Strong founder effect of p.P240L in CDH23 in Koreans and its significant contribution to severe-to-profound nonsyndromic hearing loss in a Korean pediatric population

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.

Segregation of Trans Mutations in the CDH23 Gene in an Emirati Family with Sensorineural Hearing Loss

BACKGROUND/OBJECTIVES

Hearing loss (HL) is a significant global health concern, affecting approximately 1 in every 1000 newborns, with over half of these cases attributed to genetic factors. This study focuses on identifying the genetic basis of autosomal recessive non-syndromic hearing loss (ARNSHL) in a consanguineous Emirati family.

METHODS

Clinical exome sequencing (CES) was performed on affected members of the family, followed by Sanger sequencing to validate the findings. Specific primers were used for PCR amplification of target CDH23 exons. Mutations were analyzed using various computational tools to assess their pathogenicity.

RESULTS

We identified two heterozygous mutations in the CDH23 gene: a novel nonsense variant (c.264G>A, p.Trp88Ter) and a missense variant (c.5168G>A, p.Arg1723His). Both mutations were found in trans configuration, suggesting a compound heterozygous state contributing to the phenotype. In silico analysis predicted a significant impact on protein function, potentially leading to the observed ARNSHL.

CONCLUSIONS

This study emphasizes the complexity of genetic factors in hearing loss, particularly in highly consanguineous populations. The identification of both nonsense and missense mutations in the CDH23 gene enhances understanding of its role in hearing loss and provides essential insights for genetic counseling and future therapeutic strategies.

A case of primary ciliary dyskinesis with DRC1 deletion and literature review: Additional evidence on the founder effect

BACKGROUND

Primary ciliary dyskinesia (PCD) is a rare genetic disease caused by defects in various genes affecting ciliary function. It is currently unclear why DRC1 gene variants are a relatively frequent cause of disease in Japanese and Korean patients.

METHODS

A 12-year-old Japanese girl with bronchiectasis was suspected of PCD and examined using whole-exome sequencing (WES). The breakpoint region was confirmed by Sanger sequencing and evaluation of transposable elements.

RESULTS

Whole-exome sequencing revealed a deletion of DRC1 exons 1-4 in the patient, followed by validation with Sanger sequencing. A DRC1 exon 1-4 deletion is recurrently observed in Japanese and Korean patients with PCD. All reported patients carry the same breakpoint region, which shows signs of Alu-mediated recombination. Intriguingly, common haplotypes were observed around the DRC1 gene in Japanese and Korean patients.

CONCLUSION

The recurrent DRC1 exon 1-4 deletion is therefore likely to be a founder variant and should be considered a major genetic cause of PCD in Japanese and Korean patients with PCD.

Global Distribution of Founder Variants Associated with Non-Syndromic Hearing Impairment

The genetic etiology of non-syndromic hearing impairment (NSHI) is highly heterogeneous with over 124 distinct genes identified. The wide spectrum of implicated genes has challenged the implementation of molecular diagnosis with equal clinical validity in all settings. Differential frequencies of allelic variants in the most common NSHI causal gene, gap junction beta 2 (GJB2), has been described as stemming from the segregation of a founder variant and/or spontaneous germline variant hot spots. We aimed to systematically review the global distribution and provenance of founder variants associated with NSHI. The study protocol was registered on PROSPERO, the International Prospective Register of Systematic Reviews, with the registration number "CRD42020198573". Data from 52 reports, involving 27,959 study participants from 24 countries, reporting 56 founder pathogenic or likely pathogenic (P/LP) variants in 14 genes (GJB2, GJB6, GSDME, TMC1, TMIE, TMPRSS3, KCNQ4, PJVK, OTOF, EYA4, MYO15A, PDZD7, CLDN14, and CDH23), were reviewed. Varied number short tandem repeats (STRs) and single nucleotide polymorphisms (SNPs) were used for haplotype analysis to identify the shared ancestral informative markers in a linkage disequilibrium and variants' origins, age estimates, and common ancestry computations in the reviewed reports. Asia recorded the highest number of NSHI founder variants (85.7%; 48/56), with variants in all 14 genes, followed by Europe (16.1%; 9/56). GJB2 had the highest number of ethnic-specific P/LP founder variants. This review reports on the global distribution of NSHI founder variants and relates their evolution to population migration history, bottleneck events, and demographic changes in populations linked with the early evolution of deleterious founder alleles. International migration and regional and cultural intermarriage, coupled to rapid population growth, may have contributed to re-shaping the genetic architecture and structural dynamics of populations segregating these pathogenic founder variants. We have highlighted and showed the paucity of data on hearing impairment (HI) variants in Africa, establishing unexplored opportunities in genetic traits.

