Nonsyndromic Sensorineural Hearing Loss Research Articles

Correlation analysis of phenotype and genotype of GJB2 in patients with non-syndromic hearing loss in China

BackgroundDisease-associated mutations in GJB2 gene are one of the major reasons that can cause non-syndromic sensorineural hearing loss (NSHL). GJB2 gene deafness has various clinical phenotypes. This study aims to analyze characteristics and relationships of clinical phenotypes through analyzing 1481 NSHL cases and 190 GJB2 deafness patients (with dual gene mutations). Patients and methodsAll the patients diagnosed as deaf disease molecular diagnostics were obtained from the people's liberation army general hospital from March 2007 to March 2011. The accession number of GJB2 was NM_004004 in GenBank, and sequence alignment and annotation were performed using GeneTool software. ResultsIn NSHL patients, mutated allele frequency in GJB2 was 20.57%, and the preponderant type was c.235delC (11.84%) followed by c.109G>A (3.75%). Mutation rate of double allelic gene was 16.18%, including 8.43% of homozygous mutation rate and 7.75% of recombination heterozygosis mutation. Moreover, auditory threshold of GJB2 biallelic marker was associated with ages of onset, while no significant correlation was detected with disease time and whether the inner ear malformation. Similar clinical phenotype could be detected between patients with c.109G>A dual gene mutation and dual gene mutation. However, in the aspect of hearing impairment, the phenomenon of pathopoiesia caused by mutation of c.109G>A was poorer than the other mutations, and even near those patients without pathogenic mutations. ConclusionOur study further shows the definite relationship of clinical phenotype and genotype in GJB2 gene correlated deafness, and these results can provide basis for revealing pathogenesis, gene diagnosis and consult of deafness.The level of evidence in the study is level 4 (case series).

Targeted next-generation sequencing in Uyghur families with non-syndromic sensorineural hearing loss.

The mutation spectrum of deafness genes may vary in different ethnical groups. In this study, we investigated the genetic etiology of nonsyndromic deafness in four consanguineous and two multiplex Uyghur families in which mutations in common deafness genes GJB2, SLC26A4 and MT-RNR1 were excluded. Targeted next-generation sequencing of 97 deafness genes was performed in the probands of each family. Novel pathogenic mutations were identified in four probands including the p.L416R/p.A438T compound heterozygous mutations in TMC1, the homozygous p.V1880E mutation in MYO7A, c.1238delT frameshifting deletion in PCDH15 and c.9690+1G>A splice site mutation in MYO15A. Co-segregation of the mutations and the deafness were confirmed within each family by Sanger sequencing. No pathogenic mutations were identified in one multiplex family and one consanguineous family. Our study provided a useful piece of information for the genetic etiology of deafness in Uyghurs.

Novel biallelic OTOGL mutations in a Chinese family with moderate non-syndromic sensorineural hearing loss

ObjectiveAutosomal recessive non-syndromic hearing loss (DFNB) is a genetically heterogeneous disorder. So far, 55 pathogenic genes have been identified. In this study, we aim to characterize the clinical feature and the genetic cause of a Chinese DFNB family. MethodsWhole exome sequencing was performed on the proband. Co-segregation between the hearing loss phenotype and the potential causative mutations was verified in all family members by Sanger sequencing. ResultsAudiologic profiles of the affected family members revealed a moderate hearing loss mainly affecting higher frequencies. Novel biallelic OTOGL mutations, c.6467C>A (p.Ser2156*) and c.6474dupA (p.Ser2159Metfs*2), were identified in this family segregating with the childhood onset DFNB. Both mutations were predicted to cause either nonsense mediated mRNA decay or premature terminations of protein synthesis. ConclusionsWe identified novel biallelic OTOGL mutations in a Chinese DFNB family. To the best of our knowledge, this is the first report of OTOGL mutations causing hearing loss in the East Asian population. Our finding enriched the mutation spectrum of OTOGL associated hearing loss.

Downsloping high-frequency hearing loss due to inner ear tricellular tight junction disruption by a novel ILDR1 mutation in the Ig-like domain.

