Biallelic p.V37I variant in GJB2 is associated with increasing incidence of hearing loss with age

Generation and characterization of a humanized GJB2 p.V37I knock-in mouse model for studying age-related hearing loss

Age-related hearing loss (ARHL) has been closely linked to genetic factors, with studies identifying the p.V37I mutation in the GJB2 gene as a potential contributor to ARHL. To investigate this, we generated a humanized p.V37I mutant mouse model and performed auditory brainstem response (ABR) testing, cochlear morphology assessments, and transcriptional sequence of mutant and wild-type (WT) mice at different ages. Our results indicated that this kind of GJB2 mutation does not lead to cochlear developmental abnormalities, and aging mutant mice exhibit only mild hearing loss compared to WT mice, without significant cochlear morphological differences. However, transcriptional analyses revealed substantial differences between mutant and WT mice. GO enrichment analysis of the DEGs between aging mutant and WT mice highlights significant enrichment in biological processes related to neural and sensory functions. Notably enriched terms include "neuron-to-neuron synapse," "immune response-activating signaling pathway," "regulation of synapse structure or activity," and "sensory perception of sound." These findings suggest that the p.V37I mutation in aging mice affects synaptic and calcium signaling pathways, as well as sensory system development. Despite these molecular changes, cochlear function remains normal in early life; however, as the mice age, hearing loss accelerates, likely due to a diminished capacity for gene-mediated protection against external stimuli.

Downregulation of Dmxl2 disrupts the hearing development in mice

Congenital hearing loss is a major type of sensorineural deafness. Recently, Dmxl2 has been identified as a new gene associated with familial deafness. However, its role in auditory development remains unclear. This study investigated the expression and localization of DmX-like protein 2 (DMXL2), encoded by Dmxl2, in the mouse cochlea at various postnatal stages. DMXL2 was predominantly expressed in inner and outer hair cells, with the highest levels at postnatal day 7, followed by a rapid decline, nearly disappearing by day 14. To elucidate Dmxl2's function, we administered short hairpin RNA (shRNA) targeting Dmxl2 to the cochlea within 24 h post-birth, effectively knocking down its expression in the mouse inner ear. This resulted in profound hearing loss in treated mice, accompanied by disruption of development of cochlear ribbon synapses and spiral ganglion cells (SGCs). In conclusion, our study demonstrates the critical role of Dmxl2 in hearing development, suggesting it as a potential molecular target for future gene therapy in hearing loss treatment.

Targeted gene sequencing and hearing follow-up in 7501 newborns reveals an improved strategy for newborn hearing screening

Hearing loss is a common congenital condition. Concurrent newborn hearing and limited genetic screening has been implemented in China for the last decade. However, the role of gene sequencing screening has not been evaluated. In this study, we enrolled 7501 newborns (52.7% male, 47.3% female) in our Newborn Screening with Targeted Sequencing (NESTS) program, and 90 common deafness genes were sequenced for them. Hearing status assessments were conducted via telephone from February 2021 to August 2022, for children aged 3 to 48 months. Of the universal newborn hearing screening, 126 (1.7%) newborns did not pass. Targeted sequencing identified 150 genetically positive newborns (2.0%), with 25 exhibiting dual-positive results in both screening. Following diagnostic audiometry revealed 18 hearing loss newborns and half of them had abnormal results in both screening. The positive predictive value for universal newborn hearing screening alone was merely 14.3% (18/126). However, when combined with targeted sequencing, this rate increased to 36.0% (9/25). Furthermore, limited genetic screening identified 316 carriers of hot-spot variants, but none exhibited biallelic variants. All 15 hot-spot carriers who failed physical screening demonstrated normal hearing during follow-up. In this cohort study of 7501 Newborns, Combining targeted sequencing with universal newborn hearing screening demonstrated technical feasibility and clinical utility of identifying individuals with hearing loss, especially when coupled with genetic counseling and closed-loop management. It is suggested to use this integrated method as an improved strategy instead of the current limited genetic screening program in some regions of China.

