Developing regional genetic counseling for southern Chinese with nonsyndromic hearing impairment: a unique mutational spectrum

Low frequency of SLC26A4 c.919-2A > G variant among patients with nonsyndromic hearing loss in Yunnan of Southwest China

BACKGROUND

Gene variants are responsible for more than half of hearing loss, particularly in nonsyndromic hearing loss (NSHL). The most common pathogenic variant in SLC26A4 gene found in East Asian populations is c.919-2A > G followed by c.2168A > G (p.H723R). This study was to evaluate their variant frequencies in patients with NSHL from special education schools in nine different areas of Southwest China's Yunnan.

METHODS

We performed molecular characterization by PCR-products directly Sanger sequencing of the SLC26A4 c.919-2AG and c.2168 A > G variants in 1167 patients with NSHL including 533 Han Chinese and 634 ethnic minorities.

RESULTS

The SLC26A4 c.919-2A > G variant was discovered in 8 patients with a homozygous state (0.69%) and twenty-five heterozygous (2.14%) in 1167 patients with NSHL. The total carrier rate of the c.919-2A > G variant was found in Han Chinese patients with 4.50% and ethnic minority patients with 1.42%. A significant difference existed between the two groups (P < 0.05). The c.919-2A > G allele variant frequency was ranged from 3.93% in Kunming to zero in Lincang and Nvjiang areas of Yunnan. We further detected the SLC26A4 c.2168 A > G variant in this cohort with one homozygotes (0.09%) and seven heterozygotes (0.60%), which was detected in Baoshan, Honghe, Licang and Pu`er areas. Between Han Chinese group (0.94%) and ethnic minority group (0.47%), there was no statistical significance (P > 0.05). Three Han Chinese patients (0.26%) carried compound heterozygosity for c.919-2A > G and c.2168 A > G.

CONCLUSION

These data suggest that the variants in both SLC26A4 c.919-2A > G and c.2168 A > G were relatively less frequencies in this cohort compared to the average levels in most regions of China, as well as significantly lower than that in Han-Chinese patients. These results broadened Chinese population genetic information resources and provided more detailed information for regional genetic counselling for Yunnan.

Non-syndromic enlarged vestibular aqueduct caused by novel compound mutations of the SLC26A4 gene: a case report and literature review

Enlarged vestibular aqueduct is an autosomal genetic disease mainly caused by mutations in the SLC26A4 gene and includes non-syndromic and syndromic types. This study aimed to identify genetic defects in a Chinese patient with non-syndromic enlarged vestibular aqueduct (NSEVA) and to investigate the impact of variants on the severity of non-syndromic enlarged vestibular aqueduct. A male patient with NSEVA, aged approximately 6 years, was recruited for this study. The clinical characteristics and results of auxiliary examinations, including laboratory and imaging examinations, were collected, and 127 common hereditary deafness genes were detected by chip capture high-throughput sequencing. Protein structure predictions, the potential impact of mutations, and multiple sequence alignments were analyzed in silico. Compound heterozygote mutations c.1523_1528delinsAC (p.Thr508Asnfs*3) and c.422T>C (p.Phe141Ser) in the SLC26A4 gene were identified. The novel frameshift mutation c.1523_1528delinsAC produces a severely truncated pendrin protein, and c.422T>C has been suggested to be a disease-causing mutation. Therefore, this study demonstrates that the novel mutation c.1523_1528delinsAC in compound heterozygosity with c.422T>C in the SLC26A4 gene is likely to be the cause of NSEVA. Cochlear implants are the preferred treatment modality for patients with NSEVA and severe-to-profound sensorineural hearing loss Genetic counseling and prenatal diagnosis are essential for early diagnosis. These findings expand the mutational spectrum of SLC26A4 and improve our understanding of the molecular mechanisms underlying NSEVA.

A dominant variant in apoptosis-related gene XKR8 is relevant to hereditary auditory neuropathy

BACKGROUND

Auditory neuropathy is an unusual type of hearing loss. At least 40% of patients with this disease have underlying genetic causes. However, in many hereditary auditory neuropathy cases, etiology remains undetermined.

