GJB2 Mutations Research Articles

Investigation of GJB2 and SLC26A4 genes related to pendred syndrome genetic deafness patients

Deafness can occur due to damage to the ear, especially the inner ear. In other cases, the cause is a heterogeneous genetic abnormality and is caused by the changes that occur in the genes involved in the hearing process. Mutations in GJB2 and SLC26A4 genes are one of the most important causes of deafness in the world, which causes syndromic and non-syndromic hereditary hearing loss. The purpose of this study is to investigate GJB2 and SLC26A4 genes related to genetic syndromes of deafness and bioinformatic analysis at the genome and proteome level and to evaluate and compare the expression of these genes in different tissues of the human body. For this purpose, tools related to bioinformatics analysis such as UCSC and OMIM databases were used. One of the common genetic syndromes caused by mutations in these genes is pendred syndrome. The clinical symptoms of this disease are weight gain, constipation, dry skin, and hair, decreased energy, sleepiness, bulging belly, decreased body temperature, and slow growth. This disease does not currently have a specific treatment, so it is very important and fundamental to investigate the genetic factors affecting this disease. The results of this research showed that the transfer of potassium, sodium, and chlorine ions as well as the mutation in the SLC26A4 gene, which is responsible for the synthesis of pendrin protein, is very effective in the occurrence of pendred syndrome. To diagnose pendred syndrome more accurately, molecular methods should be used in genetic tests. The results of comparing the expression profiles of these two genes showed that the difference in the expression of these two genes is very high and, in general, the expression of the SLC26A4 gene in the body is very low. Because people with hearing loss have other problems including damage to other parts of the body such as the heart, kidneys, or eyes. Knowing the genetic cause in these cases allows the doctor to be aware of problems in other systems as well.

Exome sequencing identifies novel variants associated with non-syndromic hearing loss in the Iranian population.

Autosomal recessive non-syndromic hearing loss (ARNSHL) is a public health concern in the Iranian population, with an incidence of 1 in 166 live births. In the present study, the whole exome sequencing (WES) method was applied to identify the mutation spectrum of NSHL patients negative for GJB2 gene mutations. First, using ARMS PCR followed by Sanger sequencing of the GJB2 gene, 63.15% of mutations in patients with NSHL were identified. Among the identified mutations in GJB2:p.Val43Met and p.Gly21Arg were novel. The remaining patients were subjected to WES, which identified novel mutations including MYO15A:p.Gly39LeufsTer188, ADGRV1:p.Ser5918ValfsTer23, MYO7A: c.5856+2T>c (splicing mutation), FGF3:p.Ser156Cys. The present study emphasized the application of WES as an effective method for molecular diagnosis of NSHL patients negative for GJB2 gene mutations in the Iranian population.

Prevalence of TECTA and GJB2 mutations in Asian children with nonsyndromic hearing loss: A meta-analysis

Prevalence of TECTA and GJB2 mutations in Asian children with nonsyndromic hearing loss: A meta-analysis

Preservation of developmental spontaneous activity enables early auditory system maturation in deaf mice.

Intrinsically generated neural activity propagates through the developing auditory system to promote maturation and refinement of sound processing circuits prior to hearing onset. This early patterned activity is induced by non-sensory supporting cells in the organ of Corti, which are highly interconnected through gap junctions containing connexin 26 (Gjb2). Although loss of function mutations in Gjb2 impair cochlear development and are the most common cause of congenital deafness, it is not known if these variants disrupt spontaneous activity and the developmental trajectory of sound processing circuits in the brain. Here, we show in a new mouse model of Gjb2-mediated congenital deafness that cochlear supporting cells adjacent to inner hair cells (IHCs) unexpectedly retain intercellular coupling and the capacity to generate spontaneous activity, exhibiting only modest deficits prior to hearing onset. Supporting cells lacking Gjb2 elicited coordinated activation of IHCs, leading to coincident bursts of activity in central auditory neurons that will later process similar frequencies of sound. Despite alterations in the structure of the sensory epithelium, hair cells within the cochlea of Gjb2-deficient mice were intact and central auditory neurons could be activated within appropriate tonotopic domains by loud sounds at hearing onset, indicating that early maturation and refinement of auditory circuits was preserved. Only after cessation of spontaneous activity following hearing onset did progressive hair cell degeneration and enhanced auditory neuron excitability manifest. This preservation of cochlear spontaneous neural activity in the absence of connexin 26 may increase the effectiveness of early therapeutic interventions to restore hearing.