Identification of novel CDH23 heterozygous variants causing autosomal recessive nonsyndromic hearing loss

BACKGROUND

Hearing loss adversely impacts language development, acquisition, and the social and cognitive maturation of affected children. The hearing loss etiology mainly includes genetic factors and environmental factors, of which the former account for about 50-60%.

OBJECTIVE

This study aimed to investigate the genetic basis of autosomal recessive non-syndromic hearing loss (NSHL) by identifying and characterizing novel variants in the CDH23 gene. Furthermore, it seeks to determine the pathogenic potential of the noncanonical splice site variant c.2398-6G > A.

METHODS

Comprehensive clinical evaluation and whole-exome sequencing (WES) were performed on the girl. The WES analysis revealed two novel variants in the CDH23 gene, associated with nonsyndromic deafness 12 (DFNB12). To further explore the pathogenicity of these variants, functional studies involving in vivo splicing analysis were performed on the novel noncanonical splice site variant, c.2398-6G > A, which was initially classified as a variant of uncertain significance (VUS).

RESULTS

Whole-exome sequencing of the patient identified two compound heterozygous variants in CDH23: c.2398-6G > A, a noncanonical splice site variant, and c.6068C > A (p. Ser2023Ter), a nonsense mutation. In vitro splicing assays demonstrated that c.2398-6G > A caused aberrant splicing, leading to a frameshift (p. Val800Alafs*6) and the production of a truncated protein, as confirmed by structural protein analysis. The study revealed novel mutations as likely pathogenic, linking both variants to autosomal recessive NSHL.

CONCLUSIONS

Our analyses revealed novel compound heterozygous mutations in CDH23 associated with autosomal recessive NSHL, thereby expanding the mutational landscape of CDH23-related hearing loss and increasing knowledge about the CDH23 splice site variants.

Expanded carrier screening for 224 monogenic disease genes in 1,499 Chinese couples: a single-center study

OBJECTIVES

Expanded carrier screening (ECS) is a preventive genetic test that enables couples to know their risk of having a child affected by certain monogenetic diseases. This study aimed to evaluate the carrier frequency for rare monogenic diseases in the general Chinese population and the impacts of ECS on their reproductive decisions and pregnancy outcomes.

METHODS

This single-center study was conducted between September 2022 and April 2023. An ECS panel containing 224 recessive genes was offered to 1,499 Chinese couples from the general population who were at early gestational ages or planned to conceive.

RESULTS

Overall, 55.0 % of the individuals carried for at least one recessive condition. There were 16 autosomal recessive (AR) genes with a carrier frequency of ≥1/100 and 22 AR genes with a carrier frequency of <1/100 to ≥1/200. The most common AR and X-linked diseases were GJB2-related non-syndromic hearing loss, and hemolytic anemia, respectively. Fifty-five couples (3.67 %; 1 in 27.3) were at increased risk of having an affected child with 19 pregnant at the time of testing. Of these, 10 opted for amniocentesis, and four affected pregnancies were identified, with three of them being terminated.

CONCLUSIONS

This study not only provides valuable information about the recessive genetic landscape, but also establishes a solid foundation for couple-based ECS in a real clinical setting.

Clinical utility of expanded carrier screening in the preconception and prenatal population: A Chinese cohort study

OBJECTIVES

To evaluate the clinical utility of expanded carrier screening (ECS) in Chinese preconception and prenatal populations, focusing on carrier frequency and the impact on at-risk couples (ARCs).

METHODS

Data from 6,298 Chinese individuals from 4,420 families who underwent a 149-gene ECS panel at a single center were analyzed. The prevalence of positive carriers and ARCs was determined, with follow-up on reproductive decisions and pregnancy outcomes for ARCs.

