The genetic bases for non-syndromic hearing loss among Chinese

Noninvasive prenatal diagnosis (NIPD) of non-syndromic hearing loss (NSHL) for singleton and twin pregnancies in the first trimester

BACKGROUND

Noninvasive prenatal diagnosis (NIPD) has been proven feasible for non-syndromic hearing loss (NSHL) in singleton pregnancies. However, previous research is limited to the second trimester and the application in twin pregnancies is blank. Here we provide a novel algorithmic approach to assess singleton and twin pregnancies in the first trimester.

METHODS

A 324.614 kb capture panel was designed to selectively enrich target regions. Parental haplotypes were constructed by target sequencing of blood samples from the parents and the proband. Then single nucleotide polymorphisms (SNP) within target regions were classified into four and six categories in singleton and twin pregnancy, respectively. Combining relative haplotype dosage change (RHDO) and the Bayes factor (BF), fetal fraction (FF) and fetal genotype were deduced in singleton and twin pregnancies. The pregnant women's NIPD results were validated by invasive prenatal diagnosis and Sanger sequencing.

RESULTS

Sixteen women with singleton pregnancies and one woman with a twin pregnancy were recruited. Among the 16 singleton pregnancies, NIPD was successfully applied in 15 families and the coincidence rate with invasive prenatal diagnosis was 100% (15/15). Only one family NIPD result is "no call" because the imbalance distribution of SNP sites makes it difficult to estimate recombination events. Most (13/15) of pregnant women were diagnosed in the first trimester and the earliest gestation week was the 7th week. The twin pregnancy was a dichorionic diamniotic twin (DCDA). NIPD confirmed one fetus is affected, and another is a carrier with c.299_300delAT of GJB2 gene.

CONCLUSION

This study represents the pioneering evidence in the field, demonstrating the feasibility of NIPD for NSHL in twin pregnancies. Moreover, it provides a novel and advanced diagnostic approach for families at high risk of NSHL during pregnancy, offering earlier detection, enhanced safety, and improved accuracy.

Common genetic etiologies of sensorineural hearing loss in Koreans

Hearing loss is the most common sensory disorder. Genetic factors contribute substantially to this condition, although allelic heterogeneity and variable expressivity make a definite molecular diagnosis challenging. To provide a brief overview of the genomic landscape of sensorineural hearing loss in Koreans, this article reviews the genetic etiologies of nonsyndromic hearing loss in Koreans as well as the clinical characteristics, genotype-phenotype correlations, and pathogenesis of hearing loss arising from common variants observed in this population. Furthermore, potential genetic factors associated with age-related hearing loss, identified through genome-wide association studies, are briefly discussed. Understanding these genetic etiologies is crucial for advancing precise molecular diagnoses and developing targeted therapeutic interventions for hearing loss.

Targeted Linked-Read Sequencing for Direct Haplotype Phasing of Parental GJB2/SLC26A4 Alleles: A Universal and Dependable Noninvasive Prenatal Diagnosis Method Applied to Autosomal Recessive Nonsyndromic Hearing Loss in At-Risk Families

Noninvasive prenatal diagnosis (NIPD) for autosomal recessive nonsyndromic hearing loss (ARNSHL) has been rarely reported until recent years. Additionally, the existing method can not be used for challenging genome loci (eg, copy number variations, deletions, inversions, or gene recombinants) or on families without proband genotype. This study assessed the performance of relative haplotype dosage analysis (RHDO)-based NIPD for identifying fetal genotyping in pregnancies at risk of ARNSHL. Fifty couples carrying pathogenic variants associated with ARNSHL in either GJB2 or SLC26A4 were recruited. The RHDO-based targeted linked-read sequencing combined with whole gene coverage probes was used to genotype the fetal cell-free DNA of 49 families who met the quality control standard. Fetal amniocyte samples were genotyped using invasive prenatal diagnosis (IPD) to assess the performance of NIPD. The NIPD results showed 100% (49/49) concordance with those obtained through IPD. Two families with copy number variation and recombination were also successfully identified. Sufficient specific informative single-nucleotide polymorphisms for haplotyping, as well as the fetal cell-free DNA concentration and sequencing depth, are prerequisites for RHDO-based NIPD. This method has the merits of covering the entire genes of GJB2 and SLC26A4, qualifying for copy number variation and recombination analysis with remarkable sensitivity and specificity. Therefore, it has clinical potential as an alternative to traditional IPD for ARNSHL.

Hereditary deafness carrier screening in 9,993 Chinese individuals

Background: Preconception or prenatal carrier screening plays an important role in reproductive decision-making, but current research on hereditary deafness is limited. This study aimed to investigate the carrier frequencies of common deafness genes in the Chinese population who underwent carrier screening and to follow up on pregnancy outcomes in high-chance couples. Methods: Individual females or couples in preconception or early pregnancy were recruited from two hospitals in China. Carrier screening for common deafness genes in the Chinese population, including the GJB2 and SLC26A4 genes, was performed using next-generation sequencing technology. Genetic counseling was provided to subjects before and after testing. Results: Of the 9,993 subjects screened, the carrier rate was 2.86% for the GJB2 gene and 2.63% for the SLC26A4 gene. The variant with the highest carrier frequency in GJB2 was c.235delC (1.89%), and c.919-2A>G (1.08%) in SLC26A4. Of the six high-chance couples, four made alternative reproductive decisions (three with prenatal diagnosis and one with preimplantation genetic testing), with consequent termination of the birth of two affected fetuses. Conclusion: These findings confirmed the clinical utility of preconception or prenatal carrier screening for hereditary deafness.

Analysis of deafness susceptibility gene of neonates in northern Guangdong, China

This study aimed to explore the molecular epidemiology characteristics of deafness susceptibility genes in neonates in northern Guangdong and provide a scientific basis for deafness prevention and control. A total of 10,183 neonates were recruited between January 2018 and December 2022 at Yuebei People's Hospital. Among these, a PCR hybridization screening group of 8276 neonates was tested for four deafness genes: GJB2, SLC26A4, mtDNA, and GJB3 by PCR hybridization. Another group used next-generation sequencing (NGS) to detect genetic susceptibility genes in 1907 neonates. In PCR hybridization screening group, 346 (4.18%) of 8276 neonates were found to be carriers of the deafness gene. Among these, 182 (2.2%) had GJB2 variants, 114 (1.38%) had SLC26A4 variants, 35 (0.42%) had mtDNA variants, and 15 (0.18%) had GJB3 variants. In NGS Screening Group, 195 out of 1907 neonates were found to be carriers of the deafness gene, with a positive rate of 10.22%. Among these, 137 (7.18%) had GJB2 variants, 41 (2.15%) had SLC26A4 variants, 11 (0.58%) had mtDNA variants, and 6 (0.31%) had GJB3 variants. The prevalence of deafness gene variants was high in Northern Guangdong Province. The most common gene for deafness was GJB2, followed by SLC26A4 and mtDNA. GJB3 variants are rare. Compared with PCR hybridization method, NGS technology can expand the screening scope and greatly improve the detection rate of deafness genes. The c.109G>A of GJB2 was found to occur at a high frequency, which should be considered. Therefore, it is important to conduct neonatal deafness gene screening to prevent and control hereditary deafness.

