Comparison of vestibular function in hereditary hearing loss patients with GJB2, CDH23, and SLC26A4 variants.

To investigate the association between hereditary hearing loss and vestibular function, we compared vestibular function and symptoms among patients with GJB2, SLC26A4, and CDH23 variants. Thirty-nine patients with sensory neural hearing loss (11 males and 28 females) with biallelic pathogenic variants in either GJB2, SLC26A4, or CDH23 were included in this study (13 GJB2, 15 SLC26A4, and 11 CDH23). The patients were examined using caloric testing and cervical and ocular vestibular-evoked myogenic potentials (cVEMP and oVEMP). We also compared vestibular function and symptoms between patients with these gene variants and 78 normal-hearing ears without vestibular symptoms as controls. The frequency of semicircular canal hypofunction in caloric testing was higher in patients with SLC26A4 variants (47%) than in those with GJB2 (0%) and CDH23 variants (27%). According to the cVEMP results, 69% of patients with GJB2 variants had saccular hypofunction, a significantly higher proportion than in those carrying other variants (SLC26A4, 20%; CDH23, 18%). In oVEMP, which reflects utricular function, no difference was observed in the frequency of hypofunction among the three genes (GJB2, 15%; SLC26A4, 40%; and CDH23, 36%). Hence, discernable trends indicate vestibular dysfunction associated with each gene.

Structural basis for pathogenic variants of GJB2 and hearing levels of patients with hearing loss.

OBJECTIVES: The crystal structure of the six protomers of gap junction protein beta 2 (GJB2) enables prediction of the effect(s) of an amino acid substitution, thereby facilitating investigation of molecular pathogenesis of missense variants of GJB2. This study mainly focused on R143W variant that causes hearing loss, and investigated the relationship between amino acid substitution and 3-D structural changes in GJB2. METHODS: Patients with nonsyndromic hearing loss who appeared to have two GJB2 pathogenic variants, including the R143W variant, were investigated. Because the X-ray crystal structure of the six protomers of the GJB2 protein is known, R143W and structurally related variants of GJB2 were modeled using this crystal structure as a template. The wild-type crystal structure and the variant computer-aided model were observed and the differences in molecular interactions within the two were analyzed. RESULTS: The predicted structure demonstrated that the hydrogen bond between R143 and N206 was important for the stability of the protomer structure. From this prediction, R143W related N206S and N206T variants showed loss of the hydrogen bond. CONCLUSION: Investigation of the genotypes and clinical data in patients carrying the R143W variant on an allele indicated that severity of hearing loss depends largely on the levels of dysfunction of the pathogenic variant on the allele, whereas a patient with the homozygous R143W variant demonstrated profound hearing loss. We concluded that these hearing impairments may be due to destabilization of the protomer structure of GJB2 caused by the R143W variant.

Unusual phenotype in 35delG mutation: a case report.

BACKGROUND: Mutations in the GJB2 gene, which encodes the protein connexin 26 and is involved in inner ear homeostasis, are identified in approximately 50% of patients with autosomal recessive nonsyndromic hearing loss, making it one of the primary causes of prelingual nonsyndromic hearing loss in various populations. The 35delG mutation, one of the most common mutations of the GJB2 gene, usually causes prelingual, bilateral mild to profound, nonprogressive sensorineural hearing loss. CASE PRESENTATION: We present an unusual case of an 18-year-old Turkish female with heterozygous 35delG mutation and postlingual, profound-sloping, progressive and fluctuating unilateral sensorineural hearing loss. The phenotype is different from the usual findings. CONCLUSIONS: The 35delG mutation causing hearing loss may not always be reflected in the phenotype as expected and therefore may have different audiologic manifestations.

A murine model for the del(GJB6-D13S1830) deletion recapitulating the phenotype of human DFNB1 hearing impairment: generation and functional and histopathological study.