Variants in CDH23 cause a broad spectrum of hearing loss: from non-syndromic to syndromic hearing loss as well as from congenital to age-related hearing loss

Variants in the CDH23 gene are known to be responsible for both syndromic hearing loss (Usher syndrome type ID: USH1D) and non-syndromic hearing loss (DFNB12). Our series of studies demonstrated that CDH23 variants cause a broad range of phenotypes of non-syndromic hearing loss (DFNB12); from congenital profound hearing loss to late-onset high-frequency-involved progressive hearing loss. In this study, based on the genetic and clinical data from more than 10,000 patients, the mutational spectrum, clinical characteristics and genotype/phenotype correlations were evaluated. The present results reconfirmed that the variants in CDH23 are an important cause of non-syndromic sensorineural hearing loss. In addition, we showed that the mutational spectrum in the Japanese population, which is probably representative of the East Asian population in general, as well as frequent CDH23 variants that might be due to some founder effects. The present study demonstrated CDH23 variants cause a broad range of phenotypes, from non-syndromic to syndromic hearing loss as well as from congenital to age-related hearing loss. Genotype (variant combinations) and phenotype (association with retinal pigmentosa, onset age) are shown to be well correlated and are thought to be related to the residual function defined by the CDH23 variants.

Cochlear Implantation Outcomes in Children With CDH23 Mutations-Associated Hearing Loss

OBJECTIVE

Mutations in the cadherin 23 gene (CDH23) have been reported to cause cochlear damage, but few studies have investigated the auditory and speech outcome of patients after cochlear implantation. Here, we describe the genetic, auditory, and postoperative outcomes of patients with CDH23 mutations who received cochlear implants.

STUDY DESIGN

Retrospective case review.

SETTING

Tertiary referral center.

METHODS

Targeted deafness-related gene panels were sequenced in Chinese families with profound sensorineural hearing loss. The clinical features of subjects carrying potentially pathogenic CDH23 mutations were analyzed.

RESULTS

Between 2017 and 2019, we identified 5 children with prelinguistically profound hearing loss at our center who harbored 6 variants of CDH23 that segregated with the disease. Of these, 4 variants were novel (c.2591G>T, c.4785G>C, c.5765A>G, and c.9280_9281insTT). All affected individuals had a loss of outer hair cell function, with an average residual hearing level of 3 to 10 dB SPL. Cochlear implantations were arranged for the patients at 11 to 36 months of age. All children made gains in their hearing, language, and speech performances 14 to 120 months after surgery. Their auditory outcomes improved during follow-up intervals.

CONCLUSION

This study revealed that children with congenital cochlear defects caused by CDH23 variants can acquire an acceptable auditory and speech outcome after cochlear implantation. Early genetic detection and prenatal counseling for rare deafness genes such as CDH23 remain a priority for the future.

The genetic etiology of hearing loss in Japan revealed by the social health insurance-based genetic testing of 10K patients

Etiological studies have shown genetic disorders to be a major cause of sensorineural hearing loss, but there are a limited number of comprehensive etiological reports based on genetic analysis. In the present study, the same platform using a diagnostic DNA panel carrying 63 deafness genes and the same filtering algorithm were applied to 10,047 samples obtained from social health insurance-based genetic testing of hearing loss. The most remarkable result obtained in this comprehensive study was that the data first clarified the genetic epidemiology from congenital/early-onset deafness to late-onset hearing loss. The overall diagnostic rate was 38.8%, with the rate differing for each age group; 48.6% for the congenital/early-onset group (~5y.o.), 33.5% for the juvenile/young adult-onset group, and 18.0% for the 40+ y.o. group. Interestingly, each group showed a different kind of causative gene. With regard to the mutational spectra, there are certain recurrent variants that may be due to founder effects or hot spots. A series of haplotype studies have shown many recurrent variants are due to founder effects, which is compatible with human migration. It should be noted that, regardless of differences in the mutational spectrum, the clinical characteristics caused by particular genes can be considered universal. This comprehensive review clarified the detailed clinical characteristics (onset age, severity, progressiveness, etc.) of hearing loss caused by each gene, and will provide useful information for future clinical application, including genetic counseling and selection of appropriate interventions.