Analysis of SLC26A4 Gene in Individuals with Non Syndromic Hearing Impairment in Relation with GJB2 Associated Mutations

Background

Hearing Loss (HL) is the most common sensory disorder. HL commonly ranges from mild to severe. Persons with HL face difficulty in hearing conversations or sounds through one ear or both ears, which impacts one's ability to interact with others. Hence it is a communicable disorder that makes people socially isolated, lonely, and frustrated. HL in children severely affects language development. The people who are referred to as 'Deaf' with very little or no hearing capabilities, are considered as having profound hearing loss. More than 124 genes are causative for Non-Syndromic HL (NSHL) with varying inheritance, among which the SLC26A4 mutations are the second commonest cause of hereditary HL across the globe.

Methods

Samples from 70 NSHL patients were analyzed through Next-Generation Sequencing (NGS) and generated five pathogenic variants [N246fs (rs918684449), K564fs (rs746427774), F122fs, V239D (rs111033256), T721M (rs121908363)] each with frequency of 1.42%. Three missense variants [S399P (rs747431002), L597S (rs55638457), and G6V (rs111033423)] were reported under the "uncertain" category. All the collected samples were further genotyped to look for the possibility of having GJB2 and HL-associated mutations.

Results

Out of five SLC26A4 pathogenic mutations N246fs (rs918684449) and K564fs (rs746427774) were observed in samples which were positive for GJB2-HL associated candidate mutations [W24X (rs104894396), Q124X (rs397516874) and W77X (rs80338944)]. Similarly, pathogenic variants F122fs, V239D (rs111033256) and T721M (rs121908363) were observed in patient samples which were negative for GJB2-HL associated mutations.

Conclusion

Our data will expand the list of variants underlying NSHL and encourage further genotype SLC26A4 gene concerning the south Indian population with a large sample size.

Preventing autosomal-dominant hearing loss in Bth mice with CRISPR/CasRx-based RNA editing

CRISPR/RfxCas13d (CasRx) editing system can specifically and precisely cleave single-strand RNAs, which is a promising treatment for various disorders by downregulation of related gene expression. Here, we tested this RNA-editing approach on Beethoven (Bth) mice, an animal model for human DFNA36 due to a point mutation in Tmc1. We first screened 30 sgRNAs in cell cultures and found that CasRx with sgRNA3 reduced the Tmc1Bth transcript by 90.8%, and the Tmc1 wild type transcript (Tmc1+) by 44.3%. We then injected a newly developed AAV vector (AAV-PHP.eB) based CasRx into the inner ears of neonatal Bth mice, and we found that Tmc1Bth was reduced by 70.2% in 2 weeks with few off-target effects in the whole transcriptome. Consistently, we found improved hair cell survival, rescued hair bundle degeneration, and reduced mechanoelectrical transduction current. Importantly, the hearing performance, measured in both ABR and DPOAE thresholds, was improved significantly in all ages over 8 weeks. We, therefore, have validated the CRISPR/CasRx-based RNA editing strategy in treating autosomal-dominant hearing loss, paving way for its further application in many other hereditary diseases in hearing and beyond.

A novel missense variant in ESRRB gene causing autosomal recessive non-syndromic hearing loss: in silico analysis of a case

Background

Hereditary hearing loss (HHL) is a common heterogeneous disorder affecting all ages, ethnicities, and genders. The most common form of HHL is autosomal recessive non-syndromic hearing loss (ARNSHL), in which there is no genotype–phenotype correlation in the majority of cases. This study aimed to identify the genetic causes of hearing loss (HL) in a family with Iranian Azeri Turkish ethnicity negative for gap junction beta-2 (GJB2), gap junction beta-6 (GJB6), and mitochondrially encoded 12S rRNA (MT-RNR1) deleterious mutations.

Methods

Targeted genome sequencing method was applied to detect genetic causes of HL in the family. Sanger sequencing was employed to verify the segregation of the variant. Finally, we used bioinformatics tools and American College of Medical Genetics and Genomics/Association for Molecular Pathology (ACMG/AMP) guidelines to determine whether the detected variant might affect the corresponding protein or not.

Results

A novel homozygous missense mutation, c.499G>A (p.G167R), was identified in exon 5 of the ESRRB (estrogen-related receptor beta) gene. Healthy and affected family members confirmed the co-segregation of the variant with ARNSHL. Eventually, the variant's pathogenicity was confirmed by the in silico analysis and the ACMG/AMP guidelines.

Conclusion

The study suggests that the detected variant, c.499G>A, plays a crucial role in the development of ARNSHL, emphasizing the clinical significance of the ESRRB gene in ARNSHL patients. Additionally, it would be helpful for genetic counseling and clinical management of ARNSHL patients and providing preventive opportunities.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12920-022-01165-4.

Genetic Susceptibility Study of Chinese Sudden Sensorineural Hearing Loss Patients with Vertigo

OBJECTIVE

To investigate the genetic causes of sudden sensorineural hearing loss (SSNHL) patients in China. This study focused on analyzing variations of coding sequence of common genes related to deafness, revealing the molecular pathogenesis of sudden deafness from a genomics perspective, discovering molecular markers associated with the onset of deafness, and then supplying prevention to high-risk populations, classifying disease according to accurate etiology, and choosing a much more precision therapy.

METHODS

We retrospectively analyzed the clinical characteristics of 51 patients diagnosed as SSNHL with vertigo treated in the Chinese PLA General Hospital. In this study, mutation screening of 307 nuclear genes and mitochondrial genome responsible for human or mouse deafness was performed on the 51 cases of unilateral sudden deafness patients with vertigo.

RESULTS

We identified 51 cases of unilateral sudden deafness, including 2 cases of low-mid frequency hearing impairment, 18 cases of mid-high frequency hearing loss, 11 cases of flat-type hearing loss, and 20 cases of all frequency hearing loss. Among the 51 cases, 8 (15.69%) cases of GJB2 heterozygous variations, 1 (1.96%) case of GJB3 heterozygous variations, 5 (9.8%) cases of SLC26A4 heterozygous variations, 2 (3.92%) cases of COCH heterozygous variations, 14 (27.45%) cases of CDH23 heterozygous variations, 14 (27.45%) cases of OTOF heterozygous variations, 1 (1.96%) case of SLC17A8 heterozygous variations and 2 (3.92%) cases of KCNE1 heterozygous variations. No mtDNA gene variations were identified.

CONCLUSION

SSNHL has some relationship with hereditary in Chinese population, but its complex genetic pathogenic mechanisms need further study.

Evaluation of the GJB2 and GJB6 Polymorphisms with Autosomal Recessive Nonsyndromic Hearing Loss in Iranian Population

INTRODUCTION

Hearing loss (HL), with more than 100 gene loci, is the most common sensorineural defects in humans. The mutations in two GJB2 and GJB6 (Gap Junction Protein Beta 2, 6) genes are responsible for nearly 50% of autosomal recessive nonsyndromic hearing loss. The aim of the present study was to evaluate polymorphisms of 111C>T (rs7329857) and 337G>T (rs7333214) in GJB2 (encoding connexin 26) and GJB6 (encoding connexin 32) genes, respectively.