Inherited hearing impairment is a remarkably heterogeneous monogenic condition, involving hundreds of genes, most of them with very small (< 1%) epidemiological contributions. The exception is GJB2, the gene encoding connexin-26 and underlying DFNB1, which is the most frequent type of autosomal recessive non-syndromic hearing impairment (ARNSHI) in most populations (up to 40% of ARNSHI cases). DFNB1 is caused by different types of pathogenic variants in GJB2, but also by large deletions that keep the gene intact but remove an upstream regulatory element that is essential for its expression. Such large deletions, found in most populations, behave as complete loss-of-function variants, usually associated with a profound hearing impairment. By using CRISPR-Cas9 genetic edition, we have generated a murine model (Dfnb1em274) that reproduces the most frequent of those deletions, del(GJB6-D13S1830). Dfnb1em274 homozygous mice are viable, bypassing the embryonic lethality of the Gjb2 knockout, and present a phenotype of profound hearing loss (> 90 dB SPL) that correlates with specific structural abnormalities in the cochlea. We show that Gjb2 expression is nearly abolished and its protein product, Cx26, is nearly absent all throughout the cochlea, unlike previous conditional knockouts in which Gjb2 ablation was not obtained in all cell types. The Dfnb1em274 model recapitulates the clinical presentation of patients harbouring the del(GJB6-D13S1830) variant and thus it is a valuable tool to study the pathological mechanisms of DFNB1 and to assay therapies for this most frequent type of human ARNSHI.

[Analysis of the results for genetic disease screening among 1 000 newborns from Huzhou].

OBJECTIVE: To analyze the types and distribution of pathogenic variants for neonatal genetic diseases in Huzhou, Zhejiang Province. METHODS: One thousand neonates (48 ~ 42 h after birth) born to Huzhou region were selected as the study subjects. Dry blood spot samples were collected from the newborns, and targeted capture high-throughput sequencing was carried out for pathogenic genes underlying 542 inherited diseases. Candidate variants were verified by Sanger sequencing. RESULTS: Among the 1 000 newborns, the male to female ratio was 1.02 : 1.00. No pathogenic variants were detected in 253 cases, whilst 747 cases were found to carry at least one pathogenic variant, which yielded a carrier rate of 74.7%. The most frequently involved pathogenic gene was FLG, followed by GJB2, UGT1A1, USH2A and DUOX2. The variants were classified as homozygous, compound heterozygous, and hemizygous variants. Based on the guidelines from the American College of Medical Genetics and Genomics (ACMG), 213 neonates were verified to have carried pathogenic and/or likely pathogenic variants, with a positive rate of 21.3%. The most commonly involved genes had included UGT1A1, FLG, GJB2, MEFV and G6PD. CONCLUSION: Newborn screening based on high-throughput sequencing technology can expand the scope of screening and improve the positive predictive value. Genetic counseling based on the results can improve the patients' medical care and reduce neonatal mortality and childhood morbidity, while provide assistance to family members' health management and reproductive decisions.

[Mutation spectrum analysis of 23-site chip neonatal deafness genetic screening].

Objective:To analyze the mutation spectrum of 23-site chip newborn deafness genetic screening in Beijing, and to provide basis for genetic counseling and clinical diagnosis and treatment. Methods:The study included 21 006 babies born in Beijing from December 2022 to June 2023. All subjects underwent newborn deafness genetic screening in Beijing Tongren Hospital, covering 23 variants in 4 genes, the GJB2 gene（c.35delG, c.176_191del16, c.235delC, c.299_300delAT, c.109G>A, c.257C>G, c.512insAACG, c.427C>T, c.35insG）, SLC26A4 gene（c.919-2A>G, c.2168A>G, c.1174A>T, c.1226G>A, c.1229C>T, c.1975G>C, c.2027T>A, c.589G>A, c.1707+5G>A, c.917insG, c.281C>T）, Mt12SrRNA（m.1555A>G, m.1494C>T） and GJB3 gene（c.538C>T）. The mutation detection rate and allele frequency were analyzed. Results:The overall mutation detection rate was 11.516%（2 419/21 006）, with the GJB2 gene being the most frequently involved at 9.097%（1 911/21 006）, followed by the SLC26A4 gene at 2.123%（446/21 006）, the GJB3 gene at 0.362%（76/21 006） and Mt12SrRNA at 0.176%（37/21 006）. Among the GJB2 genes, c.109G>A and c.235delC mutation detection rates were the highest, with 6.579%（1 382/21 006） and 1.795%（377/21 006）, respectively. Of the SLC26A4 genes, c.919-2A>G and c.2168A>G had the highest mutation rates of 1.423%（299/21 006） and 0.233%（49/21 106）, respectively. Regarding the allele frequency, GJB2 c.109G>A was the most common variant with an allele frequency of 3.359%（1 411/42 012）, followed by the GJB2 c.235delC at 0.897%（377/42 012） and the SLC26A4 c.919-2A>G at 0.719%（302/42 012）. Conclusion:23-site chip newborn deafness genetic screening in Beijing showed that GJB2 c.109G>A mutation detection rate and allele frequency were the highest. This study has enriched the epidemiological data of 23-site chip genetic screening mutation profiles for neonatal deafness, which can provide evidence for clinical practice.