METHODS

We collected data and blood samples from a four-generation Chinese family. After excluding relevant variants in known deafness-related genes, exome sequencing was conducted. Candidate genes were verified by pedigree segregation, transcript/protein expression in the mouse cochlea, and plasmid expression studies in HEK 293T cells. Moreover, a mutant mouse model was generated and underwent hearing evaluations; protein localization in the inner ear was also assessed.

RESULTS

The clinical features of the family were diagnosed as auditory neuropathy. A novel variant c.710G > A (p.W237X) in apoptosis-related gene XKR8 was identified. Genotyping of 16 family members confirmed the segregation of this variant with the deafness phenotype. Both XKR8 mRNA and XKR8 protein were expressed in the mouse inner ear, predominantly in regions of spiral ganglion neurons; Moreover, this nonsense variant impaired the surface localization of XKR8 in cells. Transgenic mutant mice exhibited late-onset auditory neuropathy, and their altered XKR8 protein localization in the inner ear confirmed the damaging effects of this variant.

CONCLUSIONS

We identified a variant in the XKR8 gene that is relevant to auditory neuropathy. The essential role of XKR8 in inner ear development and neural homeostasis should be explored.

Insight into the Natural History of Pathogenic Variant c.919-2A>G in the SLC26A4 Gene Involved in Hearing Loss: The Evidence for Its Common Origin in Southern Siberia (Russia)

Pathogenic variants in the SLC26A4 gene leading to nonsyndromic recessive deafness (DFNB4), or Pendred syndrome, are some of the most common causes of hearing loss worldwide. Earlier, we found a high proportion of SLC26A4-related hearing loss with prevailing pathogenic variant c.919-2A>G (69.3% among all mutated SLC26A4 alleles that have been identified) in Tuvinian patients belonging to the indigenous Turkic-speaking Siberian people living in the Tyva Republic (Southern Siberia, Russia), which implies a founder effect in the accumulation of c.919-2A>G in Tuvinians. To evaluate a possible common origin of c.919-2A>G, we genotyped polymorphic STR and SNP markers, intragenic and flanking SLC26A4, in patients homozygous for c.919-2A>G and in healthy controls. The common STR and SNP haplotypes carrying c.919-2A>G were revealed, which convincingly indicates the origin of c.919-2A>G from a single ancestor, supporting a crucial role of the founder effect in the c.919-2A>G prevalence in Tuvinians. Comparison analysis with previously published data revealed the identity of the small SNP haplotype (~4.5 kb) in Tuvinian and Han Chinese carriers of c.919-2A>G, which suggests their common origin from founder chromosomes. We assume that c.919-2A>G could have originated in the geographically close territories of China or Tuva and subsequently spread to other regions of Asia. In addition, the time intervals of the c.919-2A>G occurrence in Tuvinians were roughly estimated.

Report of rare and novel mutations in candidate genes in a cohort of hearing-impaired patients

BACKGROUND

Many hearing-impaired patients carry mutations in rare or novel genes undetected in regular genetic hot regions/genes screening.

METHODS

We collected clinical and genetic data from subjects with hearing loss who visited our department for genetic counseling. Next-generation sequencing was conducted after 154 deafness-related genes were captured using a designed genes panels in 14 unrelated families (37 participants). The results were filtered and assessed with in silico tools, in combination with pedigree mapping.

RESULTS

Ten mutations in regular deafness genes (GJB2, SLC26A4) and uncommon genes (OTOF, MYO7A, MYO15A, and KARS) were detected, which constituted 57.2% of yielded rate. In particular, two patients with nonsyndromic deafness carried biallelic KARS mutations. In addition, we identified an unreported digenic mutational inheritance in GRP98/USH2A genes in a proband with isolated hearing loss. Functional analyses and molecular modeling suggested the damaging consequence of these variants on encoded proteins. According to the variant pathogenicity guidelines, the 17 identified variants in total were classified as "pathogenic" or "likely pathogenic."