MATERIALS AND METHODS

In this study, 32 blood samples were obtained from Iranian patients with HL defect and 32 normal blood samples were prepared. After genomic deoxyribonucleic acid extraction, genotyping in rs7333214 and rs7329857 polymorphisms was conducted using tetra-amplification refractory mutation system-polymerase chain reaction and the obtained data were analyzed.

RESULTS

In this study, the prevalence rates of CC, CT, and TT genotypes in GJB2 gene were reported as 84.4%, 68.7%, and 0% in the affected subjects and 0%, 15.6%, and 31.3% in the control samples, respectively, which were statistically significant (P=0.004). In relation to GJB6 gene, the prevalence rates of GG, GT, and TT genotypes were 65.2%, 78.1%, and 25% in the control subjects and 21.9%, 9.4%, and 0% in the affected samples, respectively, which were not statistically significant (P>0.05).

CONCLUSION

The results of this study revealed that 111C>T polymorphism in GJB2 gene was involved in the incidence of HL in the studied population and could be suggested as a prognostic factor in genetic counseling before marriage and pregnancy.

A multiplex PCR amplicon sequencing assay to screen genetic hearing loss variants in newborns

BACKGROUND

Congenital hearing loss is one of the most common birth defects. Early identification and management play a crucial role in improving patients' communication and language acquisition. Previous studies demonstrated that genetic screening complements newborn hearing screening in clinical settings.

METHODS

We developed a multiplex PCR amplicon sequencing assay to sequence the full coding region of the GJB2 gene, the most pathogenic variants of the SLC26A4 gene, and hotspot variants in the MT-RNR1 gene. The sensitivity, specificity, and reliability were validated via samples with known genotypes. Finally, a pilot study was performed on 300 anonymous dried blood samples.

RESULTS

Of 103 samples with known genotypes, the multiplex PCR amplicon sequencing assay accurately identified all the variants, demonstrating a 100% sensitivity and specificity. The consistency is high in the analysis of the test-retest reliability and internal consistency reliability. In the pilot study, 12.3% (37/300) of the newborns were found to carry at least one pathogenic variant, including 24, 10, and 3 from the GJB2, SLC26A4, and MT-RNR1 gene, respectively. With an allele frequency of 2.2%, the NM_004004.6(GJB2):c.109G>A was the most prevalent variant in the study population.

CONCLUSION

The multiplex PCR amplicon sequencing assay is an accurate and reliable test to detect hearing loss variants in the GJB2, SLC26A4, and MT-RNR1 genes. It can be used to screen genetic hearing loss in newborns.

Low penetrance of hearing loss in two Chinese families carrying the mitochondrial tRNASer(UCN) mutations

Mutations in mitochondrial DNA (mtDNA), especially in mitochondrial 12S rRNA and transfer RNA(tRNA)^Ser(UCN) genes, are important causes of non-syndromic hearing loss. However, the molecular mechanism underlying mt-tRNA mutations in clinical hearing impairment are not fully understood. The present study assessed the molecular characterization of two Chinese families with non-syndromic hearing loss, who both exhibited very low penetrance of deafness (9.1 and 12.5% for Family 1 and 2, respectively). Mutational analysis of the complete mtDNA genes identified the presence of cytochrome c oxidase 1/tRNA^Ser(UCN) G7444A and tRNA^Ser(UCN) C7492T mutations, together with polymorphisms belonging to human mitochondrial haplogroup D4 and G2b, respectively. Moreover, the G7444A and C7492T mutations occurred at highly conserved tRNA^Ser(UCN) nucleotides and may cause tRNA metabolism failure, which is involved in mitochondrial translation defects. Therefore, the G7444A and C7492T mutations may lead to the mitochondrial dysfunction that responsible for deafness. However, the absence of any functional variants in Gap junction β-2, Solute Carrier Family 26 Member 4 and TRNA 5-methylaminomethyl-2-thiouridylate methyltransferase suggested that nuclear genes may not play active roles in the occurrence of deafness. In the present study, the observed incomplete penetrance of hearing loss and mild mitochondrial dysfunction indicated that mtDNA G7444A and C7492T mutations are insufficient to produce the deafness phenotype. Therefore, other risk factors such as environmental factors and epigenetic regulation may be involved in the pathogenesis of hearing loss in the families recruited in the present study.

Identification of six novel variants in Waardenburg syndrome type II by next-generation sequencing

Background

Waardenburg syndrome (WS) is a dominantly inherited, genetically heterogeneous auditory‐pigmentary syndrome characterized by nonprogressive sensorineural hearing loss and iris discoloration. This study aimed to investigate the underlying molecular pathology in Chinese WS families.

Methods

A total of 13 patients with Waardenburg syndrome type II (WS2) from six unrelated Chinese families were enrolled. We investigated the mutation profile of genes related to congenital deafness in these families through a targeted sequencing technology and validated the candidate variants by Sanger sequencing.

Results

We identified six novel variants in microphthalmia‐associated transcription factor (MITF) and SRY‐box 10 (SOX10), which were predicted to be disease causing by in silico analysis. Our results showed that mutations in SOX10 and MITF are two major causes of deafness associated with WS, and de novo mutations were frequently found in probands with SOX10 mutations but not in those with MITF mutations.

Conclusion

Results showed that targeted next‐generation sequencing (NGS) enabled us to detect disease‐causing mutations with high accuracy, stability, speed and throughput. Our study extends the pathogenic mutation spectrum of MITF and SOX10.

Association of Racial/Ethnic Categories With the Ability of Genetic Tests to Detect a Cause of Cardiomyopathy

Importance

Individuals of all races/ethnicities have a fundamental right to access health care and benefit from advances in science and medicine, including genetic testing.

Objective

To determine whether detection rates for cardiomyopathy genetic testing differed between white people, Asian people, and underrepresented minorities (individuals of black, Hispanic, Native American, Alaskan Native, or Pacific Islander descent).

Design, Setting, and Participants

We conducted a cross-sectional analysis of the genetic panel test results of 5729 probands who had a suspected diagnosis or family history of cardiomyopathy and who had been referred for testing between October 2003 and December 2017. Testing was performed at the Laboratory for Molecular Medicine at Partners Personalized Medicine in Cambridge, Massachusetts. Results were stratified into 3 categories of self-reported race/ethnicity: white, Asian, and underrepresented minorities.

Main Outcomes and Measures

The primary outcome was whether a pathogenic or likely pathogenic variant was identified that explained the features or family history of cardiomyopathy. A secondary outcome was the number of test results that were inconclusive because of the presence of 1 or more variants of uncertain significance in the absence of an explanation for cardiomyopathy features or family history.

Results

A total of 5729 probands were studied (of whom 3523 [61.5%] were male). Of these, 4539 (79.2%) were white, 348 (6.1%) were Asian individuals, and 842 (14.7%) were underrepresented minorities. Positive detection occurred in 1314 white individuals (29.0%) compared with 155 underrepresented minorities (18.4%; χ21 = 39.8; P < .001) and 87 Asian individuals (25.0%; χ21 = 2.5; P = .12). Inconclusive results were found in 1115 white individuals (24.6%) compared with 335 underrepresented minorities (39.8%; χ21 = 83.6; P < .001) and 136 Asian individuals (39.2%; χ21 = 35.8; P < .001).