RESULTS

Of the individuals screened, 2,673 (42.4 %) were carriers of at least one pathogenic or likely pathogenic variant, and 98 (2.22 %) ARCs were identified. GJB2-related deafness and Duchenne muscular dystrophy were the most common autosomal recessive (AR) and X-linked disorders. Screening the top 11 (gene carrier rate [GCR] ≥ 1/100), 22 (GCR ≥ 1/200), and 41 (GCR ≥ 1/331) AR genes could identify 53.5 %, 67.9 %, and 81.3 % of variants, respectively. The corresponding ratios for identified ARCs were 90.4 %, 94.0 %, and 100 %. Follow-up data from 80 ARCs indicated that 75.0 % (60/80) took significant action based on the ECS results. Additionally, four families (3.5 %, 4/115) were identified at risk for a second disease unrelated to their initial family monogenic history.

CONCLUSIONS

This study, representing the largest cohort of a moderate-sized ECS panel test in the Chinese population, demonstrates the clinical utility of ECS in both healthy individuals and those with a family history of monogenic disorders. The data obtained provide valuable insights for developing a Chinese-specific ECS panel. Tailored approaches are critical for wider adoption and successful routine application of ECS.

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.

Genotype-phenotype analysis of hearing function in patients with DFNB1A caused by the c.-23+1G>A splice site variant of the GJB2 gene (Cx26)

The audiological features of hearing loss (HL) in patients with autosomal recessive deafness type 1A (DFNB1A) caused by splice site variants of the GJB2 gene are less studied than those of patients with other variants of this gene. In this study, we present the audiological features of DFNB1A in a large cohort of 134 patients with the homozygous splice site variant c.-23+1G>A and 34 patients with other biallelic GJB2 genotypes (n = 168 patients with DFNB1A). We found that the preservation of hearing thresholds in the speech frequency range (PTA0.5,1.0,2.0,4.0 kHz) in patients with the c.[-23+1G>A];[-23+1G>A] genotype is significantly better than in patients with the "severe" c.[35delG];[35delG] genotype (p = 0.005) and significantly worse than in patients with the "mild" c.[109G>A];[109G>A] genotype (p = 0.041). This finding indicates a "medium" pathological effect of this splice site variant on hearing function. A detailed clinical and audiological analysis showed that in patients with the c.[-23+1G>A];[-23+1G>A] genotype, HL is characterized as congenital or early onset (57.5% onset before 12 months), sensorineural (97.8%), bilateral, symmetrical (82.8%), variable in severity (from mild to profound HL, median hearing threshold in PTA0.5,1.0,2.0,4.0 kHz is 86.73±21.98 dB), with an extremely "flat" audioprofile, and with a tendency toward slow progression (a positive correlation of hearing thresholds with age, r = 0.144, p = 0.041). In addition, we found that the hearing thresholds in PTA0.5,1.0,2.0,4.0 kHz were significantly better preserved in females (82.34 dB) than in males (90.62 dB) (p = 0.001). We can conclude that in patients with DFNB1A caused by the c.-23+1G>A variant, male sex is associated with deteriorating auditory function; in contrast, female sex is a protective factor.

Age-related hearing loss in older adults: etiology and rehabilitation strategies

Age-related hearing loss (ARHL) is a prevalent sensory organ disorder among elderly individuals that significantly impacts their cognitive function, psychological well-being, and ability to perform activities of daily living. As the population ages, the number of ARHL patients is increasing. However, the Audiological rehabilitation (AR) status of patients is not promising. In recent years, there has been an increasing focus on the health and rehabilitation of elderly individuals, and significant progress has been made in researching various age-related disorders. However, a unified definition of ARHL in terms of etiology and rehabilitation treatment is still lacking. This study aims to provide a reference for future research on ARHL and the development of AR strategies by reviewing the classification, etiology, and rehabilitation of ARHL.