CONCLUSION

The candidate mutations in deafness genes were suggested to be co-segregated in at least 57.2% of the studied pedigrees. This is the new report of rare/novel mutations causing inherited hearing loss in Chinese.

Novel CRISPR/Cas12a-based genetic diagnostic approach for SLC26A4 mutation-related hereditary hearing loss

Hereditary hearing loss is a common defect of the auditory nervous system with high-incidence, seriously affecting the quality of life of the patients. The clinical manifestations of SLC26A4 mutation-related hearing loss are congenital sensorineural or mixed deafness. Sensitive and specific SLC26A4 mutation detection in the early clinical stage is key for the early indication of potential hearing loss in the lack of effective treatment. Using clustered regularly interspaced short palindromic repeats (CRISPR)-based nucleic acid detection technology, we designed a fast and sensitive detection system for SLC26A4 pathogenic mutations (c.919-2A > G, c.2168A > G and c.1229C > T). This recombinase-aided amplification-based detection system allows rapid target gene amplification and, in combination with the CRISPR-based nucleic acid testing (NAT) system, mutation site detection. Moreover, mismatches were introduced in CRISPR-derived RNA (crRNA) to increase signal differences between the wild-type genes and mutant genes. A total of 64 samples were examined using this approach and all results were verified using Sanger sequencing. The detection results were consistent with the polymerase chain reaction-Sanger sequencing results. Overall, this CRISPR-based NAT technology provides a sensitive and fast new approach for the detection of hereditary deafness and provides a crRNA optimization strategy for single-nucleotide polymorphism detection, which could be helpful for the clinical diagnosis of SLC26A4 mutation-related hereditary hearing loss.

Increased diagnosis of enlarged vestibular aqueduct by multiplex PCR enrichment and next-generation sequencing of the SLC26A4 gene

Background

The enlarged vestibular aqueduct (EVA) is the commonest malformation of inner ear accompanied by sensorineural hearing loss in children. Three genes SLC26A4, FOXI1, and KCNJ10 have been associated with EVA, among them SLC26A4 being the most common. Yet, hotspot mutation screening can only diagnose a small number of patients.

Methods

Thus, in this study, we designed a new molecular diagnosis panel for EVA based on multiplex PCR enrichment and next‐generation sequencing of the exon and flanking regions of SLC26A4. A total of 112 hearing loss families with EVA were enrolled and the pathogenicity of the rare variants detected was interpreted according to the American College of Medical Genetics and Genomics (ACMG) guidelines.

Results

Our results showed that 107/112 (95.54%) families carried SLC26A4 biallelic mutations, 4/112 (3.57%) carried monoallelic variants, and 1/112 (0.89%) had none variant, resulting in a diagnostic rate of 95.54%. A total of 49 different variants were detected in those patients and we classified 30 rare variants as pathogenic/likely pathogenic, of which 13 were not included in the Clinvar database.

Conclusion

Our diagnostic panel has an increased diagnostic yield with less cost, and the curated list of pathogenic variants in the SLC26A4 gene can be directly used to aid the genetic counseling to patients.

Genetic testing involving 100 common mutations for antenatal diagnosis of hereditary hearing loss in Chongqing, China

