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DFNA9 is a dominantly inherited form of adult-onset progressive hearing impairment caused by mutations in the COCH gene. COCH encodes cochlin, a crucial extracellular matrix protein. We established a genomically humanized mouse model for the Dutch/Belgian c.151C>T founder mutation in COCH. Considering upcoming sequence-specific genetic therapies, we exchanged the genomic murine Coch exons 3-6 for the corresponding human sequence. Introducing human-specific genetic information into mouse exons can be risky. To mitigate unforeseen consequences on cochlin function resulting from the introduction of the human COCH protein-coding sequence, we converted all human-specific amino acids to mouse equivalents. We furthermore optimized the recognition of the human COCH exons by the murine splicing machinery during pre-mRNA splicing. Subsequent observations in mouse embryonic stem cells revealed correct splicing of the hybrid Coch transcript. The inner ear of the established humanized Coch mice displays correctly-spliced wild-type and mutant humanized Coch alleles. For a comprehensive study of auditory function, mice were crossbred with C57BL/6 Cdh23 753A> G mice to remove the Cdh23 ahl allele from the genetic background of the mice. At 9 months, all humanized Coch genotypes showed hearing thresholds comparable to wild-type C57BL/6 Cdh23 753A> G mice. This indicates that both the introduction of human wildtype COCH, and correction of Cdh23 ahl in the humanized Coch lines was successful. Overall, our approach proved beneficial in eliminating potential adverse events of genomic humanization of mouse genes, and provides us with a model in which sequence-specific therapies directed against the human mutant COCH alle can be investigated. With the hearing and balance defects anticipated to occur late in the second year of life, a long-term follow-up study is ongoing to fully characterize the humanized Coch mouse model., Competing Interests: Declaration of Competing Interest The authors have no competing interests, (Copyright © 2023. Published by Elsevier B.V.)

Objective: To investigate the diagnostic yield of targeted next-generation sequencing using hearing loss panels and to identify patient-related factors that are associated with a definite genetic cause., Study Design: Retrospective chart review., Setting: Tertiary referral center., Patients: Children with congenital or late-onset, bilateral sensorineural hearing loss., Interventions: Diagnostic., Main Outcome Measures: The number of patients with a definite genetic diagnosis., Results: We report on 238 patients with hearing loss: 130 were male and 108 were female. About 55% had congenital hearing loss. A genetic cause was identified in 94 of the patients (39.5%), with 72.3% of these showing nonsyndromic and 27.6% showing syndromic hearing loss. The diagnostic yield was highest among North African patients (66.7%). A multiple linear regression model shows that profound hearing loss, family history of hearing loss, congenital hearing loss, and North African ethnicity are significantly related to identifying a genetic cause., Conclusions: Targeted next-generation sequencing using a panel of hearing loss genes identified a genetic diagnosis in almost 40% of children with bilateral sensorineural hearing loss. We describe the predictors of a genetic diagnosis, and this information may be used during genetic counseling., Competing Interests: The authors disclose no conflicts of interest., (Copyright © 2023, Otology & Neurotology, Inc.)

Background: Advances in gene therapeutic approaches to treat sensorineural hearing loss (SNHL) confront us with future challenges of translating these animal studies into clinical trials. Little is known on patient attitudes towards future innovative therapies., Objective: We aimed to better understand the willingness of patients with progressive SNHL and vestibular function loss of autosomal dominant (AD) inheritance to participate in potential gene therapy trials to prevent, stabilize, or slow down hearing loss., Methods: A survey was performed in carriers of the P51S and G88E pathogenic variant in the COCH gene (DFNA9). Various hypothetical scenarios were presented while using a Likert scale., Results: Fifty three participants were included, incl. 49 symptomatic patients, one presymptomatic patient, and three participants at risk. Their attitude towards potential trials studying innovative therapies was overall affirmative, even if the treatment would only slow down the decline of hearing and vestibular function, rather than cure the disease. Among the different potential scenarios, the less invasive and less frequent treatments increased the likelihood to enroll. Daily oral medication and annual intravenous infusion were awarded the highest scores. The more invasive, more frequent, and more at-risk treatments were still likely to be accepted but decreased the willingness to participate. The presence of a placebo arm was met with the lowest scores of willingness to participate., Conclusions: Overall, most symptomatic DFNA9 patients would likely consider participation in future innovative inner ear therapy trials, even if it would only slow down the decline of hearing and vestibular function., Competing Interests: The authors disclose no conflicts of interest., (Copyright © 2020, Otology & Neurotology, Inc.)

Pathogenic variant in COCH are a known cause of DFNA9 autosomal dominant progressive hearing loss and vestibular dysfunction with adult onset. Hitherto, only dominant nonsynonymous variants and in-frame deletions with a presumed dominant negative or gain-of-function effect have been described. Here, we describe two brothers with congenital prelingual deafness and a homozygous nonsense c.292C>T(p.Arg98*) COCH variant, suggesting a loss-of-function effect. Vestibular dysfunction starting in the first decade was observed in the older patient. The heterozygous parents and sibling have normal hearing and vestibular function, except for the mother, who shows vestibular hyporeflexia and abnormal smooth pursuit tests, most likely due to concomitant disease. This is the first report of autosomal recessive inheritance of cochlea-vestibular dysfunction caused by a pathogenic variant in the COCH gene. An earlier onset of hearing impairment and vestibular dysfunction compared to the dominant hearing loss causing COCH variants is observed.