Rising of LOXHD1 as a signature causative gene of down-sloping hearing loss in people in their teens and 20s

BACKGROUND

Down-sloping sensorineural hearing loss (SNHL) in people in their teens and 20s hampers efficient learning and communication and in-depth social interactions. Nonetheless, its aetiology remains largely unclear, with the exception of some potential causative genes, none of which stands out especially in people in their teens and 20s. Here, we examined the role and genotype-phenotype correlation of lipoxygenase homology domain 1 (LOXHD1) in down-sloping SNHL through a cohort study.

METHODS

Based on the Seoul National University Bundang Hospital (SNUBH) genetic deafness cohort, in which the patients show varying degrees of deafness and different onset ages (n=1055), we have established the 'SNUBH Teenager-Young Adult Down-sloping SNHL' cohort (10-35 years old) (n=47), all of whom underwent exome sequencing. Three-dimensional molecular modelling, minigene splicing assay and short tandem repeat marker genotyping were performed, and medical records were reviewed.

RESULTS

LOXHD1 accounted for 33.3% of all genetically diagnosed cases of down-sloping SNHL (n=18) and 12.8% of cases in the whole down-sloping SNHL cohort (n=47) of young adults. We identified a potential common founder allele, as well as an interesting genotype-phenotype correlation. We also showed that transcript 6 is necessary and probably sufficient for normal hearing.

CONCLUSIONS

LOXHD1 exceeds other genes in its contribution to down-sloping SNHL in young adults, rising as a signature causative gene, and shows a potential but interesting genotype-phenotype correlation.

The GBA p.G85E mutation in Korean patients with non-neuronopathic Gaucher disease: founder and neuroprotective effects

Background

Gaucher disease (GD) is caused by a deficiency of β-glucocerebrosidase, encoded by GBA. Haplotype analyses previously demonstrated founder effects for particular GBA mutations in Ashkenazi Jewish and French-Canadian populations. This study aimed to investigate the clinical characteristics and mutation spectrum of GBA in Korean GD patients and to identify founder effect of GBA p.G85E in non-neuronopathic GD patients.

Results

The study cohort included 62 GD patients from 58 unrelated families. Among them, 18 patients from 17 families harbored the p.G85E mutation. Haplotype analysis was performed for 9 probands and their parents for whom DNA samples were available. In 58 unrelated probands, the GBA mutation p.L483P was the most common (30/116 alleles, 26%), followed by p.G85E (16%), p.F252I (13%), and p.R296Q (9%). The median age at diagnosis of the 18 patients harboring the p.G85E mutation was 3.8 (range 1.2–57) years. No patients developed neurological symptoms during follow-up periods of 2.2–20.3 (median 13.9) years. The size of the shared haplotype containing GBA p.G85E was 732 kbp, leading to an estimated age of 3075 years.

Conclusion

The GBA p.G85E mutation, which appears to be neuroprotective despite producing distinctive visceromegaly and skeletal symptoms, exhibited a potential founder effect in Korean GD patients.

Haplotype Analysis of GJB2 Mutations: Founder Effect or Mutational Hot Spot?

