Molecular epidemiology of Chinese Han deaf patients with bi-allelic and mono-allelic GJB2 mutations

Distribution of mitochondrial MT-RNR1, MT-TL1, MT-TS1, MT-TK and MT-TE genes variants associated with hearing loss in Southwestern China

BACKGROUND

Maternally inherited hearing loss has been associated with mitochondrial genes, including MT-RNR1, MT-TL1, MT-TS1, MT-TK and MT-TE. Among these genes, MT-RNR1 is known to be a hotspot for pathogenic variants related to aminoglycoside ototoxicity and nonsyndromic hearing loss. However, the frequency and spectrum of variants in these genes, particularly in multi-ethnic hearing loss patients from Southwestern China, are still not fully understood.

METHODS

In this study, we enrolled 460 hearing loss patients from various ethnic backgrounds (Han, Yi, Dai, Hani, etc.) in Southwestern China. Next-generation sequencing was used to analyze the mitochondrial MT-RNR1, MT-TL1, MT-TS1, MT-TK and MT-TE genes. Subsequently, bioinformatical methods were employed to evaluate the identified variants.

RESULTS

Among the patients with hearing loss, we identified 70 variants in MT-RNR1 (78.6 %, 55/70), MT-TL1 (4.3 %, 3/70), MT-TS1 (4.3 %, 3/70), MT-TK (7.1 %, 5/70) and MT-TE (5.7 %, 4/70) genes. We found that 15 variants were associated with hearing loss, including m.1555 A > G and m.1095 T > C. Additionally, we discovered three reported mitochondrial variants (m.676 G > A, m.7465 insC, and m.7474 A > G) newly correlated with hearing loss. Notably, certain pathogenic variants, such as m.1555 A > G, displayed non-consistent distributions among the multi-ethnic patients with hearing loss. Furthermore, the number of variants associated with hearing loss was higher in the Sinitic group (n = 181) and Tibeto-Burman group (n = 215) compared to the Kra-Dai group (n = 38) and Hmong-Mien group (n = 26).

CONCLUSIONS

This present study revealed the distribution of mitochondrial variants linked to hearing loss across various ethnic groups in Southwestern China. These data suggest a potential correlation between the distribution of mitochondrial variants associated with hearing loss and ethnic genetic backgrounds.

Next-generation sequencing for genetic testing of hearing loss populations

BACKGROUND AND AIMS

Hearing loss is a common sensorineural disease with genetic heterogeneity. More than 140 genes are known to cause hereditary hearing loss. We aim to uncover the etiologies of hearing loss and provide patients with reasonable reproductive choices.

MATERIALS AND METHODS

Total 825 participants were recruited, including 74 individuals, 47 couples, and 219 families, to identify the molecular etiologies of hearing loss using next-generation sequencing (NGS). Novel mutations were verified with a minigene splicing assay and the construction of three-dimensional protein models.

RESULTS

A positive molecular diagnosis was obtained for 244 patients, a rate of 63.05 %. Total 470 mutations were identified in 18 causative genes in positive patients. The most common genes mutated were GJB2 and SLC26A4. 47 novel mutations were identified. Further analysis predicted that two splicing mutations would cause abnormal mRNA splicing and three missense mutations would affect the protein structure. The results of prenatal diagnosis showed that the genotypes of 15 fetuses were the same as the probands.

CONCLUSION

Our findings expand the mutation spectrum of hearing loss and highlight the importance of genetic diagnosis and prenatal diagnosis to allow accurate and personalized guidance for those at high risk of deafness.