Implementing DNA diagnostics in clinical practice for extremely heterogeneous diseases such as hearing loss is challenging, especially when attempting to reach high sensitivity and specificity in a cost-effective fashion. Next generation sequencing has enabled the development of such a test, but the most commonly used genomic target enrichment methods such as hybridization-based capture suffer from restrictions. In this study, we have adopted a new flexible approach using microdroplet PCR-based technology for target enrichment, in combination with massive parallel sequencing to develop a DNA diagnostic test for autosomal recessive hereditary hearing loss. This approach enabled us to identify the genetic basis of hearing loss in 9 of 24 patients, a success rate of 37.5%. Our method also proved to have high sensitivity and specificity. Currently, routine molecular genetic diagnostic testing for deafness is in most cases only performed for the GJB2 gene and a positive result is typically only obtained in 10-20% of deaf children. Individuals with mutations in GJB2 had already been excluded in our selected set of 24 patients. Therefore, we anticipate that our deafness test may lead to a genetic diagnosis in roughly 50% of unscreened autosomal recessive deafness cases. We propose that this diagnostic testing approach represents a significant improvement in clinical practice as a standard diagnostic tool for children with hearing loss., (Copyright © 2012 Wiley Periodicals, Inc.)

Background: Hereditary hearing loss (HL) can originate from mutations in one of many genes involved in the complex process of hearing. Identification of the genetic defects in patients is currently labor intensive and expensive. While screening with Sanger sequencing for GJB2 mutations is common, this is not the case for the other known deafness genes (> 60). Next generation sequencing technology (NGS) has the potential to be much more cost efficient. Published methods mainly use hybridization based target enrichment procedures that are time saving and efficient, but lead to loss in sensitivity. In this study we used a semi-automated PCR amplification and NGS in order to combine high sensitivity, speed and cost efficiency., Results: In this proof of concept study, we screened 15 autosomal recessive deafness genes in 5 patients with congenital genetic deafness. 646 specific primer pairs for all exons and most of the UTR of the 15 selected genes were designed using primerXL. Using patient specific identifiers, all amplicons were pooled and analyzed using the Roche 454 NGS technology. Three of these patients are members of families in which a region of interest has previously been characterized by linkage studies. In these, we were able to identify two new mutations in CDH23 and OTOF. For another patient, the etiology of deafness was unclear, and no causal mutation was found. In a fifth patient, included as a positive control, we could confirm a known mutation in TMC1., Conclusions: We have developed an assay that holds great promise as a tool for screening patients with familial autosomal recessive nonsyndromal hearing loss (ARNSHL). For the first time, an efficient, reliable and cost effective genetic test, based on PCR enrichment, for newborns with undiagnosed deafness is available.

Objectives: The DFNA5 gene was identified in 1998 as a gene that causes an autosomal dominant form of hearing impairment. Five different DFNA5 mutations have been found; each results in skipping of exon 8 at the messenger RNA level. This finding indicates that DFNA5-associated hearing loss is attributable to a highly specific gain-of-function mutation. Interestingly, later reports revealed that DFNA5 also plays a role in tumor biology., Methods: Recent data have shed more light on the biological function of DFNA5. Through a literature search, the current knowledge of this gene is reviewed., Results: DFNA5 is the first gene for monogenic deafness that is known to involve apoptosis as a disease mechanism--a mechanism that was shown to be involved in frequent types of hearing loss caused by age, noise, or drugs. In line with its apoptosis-inducing properties, DFNA5 is a tumor suppressor gene with an important role in major types of tumors., Conclusions: DFNA5 is a tumor suppressor gene that is involved in apoptosis pathways and as such performs a basic role in cell survival. In view of the known role of apoptosis in several forms of hearing loss, DFNA5 may be a player in the underlying disease mechanisms.

The DFNB74 locus for autosomal-recessive, nonsyndromic deafness segregating in three families was previously mapped to a 5.36 Mb interval on chromosome 12q14.2-q15. Subsequently, we ascertained five additional consanguineous families in which deafness segregated with markers at this locus and refined the critical interval to 2.31 Mb. We then sequenced the protein-coding exons of 18 genes in this interval. The affected individuals of six apparently unrelated families were homozygous for the same transversion (c.265T>G) in MSRB3, which encodes a zinc-containing methionine sulfoxide reductase B3. c.265T>G results in a substitution of glycine for cysteine (p.Cys89Gly), and this substitution cosegregates with deafness in the six DFNB74 families. This cysteine residue of MSRB3 is conserved in orthologs from yeast to humans and is involved in binding structural zinc. In vitro, p.Cys89Gly abolished zinc binding and MSRB3 enzymatic activity, indicating that p.Cys89Gly is a loss-of-function allele. The affected individuals in two other families were homozygous for a transition mutation (c.55T>C), which results in a nonsense mutation (p.Arg19X) in alternatively spliced exon 3, encoding a mitochondrial localization signal. This finding suggests that DFNB74 deafness is due to a mitochondrial dysfunction. In a cohort of 1,040 individuals (aged 53-67 years) of European ancestry, we found no association between 17 tagSNPs for MSRB3 and age-related hearing loss. Mouse Msrb3 is expressed widely. In the inner ear, it is found in the sensory epithelium of the organ of Corti and vestibular end organs as well as in cells of the spiral ganglion. Taken together, MSRB3-catalyzed reduction of methionine sulfoxides to methionine is essential for hearing.

