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.     

The Relationship between the p.V37I Mutation in GJB2 and Hearing Phenotypes in Chinese Individuals

The most common cause of nonsyndromic autosomal recessive hearing loss is mutations in GJB2. The mutation spectrum and prevalence of mutations vary significantly among ethnic groups, and the relationship between p.V37I mutation in GJB2 and the hearing phenotype is controversial. Among the 3,864 patients in this study, 106 (2.74%) had a homozygous p.V37I variation or a compound p.V37I plus other GJB2 pathogenic mutation, a frequency that was significantly higher than that in the control group (600 individuals, 0%). The hearing loss phenotype ranged from mild to profound in all patients with the homozygous p.V37I variation or compound p.V37I plus other GJB2 pathogenic mutation. There was no difference in the distribution of the hearing level in the group with the homozygous p.V37I variation and the group with the compound p.V37I variation plus pathogenic mutation. Most patients (66.04%) with the V37I-homozygous variation or p.V37I plus other pathogenic mutation had a mild or moderate hearing level. This study found a definite relationship between p.V37I and deafness, and most patients who carried the pathogenic combination with p.V37I mutation had mild or moderate hearing loss. Therefore, otolaryngologists should consider that the milder phenotype might be caused by the GJB2 p.V37I mutation.     

GJB2-associated hearing loss undetected by hearing screening of newborns

The hearing loss caused by GJB2 mutations is usually congenital in onset, moderate to profound in degree, and non-progressive. The objective of this study was to study genotype/phenotype correlations and to document 14 children with biallelic GJB2 mutations who passed newborn hearing screening (NHS). Genetic testing for GJB2 mutations by direct sequencing was performed on 924 individuals (810 families) with hearing loss, and 204 patients (175 families) were found to carry biallelic GJB2 mutations. NHS results were obtained through medical records. A total of 18 pathological mutations were identified, which were subclassified as eight inactivating and 10 non-inactivating mutations. p.I128M and p.H73Y were identified as novel missense GJB2 mutations. Of the 14 children with biallelic GJB2 mutations who passed NHS, eight were compound heterozygotes and 3 were homozygous for the c.235delC mutation in GJB2, and the other three combinations of non-c.235delC mutations identified were p.Y136X-p.G45E/p.V37I heterozygous, c.512ins4/p.R143W heterozygous, and p.V37I/p.R143W heterozygous. These 14 cases demonstrate that the current NHS does not identify all infants with biallelic GJB2 mutations. They suggest that the frequency of non-penetrance at birth is approximately 6.9% or higher in DFNB1 patients and provide further evidence that GJB2 hearing loss may not always be congenital in onset.     

Prevalence of p.V37I Variant of GJB2 in Mild or Moderate Hearing Loss in a Pediatric Population and the Interpretation of Its Pathogenicity

A p.V37I variant of GJB2 has been reported from subjects with moderate or slight hearing loss especially in East Asian populations. This study aimed to estimate the prevalence of the p.V37I variant among such subjects and prove, epidemiologically, its pathogenic potential to cause mild hearing loss. A total of 380 subjects from 201 families with hearing loss were enrolled. From them, 103 families were selected who had autosomal recessive inheritance or sporadic occurrence of hearing loss and who were younger than 15 years old. GJB2 sequencing was carried out for the probands of all 103 families. The prevalence of the p.V37I variant was compared between the subtle, mild or moderate hearing loss (group I) and the severe or profound hearing loss (group II) groups. Where possible, a targeted next generation sequencing of 82 deafness genes was performed from the p.V37I carrier to exclude the existence of other pathogenic genes. Five (4.8%) of 103 probands were found to carry p.V37I. The carrier frequency of p.V37I among group I (18.2%) was significantly higher than that of group II (1.2%) or the reported Korean normal hearing control group (1.0%). Detection of the p.V37I variant of GJB2 in 18.2% of Koreans with mild hearing loss strongly suggests its contribution to the pathogenesis of milder hearing loss, which might justify sequencing of GJB2 from these subjects in the Korean population.     

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.     

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.     

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.     

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.     

