GJB2 Mutations Research Articles

Biallelic mutations in pakistani families with autosomal recessive prelingual nonsyndromic hearing loss.

Nonsyndromic autosomal recessive hearing loss (DFNB) is an etiologically heterogeneous disorder group showing a wide spectrum of onset ages and severity. DFNB genes are very diverse in their types and functions, making molecular diagnosis difficult. DFNB is particularly frequent in Pakistan, which may be partly due to consanguinity. This study was performed to determine the genetic causes in Pakistani DFNB families with prelingual onset and to establish genotype-phenotype correlation. Whole exome sequencing and subsequent genetic analysis were performed for 11 Pakistani DFNB families including eight consanguineous families. We identified eight pathogenic or likely pathogenic mutations in LOXHD1, GJB2, SLC26A4, MYO15A, and TMC1 from six families. The GJB2 mutations were identified in two families each with compound heterozygous mutations and a homozygous mutation. The compound heterozygous mutations in LOXHD1 ([p.D278Y] + [p.D1219E]) and GJB2 [p.M1?] + [p.G12Vfs*2]) were novel. The four missense or start-loss mutations were located at well conserved residues, and most in silico analysis predicted their pathogenicity. In addition to causative mutations, we found compound heterozygous mutations in PTPRQ as variants of uncertain significance. This study identified biallelic mutations as the underlying cause of early onset DFNB in six Pakistani families. This study will be helpful in providing an exact molecular diagnosis and treatment of prelingual onset deafness patients.

The germline mutational landscape of genitourinary cancers and its indication for prognosis and risk

BackgroundGermline mutations represent a high risk of hereditary cancers in population. The landscape and characteristics of germline mutations in genitourinary cancer are largely unknown, and their correlation with patient prognosis has not been defined.MethodsVariant data and relevant clinical data of 10,389 cancer patients in The Cancer Genome Atlas (TCGA) database was downloaded. The subset of data of 206 genitourinary cancer patients containing bladder urothelial carcinoma (BLCA), kidney chromophobe carcinoma (KICH), kidney renal clear cell carcinoma (KIRC), kidney renal papillary cell carcinoma (KIRP) and prostate adenocarcinoma (PRAD) cancer with germline mutation information was filtered for further analysis. Variants were classified into pathogenic, likely pathogenic and non-pathogenic categories based on American College of Medical Genetics and Genomics (ACMG) guidelines. Genome Aggregation Database (gnomAD) database was used to assist risk analysis.ResultsThere were 48, 7, 44, 45 and 62 patients with germline mutations identified in BLCA, KICH, KIRC, KIRP and PRAD, respectively. Pathogenic germline mutations from 26 genes and likely pathogenic mutations from 33 genes were revealed. GJB2, MET, MUTYH and VHL mutations ranked top in kidney cancers, and ATM and CHEK2 mutations ranked top for bladder cancer, while ATM and BRCA1 mutations ranked top for prostate cancer. Frameshift, stop gained and missense mutations were the predominant mutation types. BLCA exhibited the highest ratio of stop gained mutations (22/48 = 45.8%). No difference in patient age was found among pathogenic, likely pathogenic and non-pathogenic groups for all cancer types. The number of male patients far overweight female patients whether PRAD was included (P = 0) or excluded (P < 0.001). Patients with pathogenic or likely pathogenic germline mutations exhibited significantly worse overall survival rate than the non-pathogenic group for all genitourinary cancers. More important, analyses assisted by gnomAD database revealed that pathogenic or likely pathogenic germline mutations significantly increased the risk for genitourinary cancer in population, with the odds ratio at 14.88 (95%CI 11.80–18.77) and 33.18 (95%CI 24.90–44.20), respectively.ConclusionsThe germline mutational status for genitourinary cancers has been comprehensively characterized. Pathogenic and likely pathogenic germline mutations increased the risk and indicated poor prognosis of genitourinary cancers.