Clinical and audiological examination was done in 2 Belgian families with autosomal dominant sensorineural hearing loss (SNHL) linked to DFNA22. Nineteen subjects in family 1 had mild to moderate SNHL starting in the third decade. The hearing loss was characterized by a flat audiogram affecting all tested frequencies with statistically significant progression. In family 2 eleven subjects were affected with mild to moderate SNHL starting in the second decade. Most of them showed a flat audiogram, but some had mid-frequency hearing loss. Significant progression of thresholds was present at 4 and 8 kHz. For all hitherto known DFNA22 families the audiological and clinical characteristics were correlated with the molecular data. This study describes the phenotype of 2 Belgian families with SNHL linked to DFNA22, both with a pathogenic change in the deafness gene MYO6. The phenotypes of all hitherto reported DFNA22 families with mutations in the MYO6 gene have been studied and compared. It seems that genetic defects that spare the motor domain of the myosin VI protein have a milder phenotype., (Copyright 2009 S. Karger AG, Basel.)

Hearing loss is the most common sensory disorder, present in 1 of every 500 newborns. To date, 46 genes have been identified that cause nonsyndromic hearing loss, making it an extremely heterogeneous trait. This review provides a comprehensive overview of the inner ear function and expression pattern of these genes. In general, they are involved in hair bundle morphogenesis, form constituents of the extracellular matrix, play a role in cochlear ion homeostasis or serve as transcription factors. During the past few years, our knowledge of genes involved in hair bundle morphogenesis has increased substantially. We give an up-to-date overview of both the nonsyndromic and Usher syndrome genes involved in this process, highlighting proteins that interact to form macromolecular complexes. For every gene, we also summarize its expression pattern and impact on hearing at the functional level. Gene-specific cochlear expression is summarized in a unique table by structure/cell type and is illustrated on a cochlear cross-section, which is available online via the Hereditary Hearing Loss Homepage. This review should provide auditory scientists the most relevant information for all identified nonsyndromic deafness genes.

Approximately one in 1,000 children is affected by severe or profound hearing loss at birth or during early childhood (prelingual deafness). Up to 40% of congenital, autosomal recessive, severe to profound hearing impairment cases result from mutations in a single gene, GJB2, that encodes the connexin 26 protein. One specific mutation in this gene, 35delG, accounts for the majority of GJB2 mutations detected in Caucasian populations. Some previous studies have assumed that the high frequency of the 35delG mutation reflects the presence of a mutational hot spot, while other studies support the theory of a common founder. Greece is among the countries with the highest carrier frequency of the 35delG mutation (3.5%), and a recent study raised the hypothesis of the origin of this mutation in ancient Greece. We genotyped 60 Greek deafness patients homozygous for the 35delG mutation for six single nucleotide polymorphisms (SNPs) and two microsatellite markers inside or flanking the GJB2 gene. The allele distribution in the patients was compared to 60 Greek normal hearing controls. A strong linkage disequilibrium was found between the 35delG mutation and markers inside or flanking the GJB2 gene. Furthermore, we found a common haplotype with a previous study, suggesting a common founder for the 35delG mutation., ((c) 2008 Wiley-Liss, Inc.)

Hearing loss is the most frequent sensorineural disorder affecting 1 in 1000 newborns. In more than half of these babies, the hearing loss is inherited. Hereditary hearing loss is a very heterogeneous trait with about 100 gene localizations and 44 gene identifications for non-syndromic hearing loss. Transmembrane channel-like gene 1 (TMC1) has been identified as the disease-causing gene for autosomal dominant and autosomal recessive non-syndromic hearing loss at the DFNA36 and DFNB7/11 loci, respectively. To date, 2 dominant and 18 recessive TMC1 mutations have been reported as the cause of hearing loss in 34 families. In this report, we describe linkage to DFNA36 and DFNB7/11 in 1 family with dominant and 10 families with recessive non-syndromic sensorineural hearing loss. In addition, mutation analysis of TMC1 was performed in 51 familial Turkish patients with autosomal recessive hearing loss. TMC1 mutations were identified in seven of the families segregating recessive hearing loss. The pathogenic variants we found included two known mutations, c.100C>T and c.1165C>T, and four new mutations, c.2350C>T, c.776+1G>A, c.767delT and c.1166G>A. The absence of TMC1 mutations in the remaining six linked families implies the presence of mutations outside the coding region of this gene or alternatively at least one additional deafness-causing gene in this region. The analysis of copy number variations in TMC1 as well as DNA sequencing of 15 additional candidate genes did not reveal any proven pathogenic changes, leaving both hypotheses open.

