 through January 2014. GJB2 sequencing was carried out for 130 probands with sporadic or autosomal recessive non syndromic hearing loss. The audiograms were evaluated in the GJB2 mutants.

Results

Of the 130 subjects, 22 (16.9%) were found to carry at least one mutant allele of GJB2. The c.235delC mutation was shown to have the most common allele frequency (39.0%) among GJB2 mutations, followed by p.R143W (26.8%) and p.V37I (9.8%). Among those probands without the p.V37I allele in a trans configuration who showed some degree of residual hearing, the mean air conduction thresholds at 250 and 500 Hz were 57 dB HL and 77.8 dB HL, respectively. The c.235delC mutation showed a particularly wide spectrum of hearing loss, from mild to profound and significantly better hearing thresholds at 250 Hz and 2k Hz than in the non-p.V37I and non-235delC nonsyndromic hearing loss and deafness 1(DFNB1) subjects.

Conclusion

Despite its reputation as the cause of severe to profound deafness, c.235delC, the most frequent DFNB1 mutation in our cohort, caused a wide range of hearing loss with some residual hearing in low frequencies. This finding can be of paramount help for prediction of low frequency hearing thresholds in very young DFNB1 patients and highlights the importance of soft surgery for cochlear implantation in these patients.     

GJB2 mutations and degree of hearing loss: a multicenter study

Hearing impairment (HI) affects 1 in 650 newborns, which makes it the most common congenital sensory impairment. Despite extraordinary genetic heterogeneity, mutations in one gene, GJB2, which encodes the connexin 26 protein and is involved in inner ear homeostasis, are found in up to 50% of patients with autosomal recessive nonsyndromic hearing loss. Because of the high frequency of GJB2 mutations, mutation analysis of this gene is widely available as a diagnostic test. In this study, we assessed the association between genotype and degree of hearing loss in persons with HI and biallelic GJB2 mutations. We performed cross-sectional analyses of GJB2 genotype and audiometric data from 1,531 persons, from 16 different countries, with autosomal recessive, mild-to-profound nonsyndromic HI. The median age of all participants was 8 years; 90% of persons were within the age range of 0-26 years. Of the 83 different mutations identified, 47 were classified as nontruncating, and 36 as truncating. A total of 153 different genotypes were found, of which 56 were homozygous truncating (T/T), 30 were homozygous nontruncating (NT/NT), and 67 were compound heterozygous truncating/nontruncating (T/NT). The degree of HI associated with biallelic truncating mutations was significantly more severe than the HI associated with biallelic nontruncating mutations (P<.0001). The HI of 48 different genotypes was less severe than that of 35delG homozygotes. Several common mutations (M34T, V37I, and L90P) were associated with mild-to-moderate HI (median 25-40 dB). Two genotypes--35delG/R143W (median 105 dB) and 35delG/dela(GJB6-D13S1830) (median 108 dB)--had significantly more-severe HI than that of 35delG homozygotes.     

Digenic inheritance of non-syndromic deafness caused by mutations at the gap junction proteins Cx26 and Cx31

Mutations in the genes coding for connexin 26 (Cx26) and connexin 31 (Cx31) cause non-syndromic deafness. Here, we provide evidence that mutations at these two connexin genes can interact to cause hearing loss in digenic heterozygotes in humans. We have screened 108 GJB2 heterozygous Chinese patients for mutations in GJB3 by sequencing. We have excluded the possibility that mutations in exon 1 of GJB2 and the deletion of GJB6 are the second mutant allele in these Chinese heterozygous probands. Two different GJB3 mutations (N166S and A194T) occurring in compound heterozygosity with the 235delC and 299delAT of GJB2 were identified in three unrelated families (235delC/N166S, 235delC/A194T and 299delAT/A194T). Neither of these mutations in Cx31 was detected in DNA from 200 unrelated Chinese controls. Direct physical interaction of Cx26 with Cx31 is supported by data showing that Cx26 and Cx31 have overlapping expression patterns in the cochlea. In addition, by coimmunoprecipitation of mouse cochlear membrane proteins, we identified the presence of heteromeric Cx26/Cx31 connexons. Furthermore, by cotransfection of mCherry-tagged Cx26 and GFP-tagged Cx31 in human embryonic kidney (HEK)-293 cells, we demonstrated that the two connexins were able to co-assemble in vitro in the same junction plaque. Together, our data indicate that a genetic interaction between these two connexin genes can lead to hearing loss.     