The GJB2 gene is the most frequent cause of congenital or early onset hearing loss worldwide. In this study, we investigated the haplotypes of six GJB2 mutations frequently observed in Japanese hearing loss patients (i.e., c.235delC, p.V37I, p.[G45E; Y136X], p.R143W, c.176_191del, and c.299_300delAT) and analyzed whether the recurring mechanisms for each mutation are due to founder effects or mutational hot spots. Furthermore, regarding the mutations considered to be caused by founder effects, we also calculated the age at which each mutation occurred using the principle of genetic clock analysis. As a result, all six mutations were observed in a specific haplotype and were estimated to derive from founder effects. Our haplotype data together with their distribution patterns indicated that p.R143W and p.V37I may have occurred as multiple events, and suggested that both a founder effect and hot spot may be involved in some mutations. With regard to the founders' age of frequent GJB2 mutations, each mutation may have occurred at a different time, with the oldest, p.V37I, considered to have occurred around 14,500 years ago, and the most recent, c.176_191del, considered to have occurred around 4000 years ago.

Differential disruption of autoinhibition and defect in assembly of cytoskeleton during cell division decide the fate of human DIAPH1-related cytoskeletopathy

Background

Diaphanous-related formin 1 (DIA1), which assembles the unbranched actin microfilament and microtubule cytoskeleton, is encoded by DIAPH1. Constitutive activation by the disruption of autoinhibitory interactions between the N-terminal diaphanous inhibitory domain (DID) and C-terminal diaphanous autoregulatory domain (DAD) dysregulates DIA1, resulting in both hearing loss and blood cell abnormalities.

Methods and results

Here, we report the first constitutively active mutant in the DID (p.A265S) of humans with only hearing loss and not blood cell abnormality through whole exome sequencing. The previously reported DAD mutants and our DID mutant (p.A265S) shared the finding of diminished autoinhibitory interaction, abnormally upregulated actin polymerisation activity and increased localisations at the plasma membrane. However, the obvious defect in the DIA1-driven assembly of cytoskeleton ‘during cell division’ was only from the DAD mutants, not from p.A265S, which did not show any blood cell abnormality. We also evaluated the five DID mutants in the hydrophobic pocket since four of these five additional mutants were predicted to critically disrupt interaction between the DID and DAD. These additional pathogenic DID mutants revealed varying degrees of defect in the DIA1-driven cytoskeleton assembly, including nearly normal phenotype during cell division as well as obvious impaired autoinhibition, again coinciding with our key observation in DIA1 mutant (p.A265S) in the DID.

Conclusion

Here, we report the first mutant in the DID of humans with only hearing loss. The differential cell biological phenotypes of DIA1 during cell division appear to be potential determinants of the clinical severity of DIAPH1-related cytoskeletopathy in humans.

Elucidation of the unique mutation spectrum of severe hearing loss in a Vietnamese pediatric population

The mutational spectrum of deafness in Indochina Peninsula, including Vietnam, remains mostly undetermined. This significantly hampers the progress toward establishing an effective genetic screening method and early customized rehabilitation modalities for hearing loss. In this study, we evaluated the genetic profile of severe-to-profound hearing loss in a Vietnamese pediatric population using a hierarchical genetic analysis protocol that screened 11 known deafness-causing variants, followed by massively parallel sequencing targeting 129 deafness-associated genes. Eighty-seven children with isolated severe-to-profound non-syndromic hearing loss without family history were included. The overall molecular diagnostic yield was estimated to be 31.7%. The mutational spectrum for severe-to-profound non-syndromic hearing loss in our Vietnamese population was unique: The most prevalent variants resided in the MYO15A gene (7.2%), followed by GJB2 (6.9%), MYO7A (5.5%), SLC26A4 (4.6%), TMC1 (1.8%), ESPN (1.8%), POU3F4 (1.8%), MYH14 (1.8%), EYA1 (1.8%), and MR-RNR1 (1.1%). The unique spectrum of causative genes in the Vietnamese deaf population was similar to that in the southern Chinese deaf population. It is our hope that the mutation spectrum provided here could aid in establishing an efficient protocol for genetic analysis of severe-to-profound hearing loss and a customized screening kit for the Vietnamese population.

Outcome of Cochlear Implantation in Prelingually Deafened Children According to Molecular Genetic Etiology

OBJECTIVES

About 60% of Korean pediatric cochlear implantees could be genetically diagnosed (GD) and we previously reported that a substantial portion of undiagnosed cases by deafness gene panel sequencing were predicted to have a nongenetic or complex etiology. We aimed to compare the outcomes of cochlear implantation (CI) in GD and genetically undiagnosed (GUD) patients and attempted to determine CI outcomes according to etiology.