Genetic screening of newborns for deafness over 11 years in Beijing, China: More infants could benefit from an expanded program

Genetic screening of newborns for deafness plays an important role in elucidating the etiology of deafness, diagnosing it early, and intervening in it. Genetic screening of newborns has been conducted for 11 years in Beijing. It started with a chip to screen for 9 variants of 4 genes in 2012; the chip screened for 15 variants of those genes in 2018, and it now screens for 23 variants of those genes. In the current study, a comparative analysis of three screening protocols and follow-up for infants with pathogenic variants was performed. The rates of detection and hearing test results of infants with pathogenic variants were analyzed. Subjects were 493,821 infants born at 122 maternal and child care centers in Beijing from April 2012 to August 2023. Positivity increased from 4.599% for the chip to screen for 9 variants to 4.971% for the chip to screen for 15 variants, and further to 11.489% for the chip to screen for 23 variants. The carrier frequency of the GJB2 gene increased from 2.489% for the chip to screen for 9 variants and 2.422% for the chip to screen for 15 variants to 9.055% for the chip to screen for 23 variants. The carrier frequency of the SLC26A4 gene increased from 1.621% for the chip to screen for 9 variants to 2.015% for the chip to screen for 15 variants and then to 2.151% for the chip to screen for 23 variants. According to the chip to screen for 9 variants and the chip to screen for 15 variants, the most frequent mutant allele was c.235delC. According to the chip to screen for 23 variants, the most frequent mutant allele was c.109G>A. The chip to screen for 15 variants was used to screen 66.67% (14/21) of newborns with biallelic variants in the SLC26A4 gene for newly added mutations. The chip to screen for 23 variants was used to screen 92.98% (53/57) of newborns with biallelic variants in the GJB2 gene (52 cases were biallelic c.109G>A) and 25% (1/4) of newborns with biallelic variants in the SLC26A4 gene for newly added mutations. Among the infants with pathogenic variants (biallelic variants in GJB2 or SLC26A4), 20.66% (25/121) currently have normal hearing. In addition, 34.62% (9/26) of newborns who passed the hearing screening were diagnosed with hearing loss. Findings indicate that a growing number of newborns have benefited, and especially in the early identification of potential late-onset hearing loss, as the number of screening sites has increased. Conducting long-term audiological monitoring for biallelic variants in individuals with normal hearing is of paramount significance.

Deficient Gap Junction Coupling in Two Common Hearing Loss-Related Variants of GJB2

OBJECTIVES

The aim of this study was to explore the functional consequences of two common variants, p.V37I and c.299-300delAT, in the hearing loss-associated gene GJB2.

METHODS

Connexin 26 expression and gap junctional permeability were studied in HEK 293T cells transfected with plasmids expressing GJB2 wild-type, p.V37I, or c.299-300delAT CX26 proteins tagged with fluorescent markers. Functional analyses of various GJB2 haplotypes were conducted to thoroughly evaluate alterations in ionic and small-molecule coupling.

RESULTS

The p.V37I protein was localized at the plasma membrane, but it failed to effectively transport intercellular propidium iodide or Ca2+ efficiently, indicating an impairment in both biochemical and ionic coupling. The presence of GJB2 p.V37I seemed to increase the cells' sensitivity to H2O2 treatment. In contrast, the known variant c.299-300delAT protein was not transported to the cell membrane and was unable to form gap junctions, remaining confined to the cytoplasm. Both ionic and biochemical coupling were defective in cells transfected with c.299-300delAT.

CONCLUSION

The p.V37I and c.299-300delAT GJB2 mutations resulted in deficient gap junction-mediated coupling. Additionally, environmental factors could influence the functional outcomes of the GJB2 p.V37I mutation. These findings could pave the way for the development of molecular therapies targeting GJB2 mutations to treat hearing loss.

Population genetic admixture and evolutionary history in the Shandong Peninsula inferred from integrative modern and ancient genomic resources

BACKGROUND

Ancient northern East Asians (ANEA) from the Yellow River region, who pioneered millet cultivation, play a crucial role in understanding the origins of ethnolinguistically diverse populations in modern China and the entire landscape of deep genetic structure and variation discovery in modern East Asians. However, the direct links between ANEA and geographically proximate modern populations, as well as the biological adaptive processes involved, remain poorly understood.