[Genetic characteristic analysis of slight-to-moderate sensorineural hearing loss in children]

Objective:To analyze genetic factors and phenotype characteristics in pediatric population with slight-to-moderate sensorineural hearing loss. Methods:Children with slight-to-moderate sensorineural hearing loss of and their parents, enrolled from the Chinese Deafness Genome Project, were studied. Hearing levels were assessed using pure tone audiometry, behavioral audiometry, auditory steady state response（ASSR）, auditory brainstem response（ABR） thresholds, and deformed partial otoacoustic emission（DPOAE）. Classification of hearing loss is according to the 2022 American College of Medical Genetics and Genomics（ACMG） Clinical Practice Guidelines for Hearing Loss. Whole exome sequencing（WES） and deafness gene Panel testing were performed on peripheral venous blood from probands and validations were performed on their parents by Sanger sequencing. Results:All 134 patients had childhood onset, exhibiting bilateral symmetrical slight-to-moderate sensorineural hearing loss, as indicated by audiological examinations. Of the 134 patients, 29（21.6%） had a family history of hearing loss, and the rest were sporadic patients. Genetic causative genes were identified in 66（49.3%） patients. A total of 11 causative genes were detected, of which GJB2 was causative in 34 cases（51.5%）, STRC in 10 cases（15.1%）, MPZL2 gene in six cases（9.1%）, and USH2A in five cases（7.6%）.The most common gene detected in slight-to-moderate hearing loss was GJB2, with c. 109G>A homozygous mutation found in 16 cases（47.1%） and c. 109G>A compound heterozygous mutation in 9 cases（26.5%）. Conclusion:This study provides a crucial genetic theory reference for early screening and detection of mild to moderate hearing loss in children, highlighting the predominance of recessive inheritance and the significance of gene like GJB2, STRC, MPZL2, USH2A.

Characteristics of hearing loss-associated gene mutations: A multi-center study of 119,606 neonates in Gannan

BACKGROUND

HL is the second most common congenital disability in China, and its high incidence brings a serious burden of medical and educational sequelae. HL genetic screening enables the identification of individuals with inherited HL and carriers in a large scale.

OBJECTIVE

This study aimed to measure the detection rates of hearing loss (HL)-associated gene mutations in the Gannan population. The molecular etiology and risk factors of hereditary HL were also analyzed.

METHODS

In total, 119,606 newborns from 18 districts of Gannan were enrolled in this multi-center study conducted between April 2019 and April 2021. Otoacoustic Emission (OAE) was used for primary hearing screening 3 days after birth in quiet conditions, and OAE combined with automated auditory brainstem response (AABR) was applied 29-42 days after birth for those who failed or missed the initial screening. Meanwhile, high-throughput sequencing of hotspot HL-associated mutations in GJB2, GJB3, MTRNR1, and SLC26A4 were performed.

RESULTS

Among the 119,606 newborns, 7796 (6.52%) failed the hearing screening. Genetic screening revealed that 5092 neonates (4.26%) carried HL-associated mutations. The detection rate of GJB2, SLC26A4, MTRNR1 and GJB3 mutations were 2.09%, 1.51%, 0.42% and 0.24%, respectively. The most prevalent variant was GJB2 c.235delC (1.74%). The second most prevalent variant was SLC26A4 c.919-2A > G (0.93%). The population who failed the hearing screening had a lower proportion (24.64%) of SLC26A4 gene variants compared to the population who passed (37.46%). Genetic screening identified 4612 (3.86%) carriers who were normal in hearing screenings. The concurrent hearing and genetic screening identified 480 (0.40%) neonates at high risk for hereditary HL.

CONCLUSIONS

The results of this study suggest that the concurrent hearing screening and high-throughput genetic screening would greatly improve the effectiveness of newborn HL programs. This integration also facilitates the management of congenital HL, and aids in the prevention of aminoglycoside antibiotics-induced HL.

Genotypic and Allelic Frequencies of GJB2 Variants and Features of Hearing Phenotypes in the Chinese Population of the Dongfeng-Tongji Cohort

BACKGROUND

This study aimed to describe the distribution of the genotype and allele frequencies of GJB2 variants in the Chinese population of the Dongfeng Tongji cohort and to analyze the features of the hearing phenotype.

METHODS

We used data from 9910 participants in the Dongfeng Tongji cohort in 2013 and selected nine GJB2 variants. Pure tone audiometry was employed to measure hearing. Differences in genotype and allele frequencies were analyzed via chi-squared test or Fisher's exact test.

