Non-syndromic Deafness Research Articles

Mutations in eight small DFNB genes are not a frequent cause of non-syndromic hereditary hearing loss in Czech patients

ObjectivesTo evaluate the contribution of eight small NSHL-AR (non-syndromic deafness, autosomal recessive) genes to hereditary hearing loss in Czech patients. Patients and MethodsUnrelated Czech patients, adults and children, diagnosed with pre-lingual hereditary hearing loss with at least one similarly affected deaf sibling and with previously excluded mutations in the GJB2 gene were investigated by Sanger sequencing of the selected eight small NSHL-AR associated genes (CABP2 - 51 patients, CIB2 - 45 patients, PJVK/DFNB59 - 53 patients, GJB3 - 46 patients, ILDR1 - 48 patients, LHFPL5 - 66 patients, LRTOMT - 60 patients, TMIE - 64 patients). ResultsMutations were detected in the LHFPL5 (DFNB67) gene. The patient is heterozygote for two already described pathogenic variants (p.Tyr127Cys, p.Thr165Met). In five samples, five rare heterozygous variants (two novel) predicted as pathogenic were detected in genes CABP2, ILDR1, LHFPL5 and LRTOMT. ConclusionMutations in eight small NSHL-AR genes are not a frequent cause of hereditary hearing loss in the Czech Republic. This diagnostic approach permitted the clarification of HL in only one patient – two heterozygous mutations were detected in LHFPL5 gene for the first time in Central Europe. As the use of panel base MPS certainly improves the diagnostic yield, future studies should rather profit from that diagnostic strategy.

Loss of function of Ywhah in mice induces deafness and cochlear outer hair cell’s degeneration

Loss of function of Ywhah in mice induces deafness and cochlear outer hair cell’s degeneration

Mutation Screening of Exons 7 and 13 of the TMC1 Gene in Autosomal Recessive Non-syndromic Hearing Loss (ARNSHL) in Iran.

Background:Non-syndromic hearing loss (NSHL) is the most common birth defect and occurs in approximately 1/1,000 newborns. NSHL is a heterogeneous trait and can arise due to both genetic and environmental factors. Mutations of the transmembrane channel-like 1 (TMC1) gene cause non-syndromic deafness in humans and mice.Objectives:The aim of the present study was to investigate the association of TMC1 gene mutations of the locus DFNB7/11 in exons 7 and 13 in a cohort of 100 patients with hearing loss in Iran using polymerase chain reaction–single-stranded conformation polymorphism (PCR-SSCP), heteroduplex analysis (HA), and DNA sequencing.Patients and Methods:In this experimental study, the blood samples of 100 NSHL patients were collected from 10 provinces in Iran. These patients had a mean age of 16.5 ± 2.01 years and 74.15% of their parents had consanguinity. DNA was extracted from specimens and mutations of exons 7 and 13 of the TMC1 gene were investigated using PCR-SSCP. All samples were checked via HA reaction and suspected specimens with shift bands were subjected to DNA sequencing for investigation of any gene variation.Results:In this study, no mutation was found in the two exons of TMC1 gene. It was concluded from these results that mutations of the TMC1 gene’s special exons 7 and 13 have a low contribution in patients and are not great of clinical importance in these Iranian provinces.Conclusions:More studies are needed to investigate the relationship between other parts of this gene with hearing loss in different populations through the country. More research could clarify the role of this gene and its relation with deafness and provide essential information for the prevention and management of auditory disorders caused by genetic factors in the Iranian population.