Programming Levels and Speech Perception in Pediatric Cochlear Implant Recipients With Enlarged Vestibular Aqueduct or GJB2 Mutation.

To determine the relationship between hearing loss etiology, cochlear implant (CI) programming levels, and speech perception performance in a large clinical cohort of pediatric CI recipients. Retrospective chart review. Tertiary care hospitals. A total of 136 pediatric CI recipients (218 ears) were included in this study. All patients had diagnoses of either enlarged vestibular aqueduct (EVA) or GJB2 (Connexin-26) mutation confirmed via radiographic data and/or genetic reports. All patients received audiologic care at either Boston Children's Hospital or Massachusetts Eye and Ear in Boston, MA, between the years 1999 and 2020. Electrode impedances and programming levels for each active electrode and speech perception scores were evaluated as a function of etiology (EVA or GJB2 mutation). Children with EVA had significantly higher impedances and programming levels (thresholds and upper stimulation levels) than the children with GJB2 mutation. Speech perception scores did not differ as a function of etiology in this sample; rather, they were positively correlated with duration of CI experience (time since implantation). Differences in electrode impedances and CI programming levels suggest that the electrode-neuron interface varies systematically as a function of hearing loss etiology in pediatric CI recipients with EVA and those with GJB2 mutation. Time with the CI was a better predictor of speech perception scores than etiology, suggesting that children can adapt to CI stimulation with experience.

The pathogenesis of common Gjb2 mutations associated with human hereditary deafness in mice

Mutations in GJB2 (Gap junction protein beta 2) are the most common genetic cause of non-syndromic hereditary deafness in humans, especially the 35delG and 235delC mutations. Owing to the homozygous lethality of Gjb2 mutations in mice, there are currently no perfect mouse models carrying Gjb2 mutations derived from patients for mimicking human hereditary deafness and for unveiling the pathogenesis of the disease. Here, we successfully constructed heterozygous Gjb2+/35delG and Gjb2+/235delC mutant mice through advanced androgenic haploid embryonic stem cell (AG-haESC)-mediated semi-cloning technology, and these mice showed normal hearing at postnatal day (P) 28. A homozygous mutant mouse model, Gjb235delG/35delG, was then generated using enhanced tetraploid embryo complementation, demonstrating that GJB2 plays an indispensable role in mouse placenta development. These mice exhibited profound hearing loss similar to human patients at P14, i.e., soon after the onset of hearing. Mechanistic analyses showed that Gjb2 35delG disrupts the function and formation of intercellular gap junction channels of the cochlea rather than affecting the survival and function of hair cells. Collectively, our study provides ideal mouse models for understanding the pathogenic mechanism of DFNB1A-related hereditary deafness and opens up a new avenue for investigating the treatment of this disease.

Genotypic And Phenotypic Features of Patients with GJB1 Mutations: Single Center Experience (P11-8.003)