RESULTS

Of the 9910 participants, 5742 had hearing loss. The genotype frequency of the GJB2 variant c.109G>A was statistically significantly distributed between the normal and impaired hearing groups, but not for the variant c.235delC. A higher frequency of the c.109G>A homozygous genotype was found in the hearing loss group (0.5%) than in the normal hearing group (0.1%). Patients with c.109G>A and c.235delC homozygous mutations exhibited varying degrees of hearing loss, mainly presenting sloping and flat audiogram shapes.

CONCLUSIONS

A significant difference was found in the genotype frequency of the GJB2 variant c.109G>A between the case and control groups, but not in that of the variant c.235delC. Different degrees of hearing loss and various audiogram shapes were observed in patients with c.109G>A and c.235delC homozygous mutations.

Increased diagnostic yield in a cohort of hearing loss families using a comprehensive stepwise strategy of molecular testing

Hearing loss is one of the most common sensory disorders in humans. This study proposes a stepwise strategy of deafness gene detection using multiplex PCR combined with high-throughput sequencing, Sanger sequencing, multiplex ligation-dependent probe amplification (MLPA), and whole-exome sequencing (WES) to explore its application in molecular diagnosis of hearing loss families. A total of 152 families with hearing loss were included in this study, the highest overall diagnosis rate was 73% (111/152). The diagnosis rate of multiplex PCR combined with high-throughput sequencing was 52.6% (80/152). One families was diagnosed by Sanger sequencing of GJB2 exon 1. Two families were diagnosed by MLPA analysis of the STRC gene. The diagnosis rate with additional contribution from WES was 18.4% (28/152). We identified 21 novel variants from 15 deafness genes by WES. Combining WES and deep clinical phenotyping, we diagnosed 11 patients with syndromic hearing loss (SHL). This study demonstrated improved diagnostic yield in a cohort of hearing loss families and confirmed the advantages of a stepwise strategy in the molecular diagnosis of hearing loss.

Genetic profiles of non-syndromic severe-profound hearing loss in Chinese Hans by whole-exome sequencing

Hereditary hearing loss is highly heterogeneous. Despite over 120 non-syndromic deafness genes have been identified, there are still some of novel genes and variants being explored. In the study, we investigated 105 Chinese Han children with non-syndromic, prelingual, severe-profound hearing loss by whole-exome sequencing on DNA samples. The most common deafness gene was GJB2, mainly in variant c.235delC (p.Leu79CysfsTer3). 14 children were identified with pathogenic mutations in three genes, GJB2, SLC26A4, and OTOF. Two mutations have been identified to be pathogenic and not recorded previously, including c.4691G > A (p.Trp1564Ter) and c.3928_3930dup (p.Lys1310dup) in OTOF. The rare variants c.1349G > A (p.Arg450His) and c.456 T > G (p.Asn152Lys) in GSDME, and c.1595G > T (p.Ser532Ile) in SLC26A4 were detected. The frequency of nonsense variant c.2359G > T (p.Glu787Ter) in OTOA was very high in 17 cases. Four of them were identified to be digenic inheritance, including GJB2 and COL4A4, GJB2 and EYA1, GJB2 and COL4A5, and GJB2 and DFNA5. The findings showed that a novel pathogenic variant and rare variants may be associated with severe and profound hearing loss.

Change to Hearing Loss-Related Risks and Screening in Preterm Infants

Hearing loss is one of the most common congenital defects in infancy; it increases speech and language delays and adversely affects academic achievement and socialemotional development. The risk of hearing loss in premature infants is higher than that in normal newborns, and because of the fragility of the auditory nervous system, it is more vulnerable to different risk factors. The hearing screening guidelines in current use were proposed by the American Academy of Pediatrics and updated in 2007, but there are no uniform guidelines for hearing screening in preterm infants. This review focuses on the risk factors related to hearing loss in premature infants, hearing screening strategies, and reasons for failure. The aim is to provide a more comprehensive understanding of hearing development in preterm infants to achieve early detection and early intervention. At the same time, attention should be paid to delayed auditory maturation in preterm infants to avoid excessive intervention. KEY POINTS: · Hearing loss is very common in infancy, especially in premature infants.. · Genetic factors, infection, hyperbilirubinemia, drugs, and noise are the main causes.. · We should pay attention to the delayed hearing maturity of premature infants and avoid excessive intervention..