Impact of socio-demographic structure of the deaf people communities in prevalence of hereditary hearing loss

Hearing loss caused by environmental or genetic factors concerns more than 10 % of the world population. It leads to disability and considerably reduces the life quality of deaf people. On average, 1 in 1,000 newborns are born deaf, and 50-60 % of cases are due to genetic causes. Nonsyndromic hereditary deafness is a monogenic disease with uniquely high genetic heterogeneity. The prevalence of some forms of genetic deafness varies in different populations and could be determined, as for many other genetic diseases, by the ethnic composition of a population, isolation, founder and «bottleneck» effects, the proportion of consanguineous marriages, and probable heterozygote advantage. It is assumed that high prevalence of hearing loss due to mutations in the GJB2 (Cx26) gene was also influenced by some social factors: a long-standing tradition of assortative marriages between deaf people, combined with growth of their social adaptation and genetic fitness. The start for these events was the breakdown of the deep social isolation of deaf people, which occurred about 300 years ago in Europe, and later in the US, when special schools for the deaf with learning sign language as a common tool for communication were established (linguistic homogamy). Computer simulations and comparative retrospective study showed that over the past 200 years these social processes can have doubled the frequency of deafness in the US caused by the GJB2 gene mutations. Information about the sociodemographic structure of deaf communities in the past is extremely limited by an almost complete lack of relevant archival data. Nevertheless, studies of sociodemographic and medical-genetic characteristics of deaf people’s contemporary communities are important for predicting the prevalence of inherited forms of deafness, as well as for understanding the impact of social factors on the evolutionary processes occurring in human populations.

Loss of function of Ywhah in mice induces deafness and cochlear outer hair cells' degeneration.

In vertebrates, 14-3-3 proteins form a family of seven highly conserved isoforms with chaperone activity, which bind phosphorylated substrates mostly involved in regulatory and checkpoint pathways. 14-3-3 proteins are the most abundant protein in the brain and are abundantly found in the cerebrospinal fluid in neurodegenerative diseases, suggesting a critical role in neuron physiology and death. Here we show that 14-3-3eta-deficient mice displayed auditory impairment accompanied by cochlear hair cells' degeneration. We show that 14-3-3eta is highly expressed in the outer and inner hair cells, spiral ganglion neurons of cochlea and retinal ganglion cells. Screening of YWHAH, the gene encoding the 14-3-3eta isoform, in non-syndromic and syndromic deafness, revealed seven non-synonymous variants never reported before. Among them, two were predicted to be damaging in families with syndromic deafness. In vitro, variants of YWHAH induce mild mitochondrial fragmentation and severe susceptibility to apoptosis, in agreement with a reduced capacity of mutated 14-3-3eta to bind the pro-apoptotic Bad protein. This study demonstrates that YWHAH variants can have a substantial effect on 14-3-3eta function and that 14-3-3eta could be a critical factor in the survival of outer hair cells.

A novel technique for simultaneous multi-gene mutation screening in 225 patients with nonsyndromic hearing loss

Using simultaneous multi-gene mutation screening to investigate the new method molecular epidemiological basis of 225 patients with nonsyndromic hearing loss in Tianjin, and verifying the for simultaneous multi-gene mutation screening. Two hundred and twenty-five patients with severe non-syndromic deafness from Tianjin CDPF and Association of the Deaf were included in the study. The single nucleotide polymorphisms scan, (SNPscan) technique was used for screening the 115 spots mutations in three common deafness-related genes (GJB2, SLC26A4, mtDNA 12S rRNA) of patients with nonsyndromic hearing loss in Tianjin. We verified the results by Sanger sequencing. Among the 225 patients, there were 111 cases of deafness caused by mutation (49.3%). Using this method, up to 50% of the patients in our study were identified to have hereditary HL caused by mutations in the three genes. 56 patients with the GJB2 mutations were detected (24.9%), including 30 cases of homozygous mutations (13.3%), 26 patients (11.6%) of compound heterozygous mutations, and 21 cases (9.33%) of single heterozygous mutations. 50 patients with the SLC26A4 mutations were detected (22.2%), including 22 cases of homozygous mutations(9.8%), 28 patients (12.4%) of compound heterozygous mutations, and 22 cases (9.8%) of single heterozygous mutations. mtDNA 12S rRNA A1555G mutation was detected in 5 patients (2.2%). mtDNA 12S rRNA 1494C>T mutation was not detected. We verified the results by Sanger sequencing. The accuracy of the sequencing results was 100%. The SNPscan cost eight hours and 160 yuan (each sample). Applying SNPscan technology can be accurate, rapid and cost-effective diagnostic screening in patients with hearing loss for etiology investigation. It is expected to become an effective means of large-scale genetic testing for hereditary deafness.