<h3>Objective:</h3> To describe the clinical and genetic characteristics of patients with <i>GJB1</i> mutations in Turkey. <h3>Background:</h3> <i>GJB1</i> mutations are the most common cause of X-linked Charcot-Marie-Tooth (CMT) disease. Typical manifestation includes distal muscle weakness and atrophy in the lower limbs. On the other hand, additional clinical features, such as stroke-like episodes, vocal cord paralysis, and hearing loss, can be observed. <h3>Design/Methods:</h3> Herein, we evaluated the clinical and genetic features of 29 patients from 23 unrelated families with <i>GJB1</i> mutation at the Neuromuscular Unit of the Istanbul Faculty of Medicine, Istanbul University. <h3>Results:</h3> Eight patients were female. The mean age of onset was 19.0 ± 12.0 (between 3 and 53 years). Females (27.3 ± 13.2) had later disease onset than males (15.4 ± 11.4). The most common presenting symptom was distal muscle weakness and foot deformities (21 patients), followed by foot pain (4 patients) and hand tremor (3 patients). Family history was absent in six patients. Two patients had immunosuppressive treatment for a misdiagnosis of inflammatory neuropathy. In neurological examination, all but two female patients had distal weakness in the lower extremities, and 24 had upper extremity weakness. The most frequent skeletal deformity was pes cavus (25 patients), followed by hammer toes (16 patients). Nine patients had hand tremor, and one had vocal cord paralysis. One patient had a history of stroke-like episodes, and one had multiple-sclerosis like cranial and spinal cord MRI lesions. In a mean disease duration of 22.5 ± 14.6 years all patients were ambulatory. The mean median motor nerve conduction velocity was 36.5 ± 8.2, consistent with intermediate-type CMT disease. Eighteen different mutations were identified in the <i>GJB1</i> gene. <h3>Conclusions:</h3> Our patients exhibited diverse phenotypic features regarding the disease onset and additional symptoms. Moreover, genotypic features were also heterogeneous, considering the identified mutations were scattered throughout the gene. <b>Disclosure:</b> Dr. Parman has nothing to disclose. Arman Cakar has nothing to disclose. Ayse Candayan has nothing to disclose. Dr. Durmus has nothing to disclose. Esra Battaloglu has nothing to disclose.

Analysis of GJB2 gene mutations spectrum and the characteristics of individuals with c.109G>A in Western Guangdong.

GJB2 mutations are among the most important causes of deafness, and their prevalence varies greatly among different countries and ethnic groups. This study aimed to determine the pathogenic mutation spectrum of GJB2 in patients with nonsyndromic hearing loss (NSHL) in Western Guangdong and to explore the pathogenic characteristics of the c.109G>A locus. In total, 97 NSHL patients and 212 normal controls (NC) were included in this study. Genetic sequencing analyses were performed on GJB2. In the NSHL group, the main pathogenic mutations in GJB2 were as follows: c.109G>A, c.235delC, and c.299_300delAT with allele frequencies of 9.28%, 4.12%, and 2.06%, respectively. c.109G>A was the most frequently detected pathogenic mutation in this region. In the NC group, the allele frequency of c.109G>A among 30-50 years old subjects was markedly lower than that among 0-30 years old subjects (5.31% vs. 11.11%, p < 0.05). We found the pathogenic mutation spectrum of GJB2 in this region and showed that c.109G>A was the most common GJB2 mutation with unique characteristics, such as clinical phenotypic heterogeneity and delayed onset. Therefore, the c.109G>A mutation should be considered as an essential marker for routine genetic assessment of deafness, which can also be beneficial for preventing deafness.

A Novel Exon 2 Deletion Mutation in the GRXCR1 Gene Associated With Non-Syndromic Hearing Loss: A Case Report and Review of Literatures.

About 80% of congenital hearing loss cases have genetic causes, often autosomal recessive and non-syndromic. Autosomal Recessive Non-syndromic hearing loss is characterized by extreme genetic heterogeneity. To report a case of congenital hearing loss with novel homozygous deletion in GRXCR1 gene. Case reports and review of literatures. In this study, the proband was a 32-year-old woman seeking pre-marriage genetic counseling with non-syndromic congenital hearing loss. An owing negative test for GJB2 mutations, she underwent exome sequencing, unveiling a novel homozygous exon 2 deletion of the GRXCR1 gene. This mutation was confirmed in her affected mother and sibling by PCR and Quantitative Real-Time PCR. We identified a novel GRXCR1 gene mutation related to congenital hearing loss in a family. Our study highlights the efficiency of exome sequencing in discovering gene mutations in cases of diseases with genetic heterogeneity.

Novel WFS1 mutations in patients with low-to-middle frequency hearing loss.