High frequency of GJB2 mutation W24X among Slovak Romany (Gypsy) patients with non-syndromic hearing loss (NSHL)

Mutations in the GJB2 gene (connexin 26) represent a major cause of autosomal recessive non-syndromic hearing loss (NSHL) worldwide. In most Caucasian populations, the 35delG mutation in this gene was found to account for up to 50% of cases of the genetic non-syndromic childhood deafness. In populations of non-European ethnic background, other GJB2 gene mutations are occasionally common, e.g. 167delT in Ashkenazi Jews, R143W in Africaans and 235delC in Koreans. In this work, DNA samples from 54 unrelated NSHL patients from endogamous and inbred population of Slovak Roms (Gypsies) from Eastern Slovakia were screened for GJB2 mutations. The coding region of the GJB2 gene of patients was sequenced and mutations W24X, R127H, V153I, L90P and V37I were found. In Slovak Romany population, mutation W24X accounts for 23.2%, R127H for 19.4%, 35delG for 8.3%, V153I for 3.7%, L90P for 3.7% and V37I for 0.9% of screened chromosomes. As the W24X mutation was previously found in India and Pakistan, were from the European Romanies originate, it was brought by the European Romnanies from their Indian homeland. The carrier frequency of 35delG was estimated for Slovak non-Romany population to be 3.3%, and for Slovak Romany population to 0.88%. The carrier frequency of W24X varied in different Slovak Romany subpopulations from 0.0% up to 26.1%.     

Comorbidity of GJB2 and WFS1 mutations in one family

It is rarely reported that two distinct genetic mutations affecting hearing have been found in one family. We report on a family exhibiting comorbid mutation of GJB2 and WFS1. A four-generation Japanese family with autosomal dominant sensorineural hearing loss was studied. In 7 of the 24 family members, audiometric evaluations and genetic analysis were performed. We detected A-to-C nucleotide transversion (c.2576G>C) in exon 8 of WFS1 that was predicted to result in an arginine-to-proline substitution at codon 859 (R859P), G-to-A transition (c.109G>A) in exon 2 of GJB2 that was predicted to result in a valine-to-isoleucine substitution at codon 37 (V37I), and C-to-T transition (c.427C>T) in exon 2 of GJB2 that was predicted to result in an arginine-to-tryptophan substitution at codon 143 (R143W). Two individuals who had heterozygosity of GJB2 mutations and heterozygosity of WFS1 mutations showed low-frequency hearing loss. One individual who had homozygosity of GJB2 mutation without WFS1 mutation had moderate, gradual high tone hearing loss. On the other hand, a moderate flat loss configuration was seen in one individual who had compound heterozygosity of GJB2 and heterozygosity of WFS1 mutations. Our results indicate that the individual who has both GJB2 and WFS1 mutations can show GJB2 phenotype.     

High frequency hearing loss correlated with mutations in the GJB2 gene

Genetic hearing impairment affects approximately 1/2000 live births. Mutations in one gene, GJB2, coding for connexin 26 cause 10%-20% of all genetic sensorineural hearing loss. Mutation analysis in the GJB2 gene and audiology were performed on 106 families presenting with at least one child with congenital hearing loss. The families were recruited from a hospital-based multidisciplinary clinic, which functions to investigate the aetiology of sensorineural hearing loss in children and which serves an ethnically diverse population. In 74 families (80 children), the aetiology was consistent with non-syndromic recessive hearing loss. Six different connexin 26 mutations, including one novel mutation, were identified. We show that GJB2 mutations cause a range of phenotypes from mild to profound hearing impairment and that loss of hearing in the high frequency range (4000-8000 Hz) is a characteristic feature in children with molecularly diagnosed connexin 26 hearing impairment. We also demonstrate that this type of audiology and high frequency hearing loss is found in a similar-sized group of deaf children in whom a mutation could only be found in one of the connexin 26 alleles, suggesting connexin 26 involvement in the aetiology of hearing loss in these cases. In our study of the M34T mutation, only compound heterozygotes exhibited hearing loss, suggesting autosomal recessive inheritance.     

Phenotype and genotype of deaf patients with combined genomic and mitochondrial inheritance models

In most studies, sensorineural hearing loss is reported as a single-gene disease with autosomal dominant or autosomal recessive or with X-linked or maternal inheritance. It is uncommon that the hearing impairment is caused by a combined inheritance model including genomic and mitochondrial models. Here, we report six patients with sensorineural hearing loss caused by co-existing mutations in GJB2 or SLC26A4 and the mitochondrial gene. And there was no significant difference in hearing phenotypes between the six patients and the controls. The results indicate the complicated genetic etiology of, and may impact the diagnostic strategy for, hereditary hearing impairment. All patient siblings will carry mitochondrial DNA A1555G or C1494T mutations, and 25% of siblings may carry the same homozygous or compound heterozygote mutations in GJB2 or SLC26A4. Although this combined inheritance is not common in the Chinese deaf population (0.10%), our findings will have great impact in genetic counseling and risk prediction for deafness.     