Reduced Connexin26 in the Mature Cochlea Increases Susceptibility to Noise-Induced Hearing Lossin Mice.

Connexin26 (Cx26, encoded by GJB2) mutations are the most common cause of non-syndromic deafness. GJB2 is thought to be involved in noise-induced hearing loss (NIHL). However, the role of Cx26 in NIHL is still obscure. To explore the association between Cx26 and NIHL, we established a Cx26 knockdown (KD) mouse model by conditional knockdown of Cx26 at postnatal day 18 (P18), and then we observed the auditory threshold and morphologic changes in these mice with or without noise exposure. The Cx26 KD mice did not exhibit substantial hearing loss and hair cell degeneration, while the Cx26 KD mice with acoustic trauma experienced higher hearing loss than simple noise exposure siblings and nearly had no recovery. Additionally, extensive outer hair cell loss and more severe destruction of the basal organ of Corti were observed in Cx26 KD mice after noise exposure. These data indicate that reduced Cx26 expression in the mature mouse cochlea may increase susceptibility to noise-induced hearing loss and facilitate the cell degeneration in the organ of Corti.

Ferlins Show Tissue-Specific Expression and Segregate as Plasma Membrane/Late Endosomal or Trans-Golgi/Recycling Ferlins.

Ferlins are a family of transmembrane-anchored vesicle fusion proteins uniquely characterized by 5-7 tandem cytoplasmic C2 domains, Ca(2+)-regulated phospholipid-binding domains that regulate vesicle fusion in the synaptotagmin family. In humans, dysferlin mutations cause limb-girdle muscular dystrophy type 2B (LGMD2B) due to defective Ca(2+)-dependent, vesicle-mediated membrane repair and otoferlin mutations cause non-syndromic deafness due to defective Ca(2+)-triggered auditory neurotransmission. In this study, we describe the tissue-specific expression, subcellular localization and endocytic trafficking of the ferlin family. Studies of endosomal transit together with 3D-structured illumination microscopy reveals dysferlin and myoferlin are abundantly expressed at the PM and cycle to Rab7-positive late endosomes, supporting potential roles in the late-endosomal pathway. In contrast, Fer1L6 shows concentrated localization to a specific compartment of the trans-Golgi/recycling endosome, cycling rapidly between this compartment and the PM via Rab11 recycling endosomes. Otoferlin also shows trans-Golgi to PM cycling, with very low levels of PM otoferlin suggesting either brief PM residence, or rare incorporation of otoferlin molecules into the PM. Thus, type-I and type-II ferlins segregate as PM/late-endosomal or trans-Golgi/recycling ferlins, consistent with different ferlins mediating vesicle fusion events in specific subcellular locations.

MYO3A Causes Human Dominant Deafness and Interacts with Protocadherin 15-CD2 Isoform.

Hereditary hearing loss (HL) is characterized by both allelic and locus genetic heterogeneity. Both recessive and dominant forms of HL may be caused by different mutations in the same deafness gene. In a family with post-lingual progressive non-syndromic deafness, whole-exome sequencing of genomic DNA from five hearing-impaired relatives revealed a single variant, p.Gly488Glu (rs145970949:G>A) in MYO3A, co-segregating with HL as an autosomal dominant trait. This amino acid change, predicted to be pathogenic, alters a highly conserved residue in the motor domain of MYO3A. The mutation severely alters the ATPase activity and motility of the protein in vitro, and the mutant protein fails to accumulate in the filopodia tips in COS7 cells. However, the mutant MYO3A was able to reach the tips of organotypic inner ear culture hair cell stereocilia, raising the possibility of a local effect on positioning of the mechanoelectrical transduction (MET) complex at the stereocilia tips. To address this hypothesis, we investigated the interaction of MYO3A with the cytosolic tail of the integral tip-link protein protocadherin 15 (PCDH15), a core component of MET complex. Interestingly, we uncovered a novel interaction between MYO3A and PCDH15 shedding new light on the function of myosin IIIA at stereocilia tips.