人工耳蜗植入聋儿术前基因检测及家系分析

摘要: 国内外研究表明GJB2、SLC26A4(PDS)和线粒体DNA(Mitochondrial DNA, mtDNA)的病理性突变导致了大部分的遗传性聋。 文章收集了2006年4月~2007年9月接受人工耳蜗(Cochlear implant, CI)植入的14 例患儿及其父母的外周血, 应用基因诊断方法进行 GJB2、SLC26A4(PDS)和mtDNA 1555位点突变检测。结果显示, 35.7%的患儿检测到致病突变, 其中28.6%为GJB2基因突变, 类型均为235delC纯和突变, 其父母为携带GJB2 235delC的杂和子; 7.1%为mtDNA A1555G突变, 其母亲亦携带mtDNA A1555G突变。这表明CI 植入聋儿最常见的基因突变是GJB2 235delC突变, 其次是mtDNA A1555G突变, 通过对耳聋家系常见致病基因的检测和家系分析, 可以对优生优育及减少耳聋发病率提供科学准确的遗传信息。     

GJB2 and mitochondrial A1555G gene mutations in nonsyndromic profound hearing loss and carrier frequencies in healthy individuals

This study aimed to assess mutations in GJB2 gene (connexin 26), as well as A1555G mitochondrial mutation in both the patients with profound genetic nonsyndromic hearing loss and healthy controls. Ninety-five patients with profound hearing loss (>90 dB) and 67 healthy controls were included. All patients had genetic nonsyndromic hearing loss. Molecular analyses were performed for connexin 26 (35delG, M34T, L90P, R184P, delE120, 167delT, 235delC and IVS1+1 A-->G) mutations, and for mitochondrial A1555G mutation. Twenty-two connexin 26 mutations were found in 14.7% of the patients, which were 35delG, R184P, del120E and IVS1+1 A-->G. Mitochondrial A1555G mutation was not encountered. The most common GJB2 gene mutation was 35delG, which was followed by del120E, IVS1+1 A-->G and R184P, and 14.3% of the patients segregated with DFNB1. In consanguineous marriages, the most common mutation was 35delG. The carrier frequency for 35delG mutation was 1.4% in the controls. 35delG and del120E populations, seems the most common connexin 26 mutations that cause genetic nonsyndromic hearing loss in this country. Nonsyndromic hearing loss mostly shows DFNB1 form of segregation.     

Spectrum of the GJB2 mutations in Belarussian patients with hearing loss. Findings of pilot genetic screening of hearing impairment in newborns

A total of 111 unrelated probands and their 8 sibs from Grodno oblast (Belarus) with bilateral isolated sensorineural hearing impairment were studied for the presence of mutations in the connexin 26 (GJB2) gene. Mutations were detected in 51 probands (46% of the sample). A significantly higher frequency of the GJB2 gene mutations was observed in familial cases of the disease with the autosomal recessive mode of inheritance (in 78% of families). Detected characteristics of the GJB2 gene mutation spectrum demonstrated that the using the algorithm, which was designed for Russian patients, is optimal for the molecular study of patients from Belarus. In the sample of patients with hearing loss, the highest (among other similar samples studied in the world) allele frequency of c.313_326del14 mutation (7% of all pathological GJB2 alleles) was registered; Polish origin of this deletion was suggested. It was demonstrated that detection of the GJB2 gene mutation on one patient’s chromosome only is insufficient to confirm a molecular genetic diagnosis of hearing loss of the DFNB1 genetic type (autosomal recessive hearing loss caused by the GJB2 gene mutations). Pilot screening for the GJB2 gene mutations in newborns from Grodno oblast was performed. The material from 235 children was studied during the screening; nine heterozygous carriers of the mutation were found. The c.35delG mutation was detected in a homozygous state in a single newborn (hearing loss of moderate severity was subsequently audiologically confirmed in this child).     