Knock-in mouse models for CMTX1 show a loss of function phenotype in the peripheral nervous system

The X-linked form of Charcot-Marie-Tooth disease (CMTX1) is the second most common form of CMT. In this study we used CRISPR/Cas9 to develop new “knock-in” models of CMTX1 that are more representative of the spectrum of mutations seen with CMTX1 than the Cx32 knockout (KO) mouse model used previously. We compared mice of four genotypes - wild-type, Cx32KO, p.T55I, and p.R75W. Sciatic motor conduction velocity slowing was the most robust electrophysiologic indicator of neuropathy, showing reductions in the Cx32KO by 3 months and in the p.T55I and p.R75W mice by 6 months. At both 6 and 12 months, all three mutant genotypes showed reduced four limb and hind limb grip strength compared to WT mice. Performance on 6 and 12 mm width balance beams revealed deficits that were most pronounced at on the 6 mm balance beam at 6 months of age. There were pathological changes of myelinated axons in the femoral motor nerve in all three mutant lines by 3 months of age, and these became more pronounced at 6 and 12 months of age; sensory nerves (femoral sensory and the caudal nerve of the tail) appeared normal at all ages examined. Our results demonstrate that mice can be used to show the pathogenicity of human GJB1 mutations, and these new models for CMTX1 should facilitate the preclinical work for developing treatments for CMTX1.

A novel splicing mutation in 5'UTR of GJB1 causes X-linked Charcot-Marie-tooth disease.

Charcot-Marie-Tooth (CMT) disease is the most frequent hereditary motor sensory neurological disease. GJB1 gene is the second most frequent cause of CMT, accounting for approximately 10% of CMT cases worldwide. We identified a large Han family with X-linked CMT disease. In this study, the probands and his mother underwent electrophysiological examinations and other family members were assessed retrospectively. Whole-exome sequencing, Sanger sequencing, and SNP array linkage analysis were performed to find and confirm the variant. The functional effect of the identified variant was further investigated in HEK293 cells and MCF-7 cells by minigene splicing assay. The affected individuals had some clinical symptoms including symmetric atrophy and progressive weakness of the distal muscles in their twenties. Electrophysiological examinations result in peripheral nerve injury of the upper and lower limbs. Whole-exome sequencing identified a novel hemizygous deletion mutation (NM_000166: c.-16-8_-14del) in the GJB1 gene. SNP array linkage analysis and co-segregation analysis confirmed this mutation. Minigene splicing assay verified that this mutation leads to the activation of cryptic splicing sites in exon 2 which results in the deletion of exon 2. Our study provides theoretical guidance for prenatal diagnosis and subsequent fertility of this family. This result expands the spectrum of mutations in GJB1 known to be associated with CMTX and contributes to the diagnosis of CMT and clinical genetic counseling.

Recent insights into gap junction biogenesis in the cochlea.

In the cochlea, connexin 26 (Cx26) and connexin 30 (Cx30) co-assemble into two types of homomeric and heteromeric gap junctions between adjacent non-sensory epithelial cells. These channels provide a mechanical coupling between connected cells, and their activity is critical to maintain cochlear homeostasis. Many of the mutations in GJB2 or GJB6, which encode Cx26 and Cx30 in humans, impair the formation of membrane channels and cause autosomal syndromic and non-syndromic hearing loss. Thus, deciphering the connexin trafficking pathways in situ should represent a major step forward in understanding the pathogenic significance of many of these mutations. A growing body of evidence now suggests that Cx26/Cx30 heteromeric and Cx30 homomeric channels display distinct assembly mechanisms. Here, we review the most recent advances that have been made toward unraveling the biogenesis and stability of these gap junctions in the cochlea.

GJB2 and GJB6 gene transcripts in the human cochlea: A study using RNAscope, confocal, and super-resolution structured illumination microscopy.