Conclusions and Relevance

These results show a significantly higher positive detection rate and a significantly lower rate of inconclusive results in white individuals in comparison with underrepresented minorities. This suggests greater clinical usefulness of genetic testing for cardiomyopathy in white persons in comparison with people of other racial/ethnic groups. This clear disparity warrants further study to understand the gaps in usefulness, which may derive from a lack of clinical testing and research in underrepresented minority populations, in the hopes of improving genetic testing outcomes for cardiomyopathy in nonwhite groups.

Proband Whole-Exome Sequencing Identified Genes Responsible for Autosomal Recessive Non-Syndromic Hearing Loss in 33 Chinese Nuclear Families

Autosomal recessive non-syndromic hearing loss (ARNSHL) is a highly heterogeneous disease involving more than 70 pathogenic genes. However, most ARNSHL families have small-sized pedigrees with limited genetic information, rendering challenges for the molecular diagnosis of these patients. Therefore, we attempted to establish a strategy for identifying deleterious variants associated with ARNSHL by applying proband whole-exome sequencing (proband-WES). Aside from desiring to improve molecular diagnostic rates, we also aimed to search for novel deafness genes shared by patients with similar phenotype, making up for the deficiency of small ARNSHL families. In this study, 48.5% (16/33) families were detected the pathogenic variants in eight known deafness genes, including 10 novel variants identified in TMPRSS3 (MIM 605551), MYO15A (MIM 602666), TMC1 (MIM 606706), ADGRV1 (MIM 602851), and PTPRQ (MIM 603317). Apart from six novel variants with a truncating effect (nonsense, deletion, insertion, and splice-site), four novel missense variants were not found in 200 unrelated control population by using Sanger sequencing. It is important to note that none of novel genes were shared across different pedigrees, indicating that a larger sample size might be needed. Proband-WES is a cost-effective and precise way of identifying causative variants in nuclear families with ARNSHL. This economical strategy may be appropriated as a clinical application to provide molecular diagnostics, genetic counseling, and individualized health maintenance measures for patients with ARNSHL at hearing clinics.

Reproductive guidance through prenatal diagnosis and genetic counseling for recessive hereditary hearing loss in high-risk families

OBJECTIVE

To evaluate the accuracy and validity of our protocol for prenatal diagnosis and genetic counseling in high-risk families at a clinic.

METHODS

Fifteen unrelated families with recessive nonsyndromic hearing loss (NSHL) in their family history and a positive attitude towards prenatal diagnosis were recruited in the present study. According to genetic information for each family, Sanger sequencing, fluorescence polymerase chain reaction (PCR)-based congenital deafness gene detection kit and multiple PCR-based target gene capture and high-throughput sequencing were used. Genetic counseling was offered to all participating families by genetic counselors and otologists. Prenatal diagnosis was provided to families with detected pathogenic mutations and who were expected to participate in subsequent prenatal diagnosis.

RESULTS

In this study, confirmed pathogenic mutations were detected in eight families, who were defined as high-risk families. These families all participated in prenatal diagnosis with positive attitudes. One novel variant (c.1687dupA) in the SLC264 gene was detected in a family. Through genetic counseling, the recurrence probability of NSHL in fetuses was 25% in six families, 0% in one family, and 50% in one family. The results of fetal DNA detection showed that one fetal variant was wild type, three were heterozygous mutations in SLC26A4, and one was a compound heterozygous mutation in SLC26A4. Two variants were heterozygous mutations in GJB2, and one was a homozygous mutation in GJB2. According to the test results for fetal DNA, prenatal diagnosis found that six fetuses had normal hearing, whereas two fetuses suffered from NSHL. After birth, six infants predicted to have normal hearing passed a newborn hearing screening test and two infants predicted to have NSHL were diagnosed with NSHL and received cochlear implants.

CONCLUSION

Our protocol for prenatal diagnosis and genetic counseling provides detailed information that can assist couples in high-risk families in preparing for infant arrival and future family planning. For the affected neonates, prenatal diagnosis and genetic counseling achieve an "early screening, early diagnosis, early intervention" strategy.

X-Linked Sensorineural Hearing Loss: A Literature Review

Sensorineural hearing loss is a very diffuse pathology (about 1/1000 born) with several types of transmission. X-linked hearing loss accounts for approximately 1% - 2% of cases of non-syndromic forms, as well as for many syndromic forms. To date, six loci (DFNX1-6) and five genes (PRPS1 for DFNX1, POU3F4 for DFNX2, SMPX for DFNX4, AIFM1 for DFNX5 and COL4A6 for DFNX6) have been identified for X-linked non-syndromic hearing loss. For the syndromic forms, at least 15 genes have been identified, some of which are also implicated in non-syndromic forms. Moreover, some syndromic forms, presenting large chromosomal deletions, are associated with mental retardation too. This review presents an overview of the currently known genes related to X-linked hearing loss with the support of the most recent literature. It summarizes the genetics and clinical features of X-linked hearing loss to give information useful to realize a clear genetic counseling and an early diagnosis. It is important to get an early diagnosis of these diseases to decide the investigations to predict the evolution of the disease and the onset of any other future symptoms. This information will be clearly useful for choosing the best therapeutic strategy. In particular, regarding audiological aspects, this review highlights risks and benefits currently known in some cases for specific therapeutic intervention.

Noninvasive and Accurate Detection of Hereditary Hearing Loss Mutations with Buccal Swab Based on Droplet Digital PCR

Hereditary hearing loss is a common clinical neurosensory disorder in humans and has a high demand for genetic screening. Current screening techniques using peripheral blood or dried blood spots (DBSs) are invasive. Therefore, this study aims to develop a noninvasive and accurate detection method for eight hotspot deafness-associated mutations based on buccal swab and droplet digital PCR (ddPCR). First, this method was evaluated for analytic performance including specificity, detection limit, dynamic range using plasmid DNA. The specificity was 100% and the detection limit was 5 copies. The dynamic range of this ddPCR-based method was from 10 to 10⁵ copies/μL. Next, the method was found to accurately quantify mitochondrial gene heteroplasmy rate as low as 1% for both m.1494C > T and m.1555A > G sites. Then, we demonstrated that buccal swab was a reliable sample. DNA can be extracted and accurately quantified after a buccal swab had been stored for 90 days at either room temperature or -20 °C. Finally, clinical samples (23 DBSs and 42 buccal swabs) were tested to further evaluate the accuracy and clinical applicability of this method. All clinical samples were accurately quantified and genotyped. This noninvasive and accurate method is highly promising as a genetic screening method for deafness-associated mutations due to its high sensitivity and accuracy.

Frequency of mitochondrial m.1555A > G mutation in Syrian patients with non-syndromic hearing impairment

Background

Mitochondrial maternally inherited hearing impairment (HI) appears to be increasing in frequency. The incidence of mitochondrial defects causing HI is estimated to be between 6 and 33% of all hearing deficiencies. Mitochondrial m.1555A > G mutation is the first mtDNA mutation associated with non-syndromic sensorineural deafness and also with aminoglycoside induced HI. Its prevalence varied geographically between different populations.