The immunoglobulin (Ig)-like domain containing receptor 1 (ILDR1) gene encodes angulin-2/ILDR1, a recently discovered tight junction protein, which forms tricellular tight junction (tTJ) structures with tricellulin and lipolysis-stimulated lipoprotein receptor (LSR) at tricellular contacts (TCs) in the inner ear. Previously reported recessive mutations within ILDR1 have been shown to cause severe to profound nonsyndromic sensorineural hearing loss (SNHL), DFNB42. Whole-exome sequencing of a Korean multiplex family segregating partial deafness identified a novel homozygous ILDR1 variant (p.P69H) within the Ig-like domain. To address the pathogenicity of p.P69H, the angulin-2/ILDR1 p.P69H variant protein, along with the previously reported pathogenic ILDR1 mutations, was expressed in angulin-1/LSR knockdown epithelial cells. Interestingly, partial mislocalization of the p.P69H variant protein and tricellulin at TCs was observed, in contrast to a severe mislocalization and complete failure of tricellulin recruitment of the other reported ILDR1 mutations. Additionally, three-dimensional protein modeling revealed that angulin-2/ILDR1 contributed to tTJ by forming a homo-trimer structure through its Ig-like domain, and the p.P69H variant was predicted to disturb homo-trimer formation. In this study, we propose a possible role of angulin-2/ILDR1 in tTJ formation in the inner ear and a wider audiologic phenotypic spectrum of DFNB42 caused by mutations within ILDR1.

Identification of a novel mutation of PJVK in the Chinese non-syndromic hearing loss population with low prevalence of the PJVK mutations

Conclusion: To our knowledge, this is the first report of PJVK gene mutation in a Chinese non-syndromic sensorineural hearing loss (NSHL) family. Our data indicate that the PJVK gene contributes to hearing impairment in the Chinese population, but it is not a major cause. Objective: To investigate the contribution of PJVK mutations to NSHL in the Chinese population. Methods: We screened for the PJVK gene in a sample of 65 autosomal recessive NSHL families without GJB2, SLC26A4, or mitochondrial 12S rRNA gene mutations. Seven pairs of PCR primers were designed to amplify all of the exons and their flanking regions of the PJVK gene. The PCR products were sequenced and analyzed for identification of mutations. Results: In all, we identified one novel frameshift mutation, c.930_931del AC (p.C312W fsX19), co-segregating with the phenotype in one consanguineous family with a prevalence of 1.5% (1/65). The p.C312W fsX19 mutation was just positioned in the zinc-fingers domain, which was important to the function of pejvakin, and resulted in a stop codon after 19 additional amino acids. It was not identified in the controls and was considered as the causative mutation of family 804566 with autosomal recessive, non-syndromic, prelingual sensorineural hearing impairment.

Detection of 35delG, 167delT mutations in the connexin 26 gene among Egyptian patients with nonsyndromic sensorineural hearing loss

Abstract The aim of this study was to detect 35delG and 167delT mutations in the connexin 26 gene among Egyptian patients with nonsyndromic sensorineural hearing loss, allowing accurate diagnosis, proper genetic counseling, and carrier detection. Fifty-one patients were subjected to 35delG and 167delT mutations detection using PCR-based techniques. Seven patients had the 35delG mutation. Four patients were homozygous and four patients were heterozygous for this deletion. Two homozygotes were sibs and two heterozygotes were sibs as well. The allelic frequency for 35delG was 10.8%. The 167delT was not detected in any of the patients studied. The 35delG is a common pathogenic mutation and an important contributor toward autosomal recessive nonsyndromic hearing loss in the Egyptian population.

Exome sequencing and genome-wide copy number variant mapping reveal novel associations with sensorineural hereditary hearing loss.