RESULTS

Here, we generated genome-wide SNP data for 264 individuals from geographically different Han populations in Shandong. An integrated genomic resource encompassing both modern and ancient East Asians was compiled to examine fine-scale population admixture scenarios and adaptive traits. The reconstruction of demographic history and hierarchical clustering patterns revealed that individuals from the Shandong Peninsula share a close genetic affinity with ANEA, indicating long-term genetic continuity and mobility in the lower Yellow River basin since the early Neolithic period. Biological adaptive signatures, including those related to immune and metabolic pathways, were identified through analyses of haplotype homozygosity and allele frequency spectra. These signatures are linked to complex traits such as height and body mass index, which may be associated with adaptations to cold environments, dietary practices, and pathogen exposure. Additionally, allele frequency trajectories over time and a haplotype network of two highly differentiated genes, ABCC11 and SLC10A1, were delineated. These genes, which are associated with axillary odor and bilirubin metabolism, respectively, illustrate how local adaptations can influence the diversification of traits in East Asians.

CONCLUSIONS

Our findings provide a comprehensive genomic dataset that elucidates the fine-scale genetic history and evolutionary trajectory of natural selection signals and disease susceptibility in Han Chinese populations. This study serves as a paradigm for integrating spatiotemporally diverse ancient genomes in the era of population genomic medicine.

Recurrent missense variant identified in two unrelated families with MPZL2-related hearing loss, expanding the variant spectrum associated with DFNB111

MPZL2-related hearing loss is a rare form of autosomal recessive hearing loss characterized by progressive, mild sloping to severe sensorineural hearing loss. Thirty-five previously reported patients had biallelic truncating variants in MPZL2, with the exception of one patient with a missense variant of uncertain significance and a truncating variant. Here, we describe the clinical characteristics and genotypes of five patients from four families with confirmed MPZL2-related hearing loss. A rare missense likely pathogenic variant [NM_005797.4(MPZL2):c.280C>T,p.(Arg94Trp)] located in exon 3 was confirmed to be in trans with a recurrent pathogenic truncating variant that segregated with hearing loss in three of the patients from two unrelated families. This is the first recurrent likely pathogenic missense variant identified in MPZL2. Apparently milder or later-onset hearing loss associated with rare missense variants in MPZL2 indicates that some missense variants in this gene may cause a milder phenotype than that resulting from homozygous or compound heterozygous truncating variants. This study, along with the identification of truncating loss of function and missense MPZL2 variants in several diverse populations, suggests that MPZL2-related hearing loss may be more common than previously appreciated and demonstrates the need for MPZL2 inclusion in hearing loss testing panels.

Newborn hearing screening program in China: a narrative review of the issues in screening and management

Hearing loss is one of the most common sensory disorders in humans. The purpose of this review is to summarize the history and current status of newborn hearing screening in China and to investigate future developmental trends in newborn hearing screening with the intention of sharing experiences and providing a reference for other populations. In the 1980s, the research on hearing monitoring for high-risk infants led to the gradual development of newborn hearing screening in China. With the continuous improvement of screening technology, the newborn hearing screening program was gradually extended to the whole country and became a government-led multidisciplinary public health program. Genetic screening for deafness has been incorporated into newborn hearing screening in many regions of China to help screen for potential and late-onset deafness in newborns. In the future, it is necessary to further establish and improve whole life-cycle hearing screening and healthcare, conduct screening for congenital cytomegalovirus infection, and create a full-coverage, whole life course hearing screening and intervention system. Screening for deafness in China has been marked by 40 years of achievements, which have been a source of pride for entrepreneurs and comfort for patients and their families. Managing hearing screening data information more efficiently and establishing a quality control index system throughout the whole screening process are of paramount importance. The genetic screening for concurrent newborn hearing and deafness has a great clinical importance for the management of congenital deafness and prevention of ototoxicity. A hearing screening and intervention system across the whole life course should be developed.