ABSTRACT

To understand the possible carrier status of genes associated with hereditary hearing loss (HHL) in the general population among local residents and to give genetic counseling for pregnant women.A total of 3541 subjects were recruited. We used multiplex PCR technology combined with next-generation sequencing technology to detect 100 hotspot mutations in 18 common deafness-related genes. The homozygous mutation screening results were verified using Sanger sequencing.Of the 3541 participants, 37 alleles of 8 deafness genes were detected. A total of 145 (4.09%) were found to be GJB2 gene mutation carriers, and the hotspot mutation was c.235delC (1.54%). Twenty three (0.65%) were found to be GJB3 gene mutation carriers. A total of 132 (3.37%) were found to be SLC26A4 gene mutation carriers, and the hotspot mutation was c.919-2A > G (0.49%). Forty four (1.24%) were found to be mitochondrial DNA mutation carriers. Sanger sequencing results verified that 2 cases were homozygous for the c.235delC mutation and that 1 case was homozygous for the c.754T > C mutation.Genetic testing for pregnant women and their partners allows early identification of the molecular etiology of hearing loss (HL). On the one hand, it could give genetic counseling for pregnant women, such as early diagnosis of delayed deafness and drug-susceptible deafness. On the other hand, it could be used to assess hearing conditions during pregnancy, leading to prevention and timely intervention for newborns.

Analysis of mutation spectrum of common deafness-causing genes in Hakka newborns in southern China by semiconductor sequencing

Hearing loss is a common neurosensory disorder, approximately half of the cases are caused by genetic factors, and approximately 70% of hereditary hearing impairments are nonsyndromic hearing loss (NSHL). The mutations of GJB2 (gap junction beta-2 protein), GJB3 (gap junction beta-3 protein), SLC26A4 (solute carrier family 26 member 4), and MT-RNR1 (mitochondrially encoded 12S RNA) are the most common inherited causes of NSHL. Because of different genetic backgrounds, the mutation spectrum of these common deafness-causing genes varies among different regions in China. Because no data are known on these mutations among the Hakka population of Southern China, we aim to investigate the mutation spectrum to add these to neonatal screening and genetic counseling. A total of 1252 blood samples from newborns have been detected by semiconductor sequencing for 100 mutations loci of 18 deafness-causing genes. Of the participants, 95 subjects carried deafness-causing genes mutations with the carrier rate of 7.59%. The mutation frequencies of GJB2, SLC26A4, GJB3, and mitochondrial genes were 3.04%, 3.51%, 0.16%, and 0.88%, respectively. We followed up subjects with single-gene homozygous or compound heterozygous mutations. Our study firstly analyzed deafness-causing genes mutation spectrum in Hakka population, providing evidence for future neonatal screening and genetic counseling in this area.

GJB3/GJB6 screening in GJB2 carriers with idiopathic hearing loss: Is it necessary?

BACKGROUND

Genetic analysis detected excessive mono-allelic recessive GJB2 mutations in individuals with idiopathic deafness; the remaining alleles in trans/cis are underdetermined. The aim of this study was to assess the contributions of variants in GJB3 or GJB6 to non-syndromic sensorineural hearing impairment (NSHI) in Chinese patients with mono-allelic GJB2 mutations.

METHODS

The entire coding sequences of GJB3/GJB6, as well as deletions in GJB6, in a cohort of NSHI patients (n = 100) carrying likely pathogenic heterozygous GJB2 mutations, were tested. Targeted next generation sequencing was further performed in a multiplex family GDHY with moderate to profound NSHI.

RESULTS

Putatively causative GJB3 variant underlied 1% (1/100) in this cohort. In family GDHY, we identified a rare GJB3 c.250G>A mutation, as double heterozygotes with GJB2 c.109G>A and/or a novel GJB2 mutation c.638T>C predicted to be damaging in a digenic inheritance after precluding other attributable mutations from 127 deafness genes. No GJB6 mutation was found.

CONCLUSIONS

GJB3/GJB6 variants account for a low proportion in autosomal recessive GJB2 mutation carriers in our cohort. Environmental causes, or other NSHI relevant genes, revealed by targeted next generation sequencing or whole exome sequencing, may play major roles in triggering deafness in these patients.

Genetic mutations in non-syndromic deafness patients in Hainan Province have a different mutational spectrum compared to patients from Mainland China

OBJECTIVES

To provide appropriate genetic testing and counseling for non-syndromic hearing impairment patients in Hainan Province, an island in the South China Sea.

METHODS

299 unrelated students with non-syndromic hearing loss who attended a special education school in Hainan Province were enrolled in this study. Three prominent deafness-related genes (GJB2, SLC26A4, and mtDNA 12S rRNA) were analyzed using Sanger sequencing.