Hearing loss (HL) is the most common sensorineural disorder in human. It is estimated that genetic factors contribute to over 50% of prelingual hearing loss. Most of dominant HHL patients manifest postlingual progressive hearing loss that mainly affect high frequencies. However, mutations in a few dominant HL genes, such as WFS1, TECTA and DIAPH1, cause distinct audiogram that primarily affects the low and middle frequencies. We recruited twelve independent HL families with worse low or middle frequency audiograms. Each proband of these families was excluded for pathogenic mutations in GJB2, SLC26A4, and MT-RNR1 genes. Mutation screening was performed by whole exome sequencing. Next, candidate variants were validated in each family by sanger sequencing. Six heterozygous WFS1 variants were identified in six families, including three novel mutations (c.2519T>G, p.F840C; c.2048T>G, p.M683R and c.2419A>C, p.S807R) and three previously reported variants (c.2005T>C, p.Y669H; c.2590G>A, p.E864K and c.G2389A, p.D797N). All the novel mutations were absent in 100 ethnically matched controls and were predicted to be deleterious by multiple algorithms. We identified three novel and three previously reported WFS1 mutations in six unrelated Chinese families. Our findings enriched the genotype-phenotype spectrum of WFS1 related NSHL. Additional genotype-phenotype correlation study will clarify the detailed phenotypic range caused by WFS1 mutations.

Connexin 26 (GJB2) Mutations Associated with Congenital Hearing Loss in a Country of Different Migration Routes: Turkey.

To determine the prevalence of DFNB1 mutations containing GJB2 (connexin 26) genes with deletion 35delG mutation in congenital hearing loss, and to analyze this gene according to regional differences based on geographic and socio-economic relations in Turkish patients in Istanbul. Our study includes 51 unrelated children with non-syndromic sensorineural hearing impairment with the proof of clinical ABR results. Molecular studies were performed using PCR- Mediated Site-Directed Mutagenesis assay, PCR and direct sequencing to screen for GJB2 and 35delG mutations. Genomic DNA is obtained from the peripheral blood which is taken using a Qiagen DNA isolation kit. GJB2-35delG mutations were found in 25.5% of the patients; 19.6% were homozygous, 5.8% were heterozygous. The ratio of 35delG mutation detected in the children of families with consanguineous marriages and not; were 18.5% (n = 5) and 33.3% (n = 8) of cases respectively. The 35delG mutations in the patients whose father and mother were both from the Black Sea region were 43.18% (n = 19). Our results show that 35delG mutation is at a high frequency in our country, although it is more common in children of parents from the Black Sea region. Screening for the 35delG mutation in the GJB2 gene is the best choice for early diagnosis and emergency response plans for treatment and rehabilitation.

Identification a novel pathogenic LRTOMT mutation in Mauritanian families with nonsyndromic deafness.

Although recessive mutations in GJB2 are the common genetic etiology of sensorineural hearing impairment (SNHI), variants in LRTOMT gene were also identified, mostly in Middle East and North African populations. Using Sanger sequencing we screened the exon 7 of LRTOMT in a cohort of 128 unrelated Mauritanian children with congenital deafness. Only one biallelic missense mutation, predicted as pathogenic (c.179T > C;p.Leu60Pro) was found at homozygous state in four families. This variant, not reported before, showed a deleterious effect by SIFT (score: 0.01) and a disease-causing effect by Mutation Taster (prob: 1). Exploration of the encoded protein 3D structure revealed a disruption from an organized α helix (in the normal protein structure) into a random conformation. Early fitting of a cochlear implant seemed to improve the audition ability of the mutation carrier. Further screening using a panel of deafness genes may expose other variants underlying hearing impairment in our population.