Altered cellular localization and hemichannel activities of KID syndrome associated connexin26 I30N and D50Y mutations.

BackgroundGap junctions facilitate exchange of small molecules between adjacent cells, serving a crucial function for the maintenance of cellular homeostasis. Mutations in connexins, the basic unit of gap junctions, are associated with several human hereditary disorders. For example, mutations in connexin26 (Cx26) cause both non-syndromic deafness and syndromic deafness associated with skin abnormalities such as keratitis-ichthyosis-deafness (KID) syndrome. These mutations can alter the formation and function of gap junction channels through different mechanisms, and in turn interfere with various cellular processes leading to distinct disorders. The KID associated Cx26 mutations were mostly shown to result in elevated hemichannel activities. However, the effects of these aberrant hemichannels on cellular processes are recently being deciphered. Here, we assessed the effect of two Cx26 mutations associated with KID syndrome, Cx26I30N and D50Y, on protein biosynthesis and channel function in N2A and HeLa cells.ResultsImmunostaining experiments showed that Cx26I30N and D50Y failed to form gap junction plaques at cell-cell contact sites. Further, these mutations resulted in the retention of Cx26 protein in the Golgi apparatus. Examination of hemichannel function by fluorescent dye uptake assays revealed that cells with Cx26I30N and D50Y mutations had increased dye uptake compared to Cx26WT (wild-type) containing cells, indicating abnormal hemichannel activities. Cells with mutant proteins had elevated intracellular calcium levels compared to Cx26WT transfected cells, which were abolished by a hemichannel blocker, carbenoxolone (CBX), as measured by Fluo-3 AM loading and flow cytometry.ConclusionsHere, we demonstrated that Cx26I30N and D50Y mutations resulted in the formation of aberrant hemichannels that might result in elevated intracellular calcium levels, a process which may contribute to the hyperproliferative epidermal phenotypes of KID syndrome.Electronic supplementary materialThe online version of this article (doi:10.1186/s12860-016-0081-0) contains supplementary material, which is available to authorized users.

Molecular Effects of Deafness Mutations in Actin

Point mutations in γ-cytoplasmic actin have been shown to cause autosomal-dominant non-syndromic early onset deafness. Of the eleven known actin mutations, two are unique in that they occur in the same residue. The mutations, K118M in one family and K118N in a second family, provide a unique opportunity to compare the effects of two dissimilar amino acid substitutions that produce a similar phenotype in humans. K118 resides in a helix that runs from from K113 to T126, and mutations that alter the position, dynamics and/or biochemistry of this helix can result in a wide range of pathologies. Using a combination of computational and experimental studies, both using yeast actin, we find that these mutations at K118 result in changes in the structure and dynamics of the DNase-I loop, alterations in the structure of the H73 loop as well as the sidechain orientations of W79 and W86, changes in nucleotide exchange rates, and significant shifts in the twist of the actin monomer. Interestingly for the case of K118N, the twist of the monomer is nearly identical to that for the F-actin protomer, and in vitro polymerization assays show that this mutation actually results in faster polymerization. Taken together, it is evident that mutations at this site give rise to a series of smaller changes that can be tolerated in vivo, but result in misregulation of actin assembly and dynamics.

Characterization of a Unique Myosin IIIa Deafness Mutation which Enhances Actin-Sliding Velocity but Abolishes Filopodia Tip Localization