Methods

We carried out PCR, restriction enzyme based screening, and sequencing of 337 subjects (including 132 patients diagnosed clinically with hereditary deafness) from 54 families from Syria for m.1555A > G mitochondrial mutation.

Results

Mitochondrial m.1555A > G mutation was detected in one of fifty-four families (1.85%), six out of the 132 (4.5%) of all patients with NSHI and one propositus of the 205 individuals with normal hearing (0.48%).

Conclusion

This is the first study to report prelingual deafness causative gene mutations identified by sequencing technology in Syrian families. It is obvious from the results that the testing for the m.1555A > G mutation is useful for diagnosis of hearing loss in Syrian patients and should also be considered prior to treatment with aminoglycosides in predisposed individuals.

Efficiency of microarray and SNPscan for the detection of hearing loss gene in 71 cases with nonsyndromic hearing loss

We aim to screen the mutations of 3 hearing loss (HL) genes (GJB2, SLC26A4, and 12S rRNA) in 71 cases with nonsyndromic hearing loss (NSHL) using microarray and SNPscan, and identify the roles of nonhotspot mutation of these genes in the screening of NSHL. Seventy-one cases with moderate or severe neurosensory deafness confirmed in our department from July 2014 to December 2015 including 25 Uyghur minorities and 46 Han Chinese were included in this study. The type of mutations in GJB2, SLC26A4, and 12S rRNA genes were detected using microarray and SNPscan, respectively. Statistical difference was noticed in the detection rate of the HL genes in 71 cases. Using microassay, deafness genes were identified in 10 subjects (14.08%), while 22 cases (30.98%) were confirmed with the presence of deafness genes using the SNPscan. Compared with the microarray, remarkable difference was noticed in the detection rate of SNPscan (P < .05). Nonhotspot mutation in GJB2, SLC26A4, and 12S rRNA genes played a crucial role in the pathogenesis of NSHL. SNPscan contributed to elevation of detection rate of NSHL in clinical practice.

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

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

A quantitative cSMART assay for noninvasive prenatal screening of autosomal recessive nonsyndromic hearing loss caused by GJB2 and SLC26A4 mutations

PurposeThe aim of this study was to assess the performance of a noninvasive prenatal screening (NIPS) assay for accurate fetal genotyping of pregnancies at genetic risk for autosomal recessive nonsyndromic hearing loss (ARNSHL).MethodsA total of 80 pregnant couples carrying known mutations in either the GJB2 or SLC26A4 genes associated with a risk for ARNSHL were recruited to the study. Fetal amniocyte samples were genotyped by invasive prenatal screening (IPS), whereas the cell-free fetal DNA present in maternal plasma samples was genotyped using a novel NIPS method based on circulating single-molecule amplification and resequencing technology (cSMART).ResultsIPS of the 80 at-risk pregnancies identified 20 normal homozygote, 42 heterozygote, 5 affected homozygote, and 13 affected compound heterozygote fetuses. Benchmarking against IPS, 73 of 80 fetuses (91.3%) were correctly genotyped by the cSMART NIPS assay. A low fetal DNA fraction (<6%) was identified as the main contributing factor in five of seven discordant NIPS results. At fetal DNA fractions >6%, the sensitivity and specificity of the cSMART assay for correctly diagnosing ARNSHL were 100 and 96.5%, respectively.ConclusionBased on key performance indicators, the cSMART NIPS assay has clinical potential as an alternative to traditional IPS of ARNSHL.

Rapid and Reliable Detection of Nonsyndromic Hearing Loss Mutations by Multicolor Melting Curve Analysis

Hearing loss is a common birth defect worldwide. The GJB2, SLC26A4, MT-RNR1 and MT-TS1 genes have been reported as major pathogenic genes in nonsyndromic hearing loss. Early genetic screening is recommended to minimize the incidence of hearing loss. We hereby described a multicolor melting curve analysis (MMCA)-based assay for simultaneous detection of 12 prevalent nonsyndromic hearing loss-related mutations. The three-reaction assay could process 30 samples within 2.5 h in a single run on a 96-well thermocycler. Allelic types of each mutation could be reproducibly obtained from 10 pg ~100 ng genomic DNA per reaction. For the mitochondrial mutations, 10% ~ 20% heteroplasmic mutations could be detected. A comparison study using 501 clinical samples showed that the MMCA assay had 100% concordance with both SNaPshot minisequencing and Sanger sequencing. We concluded that the MMCA assay is a rapid, convenient and cost-effective method for detecting the common mutations, and can be expectedly a reliable tool in preliminary screening of nonsyndromic hearing loss in the Chinese Han population.

Polymorphism of the 86th amino acid in CX26 protein and hereditary deafness

Objective

To investigate the membrane localization function of the CX26 protein when its 86th amino acid is Thr, Ser or Arg, and its relations to deafness.

Methods

CX26-GFP protein with either Thr, Ser or Arg as the 86th amino acid was expressed in mouse SGN cells via the GFP fusion type lenti-virus expression system. The membrane localization of the fusion protein was observed under a fluorescence microscope.

Results

The mutated protein of CX26 T86S was localized to cell membrane and form gap conjunction structures, showing no difference to the wild type CX26 protein (with Thr as the 86th amino acid). However, the gap conjunction structure disappeared when the mutation was CX26 T86A.

Conclusion

These results indicate that the CX26 T86R mutation may be a cause of hearing loss, but CX26 T86S as a non-pathogenic polymorphism mutation does not affect functions of the CX26 protein. The results are in accordance with the results of clinical screening.

Characterization of ATPase Activity of P2RX2 Cation Channel

P2X purinergic receptors are plasma membrane ATP-dependent cation channels that are broadly distributed in the mammalian tissues. P2RX2 is a modulator of auditory sensory hair cell mechanotransduction and plays an important role in hair cell tolerance to noise. In this study, we demonstrate for the first time in vitro and in cochlear neuroepithelium, that P2RX2 possesses the ATPase activity. We observed that the P2RX2 V60L human deafness mutation alters its ability to bind ATP, while the G353R has no effect on ATP binding or hydrolysis. A non-hydrolysable ATP assay using HEK293 cells suggests that ATP hydrolysis plays a significant role in the opening and gating of the P2RX2 ion channel. Moreover, the results of structural modeling of the molecule was in agreement with our experimental observations. These novel findings suggest the intrinsic ATPase activity of P2RX2 and provide molecular insights into the channel opening.

Genetics of Nonsyndromic Congenital Hearing Loss

Congenital hearing impairment affects nearly 1 in every 1000 live births and is the most frequent birth defect in developed societies. Hereditary types of hearing loss account for more than 50% of all congenital sensorineural hearing loss cases and are caused by genetic mutations. HL can be either nonsyndromic, which is restricted to the inner ear, or syndromic, a part of multiple anomalies affecting the body. Nonsyndromic HL can be categorised by mode of inheritance, such as autosomal dominant (called DFNA), autosomal recessive (DFNB), mitochondrial, and X-linked (DFN). To date, 125 deafness loci have been reported in the literature: 58 DFNA loci, 63 DFNB loci, and 4 X-linked loci. Mutations in genes that control the adhesion of hair cells, intracellular transport, neurotransmitter release, ionic hemeostasis, and cytoskeleton of hair cells can lead to malfunctions of the cochlea and inner ear. In recent years, with the increase in studies about genes involved in congenital hearing loss, genetic counselling and treatment options have emerged and increased in availability. This paper presents an overview of the currently known genes associated with nonsyndromic congenital hearing loss and mutations in the inner ear.