Reconstructing the ancestral gene pool to uncover the origins and genetic links of Hmong-Mien speakers.

BACKGROUND: Hmong-Mien (HM) speakers are linguistically related and live primarily in China, but little is known about their ancestral origins or the evolutionary mechanism shaping their genomic diversity. In particular, the lack of whole-genome sequencing data on the Yao population has prevented a full investigation of the origins and evolutionary history of HM speakers. As such, their origins are debatable. RESULTS: Here, we made a deep sequencing effort of 80 Yao genomes, and our analysis together with 28 East Asian populations and 968 ancient Asian genomes suggested that there is a strong genetic basis for the formation of the HM language family. We estimated that the most recent common ancestor dates to 5800 years ago, while the genetic divergence between the HM and Tai-Kadai speakers was estimated to be 8200 years ago. We proposed that HM speakers originated from the Yangtze River Basin and spread with agricultural civilization. We identified highly differentiated variants between HM and Han Chinese, in particular, a deafness-related missense variant (rs72474224) in the GJB2 gene is in a higher frequency in HM speakers than in others. CONCLUSIONS: Our results indicated complex gene flow and medically relevant variants involved in the HM speakers' evolution history.

Connexins 30 and 43 expression changes in relation to age-related hearing loss.

Age-related hearing loss (ARHL), also known as presbycusis, is the number one communication disorder for aging adults. Connexin proteins are essential for intercellular communication throughout the human body, including the cochlea. Mutations in connexin genes have been linked to human syndromic and nonsyndromic deafness; thus, we hypothesize that changes in connexin gene and protein expression with age are involved in the etiology of ARHL. Here, connexin gene and protein expression changes for CBA/CaJ mice at different ages were examined, and correlations were analyzed between the changes in expression levels and functional hearing measures, such as ABRs and DPOAEs. Moreover, we investigated potential treatment options for ARHL. Results showed significant downregulation of Cx30 and Cx43 gene expression and significant correlations between the degree of hearing loss and the changes in gene expression for both genes. Moreover, dose-dependent treatments utilizing cochlear cell lines showed that aldosterone hormone therapy significantly increased Cx expression. In vivo mouse treatments with aldosterone also showed protective effects on connexin expression in aging mice. Based on these functionally relevant findings, next steps can include more investigations of the mechanisms related to connexin family gap junction protein expression changes during ARHL; and expand knowledge of clinically-relevant treatment options by knowing what specific members of the Cx family and related inter-cellular proteins should be targeted therapeutically.

The genetic basis and the diagnostic yield of genetic testing related to nonsyndromic hearing loss in Qatar.