Changes in the connexin 26 gene (<Emphasis Type="Italic">GJB2</Emphasis>) in Russian patients with hearing loss: Results of long-term molecular diagnostics of hereditary nonsyndromic hearing loss

Molecular testing for mutations in the connexin 26 gene (GJB2) is a routine diagnostic analysis for subjects with hereditary hearing loss worldwide. However, till now there is no assessment of the diagnostic significance of this analysis for Russian patients, and there are difficulties in interpretation of the results of DNA diagnostics. In the present study, a sample of 705 patients with nonsyndromic autosomal recessive hearing loss from different regions of Russian Federation was investigated. A portion of DFNB1 hearing loss caused by mutations in the GJB2 gene among the sample was 46%. The frequency of DFNB1 hearing loss was 1:1000, that is, the frequency of isolated autosomal recessive hearing loss 1:500 in the population. It was found that each sixteenth individual in Russia is a heterozygous carrier of the mutation in the GJB2 gene. Totally, 20 pathological GJB2 alleles were detected; among them, a c.35delG mutation with the allelic frequency 81% prevails. Six most frequent mutations (c.35delG, c.313_326del14, c.23+1G>A (IVS1+1G>A), c.235delC, c.167delT, and p.Glu120del), which account for 95% of pathological GJB2 alleles, were detected. Mutations previously not described in the GJB2 gene (c.129delG, p.Gly200Arg, and c[Arg127His, Gly160Ser]) were found. An optimal algorithm of molecular testing of Russian patients which detects up to 100% of mutations in the GJB2 gene was suggested. Data concerning a clinical significance of p.Met34Thr and p.Val37Ile mutations are confirmed in the study. Eight polymorphic substitutions in the GJB2 gene which do not have clinical significance (p.Val27Ile, c.*3C>A, p.Val153Ile, p.Gly160Ser, c.Arg127His, p.Glu114Gly (c.341A>G), c.-45C>A, and p.Ala149Thr) were also detected.     

A Rapid Method for Simultaneous Screening of Multi-Gene Mutations Associated with Hearing Loss in the Korean Population

Hearing loss (HL) is a congenital disease with a high prevalence, and patients with hearing loss need early diagnosis for treatment and prevention. The GJB2, MT-RNR1, and SLC26A4 genes have been reported as common causative genes of hearing loss in the Korean population and some mutations of these genes are the most common mutations associated with hearing loss. Accordingly, we developed a method for the simultaneous detection of seven mutations (c.235delC of GJB2, c.439A>G, c.919-2A>G, c.1149+3A>G, c.1229C>T, c.2168A>G of SLC26A4, and m.1555A>G of the MT-RNR1 gene) using multiplex SNaPshot minisequencing to enable rapid diagnosis of hereditary hearing loss. This method was confirmed in patients with hearing loss and used for genetic diagnosis of controls with normal hearing and neonates. We found that 4.06% of individuals with normal hearing and 4.32% of neonates were heterozygous carriers. In addition, we detected that an individual is heterozygous for two different mutations of GJB2 and SLC26A4 gene, respectively and one normal hearing showing the heteroplasmy of m.1555A>G. These genotypes corresponded to those determined by direct sequencing. Overall, we successfully developed a robust and cost-effective diagnosis method that detects common causative mutations of hearing loss in the Korean population. This method will be possible to detect up to 40% causative mutations associated with prelingual HL in the Korean population and serve as a useful genetic technique for diagnosis of hearing loss for patients, carriers, neonates, and fetuses.     

The prevalence of connexin 26 ( GJB2) mutations in the Chinese population

Mutations in GJB2, encoding gap junction beta 2 protein (connexin 26), are responsible for the commonest form of non-syndromic recessive deafness in many populations. It has been reported recently that the most common 35delG mutation in GJB2 is exceptionally low in Japanese and Korean populations, but another deletion, 235delC, is relatively frequent. Since the Chinese constitute approximately one fifth of the global population, the frequency of GJB2 mutations in the population has important implications for understanding worldwide causes of genetic deafness. To determine whether GJB2 mutations are an important cause of deafness in Chinese, we conducted mutation screening for GJB2 in 118 deaf Chinese probands, including 60 from simplex and 58 from multiplex families with non-syndromic deafness, and 150 normal hearing Chinese controls. Four mutations, including 235delC, 299-300delAT, V37I, and 35delG, were found in the patients. Thirty-nine percent of the probands had a GJB2mutation. Of the 118 probands, 19 carried two definitely pathogenic mutations: three among the 58 multiplex cases (5.2%) and 16 among the 60 simplex cases (26.7%). Twenty-seven probands (22.9%) were found to carry only single GJB2 mutations. None of them had mutations in exon 1 of GJB2 and or the 342-kb deletion of GJB6. The 235delC mutation was the most prevalent mutation (20.3% of alleles), accounting for 81% of the pathologic alleles in multiplex cases and 67% in simplex cases. Analysis of the affected haplotypes in the patients with the homozygous 235delC mutation yielded evidence for a single origin of the mutation. The carrier frequency of the 235delC mutation in control subjects with normal hearing was 1.3%. The 35delG mutation was only noted as a heterozygous change in two simplex cases (1.2% of alleles). These results indicated that mutations in GJB2 are a major cause of inherited and sporadic congenital deafness in the Chinese population. The 235delC mutation, rather than 35delG, is the most common mutation found in the Chinese deaf population. Our data support the view that specific combinations of GJB2 mutation exist in different populations.     