Alpha-tectorin (encoded by Tecta) is a component of the tectorial membrane, an extracellular matrix of the cochlea. In humans, the Y1870C missense mutation in TECTA causes a 50- to 80-dB hearing loss. In transgenic mice with the Y1870C mutation in Tecta, the tectorial membrane's matrix structure is disrupted, and its adhesion zone is reduced in thickness. These abnormalities do not seriously influence the tectorial membrane's known role in ensuring that cochlear feedback is optimal, because the sensitivity and frequency tuning of the mechanical responses of the cochlea are little changed. However, neural thresholds are elevated, neural tuning is broadened, and a sharp decrease in sensitivity is seen at the tip of the neural tuning curve. Thus, using Tecta(Y1870C/+) mice, we have genetically isolated a second major role for the tectorial membrane in hearing: it enables the motion of the basilar membrane to optimally drive the inner hair cells at their best frequency.

Fifty to eighty percent of autosomal recessive deafness is due to mutations in the GJB2 gene encoding connexin 26. Among Caucasians, the c.35delG mutation in this gene accounts for up to 30 to 70% of all cases with early childhood deafness. In this study, we present the analysis of the GJB2 gene in 159 Egyptians from 111 families with non-syndromic mild to profound hearing impairment. An additional family with Vohwinkel syndrome, a combination of hearing impairment and palmoplantar keratoderma with constriction of the digits, was also included. We used direct sequencing analysis to detect all possible coding GJB2 variants in this population. The presence of the g.1777179_2085947del mutation (hereafter called del(GJB6-D13S1830)) was also investigated as it was shown to be the second most common mutation causing non-syndromic prelingual hearing impairment in Spain. Sequencing analysis of one randomly chosen individual per family revealed that the c.35delG mutation was present in 24 out of 222 chromosomes (10.8%), making it the most frequent mutation in the GJB2 gene in Egypt. Five other mutations were already described previously [p.Thr8Met, p.Val37Ile, p.Val153Ile, c.333_334delAA, c.1-3172G>A (commonly designated as IVS1+1G>A)]. This study also revealed three other novel gene variants resulting in amino acid substitutions (p.Phe142del, p.Asp117His, p.Ala148Pro). In contrast with most populations, the del(GJB6-D13S1830) mutation upstream of the GJB2 gene was not present in this Egyptian population. A dominant mutation at a highly conserved residue, p.Gly130Val, was found in the family with Vohwinkel syndrome.

Genetic testing was completed on 1,294 persons with deafness referred to the Molecular Otolaryngology Research Laboratories to establish a diagnosis of DFNB1. Exon 2 of GJB2 was screened for coding sequence allele variants by denaturing high-performance liquid chromatography (DHPLC) complemented by bidirectional sequencing. If two deafness-causing mutations of GJB2 (encoding Connexin 26) were identified, further screening was not performed. If only a single deafness-causing mutation was identified, we screened for the g.1777179&#95;2085947del (hereafter called del(GJB6-D13S1830); GenBank NT&#95;024524.13) and mutations in the noncoding region of GJB2. Phenotype-genotype correlations were evaluated by categorizing mutations as either protein truncating or nontruncating. A total of 205 persons carried two GJB2 exon 2 mutations and were diagnosed as having DFNB1; 100 persons carried only a single deafness-causing allele variant of exon 2. A total of 37 of these persons were c.35delG carriers, and 51 carried other allele variants of GJB2. Persons diagnosed with DFNB1 segregating two truncating/nonsense mutations had a more severe phenotype than persons carrying two missense mutations, with mean hearing impairments being 88 and 37%, respectively (P < 0.05). The number of deaf c.35delG carriers was greater than expected when compared to the c.35delG carrier frequency in normal-hearing controls (P < 0.05), suggesting the existence of at least one other mutation outside the GJB2 coding region that does not complement GJB2 deafness-causing allele variants., (Copyright 2004 Wiley-Liss, Inc.)

Myosins have been implicated in various motile processes, including organelle translocation, ion-channel gating, and cytoskeleton reorganization. Different members of the myosin superfamily are responsible for syndromic and nonsyndromic hearing impairment in both humans and mice. MYH14 encodes one of the heavy chains of the class II nonmuscle myosins, and it is localized within the autosomal dominant hearing impairment (DFNA4) critical region. After demonstrating that MYH14 is highly expressed in mouse cochlea, we performed a mutational screening in a large series of 300 hearing-impaired patients from Italy, Spain, and Belgium and in a German kindred linked to DFNA4. This study allowed us to identify a nonsense and two missense mutations in large pedigrees, linked to DFNA4, as well as a de novo allele in a sporadic case. Absence of these mutations in healthy individuals was tested in 200 control individuals. These findings clearly demonstrate the role of MYH14 in causing autosomal dominant hearing loss and further confirm the crucial role of the myosin superfamily in auditive functions.