Mitochondrial DNA deletions in patients with chronic suppurative otitis media

The aim of this study was to investigate the 4977 and 7400 bp deletions of mitochondrial DNA in patients with chronic suppurative otitis media and to indicate the possible association of mitochondrial DNA deletions with chronic suppurative otitis media. Thirty-six patients with chronic suppurative otitis media were randomly selected to assess the mitochondrial DNA deletions. Tympanomastoidectomy was applied for the treatment of chronic suppurative otitis media, and the curettage materials including middle ear tissues were collected. The 4977 and 7400 bp deletion regions and two control regions of mitochondrial DNA were assessed by using the four pair primers. DNA was extracted from middle ear tissues and peripheral blood samples of the patients, and then polymerase chain reactions (PCRs) were performed. PCR products were separated in 2 % agarose gel. Seventeen of 36 patients had the heterozygote 4977 bp deletion in the middle ear tissue but not in peripheral blood. There wasn't any patient who had the 7400 bp deletion in mtDNA of their middle ear tissue or peripheral blood tissue. The patients with the 4977 bp deletion had a longer duration of chronic suppurative otitis media and a higher level of hearing loss than the others (p < 0.01). Long time chronic suppurative otitis media and the reactive oxygen species can cause the mitochondrial DNA deletions and this may be a predisposing factor to sensorineural hearing loss in chronic suppurative otitis media. An antioxidant drug as a scavenger agent may be used in long-term chronic suppurative otitis media.

Cordblood-Based High-Throughput Screening for Deafness Gene of 646 Newborns in Jinan Area of China

Objectives

Infants with slight/mild or late-onset hearing impairment might be missed in universal newborn hearing screening (UNHS). We identified the mutation hot spot of common deaf gene in the newborns in Jinan area population by screening the mutation spot with neonate cord blood, in order to make clear whether the neonate cord blood for screening is feasible.

Methods

Six hundred and forty-six newborns were subjected to both UNHS and genetic screening for deafness by using neonate cord blood. The newborn genetic screening targeted four deafness-associated genes, which were commonly found in the Chinese population including gap junction beta-2 protein (GJB2), gap junction beta-3 protein (GJB3), solute carrier family 26 member 4 (SLC26A4), and mtDNA 12S rRNA. The most common 20 spot mutations in 4 deaf genes were detected by MassARRAY iPLEX platform and mitochondrial 12S rRNA A1555G and C1494T mutations were sequenced using Sanger sequencing.

Results

Among the 646 newborns, 635 cases passed the UNHS and the other 11 cases (1.7%) did not. Of the 11 failures, two cases were found to carry homozygous GJB2 p.R143W pathogenic mutation, one case was found to have heterozygous GJB2 235delC mutation, and another one case carried heterozygous GJB3 p.R180X pathogenic mutation. Six hundred and thirty-five babies passed the newborn hearing screening, in which 25 babies were identified to carry pathogenic mutations, including 12 heterozygotes (1.9%) for GJB2 235delC, eight heterozygotes (1.3%) for SLC26A4 IVS7-2A>G, one heterozygote (0.2%) for p.R409H, two homozygotes (0.3%) for m.1494C>T, and two homozygotes (0.3%) for m.1555A>G.

Conclusion

Newborn genetic screening through the umbilical cord blood for common deafness-associated mutations may identify carriers sensitive to aminoglycoside antibiotic, and can effectively prevent or delay hearing loss occurs.

Identification of a Novel De Novo Variant in the PAX3 Gene in Waardenburg Syndrome by Diagnostic Exome Sequencing: The First Molecular Diagnosis in Korea

Waardenburg syndrome (WS) is a clinically and genetically heterogeneous hereditary auditory pigmentary disorder characterized by congenital sensorineural hearing loss and iris discoloration. Many genes have been linked to WS, including PAX3, MITF, SNAI2, EDNRB, EDN3, and SOX10, and many additional genes have been associated with disorders with phenotypic overlap with WS. To screen all possible genes associated with WS and congenital deafness simultaneously, we performed diagnostic exome sequencing (DES) in a male patient with clinical features consistent with WS. Using DES, we identified a novel missense variant (c.220C>G; p.Arg74Gly) in exon 2 of the PAX3 gene in the patient. Further analysis by Sanger sequencing of the patient and his parents revealed a de novo occurrence of the variant. Our findings show that DES can be a useful tool for the identification of pathogenic gene variants in WS patients and for differentiation between WS and similar disorders. To the best of our knowledge, this is the first report of genetically confirmed WS in Korea.

Identification of a novel homozygous mutation, TMPRSS3: c.535G>A, in a Tibetan family with autosomal recessive non-syndromic hearing loss

Different ethnic groups have distinct mutation spectrums associated with inheritable deafness. In order to identify the mutations responsible for congenital hearing loss in the Tibetan population, mutation screening for 98 deafness-related genes by microarray and massively parallel sequencing of captured target exons was conducted in one Tibetan family with familiar hearing loss. A homozygous mutation, TMPRSS3: c.535G>A, was identified in two affected brothers. Both parents are heterozygotes and an unaffected sister carries wild type alleles. The same mutation was not detected in 101 control Tibetan individuals. This missense mutation results in an amino acid change (p.Ala179Thr) at a highly conserved site in the scavenger receptor cysteine rich (SRCR) domain of the TMPRSS3 protein, which is essential for protein-protein interactions. Thus, this mutation likely affects the interactions of this transmembrane protein with extracellular molecules. According to our bioinformatic analyses, the TMPRSS3: c.535G>A mutation might damage protein function and lead to hearing loss. These data suggest that the homozygous mutation TMPRSS3: c.535G>A causes prelingual hearing loss in this Tibetan family. This is the first TMPRSS3 mutation found in the Chinese Tibetan population.

Combination of hearing screening and genetic screening for deafness-susceptibility genes in newborns

The aim of this study was to determine the clinical significance of the results of screening of newborn hearing and the incidence of deafness-susceptibility genes. One thousand newborn babies in the Handan Center Hospital (Handan, China) underwent screening of hearing and deafness-susceptibility genes. The first screening test was carried out using otoacoustic emissions (OAEs). Babies with hearing loss who failed to pass the initial screening were scheduled for rescreening at 42 days after birth. Cord blood was used for the screening of deafness-susceptibility genes, namely the GJB2, SLC26A4 and mitochondrial 12S rRNA (MTRNR1) genes. Among the 1,000 neonates that underwent the first hearing screening, 25 exhibited left-sided hearing loss, 21 exhibited right-sided hearing loss and 15 cases had binaural hearing loss. After rescreening 42 days later, only one of the initial 61 cases exhibited hearing loss under OAE testing. The neonatal deafness gene tests showed two cases with 1555A>G mutation and two cases with 1494C>T mutation of the MTRNR1 gene. In the SLC26A4 gene screening, four cases exhibited the heterozygous IVS7-2A>G mutation and one case exhibited heterozygous 1226G>A mutation. In the GJB2 gene screening, two cases exhibited the homozygous 427C>T mutation and 10 exhibited the heterozygous 235delC mutation. The genetic screening revealed 21 newborns with mutations in the three deafness-susceptibility genes. The overall carrier rate was 2.1% (21/1,000). The association of hearing and gene screening may be the promising screening strategy for the diagnosis of hearing loss.