BackgroundThe genetic diversity of loci and mutations underlying hereditary hearing loss is an active area of investigation. To identify loci associated with predominantly non-syndromic sensorineural hearing loss, we performed exome sequencing of families and of single probands, as well as copy number variation (CNV) mapping in a case–control cohort.ResultsAnalysis of three distinct families revealed several candidate loci in two families and a single strong candidate gene, MYH7B, for hearing loss in one family. MYH7B encodes a Type II myosin, consistent with a role for cytoskeletal proteins in hearing. High-resolution genome-wide CNV analysis of 150 cases and 157 controls revealed deletions in genes known to be involved in hearing (e.g. GJB6, OTOA, and STRC, encoding connexin 30, otoancorin, and stereocilin, respectively), supporting CNV contributions to hearing loss phenotypes. Additionally, a novel region on chromosome 16 containing part of the PDXDC1 gene was found to be frequently deleted in hearing loss patients (OR = 3.91, 95% CI: 1.62-9.40, p = 1.45 × 10-7).ConclusionsWe conclude that many known as well as novel loci and distinct types of mutations not typically tested in clinical settings can contribute to the etiology of hearing loss. Our study also demonstrates the challenges of exome sequencing and genome-wide CNV mapping for direct clinical application, and illustrates the need for functional and clinical follow-up as well as curated open-access databases.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-15-1155) contains supplementary material, which is available to authorized users.

Novel TECTA Mutations Identified in Stable Sensorineural Hearing Loss and Their Clinical Implications

TECTA is a causative gene of autosomal dominant (DFNA8/A12) and autosomal recessive (DFNB 21) nonsyndromic sensorineural hearing loss (NSHL). Mutations in TECTA account for 4% of all autosomal dominant NSHL cases in some populations and are thus thought to be one of the major causes of autosomal dominant NSHL. A genotype-phenotype correlation for autosomal dominant mutations in the TECTA gene has been proposed. Two families (SB146 and SB149), which segregated moderate NSHL in an autosomal dominant fashion, were included in this study. We performed targeted resequencing of 134 known deafness genes (TRS-134) and bioinformatics analyses to find causative mutations for NSHL in these 2 families. Through TRS-134, we detected 2 novel mutations, i.e. c.3995G>T (p.C1332F) and c.5618C>T (p.T1873I), in the TECTA gene. These mutations cosegregated with NSHL in the studied families and were not detected in normal controls. The mutations c.3995G>T and c.5618C>T reside in the von Willebrand factor type D3-D4 (vWFD3-D4) interdomain of the zonadhesin (ZA) domain and the zona pellucida (ZP) domain, respectively. p.C1332F is the first mutation detected in the vWFD3-D4 interdomain of the ZA domain. The mutations p.C1332F and p.T1873I were associated with stable high-frequency and mid-frequency hearing loss, respectively. Notably, the cysteine residue mutated to phenylalanine in SB146 was not related to progression of sensorineural hearing loss, which argues against the previous hypothesis. Here we confirm a known genotype-phenotype correlation for the ZP domain and propose a hypothetical genotype-phenotype correlation which relates mutations in vWFD3-D4 to stable high-frequency NSHL in Koreans. This clinical feature makes subjects with the missense mutation in the vWFD3-D4 interdomain of TECTA potentially good candidates for middle ear implantation. i 2014 S. Karger AG, Basel

Identification of a novel missense mutation in the WFS1 gene as a cause of autosomal dominant nonsyndromic sensorineural hearing loss in all‐frequencies

Hearing loss is the most common sensory disorder affecting 278 million people in the world, and more than 60% of hearing loss patients can be attributed to genetic causes. Although many loci have been linked to hereditary hearing impairment, most of the causative genes have not been identified as yet. The goal of this study was to investigate the cause of dominantly inherited sensorineural all-frequency hearing loss in a six-generation Chinese family. We performed exome sequencing to screen responsible candidate genes in three family members with all-frequency hearing loss and one member with normal hearing. Sanger sequencing was employed to examine the variant mutations in the members of this family and 200 healthy persons. PCR-RFLP was performed to further confirm the nucleotide mutation. A novel missense mutation c.2389G > A (GAC → AAC) in WFS1 gene was identified, which was co-segregated with the hearing loss phenotype. No mutation was found in 200 controls and the family members with normal hearing in this site. The present study identifies, for the first time, a novel mutation in WFS1 gene that causes non-syndromic hearing loss in all, rather than in low or high, frequencies.