Hearing loss is the most predominant sensory defect occurring in pediatrics, of which, 66% cases are attributed to genetic factors. The prevalence of hereditary hearing loss increases in consanguineous populations, and the prevalence of hearing loss in Qatar is 5.2%. We aimed to investigate the genetic basis of nonsyndromic hearing loss (NSHL) in Qatar and to evaluate the diagnostic yield of different genetic tests available. A retrospective chart review was conducted for 59 pediatric patients with NSHL referred to the Department of Adult and Pediatric Medical Genetics at Hamad Medical Corporation in Qatar, and who underwent at least one genetic test. Out of the 59 patients, 39 were solved cases due to 19 variants in 11 genes and two copy number variants that explained the NSHL phenotype. Of them 2 cases were initially uncertain and were reclassified using familial segregation. Around 36.8% of the single variants were in GJB2 gene and c.35delG was the most common recurrent variant seen in solved cases. We detected the c.283C > T variant in FGF3 that was seen in a Qatari patient and found to be associated with NSHL for the first time. The overall diagnostic yield was 30.7%, and the diagnostic yield was significantly associated with genetic testing using GJB2 sequencing and using the hearing loss (HL) gene panel. The diagnostic yield for targeted familial testing was 60% (n = 3 patients) and for gene panel was 50% (n = 5). Thus, we recommend using GJB2 gene sequencing as a first-tier genetic test and HL gene panel as a second-tier genetic test for NSHL. Our work provided new insights into the genetic pool of NSHL among Arabs and highlights its unique diversity, this is believed to help further in the diagnostic and management options for NSHL Arab patients.

Hearing Loss: Genetic Testing, Current Advances and the Situation in Latin America.

Congenital hearing loss is the most common birth defect, estimated to affect 2-3 in every 1000 births, with ~50-60% of those related to genetic causes. Technological advances enabled the identification of hundreds of genes related to hearing loss (HL), with important implications for patients, their families, and the community. Despite these advances, in Latin America, the population with hearing loss remains underdiagnosed, with most studies focusing on a single locus encompassing the GJB2/GJB6 genes. Here we discuss how current and emerging genetic knowledge has the potential to alter the approach to diagnosis and management of hearing loss, which is the current situation in Latin America, and the barriers that still need to be overcome.

[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.

[Distribution characteristics and correlation analysis of GJB2 variation in patients with auditory neuropathy].

Objective:To elucidate the correlation between the GJB2 gene and auditory neuropathy, aiming to provide valuable insights for genetic counseling of affected individuals and their families. Methods:The general information, audiological data（including pure tone audiometry, distorted otoacoustic emission, auditory brainstem response, electrocochlography）, imaging data and genetic test data of 117 auditory neuropathy patients, and the patients with GJB2 gene mutation were screened out for the correlation analysis of auditory neuropathy. Results:Total of 16 patients were found to have GJB2 gene mutations, all of which were pathogenic or likely pathogenic.was Among them, one patient had compound heterozygous variants GJB2[c. 427C>T][c. 358_360del], exhibiting total deafness. One was GJB2[c. 299_300delAT][c. 35_36insG]compound heterozygous variants, the audiological findings were severe hearing loss.The remaining 14 patients with GJB2 gene variants exhibited typical auditory neuropathy. Conclusion:In this study, the relationship between GJB2 gene and auditory neuropathy was preliminarily analyzed,and explained the possible pathogenic mechanism of GJB2 gene variants that may be related to auditory neuropathy.

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.

A novel method for detecting nine hotspot mutations of deafness genes in one tube.

Deafness is a common sensory disorder. In China, approximately 70% of hereditary deafness originates from four common deafness-causing genes: GJB2, SLC26A4, GJB3, and MT-RNR1. A single-tube rapid detection method based on 2D-PCR technology was established for nine mutation sites in the aforementioned genes, and Sanger sequencing was used to verify its reliability and accuracy. The frequency of hotspot mutations in deafness genes was analysed in 116 deaf students. 2D-PCR identified 27 genotypes of nine loci according to the melting curve of the FAM, HEX, and Alexa568 fluorescence channels. Of the 116 deaf patients, 12.9% (15/116) carried SLC26A4 mutations, including c.919-2A > G and c.2168A > G (allele frequencies, 7.3% and 2.2%, respectively). The positivity rate (29.3%; 34/116) was highest for GJB2 (allele frequency, 15.9% for c.235delC, 6.0% for c.299_300delAT, and 2.6% for c.176-191del16). Sanger sequencing confirmed the consistency of results between the detection methods based on 2D-PCR and DNA sequencing. Common pathogenic mutations in patients with non-syndromic deafness in Changzhou were concentrated in GJB2 (c.235delC, c.299_300delAT, and c.176-191del16) and SLC26A4 (c.919-2A > G and c.2168 A > G). 2D-PCR is an effective method for accurately and rapidly identifying deafness-related genotypes using a single-tube reaction, and is superior to DNA sequencing, which has a high cost and long cycle.