RESULTS

GJB2 mutations were detected in 32.78% (98/299) of the entire cohort; however, only 5.69% (17/299) had two confirmed pathogenic mutations. The most common mutation observed in this population was c.109G > A in the GJB2 gene, with an allelic frequency of 15.05% (90/598), which is significantly higher than that reported in previous cohorts. A total of 16 patients had two confirmed pathogenic SLC26A4 gene mutations, and 16 patients had one. The IVS7-2A > G mutation was the most commonly observed, with an allelic frequency of 3.51% (21/598). Three patients had a m.1555A > G mutation in the mtDNA 12S rRNA gene.

CONCLUSIONS

These results reveal that genetic etiology occurred in 11.71% (35/299) of patients, suggesting that Hainan province have a different mutational spectrum compare to Mainland China in non-syndromic deafness patients, which provide useful information to genetic counseling in Hainan province.

A novel mutation in the SLC26A4 gene in a Chinese family with non-syndromic hearing loss and enlarged vestibular aqueduct

OBJECTIVES

To identity the genetic causes of hearing loss in a Han Chinese family with enlarged vestibular aqueduct syndrome.

METHODS

Multiplex PCR technology combined with Ion Torrent™ next-generation sequencing technology was used to search for pathogenic mutations. A group of 1500 ethnically-matched normal hearing subjects screened for mutations in deafness-related genes using the same method in previously studied were included as a control.

RESULTS

The proband and his little sister suffered from typical features of sensorineural hearing loss with enlarged vestibular aqueduct (EVA). Both subjects harbored two compound heterozygous mutations in the SLC26A4 gene. A novel mutation named c.2110 G > C (p.Glu704Gln) in exon 19 and another previously reported mutation c.1673 A > T (p.Asn558Ile) were identified. These mutations were carried in the heterozygous state by the parents and therefore co-segregated with the genetic disease. The c.2110 G > C (p.Glu704Gln) mutation was absent in 1500 healthy newborns. Protein alignment indicated high evolutionary conservation of the p.E704 residue, and this mutation was predicted by online tools to be damaging and deleterious.

CONCLUSION

This study demonstrates that the novel mutation c.2110 G > C (p.Glu704Gln) in compound heterozygosity with c.1673 A > T (p.Asn558Ile) in the SLC26A4 gene corresponds to the EVA in this family. Our study will provide a foundation for elucidating the SLC26A4-related mechanisms of hearing loss.

Genetic Basis of Nonsyndromic Sensorineural Hearing Loss in the Sub-Saharan African Island Population of São Tomé and Príncipe: The Role of the DFNB1 Locus?

Hearing loss (HL) is a common condition with both genetic and environmental causes, and it greatly impacts global health. The prevalence of HL is reportedly higher in developing countries such as the Sub-Saharan African island of São Tomé and Príncipe, where the deaf community is estimated to be less than 1% of the population. We investigated the role of the DFNB1 locus (GJB2 and GJB6 genes) in the etiology of nonsyndromic sensorineural hearing loss (NSSHL) in São Tomé and Príncipe. A sample of 316 individuals, comprising 136 NSSHL patients (92 bilateral, 44 unilateral) and 180 controls, underwent a clinical and audiological examination. Sequencing of the GJB2 coding region and testing for the (GJB6-D13S1830) and del(GJB6-D13S1854) GJB6 deletions were performed. A total of 311 out of 316 individuals were successfully analyzed regarding the GJB2 and GJB6 genetic variations, respectively. The frequency of the GJB2 coding mutations in patients and controls was low. Some of those coding mutations are the most commonly found in Eurasian and Mediterranean populations and have also been identified in Portugal. None of the GJB6 deletions was present. The presence of certain coding variants in São Tomé and Príncipe suggests a non-Sub-Saharan genetic influx and supports the previously reported genetic influx from European (mainly Portuguese) ancestors. In summary, DFNB1 locus does not appear to be a major contributor to NSSHL in São Tomé and Príncipe. However, the presence of both pathogenic and likely pathogenic mutations in GJB2 suggests that GJB2-related NSSHL might still occur in this population, warranting further research on GJB2 testing in NSSHL cases.