Hearing impairment (HI) is clinically and genetically very heterogeneous, and auditory genes are discovered at a very rapid pace. The identification of deafness genes is enabling us to understand the molecular process of hearing, and it offers prospects for DNA testing of HI. However, the routine application of these tests is hampered by the large number of genes involved in HI and by the fact that molecular screening of these genes is often quite expensive and time consuming. An important gene that should be considered in congenital or childhood onset autosomal recessive HI is GJB2 since mutations in this gene account for at least 50% of this type of HI. In the present review, we describe the known deafness genes and we provide an overview of the current, routinely used diagnostic DNA tests., (Copyright 2004 S. Karger AG, Basel)

Objective: To evaluate audiometric and vestibular signs and symptoms in a new DFNA9 family., Setting: Tertiary referral centers., Methods: A multigeneration Belgian family with late-onset progressive sensorineural hearing loss and concomitant ves-tibular impairment with an autosomal dominant pattern of inheritance underwent clinical and genetic evaluation. Medical history was recorded. Blood samples were taken for genetic linkage and mutation analyses. Pure-tone audiometry, speech audiometry and vestibular examinations were performed. Onset and progression in hearing impairment were evaluated with linear regression analysis of longitudinal threshold-on-age data., Results: Linkage to DFNA9 was confirmed and mutation analysis revealed a P51S mutation in the COCH gene. Several patients had a Ménière's-like presentation. All patients developed late-onset progressive sensorineural hearing loss eventually leading to severe deafness and vestibular failure.

Connexins are the building blocks of gap junctions. In forming a gap junction, six connexins oligomerize to form a hexameric torus called a connexon. The number of gap junctions in a cell ranges from a few to over 105 and imparts to interconnected cells a uniform phenotype. The crucial role that gap junctions play in normal physiology is reflected by the diverse spectrum of human diseases in which allele variants of different gap junction genes are implicated. In particular, mutations in GJB2 are a major cause of autosomal recessive non-syndromic deafness. This discovery has impacted medical practice and makes it incumbent on clinicians to familiarize themselves with the genetic advances that are rapidly occurring in our field.

Objective: To evaluate vestibular and long-term audiometric findings in patients with Pendred syndrome., Study Design: Retrospective analysis of long-term clinical data., Setting: University hospital department., Patients: Three patients with Pendred syndrome caused by a mutation in the SLC26A4 gene., Methods: Perchlorate discharge test, mutation analysis of the SLC26A4 gene, MR imaging of temporal bones, vestibular function test (in two cases) and serial audiometry. A saturation hyperbola with onset age was fitted to the audiometric threshold-on-age data using a nonlinear regression method. The residues remaining after regression were analyzed in a correlation analysis to detect significant ipsilateral or contralateral cofluctuation., Results: All three patients had a mutation in the SLC26A4 gene and bilateral enlarged vestibular aqueduct; two of them had a positive perchlorate discharge test but in one of two siblings this test was negative. Hearing loss was significantly progressive with significant ipsilateral and contralateral cofluctuation in all evaluable cases, combined with episodes of Menière like vertigo in two cases. The episodes of vertigo are as seen in Menière disease. One case had unilateral caloric areflexia and one had bilateral vestibular hyporeflexia, proven to be progressive in a repeat examination., Conclusions: Patients with Pendred syndrome may exhibit progressive and fluctuant hearing loss with episodes of vertigo.

We have determined the molecular basis for Usher syndrome type 1F (USH1F) in two families segregating for this type of syndromic deafness. By fluorescence in situ hybridization, we placed the human homolog of the mouse protocadherin Pcdh15 in the linkage interval defined by the USH1F locus. We determined the genomic structure of this novel protocadherin, and found a single-base deletion in exon 10 in one USH1F family and a nonsense mutation in exon 2 in the second. Consistent with the phenotypes observed in these families, we demonstrated expression of PCDH15 in the retina and cochlea by RT-PCR and immunohistochemistry. This report shows that protocadherins are essential for maintenance of normal retinal and cochlear function.

Background: Earlier studies have mapped the autosomal recessive nonsyndromic deafness locus, DFNB15, to chromosomes 3q21.3-q25.2 and 19p13.3-13.1, identifying one of these chromosomal regions (or possibly both) as the site of a deafness-causing gene. Mutations in unconventional myosins cause deafness in mice and humans. One unconventional myosin, myosin 1F (MYO1F), is expressed in the cochlea and maps to chromosome 19p13.3-13.2., Objective: To evaluate MYO1F as a candidate gene for deafness at the DFNB15 locus by determining its genomic structure and screening each exon for deafness-causing mutations to identify possible allele variants of MYO1F segregating in the DFNB15 family., Methods: We used radiation hybrid mapping to localize MYO1F on chromosome arm 19p. We next determined its genomic structure using multiple long-range polymerase chain reaction experiments. Using these data, we completed mutation screening using single-stranded conformational polymorphism analysis and direct sequencing of affected and nonaffected persons in the original DFNB15 family., Results: Radiation hybrid mapping placed MYO1F in the DFNB15 interval, establishing it as a positional candidate gene. Its genomic structure consists of 24 coding exons. No mutations or genomic rearrangements were found in the original DFNB15 family, making it unlikely that MYO1F is the disease-causing gene in this kindred., Conclusions: Although we did not find MYO1F allele variants in one family with autosomal recessive nonsyndromic hearing loss, the gene remains an excellent candidate for hereditary hearing impairment. Given its wide tissue expression, MYO1F might cause syndromic deafness.