A newly identified mutation (c.2029 C > T) in SLC26A4 gene is associated with enlarged vestibular aqueducts in a Chinese family

Background

The enlarged vestibular aqueduct (EVA), associated with mutations in the SLC26A4 gene, characterized by non-syndromic hearing loss, is an autosomal recessive disorder. Here, we intended to investigate genetic causes of hearing loss in a Han Chinese man.

Method

First, whole-exome sequencing was performed to identify the gene mutations responsible for hearing loss in the proband. Sanger sequencing was used to verify the candidate mutations detected in the family. Next, we collected blood samples and clinical data from the three-generation pedigree. Finally, SLC26A4 mRNA and protein expression levels were detected by qPCR and western blotting.

Result

The proband suffered from bilateral progressive sensorineural hearing loss with EVA. The sequence analysis of SLC26A4 revealed that the proband and his sister both harbored a compound heterozygous mutation of c.2168A > G/c.2029C > T, inherited from their father and mother respectively. c.2029C > T mutation has not been recorded in the relevant literature previously. Relative mRNA levels of the SLC26A4 gene in individuals carrying a compound heterozygous mutation were significantly lower compared to a heterozygous mutation. SLC26A4 protein levels of 293t cells which transfected with recombinant plasmids [GV219-SLC26A4-mut (c.2029C > T) and GV219-SLC26A4-mut (c.2168A > G/c.2029C > T)] were significantly lower than normal control recombinant plasmids (GV219-SLC26A4-wt).

Conclusion

This study found a novel heterozygous mutation c.2029 (exon17) C > T compound with c.2168 (exon19) A > G in the SLC26A4 gene in a patient with EVA. The c.2029 (exon17) C > T mutation is proved to be pathogenic. This finding broadens the spectrum of variants in SLC26A4 gene.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12920-022-01200-4.

Analysis of Genetic Variations in Connexin 26 (GJB2) Gene among Nonsyndromic Hearing Impairment: Familial Study

Objective  The goal of this research was to investigate the gap junction beta 2 ( GJB2 ) gene mutations associated with nonsyndromic hearing loss individuals in North Karnataka, India.

Materials and Methods  For this study, patients with sensorineural genetic hearing abnormalities and a family history of deafness were included. A total of 35 patients from 20 families have been included in the study. The patient's DNA was isolated from peripheral blood samples. The GJB2 gene coding region was analyzed through Sanger sequencing.

Results  There is no changes in the first exon of the GJB2 gene. Nine different variants were recorded in second exon of the targeted gene. W24X and W77X are two nonsense mutations and three polymorphisms viz. R127H, V153I, and I33T were reported along with four 3′-UTR variants. A total (9/20) of 45% of families have been identified with mutations in the targeted gene.

Conclusion   GJB2 mutations were identified in 19 deaf-mute patients (19/35), and 13 patients were homozygous for the mutations identified in our study cohort. In our study, W24X mutation was found to be the pathogenic with a high percentage, prompting further evaluation of the other genes, along with the study of additional genetic or external causes in the families, which is essential.

A fully integrated SNP genotyping system for hereditary hearing-loss detection

Hereditary hearing loss is one of the most common human neurosensory disorders, and there is a great need for early intervention methods such as genetically screening newborns. Single nucleotide polymorphisms (SNPs) are the major genetic targets for hearing-loss screening. In this study, a fully integrated SNP genotyping system was constructed to identify hereditary hearing loss-related genetic markers from human whole blood. The entire detection process, including blood cell lysis, nucleic acid extraction, the reaction mixture distribution, the chambers sealing and the two-colour multiplex competitive allele-specific polymerase chain reaction (KASP), can be automatically conducted in a self-contained cassette within 3 hours. To critically evaluate the performance of the system, its specificity, sensitivity and stability were assessed. Then, 13 clinical samples were genotyped with this fluidic cassette system to detect seven hotspot deafness-associated mutations in three genes (MT-RNR1, GJB2 and SLC26A4). The detection results of the cassette system were 100% concordant with those obtained by Sanger sequencing, proving its accuracy in the genetic screening of inherited hearing loss.