BackgroundGap junction (GJ) proteins, connexin26 and 30, are highly prevalent in the human cochlea (HC), where they are involved in transcellular signaling, metabolic supply, and fluid homeostasis. Their genes, GJB2 and GJB6, are both located at the DFNB1 locus on chromosome 13q12. Mutations in GJB2 may cause mild to profound non-syndromic deafness. Here, we analyzed for the first time the various expressions of GJB2 and GJB6 gene transcripts in the different cell networks in the HC using the RNAscope technique.Materials and methodsArchival paraformaldehyde-fixed sections of surgically obtained HC were used to label single mRNA oligonucleotides using the sensitive multiplex RNAscope® technique with fluorescent-tagged probes. Positive and negative controls also included the localization of ATP1A1, ATP1A2, and KCNJ10 gene transcripts in order to validate the specificity of labeling.ResultsConfocal and super-resolution structured illumination microscopy (SR-SIM) detected single gene transcripts as brightly stained puncta. The GJB2 and GJB6 gene transcripts were distributed in the epithelial and connective tissue systems in all three cochlear turns. The largest number of GJB2 and GJB6 gene transcripts was in the outer sulcus, spiral ligament, and stria vascularis (SV). Oligonucleotides were present in the supporting cells of the organ of Corti (OC), spiral limbus fibrocytes, and the floor of the scala vestibuli. Multiplex gene data suggest that cells in the cochlear lateral wall contain either GJB2 or GJB6 gene transcripts or both. The GJB6, but not GJB2, gene transcripts were found in the intermediate cells but none were found in the marginal cells. There were no GJB2 or GJB6 gene transcripts found in the hair cells and only a few in the spiral ganglion cells.ConclusionBoth GJB2 and GJB6 mRNA gene transcripts were localized in cells in the adult HC using RNAscope® in situ hybridization (ISH) and high resolution microscopy. Generally, GJB6 dominated over GJB2, except in the basal cells. Results suggest that cells may contain either GJB2 or GJB6 gene transcripts or both. This may be consistent with specialized GJ plaques having separate channel permeability and gating properties. A reduction in the number of GJB2 gene transcripts was found in the basal turn. Such information may be useful for future gene therapy.

33701 Porokeratotic eccrine ostial and dermal duct nevus caused by a second-hit postzygotic GJB2 mutation

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 which predominantly affects the extremities, and the disease has recently been linked to GJB2 somatic mutations. To the best of our knowledge, only four mutations have been documented from GJB2 in pure PEODDN cases. Herein, we reported an 18-year-old female who presented with a hyperkeratotic plaque on the dorsal side of the proximal interphalangeal joint of her right ring finger as well as multiple small linear hyperkeratotic papules distributed over the lateral side of her her right index, middle and ring fingers noted since her birth. Histopathologic study revealed prominent parakeratotic cornoid lamella-like tiers at the opening of eccrine secretory ducts. Sanger sequencing focusing on the GJB2 gene revealed a germline heterozygous missense mutation, c.608T>C (p.Ile203Thr) in the blood and the epidermal tissue of the affected skin. Whole exome sequencing (WES) on the genomic DNA extracted from the lesional epidermis identified another second-hit postzygotic somatic reported missense mutation, c.263C>A (p.Ala88Glu) with low mosaic percentage of around 4% and reflecting the dilutional effect in biopsy of whole tissue and limit of detection by Sanger sequencing. In conclusion, this study presents a case of PEODDN with a complete genetic study identifying a germline mutation and a second-hit postzygotic somatic mutation; our findings strengthen the importance of second- hit somatic mutation in GJB2 as an etiology in PEODDN.

Ichthyosis follicularis syndromes in patients with mutations in GJB2.