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

Hearing Loss (HL) is the most common sensory disorder. HL commonly ranges from mild to severe. Persons with HL face difficulty in hearing conversations or sounds through one ear or both ears, which impacts one's ability to interact with others. Hence it is a communicable disorder that makes people socially isolated, lonely, and frustrated. HL in children severely affects language development. The people who are referred to as 'Deaf' with very little or no hearing capabilities, are considered as having profound hearing loss. More than 124 genes are causative for Non-Syndromic HL (NSHL) with varying inheritance, among which the SLC26A4 mutations are the second commonest cause of hereditary HL across the globe. Samples from 70 NSHL patients were analyzed through Next-Generation Sequencing (NGS) and generated five pathogenic variants [N246fs (rs918684449), K564fs (rs746427774), F122fs, V239D (rs111033256), T721M (rs121908363)] each with frequency of 1.42%. Three missense variants [S399P (rs747431002), L597S (rs55638457), and G6V (rs111033423)] were reported under the "uncertain" category. All the collected samples were further genotyped to look for the possibility of having GJB2 and HL-associated mutations. Out of five SLC26A4 pathogenic mutations N246fs (rs918684449) and K564fs (rs746427774) were observed in samples which were positive for GJB2-HL associated candidate mutations [W24X (rs104894396), Q124X (rs397516874) and W77X (rs80338944)]. Similarly, pathogenic variants F122fs, V239D (rs111033256) and T721M (rs121908363) were observed in patient samples which were negative for GJB2-HL associated mutations. Our data will expand the list of variants underlying NSHL and encourage further genotype SLC26A4 gene concerning the south Indian population with a large sample size.

Cx26 heterozygous mutations cause hyperacusis-like hearing oversensitivity and increase susceptibility to noise.

Gap junction gene GJB2 (Cx26) mutations cause >50% of nonsyndromic hearing loss. Its recessive hetero-mutation carriers, who have no deafness, occupy ~10 to 20% of the general population. Here, we report an unexpected finding that these heterozygote carriers have hearing oversensitivity, and active cochlear amplification increased. Mouse models show that Cx26 hetero-deletion reduced endocochlear potential generation in the cochlear lateral wall and caused outer hair cell electromotor protein prestin compensatively up-regulated to increase active cochlear amplification and hearing sensitivity. The increase of active cochlear amplification also increased sensitivity to noise; exposure to daily-level noise could cause Cx26+/- mice permanent hearing threshold shift, leading to hearing loss. This study demonstrates that Cx26 recessive heterozygous mutations are not "harmless" for hearing as previously considered and can cause hyperacusis-like hearing oversensitivity. The data also indicate that GJB2 hetero-mutation carriers are vulnerable to noise and should avoid noise exposure in daily life.

Auditory Outcomes in Children Who Undergo Cochlear Implantation Before 12 Months of Age: A Systematic Review.

To systematically review the literature to determine auditory outcomes of cochlear implantation in children ≤12 months old. PubMed, EMBASE, Medline, CINAHL, Cochrane, Scopus, and Web of Science databases were searched from inception to 9/1/2021 using PRISMA guidelines. Studies analyzing auditory outcomes after cochlear implantation (CI) in children ≤12 months of age were included. Non-English studies and case reports were excluded. Outcome measures included functional and objective auditory results. Two independent reviewers evaluated each abstract and article. Heterogeneity and bias across studies were evaluated. Of 305 articles identified, 17 met inclusion criteria. There were 642 children ages 2 to 12 months at CI. The most common etiologies of hearing loss were congenital CMV, meningitis, idiopathic hearing loss, and GJB2 mutations and other genetic causes. All studies concluded that early CI was safe. Overall, outcomes improved following early CI: IT-MAIS (9 studies), LittlEARS (4 studies), PTA (3 studies), CAP (3 studies), GASP (3 studies), and LNT (3 studies). Nine studies compared outcomes to an older implantation group (>12 months); of these (n = 450 early CI, n = 1189 late CI), 8 studies showed earlier CI achieved comparable or better auditory outcomes than later implantation, whereas 1 study (n = 120) concluded no differences in speech perception improvement. Auditory outcomes were overall improved in children ≤12 months old undergoing CI. Studies that compared early to late CI demonstrated similar or better auditory outcomes in early implantation group. Given the comparable safety profile and critical time period of speech and language acquisition, earlier CI should be considered for infants with hearing loss.