Undescribed GJB2 c.35dupG homozygous prelingual distinguished from c.35delG homozygous/compound heterozygous deafs, dwelling a German ancestry Venezuelan isolate

Background

Among ten hearing-impaired (HI) families mostly of German descent dwelling the Venezuelan isolate Colonia Tovar, which were initially studied several decades ago to assess the etiology of their profound/prelingual nonsyndromic deafness phenotype, an undescribed genotype/phenotype was found. Forty-eight subjects, including 8 of the still living 143 originally searched with audiograms 4 decades ago, were retested and their DNA collected. A genomic search of 27 loci involved in HI was performed on a randomly chosen prelingual deaf patient. Subsequently, GJB2 sequencing was performed in all subjects from each pedigree. Haplotypes were constructed with five intragenic GJB2 SNPs (rs117685390, rs7994748, rs2274084, rs2274083, and rs3751385). Audiograms performed along 5 decades were compared to evaluate age-related hearing loss in the different genotypes found in the population.

Results

Three prelingual deaf siblings, having the highest recorded symmetrical hearing loss of all the known affected in the isolate, carried the very rare mutation c.35dupG (p.V13Cfs*35) at GJB2 in a homozygous condition. Two additional GJB2 mutations were identified (p.W77R and c.35delG) in the isolate. Allelic disequilibrium in both c.35dupG and p.W77R carriers (with in-phase haplotype T;T;G;A;C) were found, although not so in the 2 other found c.35delG independent haplotypes. A compound heterozygote in trans (c.35delG/c.35dupG) was audiometrically distinguishable from both the c.35dupG and c.35delG homozygotes.

Conclusions

A relatively higher frequency of mutation of c.35dupG found than elsewhere was retrospectively inferred for the ancient population of the Kaiserstuhl region in Germany, having an opposite epidemiological situation to the one found with the contiguous and very frequent c.35delG. Haplotype analysis suggests founder phenomena and independent occurrence, hundreds of generations back in Caucasoid populations for both mutations.

Hearing Impairment with Monoallelic GJB2 Variants: A GJB2 Cause or Non-GJB2 Cause?

Recessive variants in GJB2 are the most common genetic cause of sensorineural hearing impairment. However, in many patients, only one variant in the GJB2 coding region is identified using conventional sequencing strategy (eg, Sanger sequencing), resulting in nonconfirmative diagnosis. Conceivably, there might be other unidentified pathogenic variants in the noncoding region of GJB2 or other deafness-causing genes in these patients. To address this, a next-generation sequencing-based diagnostic panel targeting the entire GJB2 gene and the coding regions of 158 other known deafness-causing genes was designed and applied to 95 patients with nonsyndromic sensorineural hearing impairment (including 81 Han Taiwanese and 14 Mongolian patients) in whom only a single GJB2 variant had been detected using conventional Sanger sequencing. The panel confirmed the genetic diagnosis in 24 patients (25.3%). Twenty-two of them had causative variants in several deafness-causing genes other than GJB2, including MYO15A, MYO7A, TECTA, POU4F3, KCNQ4, SLC26A4, OTOF, MT-RNR1, MITF, WFS1, and USH2A. The other two patients had causative variants in GJB2, including a Taiwanese patient with a mosaic maternal uniparental disomy c.235delC variant (approximately 69% mosaicism) and a Mongolian patient with compound heterozygous c.35dupG and c.35delG variants, which occurred at the same site. This study demonstrates the utility of next-generation sequencing in clarifying the genetic diagnosis of hearing-impaired patients with nonconfirmative GJB2 genotypes on conventional genetic examinations.