DESIGN

Ninety-three pediatric cochlear implantees underwent molecular genetic testing. Fifty-seven patients carried pathogenic variants and 36 patients remained GUD after panel sequencing of 204 known or potential deafness genes (TRS-204). Among them, 55 cochlear implantees with reliable speech evaluation results with a follow-up of longer than 24 months were recruited. Longitudinal changes in the audiologic performance were compared between the GD (n = 31) and GUD (n = 24) groups. The GD group was subdivided into cochlear implantee with SLC26A4 mutations (group 1) and cochlear implantee with other genetic etiology (group 2), and the GUD group was subdivided into groups 3 and 4, that is, patients with or without inner ear anomaly, respectively.

RESULTS

Group 1 related to SLC26A4 mutations had the highest categories of auditory perception scores among all groups pre- and postoperatively. Group 4 with inner ear anomaly had the lowest categories of auditory perception scores. At 24 months post-CI, the group 2 with another genetic etiology had significantly better outcomes than molecularly undiagnosed group 3, which had with the same condition as group 2 except that the candidate gene was not detected. This finding was recapitulated when we limited cases to those that underwent CI before 24 months of age to minimize age-related bias at implantation. Furthermore, on extending the follow-up to 36 months postoperatively, this tendency became more prominent. Additionally, our preliminary clinical data suggest a narrower sensitive window period for good CI outcomes for implantees with OTOF mutation rather than the GJB2 and other genes.

CONCLUSIONS

Current molecular genetic testing including deafness panel sequencing helps to predict the 2-year follow-up outcomes after CI in prelingually deafened children. GD cochlear implantees show better functional outcomes after CI than undiagnosed cochlear implantees as determined by deafness panel sequencing, suggesting a genotype-functional outcome correlation. The genetic testing may provide a customized optimal window period in terms of CI timing for favorable outcome according to genetic etiology.

The tip link protein Cadherin-23: From Hearing Loss to Cancer

Cadherin-23 is an atypical member of the cadherin superfamily, with a distinctly long extracellular domain. It has been known to be a part of the tip links of the inner ear mechanosensory hair cells. Several studies have been carried out to understand the role of Cadherin-23 in the hearing mechanism and defects in the CDH23 have been associated with hearing impairment resulting from defective or absence of tip links. Recent studies have highlighted the role of Cadherin-23 in several pathological conditions, including cancer, suggesting the presence of several unknown functions. Initially, it was proposed that Cadherin-23 represents a yet unspecified subtype of Cadherins; however, no other proteins with similar characteristics have been identified, till date. It has a unique cytoplasmic domain that does not bear a β-catenin binding region, but has been demonstrated to mediate cell-cell adhesions. Several protein interacting partners have been identified for Cadherin-23 and the roles of their interactions in various cellular mechanisms are yet to be explored. This review summarizes the characteristics of Cadherin-23 and its roles in several pathologies including cancer.

Functional characterization of a novel loss-of-function mutation of PRPS1 related to early-onset progressive nonsyndromic hearing loss in Koreans (DFNX1): Potential implications on future therapeutic intervention

BACKGROUND

The symptoms of phosphoribosyl pyrophosphate synthetase 1 (PRPS1) deficiency diseases have been reported to be alleviated by medication. In the present study, we report biochemical data that favor PRPS1 deficiency-related hearing loss as a potential target for pharmaceutical treatment.

METHODS

We recruited 42 probands from subjects aged less than 15 years with a moderate degree of nonsyndromic autosomal-recessive or sporadic sensorineural hearing loss (SNHL) in at least one side. Molecular genetic testing, including targeted exome sequencing (TES) of 129 genes for deafness, and in silico prediction were performed.

RESULTS

A strong candidate variant (p.A82P) of PRPS1 is co-segregated with SNHL in X-linked recessive inheritance from one Korean multiplex SNHL family. Subsequent measurement of in vitro enzymatic activities of PRPS1 from erythrocytes of affected and unaffected family members, as well as unrelated normal controls, confirmed a pathogenic role of this variant. In detail, compared to normal hearing controls (0.23-0.26 nmol/ml/h), the proband, the affected sibling and their normal hearing mother demonstrated a significantly decreased PRPS1 enzymatic activity (0.07, 0.03 and 0.11 nmol/ml/h, respectively). This novel loss-of-function mutation of PRPS1 (p.A82P) is the ninth and sixth most reported mutation in the world and in Asia, respectively.