Homozygosity mapping identifies a novel GIPC3 mutation causing congenital nonsyndromic hearing loss in a Saudi family

Hearing loss is one of the most common sensory disorders in humans and has a genetic cause in 50% of the cases. Our recent studies indicate that nonsyndromic hearing loss (NSHL) in the Saudi Arabian population is genetically heterogeneous and is not caused by mutations in GJB2 and GJB6, the most common genes for deafness in various populations worldwide. Identification of the causative gene/mutation in affected families is difficult due to extreme genetic heterogeneity and lack of phenotypic variability. We utilized an SNP array-based whole-genome homozygosity mapping approach in search of the causative gene, for the phenotype in a consanguineous Saudi family, with five affected individuals presenting severe to profound congenital NSHL. A single shared block of homozygosity was identified on chromosome 19p13.3 encompassing GIPC3, a recently identified hearing loss gene. Subsequently, a novel mutation c.122 C>A (p.T41K) in GIPC3 was found. This is the first report of GIPC3 mutation in a Saudi family. The presence of the GIPC3 mutations in only one of 100 Saudi families with congenital NSHL suggests that it appears to be a rare cause of familial or sporadic deafness in this population.     

GJB2 Mutation Spectrum and Genotype-Phenotype Correlation in 1067 Han Chinese Subjects with Non-Syndromic Hearing Loss

Mutations in Gap Junction Beta 2 (GJB2) have been reported to be a major cause of non-syndromic hearing loss in many populations worldwide. The spectrums and frequencies of GJB2 variants vary substantially among different ethnic groups, and the genotypes among these populations remain poorly understood. In the present study, we carried out a systematic and extended mutational screening of GJB2 gene in 1067 Han Chinese subjects with non-syndromic hearing loss, and the resultant GJB2 variants were evaluated by phylogenetic, structural and bioinformatic analysis. A total of 25 (23 known and 2 novel) GJB2 variants were identified, including 6 frameshift mutations, 1 nonsense mutation, 16 missense mutations and 2 silent mutations. In this cohort, c.235delC is the most frequently observed pathogenic mutation. The phylogenetic, structural and bioinformatic analysis showed that 2 novel variants c.127G>T (p.V43L), c.293G>C (p.R98P) and 2 known variants c. 107T>C (p.L36P) and c.187G>T (p.V63L) are localized at highly conserved amino acids. In addition, these 4 mutations are absent in 203 healthy individuals, therefore, they are probably the most likely candidate pathogenic mutations. In addition, 66 (24 novel and 42 known) genotypes were identified, including 6 homozygotes, 20 compound heterozygotes, 18 single heterozygotes, 21 genotypes harboring only polymorphism(s) and the wild type genotype. Among these, 153 (14.34%) subjects were homozygous for pathogenic mutations, 63 (5.91%) were compound heterozygotes, and 157 (14.71%) carried single heterozygous mutation. Furthermore, 65.28% (141/216) of these cases with two pathogenic mutations exhibited profound hearing loss. These data suggested that mutations in GJB2 gene are responsible for approximately 34.96% of non-syndromic hearing loss in Han Chinese population from Zhejiang Province in eastern China. In addition, our results also strongly supported the idea that other factors such as alterations in regulatory regions, additional genes, and environmental factors may contribute to the clinical manifestation of deafness.     

Genetic analysis of TMPRSS3 gene in the Korean population with autosomal recessive nonsyndromic hearing loss