Ichthyosis follicularis (IF) manifests as generalized spiny follicular projections found in syndromic diseases secondary to SREBF1 and MBTPS2 mutations. We sought the genetic cause of IF in two distinct families from a cohort of 180 patients with ichthyosis. In Family 1, the proband (Patient 1) presented with IF, bilateral sensorineural hearing loss and punctate palmoplantar keratoderma. Using DNA from peripheral blood lymphocytes, two compound heterozygous mutations, c.526A>G and c.35delG, were discovered in GJB2. In Family 2, the proband (Patient 2) presented with a previously unreported IF phenotype in the context of keratitis-ichthyosis-deafness syndrome, and whole-exome sequencing found a de novo heterozygous mutation, c.148G>A in GJB2. Histopathology was consistent with porokeratotic eccrine ostial and dermal duct naevus (PEODDN) and IF in Patients 1 and 2, respectively. Our findings add to the clinical and histopathological spectrum of IF and emphasize the association of PEODDN-like entities with GJB2 variants.

Mitochondrial Diabetes is Associated with tRNALeu(UUR) A3243G and ND6 T14502C Mutations.

BackgroundMutations in mitochondrial DNA (mtDNA) are associated with type 2 diabetes mellitus (T2DM). In particular, m.A3243G is the most common T2DM-related mtDNA mutation in many families worldwide. However, the clinical features and pathophysiology of m.A3243G-induced T2DM are largely undefined.MethodsTwo pedigrees with maternally inherited T2DM were underwent clinical, molecular and biochemical assessments. The mtDNA genes were PCR amplified and sequenced. Mitochondrial adenosine triphosphate (ATP) and reactive oxygen species (ROS) were measured in polymononuclear leukocytes derived from three patients with both the m.A3243G and m.T14502C mutations, three patients with only the m.A3243G mutation and three controls without these mutations. Moreover, GJB2, GJB3 and GJB6 mutations were screened by PCR-Sanger sequencing.ResultsMembers of the two pedigrees manifestated variable clinical phenotypes including diabetes and hearing and vision impairments. The age at onset of T2DM varied from 31 to 66 years, with an average of 41 years. Mutational analysis of mitochondrial genomes indicated the presence of the m.A3243G mutation in both pedigrees. Matrilineal relatives in one of the pedigrees harbored the coexisting of m.A3243G and m.T14502C mutations. Remarkably, the m.T14502C mutation, which causes the substitution of a conserved isoleucine for valine at position 58 in ND6 mRNA, may affect the mitochondrial respiratory chain functions. Biochemical analysis revealed that cell lines bearing both the m.A3243G and m.T14502C mutations exhibited greater reductions in ATP levels and increased ROS production compared with those carrying only the m.A3243G mutation. However, we did not find any mutations in the GJB2, GJB3 and GJB6 genes.ConclusionOur study indicated that mitochondrial diabetes is associated with the tRNALeu(UUR) A3243G and ND6 T14502C mutations.

Virally Mediated Connexin 26 Expression in Postnatal Scala Media Significantly and Transiently Preserves Hearing in Connexin 30 Null Mice.

Non-sensory cells in the sensory epithelium of the cochlea are connected extensively by gap junctions. Functionally null mutations in GJB6 (encoding Cx30) cause hearing loss in humans. In this study, we injected AAV1-CB7-Gjb2 into the scala media between P0-2 in the cochlea of Gjb6 −/− mice. The injection increased Cx26 expression and significantly preserved auditory functions. However, the hearing preservation gradually declined and essentially disappeared 3 months after the injections. In contrast, the morphological preservation was still significant at 3 months post-injection. We found that the expression of Cx26, at both the mRNA and protein levels, showed substantial decreases during the 3-month period. Curiously, treatments by injecting AAV1-CB7-Gjb6 with the identical approach failed to yield any hearing preservation. Our results demonstrated the first successful cochlear gene therapy treatment in mouse models by virally expressing a companion gene of Gjb6.

Maternally transmitted nonsyndromic hearing impairment may be associated with mitochondrial tRNAAla 5601C>T and tRNALeu(CUN) 12311T>C mutations.