CONCLUSIONS

DFNX1 was found to account for approximately 2.4% (1/42) of moderate SNHL in a Korean pediatric population. Confirmation of PRPS1 activity deficiency and an audiologic phenotype that initially begins in a milder form of SNHL, as in our family, should indicate the need for rigorous genetic screening as early as possible.

ATP1A3 mutations can cause progressive auditory neuropathy: a new gene of auditory synaptopathy

The etiologies and prevalence of sporadic, postlingual-onset, progressive auditory neuropathy spectrum disorder (ANSD) have rarely been documented. Thus, we aimed to evaluate the prevalence and molecular etiologies of these cases. Three out of 106 sporadic progressive hearing losses turned out to manifest ANSD. Through whole exome sequencing and subsequent bioinformatics analysis, two out of the three were found to share a de novo variant, p.E818K of ATP1A3, which had been reported to cause exclusively CAPOS (cerebellar ataxia, areflexia, pes cavus, optic atrophy, and sensorineural hearing loss) syndrome. However, hearing loss induced by CAPOS has never been characterized to date. Interestingly, the first proband did not manifest any features of CAPOS, except subclinical areflexia; however, the phenotypes of second proband was compatible with that of CAPOS, making this the first reported CAPOS allele in Koreans. This ANSD phenotype was compatible with known expression of ATP1A3 mainly in the synapse between afferent nerve and inner hair cells. Based on this, cochlear implantation (CI) was performed in the first proband, leading to remarkable benefits. Collectively, the de novo ATP1A3 variant can cause postlingual-onset auditory synaptopathy, making this gene a significant contributor to sporadic progressive ANSD and a biomarker ensuring favorable short-term CI outcomes.

Mutation Spectrum of STAR and a Founder Effect of the p.Q258* in Korean Patients with Congenital Lipoid Adrenal Hyperplasia

Congenital lipoid adrenal hyperplasia (CLAH) is the most severe form of congenital adrenal hyperplasia, caused by defects in the steroidogenic acute regulatory protein (STAR). The STAR p.Q258* mutation is the most common mutation in China, Japan, and Korea, suggesting a founder effect. This study aimed to investigate the phenotypic and mutation spectrum of STAR defects and identify a founder effect of the p.Q258* mutation in Korean patients with CLAH. For 45 patients from 42 independent pedigrees, haplotype analysis was performed in 10 unrelated trio families, including patients with the p.Q258* mutation whose DNA samples were available, using 1,972 single nucleotide polymorphism (SNP) and six short tandem repeat (STR) markers. An Illumina Infinium® Human Omni2.5-8 v1.3 performed the SNP genotyping. Among 84 alleles from 42 unrelated families, mutation p.Q258* was found in 74 alleles (88.1%) from 41 families. A shared haplotype was identified in 17 of 20 alleles from 10 patients (size, 198 kb). The age of the founder mutation was estimated as 4,875 years (95% credible set: 3,575-7,925 years) assuming an intergenerational time interval of 25 years. The STAR p.Q258* mutation is the most common in Korean patients with CLAH, suggesting a founder effect. The age of the mutation corresponded with the date when the Korean people settled in the Korean peninsula. The high prevalence of p.Q258* in Japan and China also suggests a founder effect in Asian countries.

Discovery of CDH23 as a Significant Contributor to Progressive Postlingual Sensorineural Hearing Loss in Koreans