Germinal mosaicism of PAX3 mutation caused Waardenburg syndrome type I

OBJECTIVES

Waardenburg syndrome mutations are most often recurrent or de novo. The rate of familial recurrence is low and families with several affected children are extremely rare. In this study, we aimed to clarify the underlying hereditary cause of Waardenburg syndrome type I in two siblings in a Chinese family, with a mother affected by prelingual mild hearing loss and a father who was negative for clinical symptoms of Waardenburg syndrome and had a normal hearing threshold.

METHODS

Complete characteristic features of the family members were recorded and genetic sequencing and parent-child relationship analyses were performed.

RESULTS

The two probands were found to share double mutations in the PAX3/GJB2 genes that caused concurrent hearing loss in Waardenburg syndrome type I. Their mother carried the GJB2 c.109G > A homozygous mutation; however, neither the novel PAX3 c.592delG mutation, nor the Waardenburg syndrome phenotype, was observed in either parent.

CONCLUSION

These previously unreported digenic mutations in PAX3/GJB2 resulted in deafness associated with Waardenburg syndrome type I in this family. To our knowledge, this is the first report describing germinal mosaicism in Waardenburg syndrome. This concept is important because it complicates genetic counseling of this family regarding the risk of recurrence of the mutations in subsequent pregnancies.

A New Genetic Diagnostic for Enlarged Vestibular Aqueduct Based on Next-Generation Sequencing

Enlarged vestibular aqueduct (EVA) is one of the most common congenital inner ear malformations and accounts for 1–12% of sensorineural deafness in children and adolescents. Multiple genetic defects contribute to EVA; therefore, early molecular diagnosis is critical for EVA patients to ensure that the most effective treatment strategies are employed. This study explored a new genetic diagnosis method for EVA and applied it to clinic diagnoses of EVA patients. Using next-generation sequencing technology, we set up a multiple polymerase chain reaction enrichment system for target regions of EVA pathogenic genes (SLC26A4, FOXI1, and KCNJ10). Forty-six EVA samples were sequenced by this system. Variants were detected in 87.0% (40/46) of cases, including three novel variants (SLC26A4 c.923_929del, c.1002-8C>G, and FOXI1 c.519C>A). Biallelic potential pathogenic variants were detected in 27/46 patient samples, leading to a purported diagnostic rate of 59%. All results were verified by Sanger sequencing. Our target region capture system was validated to amplify and measure SLC26A4, FOXI1, and KCNJ10 in one reaction system. The result supplemented the mutation spectrum of EVA. Thus, this strategy is an economic, rapid, accurate, and reliable method with many useful applications in the clinical diagnosis of EVA patients.

Compound heterozygous MYO7A mutations segregating Usher syndrome type 2 in a Han family

OBJECTIVE

Identification of rare deafness genes for inherited congenital sensorineural hearing impairment remains difficult, because a large variety of genes are implicated. In this study we applied targeted capture and next-generation sequencing to uncover the underlying gene in a three-generation Han family segregating recessive inherited hearing loss and retinitis pigmentosa.

METHODS

After excluding mutations in common deafness genes GJB2, SLC26A4 and the mitochondrial gene, genomic DNA of the proband of a Han family was subjected to targeted next-generation sequencing. The candidate mutations were confirmed by Sanger sequencing and subsequently analyzed with in silico tools.

RESULTS

An unreported splice site mutation c.3924+1G > C compound with c.6028G > A in the MYO7A gene were detected to cosegregate with the phenotype in this pedigree. Both mutations, located in the evolutionarily conserved FERM domain in myosin VIIA, were predicted to be pathogenic. In this family, profound sensorineural hearing impairment and retinitis pigmentosa without vestibular disorder, constituted the typical Usher syndrome type 2.