BackgroundSequence alternations in mitochondrial genomes, especially in genes encoding mitochondrial tRNA (mt‐tRNA), were the important contributors to nonsyndromic hearing loss (NSHL); however, the molecular mechanisms remained largely undetermined.MethodsA maternally transmitted Chinese pedigree with NSHL underwent clinical, genetic, and biochemical assessment. PCR and direct sequence analyses were performed to detect mitochondrial DNA (mtDNA), GJB2, and SLC26A4 gene mutations from matrilineal relatives of this family. Mitochondrial functions including mitochondrial membrane potential (MMP), ATP, and ROS were evaluated in polymononuclear leukocytes (PMNs) derived from three deaf patients and three controls from this pedigree.ResultsFour of nine matrilineal relatives developed hearing loss at the variable age of onset. Two putative pathogenic mutations, m.5601C>T in tRNAAla and m.12311T>C in tRNALeu(CUN), were identified via PCR‐Sanger sequencing, as well as 34 variants that belonged to mtDNA haplogroup G2b2. Intriguingly, m.5601C>T mutation resided at very conserved nucleotide in the TψC loop of tRNAAla (position 59), while the T‐to‐C substitution at position 12311 located at position 48 in the variable stem of tRNALeu(CUN) and was believed to alter the aminoacylation and the steady‐state level of tRNA. Biochemical analysis revealed the impairment of mitochondrial functions including the significant reductions of ATP and MMP, whereas markedly increased ROS levels were found in PMNs derived from NSHL patients with m.5601C>T and m.12311T>C mutations. However, we did not detect any mutations in GJB2 and SLC26A4 genes.ConclusionOur data indicated that mt‐tRNAAla m.5601C>T and tRNALeu(CUN) 12311T>C mutations were associated with NSHL.

Identification of GJB2 Variants in 75 Unrelated Iranian Autosomal Recessive Non-syndromic Hearing Loss Patients

Background: Hearing loss (HL) is the most prevalent sensory disease in humans. HL is among the most clinically and genetically heterogeneous disorders. Pathogenic variants in GJB2 are the principal cause of HL in many populations. Therefore, GJB2 analysis should be considered as the first step for HL. Objectives: This study aimed to find causative variants in the GJB2 gene in 75 unrelated Iranian patients who suffered from Autosomal recessive non-syndromic hearing loss (ARNSHL). Methods: Peripheral blood samples were used for genomic DNA extraction. PCR-direct sequencing was performed to detect GJB2 mutations. Results: In this study, thirty-four chromosomes (21.33%) carried GJB2 mutations. In general, 10 variants were detected among 19 patients. Seven cases were homozygous for c.35delG; (p.Gly12Valfs*2), two were homozygous for c.71G&gt;A; (p.Trp24*), two were homozygous for c.358-360delGAG (p.Glu120del), and two were homozygous for c.-23+1G&gt;A mutation. One patient was a compound heterozygote for c.35delG and c.-23+1G&gt;A mutations, and another patient with compound heterozygosity for c.290dupA and c.235delC mutations were determined. Four patients carried a mono-allelic variant in the GJB2 including c.126G&gt;T; (p.Glu42Asp), c.23C&gt;T; (p.Thr8Met), c.445G&gt;A; (p.Ala149Thr) and c.269T&gt;C; (p.Leu90Pro). Accordingly, c.35delG mutation was the most common variant in this study. Conclusions: Finding common variants of HL mutations in different populations can elevate the diagnostic value of molecular testing in the screening of affected individuals, and can improve counselling to minimize the risk of having affected offspring for at-risk couples. Besides, early diagnosis can easily lead to speech development and prevents further problems.

Long-Term Impedance Trend in Cochlear Implant Users with Genetically Determined Congenital Profound Hearing Loss.