Newborn genetic screening for high risk deafness-associated mutations with a new Tetra-primer ARMS PCR kit

OBJECTIVE

Previous epidemiological studies indicate that GJB2, SLC26A4 or mtDNA 12S rRNA mutations were chiefly responsible for the hearing loss in children. A cost-effective method for screening deafness-associated mutations at early age is needed. This study aimed to develop a simple kit for screening of high risk deafness-associated mutations in newborns using tetra-primer amplification refractory mutation system PCR.

METHODS

The screening kit was designed to detect high risk deafness-associated mutations (GJB2 c.235delC, SLC26A4 c.919-2A>G, mtDNA 12S rRNA mt.1555A>G and mt.1494C>T). The kit was able to amplify both wild-type and mutant alleles with a control fragment. The proposed method was conducted to genotype the above four deafness gene mutations in four PCR reactions. Each mutation was genotyped by a set of four primers, two allele-specific inner primers, and two common outer primers. A mismatch at the penultimate or antepenult nucleotide of the 3' terminus was introduced in order to maximize specificity. The 16 primers were used for the amplification of genomic DNA as a template. Amplified fragments were separated by electrophoresis. We designed and validated the kit with wild and mutant type DNA samples that had been previously been confirmed by Sanger sequencing. Then 1181 newborns were enrolled, and those samples with mutations were further validated with sequencing too.

RESULTS

Among 1181 newborns, 29 individuals had one or two mutant alleles, with the carrier rate being 2.46% (29/1181). For GJB2 c.235delC mutation, one case was homozygote and 12 cases were heterozygote carriers. For SLC26A4 c.919-2A>G mutation, 12 cases were heterozygotes carriers, and no homozygotes were found; for mtDNA 12S rRNA mt.1555A>G mutation, one case was identified; three cases of mtDNA 12S rRNA mt.1494C>T mutation were detected. All mutations were detected with high specificity. Mutation samples were confirmed via Sanger sequencing. No false positive was found.

CONCLUSION

A user-friendly screening kit for deafness-associated mutations was successfully developed. It provided rapid, reproducible, and cost-effective detection of deafness gene mutation without special equipment. The kit allowed the detection of the four high risk deafness-associated mutations with only 4 single tube PCR reactions. In the future, the kit could be applied to large population-based epidemiological studies for newborn hearing defects screening.

Novel mutations of SLC26A4 in Chinese patients with nonsyndromic hearing loss

CONCLUSIONS

This study demonstrated high prevalence of GJB2, SLC26A4, and mtDNA A1555G mutations in Chinese patients with nonsyndromic hearing loss and discovered eight novel mutations in SLC26A4. Most of these novel mutations were predicted pathogenic variants.

OBJECTIVES

Nonsyndromic hearing loss is the most common neurosensory deafness where the majority of patients have highly diversified genetic defects. This study aimed to define the genetic profile of deafness in a Chinese population with potential to discover novel mutations.

METHODS

A total of 227 segregating deaf students and 200 individuals with normal hearing were enrolled. With the Sanger sequencing chemistry, direct sequencing was performed on entire coding regions of GJB2, GJB3, SLC26A4, and mtDNA m.C1494T and m.A1555G.

RESULTS

Direct sequencing analysis revealed that 53 (23.35%) of 227 patients carried at least 1 mutant allele in GJB2, 40 (17.62%) patients in SLC26A4, 5 (2.20%) patients in mtDNA A1555G, and 1 (0.44%) patient in mtDNA C1494T mutations. Four patients carried three unclassified mutations in GJB3 genes. Overall 38 mutant variants were detected in this cohort of patients, including 8 novel mutations in SLC26A4. The eight novel variants were six missense substitutions (p.V163L, p.G222S, p.A456D, p.N457I, p.C466Y, p.F667L), one nonsense mutation (p.W472X), and one frameshift (p.Asn612Ilefs×23).

Targeted massive parallel sequencing: the effective detection of novel causative mutations associated with hearing loss in small families

Background

Hereditary hearing loss is one of the most common heterogeneous disorders, and genetic variants that can cause hearing loss have been identified in over sixty genes. Most of these hearing loss genes have been detected using classical genetic methods, typically starting with linkage analysis in large families with hereditary hearing loss. However, these classical strategies are not well suited for mutation analysis in smaller families who have insufficient genetic information.

Methods

Eighty known hearing loss genes were selected and simultaneously sequenced by targeted next-generation sequencing (NGS) in 8 Korean families with autosomal dominant non-syndromic sensorineural hearing loss.

Results

Five mutations in known hearing loss genes, including 1 nonsense and 4 missense mutations, were identified in 5 different genes (ACTG1, MYO1F, DIAPH1, POU4F3 and EYA4), and the genotypes for these mutations were consistent with the autosomal dominant inheritance pattern of hearing loss in each family. No mutational hot-spots were revealed in these Korean families.

Conclusion

Targeted NGS allowed for the detection of pathogenic mutations in affected individuals who were not candidates for classical genetic studies. This report is the first documenting the effective use of an NGS technique to detect pathogenic mutations that underlie hearing loss in an East Asian population. Using this NGS technique to establish a database of common mutations in Korean patients with hearing loss and further data accumulation will contribute to the early diagnosis and fundamental therapies for hereditary hearing loss.

Mitochondrial DNA mutation screening in an ethnically diverse nonsyndromic deafness cohort

Deafness is a heterogeneous trait with many known genetic and environmental causes. Hereditary hearing loss is an extremely common disorder in the general population. Mutations in mitochondrial DNA (mtDNA) are known to be associated with nonsyndromic deafness (NSD) and syndromic deafness. The objective of this article is to investigate the frequency of common mitochondrial mutations (A1555G, G7444A, and A3243G) in an ethnically diverse cohort of probands with NSD from South Florida. These patients were ascertained at the University of Miami. Polymerase chain reaction-restriction fragment length polymorphism analysis and direct sequencing methods were used for mutation screening in a cohort of 217 patients with NSD. The frequency of common mitochondrial mutations is 1.84% (4/217) in this cohort. A1555G and G7444A accounted for four patients with NSD. Our mutation frequencies are comparable with those previously reported in other populations, indicating that mutations in mtDNA are an important cause of NSD in our patient cohort.

Genetic diagnosis and cochlear implantation for patients with nonsyndromic hearing loss and enlarged vestibular aqueduct

Objective:

To review the genotype and cochlear implantation outcome of patients with nonsyndromic hearing loss and enlarged vestibular aqueduct.

Methods:

Twenty-one Chinese children with nonsyndromic hearing loss and enlarged vestibular aqueduct underwent genetic examination. A DNA microarray was used to screen for the IVS7-2A>G and H723R mutations. Any DNA samples with one or none of the two mutant alleles were sequenced to detect other mutations in the SLC26A4 and FOXI1 genes.