CONCLUSION

Identification of novel mutation in compound heterozygosity in MYO7A gene revealed the genetic origin of Usher syndrome type 2 in this Han family.

Mapping pathogenic mutations suggests an innovative structural model for the pendrin (SLC26A4) transmembrane domain

Human pendrin (SLC26A4) is an anion transporter mostly expressed in the inner ear, thyroid and kidney. SLC26A4 gene mutations are associated with a broad phenotypic spectrum, including Pendred Syndrome and non-syndromic hearing loss with enlarged vestibular aqueduct (ns-EVA). No experimental structure of pendrin is currently available, making phenotype-genotype correlations difficult as predictions of transmembrane (TM) segments vary in number. Here, we propose a novel three-dimensional (3D) pendrin transmembrane domain model based on the SLC26Dg transporter. The resulting 14 TM topology was found to include two non-canonical transmembrane segments crucial for pendrin activity. Mutation mapping of 147 clinically validated pathological mutations shows that most affect two previously undescribed TM regions.

A Novel Frameshift Mutation of SLC26A4 in a Korean Family With Nonsyndromic Hearing Loss and Enlarged Vestibular Aqueduct

Objectives

We aimed to identify the causative mutation for siblings in a Korean family with nonsyndromic hearing loss (HL) and enlarged vestibular aqueduct (EVA). The siblings were a 19-year-old female with bilateral profound HL and an 11-year-old male with bilateral moderately severe HL.

Methods

We extracted genomic DNA from blood samples of the siblings with HL, their parents, and 100 controls. We performed mutation analysis for SLC26A4 using direct sequencing.

Results

The two siblings were compound heterozygotes with the novel mutation p.I713LfsX8 and the previously described mutation p.H723R. Their parents had heterozygous mono-allelic mutations. Father had p.I713LfsX8 mutation as heterozygous, and mother had p.H723R mutation as heterozygous. However, novel mutation p.I713LfsX8 was not detected in 100 unrelated controls.

Conclusion

Both mutations identified in this study were located in the sulfate transporter and anti-sigma factor antagonist domain, the core region for membrane targeting of SulP/SLC26 anion transporters, which strongly suggests that failure in membrane trafficking by SLC26A4 is a direct cause of HL in this family. Our study could therefore provide a foundation for further investigations elucidating the SLC26A4-related mechanisms of HL.

The R130S mutation significantly affects the function of prestin, the outer hair cell motor protein

A missense mutation, R130S, was recently found in the prestin gene, SLC26A5, of patients with moderate to severe hearing loss (DFNB61). In order to define the pathology of hearing loss associated with this missense mutation, a recombinant prestin construct harboring the R130S mutation (R130S-prestin) was generated, and its functional consequences examined in a heterologous expression system. We found that R130S-prestin targets the plasma membrane but less efficiently compared to wild-type. The voltage operating point and voltage sensitivity of the motor function of R130S-prestin were similar to wild-type prestin. However, the motor activity of R130S-prestin is greatly reduced at higher voltage stimulus frequencies, indicating a reduction in motor kinetics. Our study thus provides experimental evidence that supports a causal relationship between the R130S mutation in the prestin gene and hearing loss found in patients with this missense mutation.

KEY MESSAGE

Membrane targeting of prestin is impaired by the R130S missense mutation. The fast motor kinetics of prestin is impaired by the R130S missense mutation. Our study strongly suggests that the prestin R130S missense mutation is pathogenic.

Phenotypic Heterogeneity in a DFNA20/26 family segregating a novel ACTG1 mutation

BACKGROUND

Genetic factors play an important role in hearing loss, contributing to approximately 60% of cases of congenital hearing loss. Autosomal dominant deafness accounts for approximately 20% of cases of hereditary hearing loss. Diseases with autosomal dominant inheritance often show pleiotropy, different degrees of penetrance, and variable expressivity.