Impedance is a basic parameter registered at any cochlear implant (CI) fitting section. It is useful in monitoring electrode functioning and the status of the surrounding anatomical structures. The main aim of this study is to evaluate the 5-year impedance-value trend in patients affected by congenital genetically determined profound hearing loss implanted with Cochlear Nucleus devices. Observational, retrospective, monocentric study. Twenty-seven consecutive patients (9 females: 12.0 ± 7.6 years old; range: 4.2-40.4) with genetic diagnosis of GJB2 mutation causing congenital profound hearing loss who underwent cochlear implantation from 2010 to 2020 with good auditory benefit. Impedance values of the CIs were obtained from the CIs' programming software that registers those parameters for each follow-up section of each patient. Impedance values were measured over time (activation, 6, 12, 24, and 60 months after cochlear implantation), for each of the 22 electrodes, in common ground, monopolar 1, monopolar 2, and monopolar 1 + 2 stimulation modes. A significant variation was found between CI activation and 6-month follow-up. This difference was found for each of the 22 electrodes. Electrodes 1 to 4 showed higher impedance values compared with all other electrodes in each time interval. Repeated-measures analysis of variance ruled out significant variations in impedance values from 6-month to 5-year follow-up. Impedance values were extremely stable after activation, at least for the first 5 years. In these cases, even minimal impedance variations should be carefully evaluated for their possible implications on hearing performance.

Novel m.4268T>C mutation in the mitochondrial tRNAIle gene is associated with hearing loss in two Chinese families.

BACKGROUNDHerein, we report the genetic, clinical, molecular and biochemical features of two Han Chinese pedigrees with suggested maternally transmitted non-syndromic hearing loss. AIMTo investigate the pathophysiology of hearing loss associated with mitochondrial tRNA mutations.METHODSSixteen subjects from two Chinese families with hearing loss underwent clinical, genetic, molecular, and biochemical evaluations. Biochemical characterizations included the measurements of tRNA levels using lymphoblastoid cell lines derived from five affected matrilineal relatives of these families and three control subjects.RESULTSThree of the 16 matrilineal relatives in these families exhibited a variable seriousness and age-at-onset (8 years) of deafness. Analysis of mtDNA mutation identified the novel homoplasmic tRNAIle 4268T>C mutation in two families both belonging to haplogroup D4j. The 4268T>C mutation is located in a highly conserved base pairing (6U–67A) of tRNAIle. The elimination of 6U–67A base-pairing may change the tRNAIle metabolism. Functional mutation was supported by an approximately 64.6% reduction in the level of tRNAIle observed in the lymphoblastoid cell lines with the 4268T>C mutation, in contrast to the wild-type cell lines. The reduced level of tRNA was below the proposed threshold for normal respiration in lymphoblastoid cells. However, genotyping analysis did not detect any mutations in the prominent deafness-causing gene GJB2 in any members of the family. CONCLUSIONThese data show that the novel tRNAIle 4268T>C mutation was involved in maternally transmitted deafness. However, epigenetic, other genetic, or environmental factors may be attributed to the phenotypic variability. These findings will be useful for understanding families with maternally inherited deafness.

Keratitis-Ichthyosis-Deafness Syndrome Caused by Missense Mutation in GJB2 Encoding Connexin 26 in a Chinese Patient