Comparative study of mutation spectrums of MT-RNR1 m.1555A>G, GJB2, and SLC26A4 between familial and sporadic patients with nonsyndromic sensorineural hearing loss in Chinese Han

The mutation frequencies of three common deafness genes (MT-RNR1 m.1555A>G, GJB2, and SLC26A4) among patients with nonsyndromic sensorineural hearing loss (NSHL) were different in previous studies. Inconsistent selection criteria for recruiting patients could have led to differences in estimating the frequencies of genetic mutations thus resulting in different mutation frequencies among these studies. The aim of this study was to reveal the differences in the mutation spectrums of the three common genes between familial and sporadic Chinese Han patients. Totally, 301 familial probands and 703 sporadic patients with NSHL were enrolled in this study. Three genes, MT-RNR1 m.1555A>G, GJB2, and SLC26A4, were screened for mutation in our study cohort. A χ(2) test was performed to compare the mutation frequencies between the two groups. The study showed that the disease-causing mutation frequencies of MT-RNR1 m.1555A>G, GJB2, and SLC26A4 were 12.29%, 14.62%, and 18.27% in familial probands and 3.56%, 18.63%, and 18.92% in sporadic patients, respectively. The mutation frequency of MT-RNR1 m.1555A>G in familial probands was significantly higher than in sporadic patients (χ(2) test, P = 0.000), while there were no significant differences in the mutation frequencies of GJB2 and SLC26A4 between the familial and sporadic groups (χ(2) test, P > 0.05). It is necessary to reveal the differences in gene mutation frequencies between patients of different sources or characteristics by comparative studies in order to avoid selection bias. The mutations of GJB2, SLC26A4, and MT-RNR1 m.1555A>G are the most important etiological factors in Chinese Han patients, among which SLC26A4 might be the most frequent.

OtoSeq Next‐Generation DNA Sequencing in the Evaluation of Congenital Sensorineural Hearing Loss

Objectives: Congenital sensorineural hearing loss (SNHL) is relatively common, occurring in 2 to 4 per 1000 infants, with genetic etiologies accounting for nearly 67% of cases. The clinical presentation of patients with syndromic and nonsyndromic SNHL is often indistinguishable. Establishing specific genetic causes is imperative for clinical management and genetic counseling. Recent advances in next-generation sequencing have allowed for facilitated multi-gene testing in genetically heterogeneous conditions such as SNHL. The present study evaluates the clinical utility of one such assay, OtoSeq, in genotyping pediatric patients with SNHL. Methods: Demographic, audiometric, imaging, and genetic data were retrospectively collected from 70 patients with prelingual hearing loss who underwent clinical genetic testing of 23 well-studied SNHL genes via OtoSeq, our next generation sequencing platform. The frequencies of pathogenic and likely pathogenic mutations were calculated and audiogram data were reviewed. Results: Of 70 patients studied, 15 patients (21%) were found to have an identifiable genetic etiology for their hearing loss, and 8 patients were found to have a previously undiagnosed genetic syndrome. Seven patients were diagnosed with nonsyndromic hearing loss. A total of 27 patients with mutations had adequate audiogram data available, of which 16 had mild to moderate hearing loss (59.3%) and 11 had severe to profound hearing loss (40.7%). Several unique combinations of deafness causing mutations in different genes were identified, including CDH23 and MYO7A, both Usher pathway of genes. Conclusions: This study demonstrates that OtoSeq is a valuable tool for determining genetic causes of SNHL in pediatric patients, which has direct implications for their clinical management.