Results:

Twelve SLC26A4 mutations were detected, including three novel mutations. The most common mutations detected were IVS7-2A>G and H723R. Twelve patients received cochlear implants, and subsequently demonstrated excellent speech perception.

Conclusion:

Three novel mutations were detected in Chinese patients with nonsyndromic hearing loss and enlarged vestibular aqueduct. The SLC26A4 mutation spectrum in the Chinese population is similar to that in other East Asian populations. Cochlear implantation is a safe and effective treatment in patients with enlarged vestibular aqueduct.

Genetics of hearing loss: where are we standing now?

Hearing loss (HL) is the most common sensory impairment and is caused by a broad range of inherited to environmental causes. Inherited HL consists 50-60% of all HL cases. The inherited form of HL is further classified to different categories. More than 300 syndromes and 40 genes have been identified to result in different levels of HL. Although several diagnostic or screening tests have been developed, yet there are controversies around their use.

Low frequency of GJB2 mutations in thirty-five students with hearing loss in Chinese consanguineous families

OBJECTIVE

GJB2 mutation is recognized as the prevalent causes of non-syndromic hearing impairment (NSHI) worldwide. However, the mutation profiles of this gene are unknown in deafness probands in the consanguineous pedigrees in China. Therefore, this study aimed to characterize the forms and frequencies of GJB2 mutations in 35 students with hearing loss in the consanguineous families in Hubei province, Central China.

METHODS

Genomic DNA was extracted from blood samples of 35 students with hearing loss. The target fragments were amplified by polymerase chain reaction (PCR) and subjected to sequencing to identify sequence variations.

RESULTS

Surprisingly, none of these probands harbored homozygous mutation in GJB2. Three GJB2 heterozygous mutations were identified: a single base pair substitution c.35G>T and c.139G>T, and a 2 bp deletion c.299-300delAT in three probands.

CONCLUSION

The frequency of GJB2 mutation is relatively low in these consanguineous families, most of which were minorities. Our results suggest that screening for responsible genes other than GJB2 may be necessary for NSHI in these minorities.

GJB2 and mitochondrial DNA 1555A>G mutations in students with hearing loss in the Hubei Province of China

OBJECTIVES

The GJB2 and MTRNR1 1555A>G mutations are the prevalent causes of hearing loss worldwide. However, the mutation profiles of the two genes are dependent on the ethnic or geographic origins. Therefore, this study was to characterize the forms and frequencies of the two genes in 813 students with hearing loss in Hubei province, Central China.

METHODS

Blood samples from 813 students were obtained with informed consent. Genomic DNA was extracted from peripheral blood leukocytes. The target fragments were amplified by polymerase chain reaction (PCR). Sequencing (or enzyme digestion) was applied to identify sequence variations.

RESULTS

Ten different mutations were identified in GJB2 in 146 of the 813 (17.96%) patients and 11.81% (96/813) patients had homoplasmic mtDNA 1555A>G mutation.

CONCLUSIONS

This study demonstrated the high prevalence of GJB2 and mtDNA 1555A>G mutations in Central Chinese population. Therefore, it will be effective to perform GJB2 and mtDNA 1555A>G mutation analysis for genetic screening for hearing loss in this population.

Prevalence of A1555G mitochondrial mutation in Chinese newborns and the correlation with neonatal hearing screening

OBJECTIVE

To investigate the feasibility of genetic screening for deafness causative genes in the process of newborn hearing screening in China.

METHODS

Total 865 newborn babies between November 2009 and March 2010 were enrolled for the simultaneous hearing and deafness causative gene screening in Tongji Hospital, Wuhan, China. Hearing screening followed a two-stage strategy with transient evoked otoacoustic emissions. Infants referred after the second-stage screening were tested by diagnostic auditory brainstem response (ABR). Genomic DNA was extracted from heel blood of newborns, and the mitochondrial 12S rRNA A1555G mutation was detected by polymerase chain reaction (PCR) based restriction fragment length polymorphism and confirmed by DNA sequencing.

RESULTS

In hearing screening, 134 out of the 865 newborns (15.5%) were referred after the first-stage screening and 86.6% (116/134) of them returned for the second stage. After the second-stage screening, 15 who were still referred were tested by diagnostic ABR and 3 of them failed the test. On the other hand, gene screening identified 6 of the 865 newborns (0.7%) harbored homoplasmic 12S rRNA A1555G mutation although they passed the hearing screening.

CONCLUSION

It might be practical and effective to complement routine hearing screening in newborns with gene screening for the purpose of early diagnosis and discovery of the late-onset hearing loss.

Parental attitudes toward genetic testing for prelingual deafness in China

OBJECTIVE

Recent advances in molecular biology of hearing and deafness have made genetic testing an option for deaf individuals and their families. In China, DNA microarray and other genetic testing method has been applied to rapid genetic diagnosis of non-syndromic hearing loss. However, there is no information about the interests in such testing in China. The purpose of this study is to document the attitudes of parents with normal hearing who have one or more deaf children toward diagnostic, carrier, and prenatal genetic testing for deafness.

METHODS

A structured, self-completion questionnaire was given to delegates at a conference held at Hubei Rehabilitation Research Center for Deaf Children, Wuhan, China on March 3, 2010. Of 366 surveys distributed, 290 were completed and returned.

RESULTS

Ninety-four percent of the respondents had a positive attitude toward genetic testing. Seventy-two percent stated that they were interested in genetic testing of deaf child. Of the individuals who were interested in such testing, 69% would consider having prenatal genetic testing for deafness.

CONCLUSION

The present study provided evidence of a predominantly positive attitude toward genetics. Appropriate genetic counseling can help parents to understand the risk, benefits, and limitations of genetic testing for prelingual deafness.

Genetic causes of nonsyndromic hearing loss in Iran in comparison with other populations

Hearing loss (HL) is the most prevalent sensory defect affecting 1 in 500 neonates. Genetic factors are involved in half of the cases. The extreme heterogeneity of HL makes it difficult to analyze and determine the accurate genetic causes of the impairment. Up to now, 10 genes, namely, GJB2, GJB6, SLC26A4, TECTA, PJVK, Col11A2, Myo15A, TMC1, RDX and microRNA (miR-183), have been studied in an Iranian population. The prevalence of HL in Iran was estimated to be 2-3 times higher than that in other parts of the world. Here, the most common bases of congenital nonsyndromic hearing loss (NSHL) are discussed. We reviewed GJB2, GJB6 (large deletion), TECTA, SLC26A4 and PEJVK mutations, and studied their frequencies and distributions in different ethnic groups in 1934, 500, 121, 80 and 34 unrelated families throughout Iran, respectively. GJB2 mutation was the most common factor causing NSHL, with a mean frequency of 18.17% in the Iranian population. The importance of Iran's geographical location in the migration pathway from west to east through the silk route was also highlighted. SLC26A4 and TECTA mutations were the second and third main reasons of HL and accounted for up to 10 and 4% of prelingual HL in Iran, respectively. Mutations in GJB2, SLC26, TECTA and PJVK genes have an important role in HL in Iran and a screening test should be generated for better intervention and diagnosis programs.