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.     

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.     

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。     

<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.     

Contribution of GJB2 Mutations to Hearing Loss in the Hazara Division of Pakistan

Mutations of GJB2, which encodes connexin 26, are the most common cause of hereditary hearing loss in many human populations. This study was initiated to determine the prevalence of GJB2 mutations in individuals with hearing loss from the Hazara Division in Pakistan. We recruited 70 participants with nonsyndromic deafness segregating as an apparently recessive trait and directly sequenced the GJB2 coding region from their DNA. The homozygous mutations c.71 G→A (p.W24X), c.104 T→G (p.I35S), and c.35delG (p.G12VfsX1) were identified as the cause of hearing loss in three participants (4.28%); in populations from other areas of Pakistan, frequencies of 6–7% have been observed. The mutations c.104 T→G and c.35delG were identified in Pakistan for the first time. These results confirm the low prevalence of GJB2 mutations in Hazara and suggest that mutations in other genes may play a significant role in the etiology of deafness in this population.     

Functional evaluation of GJB2 variants in nonsyndromic hearing loss

Mutations in the gap junction β2 (GJB2) gene, encoding the connexin26 (CX26) protein, are the most common cause of non-syndromic hearing loss (HL) in many populations. In the East Asian population, two variants, p.V27I (c.79G>A) and p.E114G (c.341G>A), are considered benign polymorphisms since these variants have been identified in both HL patients and normal hearing controls. However, some studies have postulated that homozygotes carrying both p.V27I and p.E114G variants could cause HL. To elucidate possible roles of these variants, we used in vitro approaches to directly assess the pathogenicity of four haplotypes generated by the two polymorphisms: VE (wild type), I*E (p.V27I variant only), VG* (p.E114G variant only), I*G* (both variants). In biochemical coupling assays, the gap junctions (GJs) composed of VG* and I*G* types displayed defective channel activities compared with those of VE wild types or I*E types, which showed normal channel activities. Interestingly, the defect in hemichannel activity was a bit less severe in I*G* type than VG* type, suggesting that I* variant (p.V27I) may compensate for the deleterious effect of G* variant (p.E114G) in hemichannel activities. Our population studies using 412 Korean individuals showed that I*G* type was detected at around 20% in both HL patients and normal controls, suggesting that I*G* type may not be a pathogenic polymorphism. In contrast, VG* type was very rare (3/824) and detected only in HL patients, suggesting that VG* homozygotes (VG*/VG*) or compound heterozygotes carrying VG* type with other mutations may cause HL.     

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.     

Detection of the 35delG/GJB2 and del(GJB6-D13S1830) mutations in Venezuelan patients with autosomal recessive nonsyndromic hearing loss

Severe to profound hearing impairment affects 1 of every 1000 newborn children each year. Inheritance accounts for 60% of these cases, of which 70% are nonsyndromic. The most common cause of autosomal recessive nonsyndromic hearing loss (ARNSHL) is mutation in GJB2, a gene on chromosome 13, which encodes a gap junction protein named Connexin 26. Mutations in GJB2 are responsible for 40% of genetic childhood deafness. The most common mutation, 35delG, predominates in many ethnic groups. Some families with linkage to the DFNB1 locus have none or only one mutated allele in GJB2, however, some subjects can exhibit a large deletion in another connexin gene, GJB6, resulting in a monogenic or digenic pattern of inheritance in this complex DFNB1 locus that contains both genes (GJB2 and GJB6). The aim of the study was to determine (1) the frequency for the 35delG (27.5%), del(GJB6-D13S1830) (2.5%) and del(GJB6-D13S1854) (0.0%) mutations in a cohort of 40 Venezuelan patients with ARNSHL and (2) the carrier frequency 35delG (4%), del(GJB6-D13S1830) (0%) and del(GJB6-D13S1854) (0%) in the Venezuelan population with no familial history of hearing impairment. One patient (2.5%) was detected as double heterozygote for the deletion del(GJB6-D13S1830) and 35delG mutation. This result has direct clinical implications because we include the molecular detection of the deletion del(GJB6-D13S1830) during the evaluation of the diagnosis of deafness in the Venezuelan population.