Investigation of clinical features and detection of 79 known deafness genes in a large Chinese family with dominant non-syndromic hearing loss

To investigate the clinical and genetic characteristics of a large family with late-onset, progressive autosomal dominant non-syndromic hearing loss. Collections of detail history hereditary features, physical and audiological examination were performed. After mutation screening of GJB2, SLC26A4, MTRNR1 (12SrRNA) genes by Sanger sequencing, the proband was investigated by targeted next-generation sequencing of 79 deafness genes. This family included seven generations and 73 members. Eleven persons with hearing loss and 11 normal-hearing persons participated in this study. All affected members but one exhibited late-onset, progressive non-syndromic sensorineural hearing loss; the ages of onset were between 9 and 30 years. Mutation screening by sanger-sequencing and targeted next-generation sequencing excluded the possibility of pathogenic mutations within known deafness gene. A Chinese family with late-onset progressive non-syndromic sensorineural hearing loss was investigated clinically and genetically. By candidate gene approach and targeted next-generation sequencing, this family was preliminary proved to be caused by unknown deafness gene.

GJB2 c.-23+1G>A mutation is second most common mutation among Iranian individuals with autosomal recessive hearing loss.

GJB2 mutation analysis is used routinely as a first step in genetic testing for autosomal recessive non-syndromic sensorineural hearing loss. Although most GJB2 mutations can be detected by sequencing of the exon 2 of this gene, a prevalent splice mutation, c.-23+1G>A (IVS1+1G>A), is not usually included in the analyzed region. In this study, we have developed an ARMS-PCR strategy for detection of this mutation among Iranian deaf individuals. A total of 418 Iranian individuals with hearing loss consistent with autosomal recessive non-syndromic sensorineural hearing loss based on audiological test result, medical history, physical examination and pedigree of the family, were included in this study. c.35delG and c.-23+1G>A mutations were detected by using ARMS-PCR. Direct sequencing of the exon 2 of the GJB2 gene was performed for mutation analysis of the coding region of this gene. Among 418 investigated cases, a total of 81 patients (~19.4 %) with biallelic pathogenic mutations in the GJB2 gene and 13 cases with only one pathogenic mutant allele were identified. The total allele frequencies of the two most frequent mutations, c.35delG and c.-23+1G>A, among mutated alleles were found to be around 59 and 15.7 %, respectively. High frequency of the c.35delG and c.-23+1G>A mutations among Iranian deaf individuals shows the importance of developing rapid and cost-effective methods for primary mutation screening methods before performing direct sequencing.

HOXA1 Mutations are Not Commonly Associated with Non-Syndromic Deafness.

Homozygous homeobox A1 (HOXA1) mutations cause a spectrum of abnormalities in humans including bilateral profound deafness. This study evaluates the possible role of HOXA1 mutations in familial, non-syndromic sensorineural deafness. Forty-eight unrelated Middle Eastern families with either consanguinity or familial deafness were identified in a large deafness clinic, and the proband from each family was evaluated by chart review, audiogram, neuroimaging, and HOXA1 sequencing. All 48 probands had normal neuro-ophthalmologic and general medical examinations except for refractive errors. All had congenital non-syndromic sensorineural hearing loss that was symmetric bilaterally and profound (>90 dBHL) in 33 individuals and varied from 40 to 90 dBHL in the remainder. Thirty-nine of these individuals had neuroimaging studies, all documenting normal internal carotid arteries and normal 6th, 7th, and 8th cranial nerves bilaterally. Of these, 27 had normal internal ear structures with the remaining 12 having mild to modest developmental abnormalities of the cochlea, semicircular canals, and/or vestibular aqueduct. No patient had homozygous HOXA1 mutations. None of these patients with non-syndromic deafness had HOXA1 mutations. None had major inner ear anomalies, obvious cerebrovascular defects, or recognized congenital heart disease. HOXA1 is likely not a common cause of non-syndromic deafness in this Middle Eastern population.