METHODS

A three-generation Chinese family with autosomal dominant nonsyndromic hearing impairment (ADNSHI) was enrolled in this study. Audiometric data and blood samples were collected from the family. In total, 129 known human deafness genes were sequenced using next-generation sequencing (NGS) to identify the responsible gene mutation in the family. Whole Exome Sequencing (WES) was performed to exclude any other variant that cosegregated with the phenotype.

RESULTS

The age of onset of the affected family members was the second decade of life. The condition began with high-frequency hearing impairment in all family members excluding III:2. The novel ACTG1 c.638A > G (p.K213R) mutation was found in all affected family members and was not found in the unaffected family members. A heterozygous c.638A > G mutation in ACTG1 and homozygous c.109G > A (p.V37I) mutation in GJB2 were found in III:2, who was born with hearing loss. The WES result concurred with that of targeted sequencing of known deafness genes.

CONCLUSIONS

The novel mutation p.K213R in ACTG1 was found to be co-segregated with hearing loss and the genetic cause of ADNSHI in this family. A homozygous mutation associated with recessive inheritance only rarely co-acts with a dominant mutation to result in hearing loss in a dominant family. In such cases, the mutations in the two genes, as in ACTG1 and GJB2 in the present study, may result in a more severe phenotype. Targeted sequencing of known deafness genes is one of the best choices to identify the genetic cause in hereditary hearing loss families.

Novel mutation located in EC7 domain of protocadherin-15 uncovered by targeted massively parallel sequencing in a family segregating non-syndromic deafness DFNB23

OBJECTIVE

Hereditary hearing loss is a clinically and genetically heterogeneous disorder associated with mutations of a large number of diverse genes. In this study we applied targeted capture and massively parallel sequencing to identify the disease-causing gene of a Chinese family segregating recessive inherited deafness.

METHODS

After excluding mutations in common deafness genes GJB2, SLC26A4, mitochondrial m.1555A>G, genomic DNA of the proband of family GDSW24 was subjected to targeted next-generation sequencing. Subsequently, a candidate homozygous mutation was confirmed by Sanger sequencing.

RESULTS

A novel PCDH15 c.2367_2369delTGT/p.V788-homozygous mutation was detected. In this family, no obvious vestibular disorder was found. The in-frame mutation c.2367_2369delTGT is located in the evolutionarily conserved EC7 domain of Protocadherin-15 and was predicted to be pathogenic.

CONCLUSION

The novel homozygous mutation in a family segregating non-syndromic hearing loss family supports previous reported observations that PCDH15 does not only causes Usher syndrome type 1F, but also DFNB23.

GJB2 and mitochondrial 12S rRNA susceptibility mutations in sudden deafness

Genetic susceptibility may play an important role in the pathogenesis of sudden deafness. However, the specific genes involved are largely unknown. We sought to explore the frequency of GJB2 and mitochondrial 12S rRNA susceptibility mutations in patients with sudden deafness. Between September 2011 and May 2012, 62 consecutive patients with sudden deafness were seen. In 50 of these, no etiological factors for sudden deafness were found. We detected GJB2 and mitochondrial 12S rRNA variants by direct sequencing in these 50 patients and in 53-aged matched controls with normal hearing. In addition, we undertook functional analyses of the mitochondrial mutations which we detected, applying structural and phylogenetic analysis. GJB2 sequencing identified six mutations, including three pathogenic mutations (c.235delC, c.299-300delAT, c.109G>A) and three polymorphisms, in the study participants, giving an allele frequency of 15.0 %. A homozygous c.109G>A mutation was detected in two participants. A total of 16 variants in mitochondrial 12S rRNA gene were identified in the participants. No significant differences were found in GJB2 heterozygosity or in mitochondrial 12S rRNA variants between patients with sudden deafness and in controls. Our results suggest that the homozygous GJB2 c.109G>A mutation may be a cause of sudden deafness involving both ears. This finding should increase awareness of the likely role of genetic factors in the etiology of sudden deafness in general.