Low dose TGF-β1 can improve vohwinkel syndrome by promoting the proliferation of keratinocytes

Vohwinkel syndrome (VS) is a very rare autosomal dominant disorder that can cause disability and deformity in severe cases. Mutations of the LOR (loricrin) and GJB2 (Cx26) genes have been found in VS so far. Many studies have indicated that the differentiation and growth of epidermal keratinocytes are regulated by mutant Cx26, and it may explain the pathogenesis of VS. It has been found that transforming growth factor β1 (TGF-β1) expression was lower in G130V (OE1) and D66H (OE2) mutant keratinocytes in the VS model with GJB2 mutation as compared to normal keratinocytes (NC). TGF-β is a cytokine involved in the regulation of processes like cell proliferation and differentiation in different types of cells. At present, many in vitro studies focus on TGF- β 1 inhibition of keratinocyte growth.However, the relationship between TGF-β1 and VS remains unknown. This study aimed at elucidating the role and potential pathogenic mechanism of TGF-β in VS. The results indicated that the down-regulation expression of TGF-β1 in VS was linked to cell proliferation inhibition through p-Smad3/c-myc. In contrast, low-dose TGF-β1 treatment of VS keratinocytes can improve their proliferation inhibition and up-regulate the expression Cyclin D1. This suggests that low doses of TGF-β1 can improve the proliferation of VS and provide new insights into its treatment.

Prevalence of GJB2 and TECTA gene mutations in children with non-syndromic hearing loss visiting an Otorhino-laryngology Hospital in Ho Chi Minh City, Viet Nam

Introduction: Non-syndromic hearing loss (NSHL) in children, which has numerous causes, can impede or even postpone the acquisition of spoken language. In Viet Nam, screening programs and genetic testing for NSHL are rarely applied. In this study, 31 pediatric patients had their medical histories collected alongside sequencing results for the GJB2 and TECTA genes to determine the prevalence of these mutations in the community and their associations with potential risk factors. Methods: Information and blood samples were collected from 31 severe-to-profound pediatric NSHL patients. DNA was extracted, amplified by polymerase chain reaction (PCR), and directly sequenced for the detection of GJB2 (connexin 26) and TECTA mutations. Results: No TECTA gene mutations were detected. GJB2 mutations were identified in eight patients (25.8%), with three (9.7%) cases of heterozygous c.109G&gt;A (V37I), four (12.9%) cases of homozygous c.109G&gt;A (V37I), and one (3.2%) case of heterozygous c.299-300delAT. There were no significant associations between having mutated GJB2 genes and living in urban areas, having a family history of prelingual deafness, or having an abnormal obstetric history (p &gt; 0.05, Fisher's exact tests). Conclusion: Our study addresses the high prevalence of&nbsp;GJB2 mutations as causative factors in hearing loss in diagnosed patients at the Otorhino-laryngology Hospital in Ho Chi Minh City, Viet Nam. Further studies are required to obtain a better understanding of the genetic spectrum of NSHL and to articulate its relationship with various risk factors.

Novel Variants in MPV17, PRX, GJB1, and SACS Cause Charcot-Marie-Tooth and Spastic Ataxia of Charlevoix-Saguenay Type Diseases.

Charcot-Marie-Tooth disease (CMT) and autosomal recessive spastic ataxia of Charlevoix-Saguenay type (ARSACS) are large heterogeneous groups of sensory, neurological genetic disorders characterized by sensory neuropathies, muscular atrophies, abnormal sensory conduction velocities, and ataxia. CMT2EE (OMIM: 618400) is caused by mutations in MPV17 (OMIM: 137960), CMT4F (OMIM: 614895) is caused by PRX (OMIM: 605725), CMTX1 (OMIM: 302800) is caused by mutations in GJB1 (OMIM: 304040), and ARSACS (OMIM: 270550) is caused by mutations in SACS (OMIM: 604490). In this study, we enrolled four families: DG-01, BD-06, MR-01, and ICP-RD11, with 16 affected individuals, for clinical and molecular diagnoses. One patient from each family was analyzed for whole exome sequencing and Sanger sequencing was done for the rest of the family members. Affected individuals of families BD-06 and MR-01 show complete CMT phenotypes and family ICP-RD11 shows ARSACS type. Family DG-01 shows complete phenotypes for both CMT and ARSACS types. The affected individuals have walking difficulties, ataxia, distal limb weakness, axonal sensorimotor neuropathies, delayed motor development, pes cavus, and speech articulations with minor variations. The WES analysis in an indexed patient of family DG-01 identified two novel variants: c.83G>T (p.Gly28Val) in MPV17 and c.4934G>C (p.Arg1645Pro) in SACS. In family ICP-RD11, a recurrent mutation that causes ARSACS, c.262C>T (p.Arg88Ter) in SACS, was identified. Another novel variant, c.231C>A (p.Arg77Ter) in PRX, which causes CMT4F, was identified in family BD-06. In family MR-01, a hemizygous missense variant c.61G>C (p.Gly21Arg) in GJB1 was identified in the indexed patient. To the best of our knowledge, there are very few reports on MPV17, SACS, PRX, and GJB1 causing CMT and ARSACS phenotypes in the Pakistani population. Our study cohort suggests that whole exome sequencing can be a useful tool in diagnosing complex multigenic and phenotypically overlapping genetic disorders such as Charcot-Marie-Tooth disease (CMT) and spastic ataxia of Charlevoix-Saguenay type.