We identified Eyes absent 4 (EYA4), a member of the vertebrate Eya family of transcriptional activators, as the causative gene of postlingual, progressive, autosomal dominant hearing loss at the DFNA10 locus. In two unrelated families from Belgium and the USA segregating for deafness at this locus, we found different mutations in EYA4, both of which create premature stop codons. Although EYA proteins interact with members of the SIX and DACH protein families in a conserved network that regulates early embryonic development, this finding shows that EYA4 is also important post-developmentally for continued function of the mature organ of Corti.

The DFNA2 locus for autosomal dominant nonsyndromic hearing impairment on chromosome 1p34 contains at least 2 genes responsible for hearing loss, GJB3 and KCNQ4. GJB3 is a member of the connexin gene family and KCNQ4 is a voltage-gated potassium channel. KCNQ4 mutations were first found in a French family, and later also in a Belgian, an American and two Dutch families. Here we present the analysis of the GJB3 and KCNQ4 genes in a third Dutch family linked to DFNA2. No mutation was found in GJB3, but a missense mutation changing a conserved Leu residue into His (L274H) was found in the coding region of the KCNQ4 gene in all patients of this DFNA2 family. Examination of the position of all known KCNQ4 mutations showed a clustering of mutations in the pore region of the KCNQ4 gene, responsible for the ion selectivity of the channel. The clustering of mutations in this domain confirms its importance.

DFNA10 originally was mapped to the long arm of chromosome 6 in a large American family segregating for autosomal dominant progressive nonsyndromic hearing impairment. By extending this American family, we have reduced the original DFNA10 candidate region from 13 cM to 3.7 cM. We also report a Belgian family with autosomal dominant nonsyndromic hearing impairment linked to DFNA10 and a Norwegian family with the same condition in which linkage is suggestive, although maximum lod scores are only 2.5. The hearing phenotype in all three DFNA10 families is similar, with losses beginning in the middle frequencies and involving the low and high frequencies later in life.

Mitochondria are intracellular organelles responsible for the majority of a cell's energy production. They have their own small maternally inherited genome which, when mutated, can give rise to a large spectrum of diseases. The phenotype most commonly includes neurological and muscular symptoms, although hearing impairment is an additional feature in some mitochondrial syndromes. Often, syndromic mutations affect only a fraction of all mitochondrial DNA molecules, a condition referred to as heteroplasmy. It is believed that the degree of heteroplasmy in different tissues contributes to the phenotypic heterogeneity that is a hallmark of these syndromes. Five homoplasmic mutations leading to nonsyndromic hearing impairment have been reported (1555A-->G, 7445A-->G, 7472insC, 7510T-->C, 7511T-->C). The 1555A-->G is in the 12S rRNA gene, and in some populations, appears to be a frequent cause of hearing impairment. Carriers of the mutation are abnormally sensitive to aminoglycoside-induced ototoxicity even at 'appropriate' drug levels; in addition, even without aminoglycoside exposure, these persons can develop hearing impairment. The other four nonsyndromic mutations are located in the tRNA(Ser(UCN)) gene. In addition to hearing impairment, with two of these mutations (7445A-->G, 7472insC), other symptoms can be present in some patients. However, why these five mutations preferentially affect the inner ear, despite the crucial role of mitochondria in nearly all cells of the body, is unknown.

GJB2 encodes the protein Connexin 26, one of the building blocks of gap junctions. Each Connexin 26 molecule can oligomerize with five other connexins to form a connexon; two connexons, in turn, can form a gap junction. Because mutations in GJB2 are the most common cause of congenital severe-to-profound autosomal recessive nonsyndromic hearing loss, the effect of the Connexin 26 allele variants on this dynamic 'construction' process and the function of any gap junctions that do form is particularly germane. One of the more controversial allele variants, M34T, has been hypothesized to cause autosomal dominant nonsyndromic hearing loss. In this paper, we present clinical and genotypic data that refutes this hypothesis and suggests that the effect of the M34T allele variant may be dependent on the mutations segregating in the opposing allele.

Nearly all genes that have been localized for autosomal dominantly inherited hearing impairment are characterized by postlingual hearing loss that is progressive in nature. This auditory phenotype is in contrast to that of genes localized for autosomal recessive hearing impairment, which generally cause nonprogressive severe-to-profound or profound prelingual hearing loss. In most cases, extended pedigrees have been used to localize autosomal dominant deafness genes, To date, 22 autosomal dominant loci have been mapped, and 10 of these genes have been cloned. The functions of these deafness-causing genes are diverse and include transcription factors, extracellular matrix components, ion channels, cytoskeletal components, and unknown functions. Interesting findings include the unexpected expression pattern of some of these genes and the discovery that in some genes, allele variants can cause either isolated hearing loss or syndromic deafness. The greatest challenge for future research will be identifying additional deafness-causing genes and elucidating their function in the inner ear. Am. J. Med. Genet. (Semin. Med. Genet.) 89:167-174, 1999. @ 2000 Wiley-Liss, Inc.