Genetic screening of 15 hearing loss variants in 77,647 neonates with clinical follow-up.

BACKGROUND: To analyze the genotype distribution and frequency of hearing loss genes in newborn population and evaluate the clinical value of genetic screening policy in China. METHODS: Genetic screening for hearing loss was offered to 84,029 neonates between March 2019 and December 2021, of whom 77,647 newborns accepted the screening program with one-year follow-up. The genotyping of 15 hot spot variants in GJB2, GJB3, SLC26A4, and MT-RNR1 was performed on microarray platform. RESULTS: A total of 3.05% (2369/77,647) newborns carried at least one genetic hearing loss-associated variant, indicated for early preventive management. The carrier frequency of GJB2 gene was the highest, at 1.48% (1147/77,647), followed by SLC26A4 gene at 1.07% (831/77,647), and GJB3 gene at 0.23% (181/77,647). GJB2 c.235delC variant and SLC26A4 IVS7-2A>G variant were the most common allelic variants with allele frequency of 0.6304% (979/155,294) and 0.3992% (620/155,294), respectively. 10 children are identified as homozygous or compound heterozygous for pathogenic variants (4 in GJB2, 6 in SLC26A4), and 7 of these infants had passed the hearing screening. Following up of the genetically screened newborns revealed that genetic screening detected more hearing-impaired infants than hearing screening alone. Genetic screening helped identify the infants who had passed the initial hearing screening, and reduced time for diagnosis and intervention of hearing aid. In addition, we identified 234 newborns (0.30%, 234/77,647) susceptible to preventable aminoglycoside antibiotic ototoxicity undetectable by hearing screening. CONCLUSION: We performed the largest-scale neonatal carrier screening for hearing loss genes in Southeast China. Our results indicated that genetic screening is an important complementation to conventional hearing screening. Our practice and experience may facilitate the application and development of neonatal genetic screening policy in mainland China.

Targeting NANOG and FAK via Cx26-derived Cell-penetrating Peptides in Triple-negative Breast Cancer.

Triple-negative breast cancer (TNBC) represents the most lethal and treatment-resistant breast cancer subtype with limited treatment options. We previously identified a protein complex unique to TNBC composed of the gap junction protein connexin 26 (Cx26), the pluripotency transcription factor NANOG, and focal adhesion kinase (FAK). We sought to determine whether a peptide mimetic of the interaction region of Cx26 attenuated tumor growth in preclinical models. We designed peptides based on Cx26 juxtamembrane domains and performed binding experiments with NANOG and FAK using surface plasmon resonance. Binding studies revealed that the Cx26 C-terminal tail and intracellular loop bound to NANOG and FAK with submicromolar-to-micromolar affinity and that a 5-amino acid sequence in the C-terminal tail of Cx26 (RYCSG) was sufficient for binding. Peptides with high affinity were engineered with a cell-penetrating antennapedia sequence and assessed in functional assays including cell proliferation, tumorsphere formation, and in vivo tumor growth, and downstream signaling changes were measured. The cell-penetrating Cx26 peptide (aCx26-pep) disrupted self-renewal while reducing nuclear FAK and NANOG and inhibiting NANOG target gene expression in TNBC cells but not luminal mammary epithelial cells. In vivo, aCx26-pep reduced tumor growth and proliferation and induced cell death. Here, we provide proof-of-concept that a Cx26 peptide-based strategy inhibits growth and alters NANOG activity specifically in TNBC, indicating the therapeutic potential of this targeting approach.