Molecular Mechanisms and Clinical Phenotypes of GJB2 Missense Variants

The GJB2 gene is the most common gene responsible for hearing loss (HL) worldwide, and missense variants are the most abundant type. GJB2 pathogenic missense variants cause nonsyndromic HL (autosomal recessive and dominant) and syndromic HL combined with skin diseases. However, the mechanism by which these different missense variants cause the different phenotypes is unknown. Over 2/3 of the GJB2 missense variants have yet to be functionally studied and are currently classified as variants of uncertain significance (VUS). Based on these functionally determined missense variants, we reviewed the clinical phenotypes and investigated the molecular mechanisms that affected hemichannel and gap junction functions, including connexin biosynthesis, trafficking, oligomerization into connexons, permeability, and interactions between other coexpressed connexins. We predict that all possible GJB2 missense variants will be described in the future by deep mutational scanning technology and optimizing computational models. Therefore, the mechanisms by which different missense variants cause different phenotypes will be fully elucidated.

Clinical Utility of Medical Exome Sequencing: Expanded Carrier Screening for Patients Seeking Assisted Reproductive Technology in China

Purpose: Expanded carrier screening (ECS) is an effective method to identify at-risk couples (ARCs) and avoid birth defects. This study aimed to reveal the carrier spectrum in the Chinese population and to delineate an expanded carrier gene panel suitable in China.

Methods: Medical exome sequencing (MES), including 4,158 disease-causing genes, was offered to couples at two reproductive centers. It was initially used as a diagnostic yield for potential patients and then used for ECS. Clinical information and ECS results were retrospectively collected.

Results: A total of 2,234 couples, representing 4,468 individuals, underwent MES. In total, 254 individuals showed genetic disease symptoms, and 56 of them were diagnosed with genetic diseases by MES. Overall, 94.5% of them were carriers of at least one disease-causing variant. The most prevalent genes were GJB2 for autosomal recessive disorders and G6PD for X-linked diseases. The ARC rate was 9.80%, and couples were inclined to undergo preimplantation genetic testing when diseases were classified as “profound” or “severe.”

Conclusion: This study provided insight to establish a suitable ECS gene panel for the Chinese population. Disease severity significantly influenced reproductive decision-making. The results highlighted the importance of conducting ECS for couples before undergoing assisted reproductive technology.

A novel MPZL2 c.68delC variant is associated with progressive hearing loss in Chinese population and literature review

Objective

The aim of this study was to identify genetic etiology in two unrelated Chinese probands with progressive sensorineural hearing loss.

Methods

Two unrelated Chinese families were recruited. Genetic etiology was identified by targeted next-generation sequencing (NGS) and verified by Sanger sequencing. Hearing evaluations included pure tone audiometry, auditory brainstem response to clicks, and otoscopic examination. Medical history and computerized tomography scan of temporal bone were also collected. In addition, linear regression was used to summarize all of the reported cases and estimate the progression of hearing loss.

Results

A 28-year-old man with variant c.68delC had progressive, moderately severe hearing loss and a suspicious history of renal impairment. His hearing result was 63.75 dB HL. The other proband was the youngest patient with MPZL2-related hearing loss reported so far in the literature (genotype: c.220C>T homozygote). Her hearing result by click-ABR was 25 dB nHL at 3 months of age, and deteriorated to 40 dB nHL at 15 months. Behavioral audiometry identified a hearing loss of 26.25 dB HL. In summarizing all of the reported cases, using linear regression, MPZL2-related hearing loss may deteriorate by 0.59 dB HL per year, and different MPZL2 variants may lead to different rates of progression.

Conclusion

In this study, we first identified two unrelated patients with MPZL2-related hearing loss in Chinese population, and a novel variant c.68delC. Our results expanded the mutation spectrum of deafness genes. Further studies are required to clarify the genotype-phenotype correlation and the progression of MPZL2-related hearing loss.