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

Conclusions: The GJB2 gene mutation characteristic of Dongxiang was the interaction result of ethnic background and geographical environment, and Yugur exhibited the typical founder effect. The SLC26A4 gene mutation characteristic of Dongxiang was related to caucasian backgrounds and selection of purpose exons, i.e. ethnic background and the penetrance of ethnic specificity caused the low mtDNA1555A>G mutation frequency in Dongxiang. Objectives: To determine the prevalence of GJB2 and SLC26A4 genes and mtDNA1555A>G mutations and analyze the ethnic specificity in the non-syndromic sensorineural hearing loss (NSHL) of unique ethnic groups in Gansu Province. Methods: Peripheral blood samples were obtained from Dongxiang, Yugur, Bonan, and ethnic Han groups with moderately severe to profound NSHL in Gansu Province. Bidirectional sequencing (or enzyme digestion) was applied to identify the sequence variations. Results: The pathogenic allele frequency of the three gene mutations was different. The frequency of the GJB2 gene among the Dongxiang, Yugur, Bonan, and ethnic Han groups was 9.03%, 12.5%, 5.88%, and 12.17%, respectively. No difference was found between the ethnic groups. The frequencies of the SLC26A4 genes were 3.23%, 8.33%, 0%, and 9.81%, respectively. The mutation frequency of mtDNA1555A>G was 0%, 0%, 0%, and 6.03%, respectively. No difference was found between the ethnic groups, except for the Dongxiang and ethnic Han groups, both in SLC26A4 gene and mtDNA1555A>G.

Genetic counseling and prenatal diagnosis for hereditary hearing loss in high-risk families

ObjectiveGenetic counseling and prenatal diagnosis are very necessary and accurate to detect hereditary hearing loss, especially in high-risk families. Prenatal diagnosis is testing for diseases or conditions in fetuses before born, which gives parents the chance to prepare psychologically, financially and medically for the probable health and educational needs of the affected neonates. Methods54 unrelated families with children affected with non-syndromic sensorineural hearing loss were enrolled in the study and received genetic analysis with microarray and DNA sequencing technologies. Genetic counseling was provided to each participating families, and prenatal diagnosis was given to those at risk and would like to know their fetuses’ genotypes and probable hearing statuses. ResultsHalf the cases in the present study were diagnosed with confirmed pathogenic mutations and clear inheritance patterns. After receiving genetic counseling, 24 carrier couples with pathogenic mutations chose to proceed prenatal diagnosis, the results of which were in accordance with the pregnancy outcomes. Infants prenatally detected to be monoallelic mutation carriers and those harbored neither deafness-causing mutations form their parents passed newborn hearing screening and six-month follow-ups, while neonates prenatally detected to be carriers of diallelic or compound heterozygous mutations developed hearing loss after birth. ConclusionsWith appropriate genetic counseling and support services provided, the genetic testing and the prenatal diagnosis of hearing loss were valued by carrier couples for the information provided for future family planning and probably the preparation for the health and educational needs of the affected neonates.

A novel splice site mutation in DFNA5 causes late-onset progressive non-syndromic hearing loss in a Chinese family

ObjectivesMutations in DFNA5 may lead to autosomal dominant non-syndromic sensorineural hearing loss (NSHL). To date, only four DFNA5 mutations have been reported, all resulting in skipping of exon 8 at the mRNA level. In this study, we aim to characterize the clinical features and the genetic cause of a Chinese DFNA5 family. MethodsTargeted next-generation sequencing of 79 known deafness genes was performed in the proband. Co-segregation between the disease phenotype and the potentially pathogenic variant was confirmed in all family members by Sanger sequencing. ResultsA novel heterozygous c.991−2A>G mutation in DFNA5 was identified in this family segregating with the autosomal dominant, late-onset NSHL. This mutation was located in the conventional splice site in intron 7 and was likely to result in skipping of exon 8. The severity of hearing impairment varied intrafamilially. ConclusionWe identified a novel c.991−2A>G mutation in DFNA5 which again may lead to exon 8 skipping at the mRNA level. Our findings supported that the DFNA5-associated NSHL results from a specific gain-of-function mechanism.