The Cause of Hereditary Hearing Loss in GJB2 Heterozygotes-A Comprehensive Study of the GJB2/DFNB1 Region

Hearing loss is a genetically heterogeneous sensory defect, and the frequent causes are biallelic pathogenic variants in the GJB2 gene. However, patients carrying only one heterozygous pathogenic (monoallelic) GJB2 variant represent a long-lasting diagnostic problem. Interestingly, previous results showed that individuals with a heterozygous pathogenic GJB2 variant are two times more prevalent among those with hearing loss compared to normal-hearing individuals. This excess among patients led us to hypothesize that there could be another pathogenic variant in the GJB2 region/DFNB1 locus. A hitherto undiscovered variant could, in part, explain the cause of hearing loss in patients and would mean reclassifying them as patients with GJB2 biallelic pathogenic variants. In order to detect an unknown causal variant, we examined 28 patients using NGS with probes that continuously cover the 0.4 Mb in the DFNB1 region. An additional 49 patients were examined by WES to uncover only carriers. We did not reveal a second pathogenic variant in the DFNB1 region. However, in 19% of the WES-examined patients, the cause of hearing loss was found to be in genes other than the GJB2. We present evidence to show that a substantial number of patients are carriers of the GJB2 pathogenic variant, albeit only by chance.

Molecular alteration in the Gap Junction Beta 2 (GJB2) gene associated with non-syndromic sensorineural hearing impairment

Non-syndromic sensory neural hearing defect is one of the genetic diseases inherited from parents to offerings. The autosomal recessive form affects a large population worldwide and has become a major concern in the social and professional lives of many people. There are many factors and genes which are involved in hearing loss but the Gap Junction Beta 2 (GJB2) gene which encodes the connexin 26 protein, is a major cause of non-syndromic recessive deafness (NSRD). This study aims to record and analyze GJB2 gene mutations in the hearing-impaired population of North Karnataka, India. In this study, we included 368 congenitally hearing-impaired children from North Karnataka, India, under 18 years of age. After thorough clinical examinations, patient's history and proper audiological results, peripheral blood samples were collected and subjected to genetic analysis. We recorded that 54.8% of the NSRD cases have an autosomal recessive mutation in the coding region of the GJB2 gene. The frequency of W24X (25%) mutation was found to be high in the present study population. From this study we can suggest that, identifying this mutation in new-borns definitely helps in the early diagnosis of hearing loss.

Reprogramming of human peripheral blood mononuclear cell (PBMC) from a patient suffering from hearing loss into iPSC line (SDQLCHi035-A) maintaining compound heterozygous variations in GJB2 gene

Mutation in the gap junction beta-2 (GJB2) gene is a main cause of autosomal-recessive nonsyndromic hearing loss (ARNSHL). The c.235delC and c.299-300del mutations are more common mutations in Chinese Han deaf patients, in which the compound heterozygous mutations of these two sites cause severe-to-profound hearing loss in a significant percentage. We established an induced pluripotent stem cell (iPSC) line from a 2-year-old boy with hearing loss, caused by compound heterozygous mutations in GJB2 (c.235delC and c.299-300del). The iPSCs was verified based on pluripotency markers and demonstrated trilineage differentiation potential in vitro.

A novel SLC26A4 splicing mutation identified in two deaf Chinese twin sisters with enlarged vestibular aqueducts

Background

Variants in the SLC26A4 gene are correlated with nonsyndromic hearing loss with an enlarged vestibular aqueduct (EVA). This study aimed to identify the genetic causes in a Chinese family with EVA, and the pathogenicity of the detected variants.

Methods

We collected blood samples and clinical data from a pair of deaf twin sisters with EVA and their family members. As controls, a group of 500 normal‐hearing people were enrolled in our study. Twenty‐one exons and flanking splice sites of the SLC26A4 gene were screened for pathogenic mutations by polymerase chain reaction and bidirectional Sanger sequencing. Minigene assays were used to verify whether the novel SLC26A4 intronic mutation influenced the normal splicing of mRNA.

Results

Hearing loss in the twins with EVA was diagnosed using auditory tests and imaging examinations. Two pathogenic mutations, c.919‐2A>G and c.1614+5G>A were detected in SLC26A4, the latter of which has not been reported in the literature. The minigene expression in vitro confirmed that c.1614+5G>A could cause aberrant splicing, resulting in skipping over exon 14.

Conclusions

On the SLC26A4 gene, c.1614+5G>A is a pathogenic mutation. This finding enriches the mutational spectrum of the SLC26A4 gene and provides a basis for the genetic diagnosis of EVA.