Mutation analysis of GJB2, SLC26A4, GJB3 and mtDNA12SrRNA genes in 251 non-syndromic hearing loss patients in Fujian, China.

OBJECTIVES: The molecular etiology of non-syndromic hearing loss (NSHL) in Southeastern China (Fujian) has not been precisely identified. our study selected patients with NSHL and analyzed their causative genes, which helped to improve the accuracy of the diagnosis of hereditary hearing loss (HHL) and its treatment. METHODS: 251 unrelated patients who attended the otolaryngology clinic of Fujian Maternal and Child Health Hospital with hearing loss were enrolled to our study. All patients had genetic tests and listening tests, of which 251 were diagnosed with NSHL. In addition, we used whole-exome sequencing (WES) in a patient who has a significant family history of HHL but negative for gene chip testing, as well as in his family members. RESULT: Among of 251 patients, Nucleotide changes were found in 63 cases (25.09%), including 34 located in GJB2(13.5%, including 235delC and 299_300delAT), 13 located in SLC26A4(5.18%, including c.919-2G > A and 2168 A > G), 1 located in GJB3(0.4%,538C > T) and 16 located in mtDNA12SrRNA (6.37%,1555 A > G). In addition, we discuss the process of identifying novel PLS1 mutations from 251 patients. CONCLUSION: Our results demonstrate the conventional deafness gene mutation in 251 NSHL patients in Fujian, China. Compared with the other area of China, we have a lower detection rate, but GJB2 235delC remains the most common mutation in Fujian. In addition, we discuss the process of discovering novel mutation locus for deafness, which provides an understanding for deafness diagnosis and genetic testing.

Hearing and Hearing Loss Progression in Patients with GJB2 Gene Mutations: A Long-Term Follow-Up.

We aimed to investigate whether the degree of hearing loss with GJB2 mutations could be predicted by distinguishing between truncating and non-truncating mutations and whether the genotype could predict the hearing loss level. Additionally, we examined the progression of hearing loss in individuals monitored for over 2 years for an average of 6.9 years. The proportion of truncating mutations was higher in patients with profound and severe hearing loss, but it was not accurate enough to predict the degree of hearing loss. Via genotype analysis, mutations of the p.Arg143Trp variants were associated with profound hearing loss, while mutations of the p.Leu79Cysfs*3 allele exhibited a wide range of hearing loss, suggesting that specific genotypes can predict the hearing loss level. Notably, there were only three cases of progression in four ears, all of which involved the p.Leu79Cysfs*3 mutation. Over the long-term follow-up, 4000 Hz was significant, and there was a trend of progression at 250 Hz, suggesting that close monitoring at these frequencies during follow-up may be crucial to confirm progression. The progression of hearing loss was observed in moderate or severe hearing loss cases at the time of the initial diagnosis, emphasizing that children with this level of hearing loss need regular follow-ups.

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.

Functional Consequences of Pathogenic Variants of the GJB2 Gene (Cx26) Localized in Different Cx26 Domains.

One of the most common forms of genetic deafness has been predominantly associated with pathogenic variants in the GJB2 gene, encoding transmembrane protein connexin 26 (Cx26). The Cx26 molecule consists of an N-terminal domain (NT), four transmembrane domains (TM1-TM4), two extracellular loops (EL1 and EL2), a cytoplasmic loop, and a C-terminus (CT). Pathogenic variants in the GJB2 gene, resulting in amino acid substitutions scattered across the Cx26 domains, lead to a variety of clinical outcomes, including the most common non-syndromic autosomal recessive deafness (DFNB1A), autosomal dominant deafness (DFNA3A), as well as syndromic forms combining hearing loss and skin disorders. However, for rare and poorly documented variants, information on the mode of inheritance is often lacking. Numerous in vitro studies have been conducted to elucidate the functional consequences of pathogenic GJB2 variants leading to amino acid substitutions in different domains of Cx26 protein. In this work, we summarized all available data on a mode of inheritance of pathogenic GJB2 variants leading to amino acid substitutions and reviewed published information on their functional effects, with an emphasis on their localization in certain Cx26 domains.