Distribution and phenotype of GJB2 mutations in 102 Sicilian patients with congenital non syndromic sensorineural hearing loss

Objective: To evaluate the frequency of GJB2 mutations and their correlation with phenotype in Sicilian non-syndromic sensorineural hearing loss (NSHL) patients. Design: Sequencing of the coding region, basal promoter, exon 1, and donor splice site of the GJB2 gene; screening for the presence of the two common GJB6 deletions. Study sample: A cohort of 102 Sicilian NSHL patients. Results: Fifteen different mutations in GJB2 and seventeen different genotypes were detected. No GJB6 mutations were found. The hearing impairment was profound in the 64.72% of probands (mean PTA0.25–4 kHz of 88.82 ± 26.52 dB HL). A total of 81.37% of patients harboured at least one c.35delG allele; c.167delT and c.-23 + 1G> A were identified in 10.78% and the 9.8% of patients respectively; c.35delG homozygotes presented more severe hearing impairment (75.59% of profound hearing loss) and a higher mean PTA0.25–4 kHz (96.79 ± 21.11 dB HL) with respect to c.35delG/non-c.35delG and c.35delG/Wt patients (P < 0.05). Conclusions: This work underlines the role of c.35delG, c.167delT and c.-23 + 1G> A as the most frequent causes of NSHL in Sicily. The c.35delG frequency found is similar to those reported in other populations of the Mediterranean area. The analysis of genetic and audiologic data confirmed a variability in the phenotype associated to a single genotype.

Connexin gene mutations among ugandan patients with nonsyndromic sensorineural hearing loss

Congenital deafness occurs in approximately 1 in 1,000 live births, and 50% of these cases are hereditary. Connexin mutations have been identified as the most common cause of hereditary hearing loss in many populations. The prevalence of this mutation in African patients has not been adequately studied. The objective of this study was to determine the prevalence of connexin 26 and 30 mutations in a population of hearing-impaired patients from Uganda. This is an observational study. Coding regions of both GJB2 and GJB6, noncoding exon 1 of GJB2, and 30 nucleotides of intronic sequence bordering the exons were analyzed in 126 subjects from Uganda with confirmed bilateral, severe-to-profound sensorineural hearing loss. All variants were analyzed for possible clinical significance using a combination of database searches and in silico tools. Complete sequence data were obtained on 115/126 individuals; 11 had only partial or no results. Only one reported pathogenic variant was found in GJB2 (c.208C>G; p.Pro70Ala) and none in GJB6. Three reported variants and two novel variants within intron 1 of GJB2 and two variants within exon 3 of GJB6 were also found. None of the most common types of deletions in the GJB2 gene (c.35delG, c.167delT or c.235delC) were found in this large cohort of deaf children from Uganda. This prompts a search for genetic causes of deafness among this and other previously studied African populations.

Particular distribution of the GJB2/GJB6 gene mutations in Mexican population with hearing impairment

BackgroundHereditary sensorineural hearing loss (SNHL) is a genetically heterogeneous disorder worldwide. Mutations in the GJB2 gene are a frequent cause of hereditary SNHL. There is a prevalence of certain mutations in various populations which suggests that specific mutations may be influenced by ethnic background. ObjectiveTo analyze the prevalence of GJB2, GJB6 mutations in several geographic areas of Mexico in patients with hereditary SNHL. Materials and methodsOne hundred and forty Mexican unrelated propositi with prelingual SNHL were included in the study. All patients had three previous generations born in Mexico and belonged to no specific ethnic group. Analyses of the GJB2 and GJB6 genes and mt.1555A<G were performed in all subjects. ResultsTwenty-three homozygous mutations, 57 heterozygous mutations, 1 double heterozygous (GJB2/GJB6) and 59 wild-type genotypes in the GJB2 gene were observed. Three patients had the homozygous c.del35 mutation whereas 26 patients were heterozygous for this gene defect. Only one patient with the GJB6 gene deletion was present (it includes the double heterozygous GJB2/GJB6). The mt.1555A>G mutation was not detected. ConclusionWe found a great variety of mutations depending on the analyzed region in patients with SNHL; 57.86% of patients had affection in one or two alleles in GJB2 or GJB6 genes whereas 42.14% were wild-type. In some cases, allele distribution depended on region. Molecular studies of more genes involved in hereditary non-syndromic SNHL are required to completely confirm the molecular basis of hearing loss in Mexican population.