MYO3A, an unconventional myosin that localizes to the distal tips of stereocilia in the sensory epithelia of the vertebrate auditory and vestibular systems, consists of an N-terminal kinase domain, an actin-activated motor domain, and a class-specific tail domain. Previous work indicates that MYO3A tip-localization is regulated through autophosphorylation. MYO3A is thought to transport the actin regulatory protein, ESPIN1, to the stereocilia tips in inner ear hair cells and mutations in MYO3A lead to non-syndromic deafness in humans. We investigated the G488E mutation in MYO3A, a deafness associated mutation located near the conserved switch I region. The G488E mutation reduces the maximum actin-activated ATPase rate 2-fold and increases 10-fold the actin concentration required to reach one-half maximal ATPase. Interestingly, G488E MYO3A increases 2-fold the actin filament sliding velocity measured with the in vitro motility assay. We also investigated the impact of the G488E mutation on cellular localization by examining GFP tagged MYO3A dK constructs transfected into COS7 cells. The G488E mutation completely abolished MYO3A dK filopodia tip localization both in the presence and absence of ESPIN1. In addition, co-transfection of G488E MYO3A dK, ESPIN1 and wild-type (WT) MYO3A dK demonstrated that the presence of WT MYO3A does not rescue the tip localization of G488E. We hypothesize that the G488E mutation disrupts the duty ratio which prevents processive movement to the tips of parallel actin bundles. In support, chimeras of the MYO3A tail with other myosin motors (MYO1A, MYO19, MYO5A, and MYO10) demonstrate that only high duty-ratio motors are capable of filopodia tip localization. Our results demonstrate that intra-filopodia motility requires high duty ratio motor activity, which may be crucial for the formation, maintenance, and ultrastructure of parallel actin bundles.

A structured interdomain linker directs self-polymerization of human uromodulin

Uromodulin (UMOD)/Tamm-Horsfall protein, the most abundant human urinary protein, plays a key role in chronic kidney diseases and is a promising therapeutic target for hypertension. Via its bipartite zona pellucida module (ZP-N/ZP-C), UMOD forms extracellular filaments that regulate kidney electrolyte balance and innate immunity, as well as protect against renal stones. Moreover, salt-dependent aggregation of UMOD filaments in the urine generates a soluble molecular net that captures uropathogenic bacteria and facilitates their clearance. Despite the functional importance of its homopolymers, no structural information is available on UMOD and how it self-assembles into filaments. Here, we report the crystal structures of polymerization regions of human UMOD and mouse ZP2, an essential sperm receptor protein that is structurally related to UMOD but forms heteropolymers. The structure of UMOD reveals that an extensive hydrophobic interface mediates ZP-N domain homodimerization. This arrangement is required for filament formation and is directed by an ordered ZP-N/ZP-C linker that is not observed in ZP2 but is conserved in the sequence of deafness/Crohn's disease-associated homopolymeric glycoproteins α-tectorin (TECTA) and glycoprotein 2 (GP2). Our data provide an example of how interdomain linker plasticity can modulate the function of structurally similar multidomain proteins. Moreover, the architecture of UMOD rationalizes numerous pathogenic mutations in both UMOD and TECTA genes.

Frequency of Usher syndrome type 1 in deaf children by massively parallel DNA sequencing

Usher syndrome type 1 (USH1) is the most severe of the three USH subtypes due to its profound hearing loss, absent vestibular response and retinitis pigmentosa appearing at a prepubescent age. Six causative genes have been identified for USH1, making early diagnosis and therapy possible through DNA testing. Targeted exon sequencing of selected genes using massively parallel DNA sequencing (MPS) technology enables clinicians to systematically tackle previously intractable monogenic disorders and improve molecular diagnosis. Using MPS along with direct sequence analysis, we screened 227 unrelated non-syndromic deaf children and detected recessive mutations in USH1 causative genes in five patients (2.2%): three patients harbored MYO7A mutations and one each carried CDH23 or PCDH15 mutations. As indicated by an earlier genotype–phenotype correlation study of the CDH23 and PCDH15 genes, we considered the latter two patients to have USH1. Based on clinical findings, it was also highly likely that one patient with MYO7A mutations possessed USH1 due to a late onset age of walking. This first report describing the frequency (1.3–2.2%) of USH1 among non-syndromic deaf children highlights the importance of comprehensive genetic testing for early disease diagnosis.

NLRP3 Is Expressed in the Spiral Ganglion Neurons and Associated with Both Syndromic and Nonsyndromic Sensorineural Deafness.