CDH23 mutations have mostly been associated with prelingual severe-to-profound sensorineural hearing loss (SNHL) in either syndromic or nonsyndromic SNHL (DFNB12). Herein, we demonstrate the contribution of CDH23 mutations to postlingual nonsyndromic SNHL (NS-SNHL). We screened 32 Korean adult probands with postlingual NS-SNHL sporadically or in autosomal recessive fashion using targeted panel or whole exome sequencing. We identified four (12.5%, 4/32) potential postlingual DFNB12 families that segregated the recessive CDH23 variants, qualifying for our criteria along with rapidly progressive SNHL. Three of the four families carried one definite pathogenic CDH23 variant previously known as the prelingual DFNB12 variant in a trans configuration with rare CDH23 variants. To determine the contribution of rare CDH23 variants to the postlingual NS-SNHL, we checked the minor allele frequency (MAF) of CDH23 variants detected from our postlingual NS-SNHL cohort and prelingual NS-SNHL cohort, among the 2040 normal control chromosomes. The allele frequency of these CDH23 variants in our postlingual cohort was 12.5%, which was significantly higher than that of the 2040 control chromosomes (5.53%), confirming the contribution of these rare CDH23 variants to postlingual NS-SNHL. Furthermore, MAF of rare CDH23 variants from the postlingual NS-SNHL group was significantly higher than that from the prelingual NS-SNHL group. This study demonstrates an important contribution of CDH23 mutations to poslingual NS-SNHL and shows that the phenotypic spectrum of DFNB12 can be broadened even into the presbycusis, depending on the pathogenic potential of variants. We also propose that pathogenic potential of CDH23 variants and the clinical fate of DFNB12 may be predicted by MAF.

Establishment of a Flexible Real-Time Polymerase Chain Reaction-Based Platform for Detecting Prevalent Deafness Mutations Associated with Variable Degree of Sensorineural Hearing Loss in Koreans

Many cutting-edge technologies based on next-generation sequencing (NGS) have been employed to identify candidate variants responsible for sensorineural hearing loss (SNHL). However, these methods have limitations preventing their wide clinical use for primary screening, in that they remain costly and it is not always suitable to analyze massive amounts of data. Several different DNA chips have been developed for screening prevalent mutations at a lower cost. However, most of these platforms do not offer the flexibility to add or remove target mutations, thereby limiting their wider use in a field that requires frequent updates. Therefore, we aimed to establish a simpler and more flexible molecular diagnostic platform based on ethnicity-specific mutation spectrums of SNHL, which would enable bypassing unnecessary filtering steps in a substantial portion of cases. In addition, we expanded the screening platform to cover varying degrees of SNHL. With this aim, we selected 11 variants of 5 genes (GJB2, SLC26A4, MTRNR1, TMPRSS3, and CDH23) showing high prevalence with varying degrees in Koreans and developed the U-TOP™ HL Genotyping Kit, a real-time PCR-based method using the MeltingArray technique and peptide nucleic acid probes. The results of 271 DNA samples with wild type sequences or mutations in homo- or heterozygote form were compared between the U-TOP™ HL Genotyping Kit and Sanger sequencing. The positive and negative predictive values were 100%, and this method showed perfect agreement with Sanger sequencing, with a Kappa value of 1.00. The U-TOP™ HL Genotyping Kit showed excellent performance in detecting varying degrees and phenotypes of SNHL mutations in both homozygote and heterozygote forms, which are highly prevalent in the Korean population. This platform will serve as a useful and cost-effective first-line screening tool for varying degrees of genetic SNHL and facilitate genome-based personalized hearing rehabilitation for the Korean population.

Exome sequencing identifies POU4F3 as the causative gene for a large Chinese family with non-syndromic hearing loss

Hearing impairment, or deafness (in its most severe form), is one of the most common human sensory disorders. There have been several reports of autosomal dominant mutations in the POU4F3 gene, which is associated with non-syndromic hearing loss. In this study, we identified a novel heterozygous mutation (c.602delT, p.L201fs) in the gene POU4F3 by taking advantage of whole-exome sequencing, which was validated by Sanger sequencing and completely co-segregated within a large hearing impaired Chinese family. We have focused on this pedigree since 2002, and we have mapped a deafness locus named DFNA42 (which has been renamed DFNA52, OMIM entry 607683) via a genome-wide scan. Furthermore, we analyzed this mutational variant and found that it was located at the beginning of the first functional domain of POU4F3, which could theoretically impair the function of POU4F3. We have identified a novel frameshift mutation in the POU4F3 gene. Further functional studies of variants of this specific gene are needed to illustrate the pathogenic mechanism(s) that underlie hearing impairment.