Nearly all genes for autosomal recessive nonsyndromal inherited hearing loss (ARNSHL) localized thus far cause prelingual severe to profound or profound hearing impairment. Of the 25 reported loci, most have been identified using single consanguineous families. Six of these genes have been cloned and encode a variety of proteins, including ion channels, extracellular matrix components, cytoskeletal components, and proteins essential for synaptic vesicular trafficking. One of these genes appears to be responsible for approximately 50% of all congenital severe to profound or profound hearing loss in many world populations, and mutations in two other genes can lead to either syndromic or nonsyndromic forms of deafness. The identification of additional genes that cause ARNSHL and elucidation of their function will refine our understanding of auditory physiology at the molecular level., (Copyright 2000 Wiley-Liss, Inc.)

We have previously found linkage to chromosome 1p34 in five large families with autosomal dominant non-syndromic hearing impairment (DFNA2). In all five families, the connexin31 gene ( GJB3 ), located at 1p34 and responsible for non-syndromic autosomal dominant hearing loss in two small Chinese families, has been excluded as the responsible gene. Recently, a fourth member of the KCNQ branch of the K+channel family, KCNQ4, has been cloned. KCNQ4 was mapped to chromosome 1p34 and a single mutation was found in three patients from a small French family with non-syndromic autosomal dominant hearing loss. In this study, we have analysed the KCNQ4 gene for mutations in our five DFNA2 families. Missense mutations altering conserved amino acids were found in three families and an inactivating deletion was present in a fourth family. No KCNQ4 mutation could be found in a single DFNA2 family of Indonesian origin. These results indicate that at least two and possibly three genes responsible for hearing impairment are located close together on chromosome 1p34 and suggest that KCNQ4 mutations may be a relatively frequent cause of autosomal dominant hearing loss.

Recently the gene responsible for Pendred syndrome (PDS) was isolated and several mutations in the PDS gene have been identified in Pendred patients. Here we report the occurrence of two different PDS mutations in an extended inbred Turkish family. The majority of patients in this family are homozygous for a splice site mutation (1143-2A-->G) affecting the 3' splice site consensus sequence of intron 7. However, two affected sibs with non-consanguineous parents are compound heterozygotes for the splice site mutation and a missense mutation (1558T-->G), substituting an evolutionarily conserved amino acid. The latter mutation has been found previously in two Pendred families originating from The Netherlands, indicating that the 1558T-->G mutation may be a common mutation.

Background: Mutations in the GJB2 gene cause one form of nonsyndromic recessive deafness. Among Mediterranean Europeans, more than 80 percent of cases of nonsyndromic recessive deafness result from inheritance of the 30delG mutant allele of GJB2. We assessed the contribution of mutations in GJB2 to the prevalence of the condition among Ashkenazi Jews., Methods: We tested for mutations in GJB2 in DNA samples from three Ashkenazi Jewish families with nonsyndromic recessive deafness, from Ashkenazi Jewish persons seeking carrier testing for other conditions, and from members of other ethnic groups. The hearing of persons who were heterozygous for mutations in GJB2 was assessed by means of pure-tone audiometry, measurement of middle-ear immittance, and recording of otoacoustic emissions., Results: Two frame-shift mutations in GJB2, 167delT and 30delG, were observed in the families with nonsyndromic recessive deafness. In the Ashkenazi Jewish population the prevalence of heterozygosity for 167delT, which is rare in the general population, was 4.03 percent (95 percent confidence interval, 2.5 to 6.0 percent), and for 30delG the prevalence was 0.73 percent (95 percent confidence interval, 0.2 to 1.8 percent). Genetic-linkage analysis showed conservation of the haplotype for 167delT but the existence of several haplotypes for 30delG. Audiologic examination of carriers of the mutant alleles who had normal hearing revealed subtle differences in their otoacoustic emissions, suggesting that the expression of mutations in GJB2 may be semidominant., Conclusions: The high frequency of carriers of mutations in GJB2 (4.76 percent) predicts a prevalence of 1 deaf person among 1765 people, which may account for the majority of cases of nonsyndromic recessive deafness in the Ashkenazi Jewish population. Conservation of the haplotype flanking the 167delT mutation suggests that this allele has a single origin, whereas the multiple haplotypes with the 30delG mutation suggest that this site is a hot spot for recurrent mutations.