Nonsyndromic deafness is genetically heterogeneous but phenotypically similar among many cases. Though a variety of targeted next-generation sequencing (NGS) panels has been recently developed to facilitate genetic screening of nonsyndromic deafness, some syndromic deafness genes outside the panels may lead to clinical phenotypes similar to nonsyndromic deafness. In this study, we performed comprehensive genetic screening in a dominant family in which the proband was initially diagnosed with nonsyndromic deafness. No pathogenic mutation was identified by targeted NGS in 72 nonsyndromic and another 72 syndromic deafness genes. Whole exome sequencing, however, identified a p.E313K mutation in NLRP3, a gene reported to cause syndromic deafness Muckle-Wells Syndrome (MWS) but not included in any targeted NGS panels for deafness in previous reports. Follow-up clinical evaluation revealed only minor inflammatory symptoms in addition to deafness in six of the nine affected members, while the rest, three affected members, including the proband had no obvious MWS-related inflammatory symptoms. Immunostaining of the mouse cochlea showed a strong expression of NLRP3 in the spiral ganglion neurons. Our results suggested that NLRP3 may have specific function in the spiral ganglion neurons and can be associated with both syndromic and nonsyndromic sensorineural deafness.

Reduction of Cellular Expression Levels Is a Common Feature of Functionally Affected Pendrin (SLC26A4) Protein Variants.

Sequence alterations in the pendrin gene (SLC26A4) leading to functionally affected protein variants are frequently involved in the pathogenesis of syndromic and nonsyndromic deafness. Considering the high number of SLC26A4 sequence alterations reported to date, discriminating between functionally affected and unaffected pendrin protein variants is essential in contributing to determine the genetic cause of deafness in a given patient. In addition, identifying molecular features common to the functionally affected protein variants can be extremely useful to design future molecule-directed therapeutic approaches. Here we show the functional and molecular characterization of six previously uncharacterized pendrin protein variants found in a cohort of 58 Brazilian deaf patients. Two variants (p.T193I and p.L445W) were undetectable in the plasma membrane, completely retained in the endoplasmic reticulum and showed no transport function; four (p.P142L, p.G149R, p.C282Y and p.Q413R) showed reduced function and significant, although heterogeneous, expression levels in the plasma membrane. Importantly, total expression levels of all of the functionally affected protein variants were significantly reduced with respect to the wild-type and a fully functional variant (p.R776C), regardless of their subcellular localization. Interestingly, reduction of expression may also reduce the transport activity of variants with an intrinsic gain of function (p.Q413R). As reduction of overall cellular abundance was identified as a common molecular feature of pendrin variants with affected function, the identification of strategies to prevent reduction in expression levels may represent a crucial step of potential future therapeutic interventions aimed at restoring the transport activity of dysfunctional pendrin variants.

Tauroursodeoxycholic acid prevents hearing loss and hair cell death in Cdh23erl/erl mice

Sensorineural hearing loss has long been the subject of experimental and clinical research for many years. The recently identified novel mutation of the Cadherin23 (Cdh23) gene, Cdh23erl/erl, was proven to be a mouse model of human autosomal recessive nonsyndromic deafness (DFNB12). Tauroursodeoxycholic acid (TUDCA), a taurine-conjugated bile acid, has been used in experimental research and clinical applications related to liver disease, diabetes, neurodegenerative diseases, and other diseases associated with apoptosis. Because hair cell apoptosis was implied to be the cellular mechanism leading to hearing loss in Cdh23erl/erl mice (erl mice), this study investigated TUDCA’s otoprotective effects in erl mice: preventing hearing impairment and protecting against hair cell death. Our results showed that systemic treatment with TUDCA significantly alleviated hearing loss and suppressed hair cell death in erl mice. Additionally, TUDCA inhibited apoptotic genes and caspase-3 activation in erl mouse cochleae. The data suggest that TUDCA could be a potential therapeutic agent for human DFNB12.

Detection of Connexion 26 GENE (GJB2) Mutations in Cases of Congenital Non Syndromic Deafness.