Introduction: Keratitis-ichthyosis-deafness (KID) syndrome is a rare congenital ectodermal disorder caused by a heterozygous missense mutation in GJB2 or GJB6, which encode connexin 26 and connexin 30, respectively. To date, three cases of KID syndrome caused by an N14Y mutation of GJB2 have been reported globally, but there is no relevant report in domestic literature. Case presentation: A 36-year-old man presented with scalp alopecia and absence of eyelashes, pubic hair, and axillary hair. Yellow-brown highly keratinized verrucous plaques were present on the perineum, palms, and soles. All 20 nails were severely abnormal. Keratitis, blepharitis, and profound sensorineural hearing loss were also observed. Foot biopsy revealed ichthyosis changes. Sequencing of GJB2 showed that the patient was heterozygous for a nucleotide change, c.40A > T, in exon 2, resulting in the substitution of asparagine for tyrosine at position 14 (N14Y) located in the N-terminal domain of connexin 26. Notably, the mutation site of KID syndrome has not been reported in domestic literature. The patient's father was heterozygous for the M195 V (c.583A > G) mutation, and his mother was heterozygous for the V37I (c.109G > A) mutation. The patient received oral retinoic acid, antibiotics and topical moisturizer packs, but was subsequently lost to follow-up. Discussion: KID syndrome manifests as the classic triad of chronic vascularizing keratitis, ichthyosiform erythroderma, and sensorineural hearing loss. Early and long-term multidisciplinary monitoring of affected individuals is essential. Genetic testing could help us detect the mutation site of connexin. Conclusion: These findings expand the mutation spectrum of KID syndrome in the Chinese population and provide a new understanding of the genotype–phenotype correlation. Functional studies on the N14Y mutation will help to reveal the underlying pathogenic mechanism.

Generation of hiPSC line UMi030-A from an individual with the hearing loss-related GJB2 mutation c.109G>A.

Genetic variants in the GJB2 gene which encodes for the Connexin 26 protein account for∼60% of cases of genetic hearing loss. A novel hiPSC line was generated from an individual with the hearing loss-related variant c.109G>A in GJB2 leading to the p.V37I alteration in the Connexin26 protein. These cells will help to delineate the role of GJB2 in hearing loss pathogenesis and serve as a platform for drug discovery and development.

Molecular screening of patients with profound hearing loss from Chengdu, China

Background The rate of genetic deafness in Chengdu is still underestimated. Objective To investigate patients’ molecular etiology with profound hearing loss and facilitate genetic counseling for their families, we screened deafness-related genes of profound hearing loss in the population. Methods A total of 1427 unrelated patients with profound hearing loss containing all age groups in the administrative area of City Chengdu (Sichuan, China) were enrolled in this study, and the average examination rate is 81.13%. Nine loci of four deaf-associated genes (GJB2, GJB3, SLC26A4, and mitochondrial 12SrRNA gene) were analyzed. Then we examined all the deaf-associated mutations and compared them between groups. Results The average age of all subjects is 48.537 ± 19.077 years, peak range in 41–70 years (985/1427, 69.03%). The positive mutation rates of patients in GJB2, SLC26A4, and 12S rRNA are respectively 8.90%, 4.84%, and 5.96%, and GJB3 none. In group A the GJB2 and SLC26A4 mutation rate is 14.17% (36/254), which is remarkably higher than group B (6.14%, 72/1173). The frequency of 12SrRNA mutations is 3.15% (8/254) in group A, which is significantly different (χ 2 = 4.34, p < .05) from that of group B (6.56%, 77/1173). Conclusions and significance The mutation rate of mtDNA 12SrRNA is higher than SLC26A4 gene in our study, which is different from other parts of China. And the deaf-related gene mutation spectrums have a distinct age difference.

Frequency and distribution of GJB2 (connexin 26) and GJB6 (connexin 30) mutations in a large North American repository of deaf probands