Hearing Phenotypes of Patients with Hearing Loss Homozygous for the GJB2 c.235delc Mutation

Hereditary hearing loss is characterized by remarkable phenotypic heterogeneity. Patients with the same pathogenic mutations may exhibit various hearing loss phenotypes. In the Chinese population, the c.235delC mutation is the most common pathogenic mutation of GJB2 and is closely related to hereditary recessive hearing loss. Here, we investigated the hearing phenotypes of patients with hearing loss associated with the homozygous c.235delC mutation, paying special attention to asymmetric interaural hearing loss. A total of 244 patients with the GJB2 c.235delC homozygous mutation encountered from 2007 to 2015 were enrolled. The severity of hearing loss was scaled with the American Speech-Language-Hearing Association (ASHA). Auditory phenotypes were analyzed, and three types of interaural asymmetry were defined based on audiograms: Type A (asymmetry of hearing loss severity), Type B (asymmetry of audiogram shape), and Type C (Type A plus Type B). Of the 488 ears (244 cases) examined, 71.93% (351) presented with profound hearing loss, 14.34% (70) with severe hearing loss, and 9.43% (46) with moderate to severe hearing loss. The most common audiogram shapes were descending (31.15%) and flat (24.18%). A total of 156 (63.93%) of the 244 patients exhibited asymmetric interaural hearing loss in terms of severity and/or audiogram shape. Type A was evident in 14 of these cases, Type B in 106, and Type C in 36. In addition, 211 of 312 ears (67.63%) in the interaural hearing asymmetry group showed profound hearing loss, and 59 (18.91%) exhibited severe hearing loss, with the most common audiogram shapes being flat (27.88%) and descending (22.12%). By contrast, in the interaural hearing symmetry group, profound hearing loss was observed in 140 ears (79.55%), and the most common audiograms were descending (46.59%) and residual (21.59%). Hearing loss associated with the GJB2 c.235delC homozygous mutation shows diverse phenotypes, and a considerable proportion of patients show bilateral hearing loss asymmetry.

Compound Heterozygous Mutations in TMC1 and MYO15A Are Associated with Autosomal Recessive Nonsyndromic Hearing Loss in Two Chinese Han Families

Genetic hearing loss is a common sensory disorder, and its cause is highly heterogeneous. In this study, by targeted next-generation sequencing of 414 known deafness genes, we identified compound heterozygous mutations p.R34X/p.M413T in TMC1 and p.S3417del/p.R1407T in MYO15A in two recessive Chinese Han deaf families. Intrafamilial cosegregation of the mutations with the hearing phenotype was confirmed in both families by the Sanger sequencing. Auditory features of the affected individuals are consistent with that previously reported for recessive mutations in TMC1 and MYO15A. The two novel mutations identified in this study, p.M413T in TMC1 and p.R1407T in MYO15A, are classified as likely pathogenic according to the guidelines of ACMG. Our study expanded the mutation spectrums of TMC1 and MYO15A and illustrated that genotype-phenotype correlation in combination with next-generation sequencing may improve the accuracy for genetic diagnosis of deafness.

Targeted Next-Generation Sequencing Identified Compound Heterozygous Mutations in MYO15A as the Probable Cause of Nonsyndromic Deafness in a Chinese Han Family

Hearing loss is a highly heterogeneous disorder, with more than 60% of congenital cases caused by genetic factors. This study is aimed at identifying the genetic cause of congenital hearing loss in a Chinese Han family. Auditory evaluation before and after cochlear implantation and targeted next-generation sequencing of 140 deafness-related genes were performed for the deaf proband. Compound heterozygous mutations c.3658_3662del (p. E1221Wfs∗23) and c.6177+1G>T were identified in MYO15A as the only candidate pathogenic mutations cosegregated with the hearing loss in this family. These two variants were absent in 200 normal-hearing Chinese Hans and were classified as likely pathogenic and pathogenic, respectively, based on the ACMG guideline. Our study further expanded the mutation spectrum of MYO15A as the c.3658_3662del mutation is novel and confirmed that deaf patients with recessive MYO15A mutations have a good outcome for cochlear implantation.