Hearing loss is most common form of genetic hearing disorder. Non-syndromic sensory neural autosomal recessive deafness (NSRD) is the most common form of genetic hearing loss. Mutations in GJB2 gene, which encodes the connexin 26 protein, are major cause of NSRD. The aim of this study is directed towards the mutations caused along the connexin 26 gene using blood samples from nonsyndromic deaf children. The study was conducted on 36 congenitally hearing impaired children who visited to our department with complains of hearing loss and reduced speech and whose age was <10years with no other congenital anomaly. After a thorough history, clinical examination and all audiological and radiological assessment, blood samples are collected and DNA extraction, PCR and sequencing were done for further genetic analysis. Annotated and documented autosomal recessive (pathogenic) mutations were observed in 57% of NSRD cases. The frequency of pathogenic mutation was commonest for Ins G between nucleotide 30-35 (40% of cases) followed by Del T at nucleotide 59(20% of cases).These two common mutations (singly or doubly) were present in 51.4% of cases. Present study helps to screen the families with hearing impaired children, which will facilitate the development of strategies for diagnosis and treatment of these common genetic disorders.

The role of transcription factors of neurosensory cells in non-syndromic sensorineural hearing loss with or without inner ear malformation

Conclusions: Previous studies have stated the roles and correlation of the four TFs (Sox2, Atoh1, Neurog1, and Neurod1) in the development of neurosensory cells. but whether they are inherited pathogenic factors to cause non-syndromic sensorineural hearing loss is unknown so far. This is the first time for screening the Sox2, Atoh1, Neurog1, and Neurod1 genes in children with NSHL. The c.133A > G in Neurod1 gene is a polymorphism, which is not associated with NSHL. Although these genes are the recognized TFs for modulating the development and transformation of NSCs, they may not be the inherited pathogenic factors to cause congenital severe or profound NSHL directly. Objective: To investigate the effect of the transcription factors (TFs) for the development of neurosensory cells (NSCs) and to explore the genetic etiology of congenital profound non-syndromic sensorineural hearing loss (NSHL). Methods: Children with NSHL, from multi-national and regional group, and control group were recruited to screen for the most common mutations for non-syndromic deafness among East Asian (mtDNA 12S rRNA: 1555A > G, 1494C > T; SLC26A4: IVS7-2 A > G, 2168 C > T). And mutational analysis of the coding regions in Sox2, Atoh1 and Neurog1, Neurod1 genes were performed. Results: Only the c.133A > G (p. Ala45Thr) in the Neurod1 gene was detected in this study. The allele frequencies of this variant were 88.00% and 84.88% in the inner ear malformation group and the normal inner ear group, respectively, while 90.85% of children in the control group carried c.133A > G. This variant existed in every group commonly and had no significant difference among them. No variant in the other two TFs was detected in this cohort.

A novel frameshift variant of COCH supports the hypothesis that haploinsufficiency is not a cause of autosomal dominant nonsyndromic deafness 9

COCH (coagulation factor C homology) encodes cochlin, and certain mutations of COCH cause autosomal dominant nonsyndromic deafness 9 (DFNA9). Hearing loss due to COCH mutation begins in adulthood, and 17 missense mutations and two in-frame mutations have been reported. Studies with animal and cellular models have suggested that the underlying biological mechanism of DFNA9 is the dominant-negative effect of mutated COCH and not haploinsufficiency. However, no human cases of DFNA9 that support this hypothesis have been reported. The proband of the present case was an 18-year-old male with congenital or infantile hearing loss. Targeted next-generation sequencing analysis detected a heterozygous novel frameshift mutation of COCH (c.146dupT, p.C50LfsX8) in the proband, whose hearing loss began earlier than what is typical for DFNA9. His mother also carried the mutation but had normal hearing. Consequently, the mutation was not considered to be the cause of the proband's hearing loss. This family is the first case of a truncating COCH variant and supports the hypothesis that COCH haploinsufficiency is not the cause of hearing loss in humans.