Non-Syndromic Hearing Loss in a Romanian Population: Carrier Status and Frequent Variants in the GJB2 Gene.

The genetic causes of autosomal recessive nonsyndromic hearing loss (ARNSHL) are heterogeneous and highly ethnic-specific. We describe GJB2 (connexin 26) variants and carrier frequencies as part of our study and summarize previously reported ones for the Romanian population. In total, 284 unrelated children with bilateral congenital NSHL were enrolled between 2009 and 2018 in northwestern Romania. A tiered diagnostic approach was used: all subjects were tested for c.35delG, c.71G>A and deletions in GJB6 (connexin 30) using PCR-based methods. Furthermore, 124 cases undiagnosed at this stage were analyzed by multiplex-ligation-dependent probe amplifications (MLPA), probe mix P163, and sequencing of GJB2 exon 2. Targeted allele-specific PCR/restriction fragment length polymorphism (RFLP) established definite ethio-pathogenical diagnosis for 72/284 (25.35%) of the cohort. Out of the 124 further analyzed, in 12 cases (9.67%), we found compound heterozygous point mutations in GJB2. We identified one case of deletion of exon 1 of the WFS1 (wolframin) gene. Carrier status evaluation used Illumina Infinium Global Screening Array (GSA) genotyping: the HINT cohort-416 individuals in northwest Romania, and the FUSE cohort-472 individuals in southwest Romania. GSA variants yielded a cumulated risk allele presence of 0.0284. A tiered diagnostic approach may be efficient in diagnosing ARNSHL. The summarized contributions to Romanian descriptive epidemiology of ARNSHL shows that pathogenic variants in the GJB2 gene are frequent among NSHL cases and have high carrier rates, especially for c.35delG and c.71G>A. These findings may serve in health strategy development.

A possible role for second-hit postzygotic GJB2 mutation in porokeratotic eccrine ostial and dermal duct nevus.

Porokeratotic eccrine ostial and dermal duct nevus (PEODDN) is a rare type of epidermal nevus involving the eccrine acrosyringia. It typically presents as asymptomatic linear keratotic papules and plaques along the lines of Blaschko and predominantly affects the extremities. This disease has recently been linked to somatic mutations within the GJB2 locus. Only four GJB2 mutations have been previously documented for PEODDN, and the underlying genetic basis remains inconclusive. Herein, we report an 18-year-old female with a hyperkeratotic plaque on the dorsa of the proximal interphalangeal joint of her right ring finger, as well as multiple small hyperkeratotic papules linearly distributed on the lateral sides of her fingers occurring since birth. Histopathological results revealed prominent parakeratotic cornoid lamella-like tiers at the opening of the eccrine secretory ducts. Whole-exome sequencing of the affected skin tissue revealed a heterozygous germline mutation and a postzygotic somatic mutation in GJB2. In summary, this study presents a case of PEODDN with compound heterozygous mutations in GJB2, which broadens the genetic spectrum of this disease entity and implies a possible role for second-hit mutations in the pathogenesis of PEODDN.