The TMPRSS3 gene (DFNB8/10), which encodes a transmembrane serine protease, is a common hearing loss gene in several populations. Accurate functions of TMPRSS3 in the hearing pathway are still unknown, but TMPRSS3 has been reported to play a crucial role in inner ear development or maintenance. To date, 16 pathogenic mutations have been identified in many countries, but no mutational studies of the TMPRSS3 gene have been conducted in the Korean hearing loss population. In this study, we performed genetic analysis of TMPRSS3 in 40 unrelated Korean patients with autosomal recessive hearing loss to identify the aspect and frequency of TMPRSS3 gene mutations in the Korean population. A total of 22 variations were detected, including a novel variant (p.V291L) and a previously reported pathogenic mutation (p.A306T). The p.A306T mutation which has been detected in only compound heterozygous state in previous studies was identified in homozygous state for the first time in this study. Moreover, the clinical evaluation identified bilateral dilated vestibules in the patient with p.A306T mutation, and it suggested that p.A306T mutation of the TMPRSS3 gene might be associated with vestibular anomalies. In conclusion, this study investigated that only 2.5% of patients with autosomal recessive hearing loss were related to TMPRSS3 mutations suggesting low prevalence of TMPRSS3 gene in Korean hearing loss population. Also, it will provide the information of genotype–phenotype correlation to understand definite role of TMPRSS3 in the auditory system.     

Genotyping with a 198 Mutation Arrayed Primer Extension Array for Hereditary Hearing Loss: Assessment of Its Diagnostic Value for Medical Practice

Molecular diagnostic testing of individuals with congenital sensorineural hearing loss typically begins with DNA sequencing of the GJB2 gene. If the cause of the hearing loss is not identified in GJB2, additional testing can be ordered. However, the step-wise analysis of several genes often results in a protracted diagnostic process. The more comprehensive Hereditary Hearing Loss Arrayed Primer Extension microarray enables analysis of 198 mutations across eight genes (GJB2, GJB6, GJB3, GJA1, SLC26A4, SLC26A5, MTRNR1 and MTTS1) in a single test. To evaluate the added diagnostic value of this microarray for our ethnically diverse patient population, we tested 144 individuals with congenital sensorineural hearing loss who were negative for biallelic GJB2 or GJB6 mutations. The array successfully detected all GJB2 changes previously identified in the study group, confirming excellent assay performance. Additional mutations were identified in the SLC26A4, SLC26A5 and MTRNR1 genes of 12/144 individuals (8.3%), four of whom (2.8%) had genotypes consistent with pathogenicity. These results suggest that the current format of this microarray falls short of adding diagnostic value beyond the customary testing of GJB2, perhaps reflecting the array''s limitations on the number of mutations included for each gene, but more likely resulting from unknown genetic contributors to this phenotype. We conclude that mutations in other hearing loss associated genes should be incorporated in the array as knowledge of the etiology of hearing loss evolves. Such future modification of the flexible configuration of the Hereditary Hearing Loss Arrayed Primer Extension microarray would improve its impact as a diagnostic tool.     

Unexpected heterogeneity due to recessive and de novo dominant mutations of GJB2 in an Iranian family with nonsyndromic hearing loss: implication for genetic counseling

Mutations in the GJB2 gene are the most common cause of nonsyndromic autosomal recessive sensorineural hearing loss (HL). A few mutations in GJB2 have also been reported to cause dominant nonsyndromic HL. Here we report a large inbred family including two individuals with nonsyndromic sensorineural hearing loss. A dominant GJB2 mutation, c.551G>A (p.R184Q), was detected in the proband, yet his parents were negative for the mutation. The second affected person had heterozygous c.35delG mutation, which was inherited from his father. Large deletions of the GJB6 gene were not detected in this family. This study highlights the importance of mutation analysis in all affected cases within a pedigree.     

黑龙江省部分地区非综合性耳聋的分子病因学调查

目的:采用基因诊断的方法调查和分析黑龙江省部分地区非综合性耳聋(NSHL)的分子病因学。方法:调查对象为哈尔滨医科大学附属第四医院耳鼻咽喉科门诊收治的116例来自黑龙江省部分地区的散发非综合征型耳聋患者和29例听力正常样本,均经过纯音听阈、声导抗、耳声发射、听性脑干诱发电位等检查,其中51例属于重度或极重度感音神经性耳聋,采集其外周血并提取DNA行GJB2、Slc26A4、GJB3、SrRNA1555基因编码区测序。结果:与耳聋相关的基因突变位点主要为GJB2-235、Slc26A4-IVS7-2和GJB2-299,其中GJB2-235基因变异为最主要方式,约占总检出耳聋患者的45.2%,其次为该基因的299位点,突变比率为16.1%。另一个主要突变基因是Slc26A4,主要在IVS7-2位点发生突变,约占Slc26A4基因位点突变的84.6%,在整个耳聋基因突变群体中约占17.7%。但上述基因突变位点在29例听力正常样本中无发生。结论:黑龙江省部分地区NSHL患者存在GJB2-235、Slc26A4-IVS7-2和GJB2-299位点突变。     