Purpose: Profound hearing loss occurs with a frequency of 1 in 1000 live births, half of which is genetic in etiology. The past decade has witnessed rapid advances in determining the pathogenesis of both syndromic and nonsyndromic deafness. The most significant clinical finding to date has been the discovery that mutations of GJB2 at the DFNB1 locus are the major cause of profound prelingual deafness in many countries.1 More recently, GJB2 mutations have been shown to cause deafness when present with a deletion of the GJB6 gene. We report on the prevalence of GJB2 and GJB6 mutations in a large North American Repository of DNA from deaf probands and document the profound effects of familial ethnicity and parental mating types on the frequency of these mutations in the population.Methods: Deaf probands were ascertained through the Annual Survey of Deaf and Hard of Hearing Children and Youth, conducted at the Research Institute of Gallaudet University. Educational, etiologic, and audiologic information was collected after obtaining informed consent. DNA studies were performed for the GJB2 and GJB6 loci by sequencing and PCR methods.Results: GJB2 mutations accounted for 22.2% of deafness in the overall sample but differed significantly among Asians, African-Americans and Hispanics and for probands from deaf by deaf and deaf by hearing matings, as well as probands from simplex and multiplex sibships of hearing parents. In our sample, the overall incidence of GJB2/GJB6 deafness was 2.57%.Conclusion: GJB2 mutations account for a large proportion of deafness in the US, with certain mutations having a high ethnic predilection. Heterozygotes at the GJB2 locus should be screened for the GJB6 deletion as a cause of deafness. Molecular testing for GJB2 and GJB6 should be offered to all patients with nonsyndromic hearing loss.

Comprehensive molecular-genetic analysis of mid-frequency sensorineural hearing loss

The genetic heterogeneity of sensorineural hearing loss (SNHL) is a major hurdle to the detection of disease-causing variants. We aimed to identify underlying causal genes associated with mid-frequency hearing loss (HL), which contributes to less than about 1% of SNHL cases, by whole exome sequencing (WES). Thirty families segregating mid-frequency SNHL, in whom biallelic GJB2 mutations had been previously excluded, were selected from among 851 families in our DNA repository of SNHL. DNA samples from the probands were subjected to WES analysis and searched for candidate variants associated with SNHL. We were able to identify the genetic aetiology in six probands (20%). In total, we found three pathogenic and three likely pathogenic variants in four genes (COL4A5, OTOGL, TECTA, TMPRSS3). One more proband was a compound heterozygote for a pathogenic variant and a variant of uncertain significance (VUS) in MYO15A gene. To date, MYO15A and TMPRSS3 have not yet been described in association with mid-frequency SNHL. In eight additional probands, eight candidate VUS variants were detected in five genes (DIAPH1, MYO7A, TECTA, TMC1, TSPEAR). Seven of these 16 variants have not yet been published or mentioned in the available databases. The most prevalent gene was TECTA, identified in 23% of all tested families. Furthermore, we confirmed the hypothesis that a substantive portion of cases with this conspicuous audiogram shape is a consequence of a genetic disorder.

Cerebellar White Matter Abnormalities in Charcot-Marie-Tooth Disease: A Combined Volumetry and Diffusion Tensor Imaging Analysis.

Charcot–Marie–Tooth disease (CMT) is a genetically heterogeneous hereditary peripheral neuropathy. Brain volumetry and diffusion tensor imaging (DTI) were performed in 47 controls and 47 CMT patients with PMP22 duplication (n = 10), MFN2 (n = 15), GJB1 (n = 11), or NEFL mutations (n = 11) to investigate for structural changes in the cerebellum. Volume of cerebellar white matter (WM) was significantly reduced in CMT patients with NEFL mutations. Abnormal DTI findings were observed in the superior, middle, and inferior cerebellar peduncles, predominantly in NEFL mutations and partly in GJB1 mutations. Cerebellar ataxia was more prevalent in the NEFL mutation group (72.7%) than the GJB1 mutation group (9.1%) but was not observed in other genotypic subtypes, which indicates that structural cerebellar abnormalities were associated with the presence of cerebellar ataxia. However, NEFL and GJB1 mutations did not affect cerebellar gray matter (GM), and neither cerebellar GM nor WM abnormalities were observed in the PMP22 duplication or MFN2 mutation groups. We found structural evidence of cerebellar WM abnormalities in CMT patients with NEFL and GJB1 mutations and an association between cerebellar WM involvement and cerebellar ataxia in these genetic subtypes, especially in the NEFL subgroup. Therefore, we suggest that neuroimaging, such as MRI volumetry or DTI, for CMT patients could play an important role in detecting abnormalities of cerebellar WM.