The tectorial membrane is an extracellular matrix of the inner ear that contacts the stereocilia bundles of specialized sensory hair cells. Sound induces movement of these hair cells relative to the tectorial membrane, deflects the stereocilia, and leads to fluctuations in hair-cell membrane potential, transducing sound into electrical signals. Alpha-tectorin is one of the major non-collagenous components of the tectorial membrane. Recently, the gene encoding mouse alpha-tectorin (Tecta) was mapped to a region of mouse chromosome 9, which shows evolutionary conservation with human chromosome 11q (ref. 3), where linkage was found in two families, one Belgian (DFNA12; ref. 4) and the other, Austrian (DFNA8; unpublished data), with autosomal dominant non-syndromic hearing impairment. We determined the complete sequence and the intron-exon structure of the human TECTA gene. In both families, mutation analysis revealed missense mutations which replace conserved amino-acid residues within the zona pellucida domain of TECTA. These findings indicate that mutations in TECTA are responsible for hearing impairment in these families, and implicate a new type of protein in the pathogenesis of hearing impairment.

We mapped expressed tagged sequences (ESTs) corresponding to two human dynein heavy chain genes: beta heavy chain of the outer dynein arm and heavy chain isotype 1B (DYH1B), by using somatic cell hybrids and radiation hybrid panels. The EST for the beta heavy chain of the outer dynein arm mapped to chromosome region 7p15, and the EST for DYH1B mapped to 11q13.5. Two loci for nonsyndromic forms of deafness, DFNA5 and DFNA11, have previously been mapped to these two chromosomal regions. Including the gene for the axonemal light chain, hp28, we have mapped three different dynein genes near loci for different forms of nonsyndromic deafness. The hypothesis that mutations in some dynein genes are associated with nonsyndromic deafness should now be tested.

Hearing impairment is inherited most frequently as an autosomal recessive isolated clinical finding (non-syndromic hearing loss, NSHL). Extreme heterogeneity and phenotypic variability in the audiometric profile preclude pooling of affected families and severely hamper gene mapping by conventional linkage analysis. However, in instances of consanguinity, homozygosity mapping can be used to identify disease loci in small nuclear families. This report demonstrates the power of this technique by identifying a locus for recessive NSHL on 14q (DFNB4).

Wilch E, Azaiez H, Fisher RA, Elfenbein J, Murgia A, Birkenhäger R, Bolz HJ, da Silva-Costa SM, del Castillo I, Haaf T, Hoefsloot L, Kremer H, Kubisch C, Le Marechal C, Pandya A, Sartorato EL, Schneider E, Van Camp G, Wuyts W, Smith RJH, Friderici KH. A novel DFNB1 deletion allele supports the existence of a distant cis-regulatory region that controls GJB2 and GJB6 expression. Eleven affected members of a large German–American family segregating recessively inherited, congenital, non-syndromic sensorineural hearing loss (SNHL) were found to be homozygous for the common 35delG mutation of GJB2, the gene encoding the gap junction protein Connexin 26. Surprisingly, four additional family members with bilateral profound SNHL carried only a single 35delG mutation. Previously, we demonstrated reduced expression of both GJB2 and GJB6 mRNA from the allele carried in trans with that bearing the 35delG mutation in these four persons. Using array comparative genome hybridization (array CGH), we have now identified on this allele a deletion of 131.4 kb whose proximal breakpoint lies more than 100 kb upstream of the transcriptional start sites of GJB2 and GJB6. This deletion, del(chr13:19,837,344–19,968,698), segregates as a completely penetrant DFNB1 allele in this family. It is not present in 528 persons with SNHL and monoallelic mutation of GJB2 or GJB6, and we have not identified any other candidate pathogenic copy number variation by arrayCGH in a subset of 10 such persons. Characterization of distant GJB2/GJB6 cis-regulatory regions evidenced by this allele may be required to find the ‘missing’ DFNB1 mutations that are believed to exist. [ABSTRACT FROM AUTHOR]

Hearing loss has a significant impact on quality of life, cognition and society in general, affecting 360 million people worldwide. As a model for late-onset sensorineural hearing loss (SNHL), we will discuss DFNA9 (DeaFNess Autosomal 9), an autosomal dominant disorder that leads to late-onset (3th-5th decade) progressive SNHL and deafness. The age of hearing loss onset varies depending on the mutation though the average onset age lies around 3rd-5th decade. It typically starts as downsloping of the audiogram at the age of onset and evolution towards deafness and vestibular failure. DFNA9 is caused by heterozygote mutations in the COCH gene (Coagulation Factor C Homology), which is located on chromosome 14q12-13 and encoding a 550 amino acid protein, cochlin. Over twenty different mutations have been identified in several regions, including North America, Japan, Australia, Korea, China and Belgium/Netherlands. Currently, no treatment is available to prevent hearing loss or balance loss in DFNA9 patients. Local gene therapy to restore hearing or prevent hearing loss has been studied in neonatal mouse models for several years. Currently, a clinical study is ongoing in adult patients with profound hearing loss to restore hair cells by injecting virus-based vectors -carrying correcting genetic information- directly into the inner ear, while local gene therapy has reached the clinical setting in disorders of the retina (eye) for blindness. DFNA9 has a unique potential because it involves an increasing number of patients that are aware of their family history and can ask for routine genetic evaluation in the pre-symptomatic stage. In the case of DFNA9, therapeutic strategies to correct genetic information may prevent or slow down the pathophysiologal process. Challenges that will need to be addressed in a preclinical stage will be discussed [ABSTRACT FROM AUTHOR]