Mutation Spectrum of Common Deafness-Causing Genes in Patients with Non-Syndromic Deafness in the Xiamen Area,China

In China, approximately 30,000 babies are born with hearing impairment each year. However, the molecular factors causing congenital hearing impairment in the Xiamen area of Fujian province have not been evaluated. To provide accurate genetic testing and counseling in the Xiamen area, we investigated the molecular etiology of non-syndromic deafness in a deaf population from Xiamen. Unrelated students with hearing impairment (n = 155) who attended Xiamen Special Education School in Fujian Province were recruited for this study. Three common deafness-related genes, GJB2, SLC26A4, and mtDNA12SrRNA, were analyzed using all-exon sequencing. GJB2 mutations were detected in 27.1% (42/155) of the entire cohort. The non-syndromic hearing loss (NSHL) hotspot mutations c.109G>A (p.V37I) and c.235delC were found in this population, whereas the Caucasian hotspot mutation c.35delG was not. The allelic frequency of the c.109G>A mutation was 9.03% (28/310), slightly higher than that of c.235delC (8.39%, 26/310), which is the most common GJB2 mutation in most areas of China. The allelic frequency of the c.109G>A mutation was significantly higher in this Xiamen’s deaf population than that in previously reported cohorts (P = 0.00). The SLC26A4 mutations were found in 16.77% (26/155) of this cohort. The most common pathogenic allele was c.IVS7-2A>G (6.13%, 19/310), and the second most common was the c.1079C>T (p.A360V) mutation (1.94%, 6/310) which has rarely been reported as a hotspot mutation in other studies. The mutation rate of mtDNA12SrRNA in this group was 3.87% (6/155), all being the m.A1555G mutation. These findings show the specificity of the common deaf gene-mutation spectrum in this area. According to this study, there were specific hotspot mutations in Xiamen deaf patients. Comprehensive sequencing analysis of the three common deaf genes can help portray the mutation spectrum and develop optimal testing strategies for deaf patients in this area.     

<Emphasis Type="Italic">GJB2</Emphasis> and <Emphasis Type="Italic">GJB6</Emphasis> gene mutations found in Indian probands with congenital hearing impairment

Genetically caused deafness is a common trait affecting one in 1000 children and is predominantly inherited in an autosomal-recessive fashion. Several mutations in the GJB2 gene and a deletion of 342 kb in GJB6 gene (delGJB6-D13S1830) have been identified worldwide in patients with hearing impairment. In the present study, 303 nonsyndromic hearing-impaired patients (140 familial; 163 sporadic) were examined clinically and screened for mutations in GJB2 and GJB6 genes. Mutations in GJB2 gene were found in 33 (10.9%) patients of whom six (18.2%) were carriers for the mutant allele. The most frequent mutation was p.W24X accounting for 87% of the mutant alleles. In addition, six other sequence variations were identified in the GJB2 gene viz., c.IVS1+1G>A, c.167delT, c.235delC, p.W77X, p.R127H (polymorphism), p.M163V. None of the samples showed del(GJB6-D13S1830) or any point mutations in GJB6 gene.     

Differential rates of frameshift alterations in four repeat sequences of hereditary nonpolyposis colorectal cancer tumors

In some Palestinian communities, the prevalence of inherited prelingual deafness is among the highest in the world. As an initial step towards understanding the genetic causes of hearing loss in the Palestinian population, 48 independently ascertained probands with non-syndromic hearing loss were evaluated for mutations in the connexin 26 gene. Of the 48 deaf probands, 11 (23%) were homozygous or compound heterozygous for mutations in GJB2. Five different mutations were identified: ivs1(+1) G-->A, 35delG, 167delT, T229C, 235delC. Nine deaf probands were homozygous and only two compound heterozygous. Among 400 hearing Palestinian controls, one carrier was observed (for 167delT). We show that GJB2 ivs1(+1) G-->A disrupts splicing, yielding no detectable message. Linkage disequilibrium analysis suggests, in the Palestinian and Israeli populations, a common origin of the 35delG mutation, which is worldwide, and of 167delT, which appears specific to Israeli Ashkenazi and Palestinian populations. A high prevalence of deafness, high frequency of homozygosity rather than compound heterozygosity among deaf, and low mutation carrier frequency together reflect the high levels of consanguinity of many extended Palestinian families. Some of the 25 families with multiple cases of inherited prelingual deafness and wildtype GJB2 sequences may represent as-yet-unknown genes for inherited hearing loss.