Genotype-Phenotype Correlations of Pathogenic COCH Variants in DFNA9: A HuGE Systematic Review and Audiometric Meta-Analysis

Pathogenic missense variants in COCH are associated with DFNA9, an autosomal dominantly inherited type of progressive sensorineural hearing loss with or without vestibular dysfunction. This study is a comprehensive overview of genotype-phenotype correlations using the PRISMA and HuGENet guidelines. Study characteristics, risk of bias, genotyping and data on the self-reported age of onset, symptoms of vestibular dysfunction, normative test results for vestibular function, and results of audiovestibular examinations were extracted for each underlying pathogenic COCH variant. The literature search yielded 48 studies describing the audiovestibular phenotypes of 27 DFNA9-associated variants in COCH. Subsequently, meta-analysis of audiometric data was performed by constructing age-related typical audiograms and by performing non-linear regression analyses on the age of onset and progression of hearing loss. Significant differences were found between the calculated ages of onset and progression of the audiovestibular phenotypes of subjects with pathogenic variants affecting either the LCCL domain of cochlin or the vWFA2 and Ivd1 domains. We conclude that the audiovestibular phenotypes associated with DFNA9 are highly variable. Variants affecting the LCCL domain of cochlin generally lead to more progression of hearing loss when compared to variants affecting the other domains. This review serves as a reference for prospective natural history studies in anticipation of mutation-specific therapeutic interventions.

A Novel COCH Mutation Affects the vWFA2 Domain and Leads to a Relatively Mild DFNA9 Phenotype

OBJECTIVE

To study the genotype and phenotype of a Dutch family with autosomal dominantly inherited hearing loss.

STUDY DESIGN

Genotype-phenotype correlation study. Genetic analysis consisted of linkage analysis, variable number of tandem repeats analysis, and Sanger sequencing. Audiovestibular function was examined. Regression analysis was performed on pure tone audiometry and speech recognition scores and correlated with the age and/or level of hearing loss.

SETTING

Tertiary referral center.

PATIENTS

A large Dutch family presenting with sensorineural hearing loss.

MAIN OUTCOME MEASURES

Identification of the underlying genetic defect of the hearing loss in this family. Results of pure tone and speech audiometry, onset age, progression of hearing loss and vestibular (dys)function.

RESULTS

A novel mutation in COCH, c.1312C > T p.(Arg438Cys), cosegregates with hearing loss and a variable degree of vestibular (dys)function in this family. The reported mean age of onset of hearing loss is 33 years (range, 18-49 yr). Hearing loss primarily affects higher frequencies and its progression is relatively mild (0.8 dB/yr). Speech perception is remarkably well preserved in affected family members when compared with other DFNA9 families with different COCH mutations.

CONCLUSION

These findings expand the genotypic and phenotypic spectrum of DFNA9. The c.1312C > T mutation, which affects the vWFA2 domain, causes a relatively mild audiovestibular phenotype when compared with other COCH mutations.

Audiological Characteristics of Some Affected Members of a Dutch DFNA13/COL11A2 Family

Members of a Dutch DFNA13/ COL11A2 family were evaluated with pure tone audiometry, stapedial reflexes, otoacoustic emissions, loudness scaling, difference limen for frequency, gap detection, and speech perception in quiet and noise. The tone audiometry showed a predominant loss for the low and middle frequencies, with only a few otoacoustic emissions at thresholds better than 25 dB hearing level. The stapedial reflexes appeared elevated, and loudness growth curves were shifted parallel to those for normal-hearing subjects, indicating a shift of the dynamic range toward higher presentation levels. The data for the difference limen for frequency, gap detection, and speech perception in noise fell within the (near-)normal range. Despite elevated thresholds, all suprathreshold functions showed fairly normal properties, suggesting an attenuation of signal energy in the cochlea with limited degradation of the cochlea's signal analyzing capabilities. The effect of DFNA13/ COL11A2 may thus be characterized as a cochlear conductive loss.

Longitudinal Phenotypic Analysis in Patients with Connexin 26 (GJB2) (DFNB1) and Connexin 30 (GJB6) Mutations

In 15 Belgian subjects with prelingual sensorineural hearing impairment, the connexin 26 (GJB2) gene and the connexin 30 (GJB6) gene were analyzed for the presence of the 35delG mutation and the △( GJB6-D13S1830) deletion first described by del Castillo et al in 2002. Seven patients were found to be homozygous for the 35delG mutation; 7 were combined heterozygotes for the 35delG mutation and the GJB6 deletion. In 11 subjects, phenotype and genotype were correlated. Significant, transient progression, in the range of 1.7 to 2.7 dB/y, was only found in 2 patients in the first part of the second decade of life. Hearing impairment was otherwise stable, with mean thresholds of 75, 90, and 100 dB at 0.125, 0.25, and 0.5 kHz, respectively, and 100 dB or higher at 1 to 4 kHz. There was no significant difference in hearing impairment between the patients with the homozygous 35delG mutation in GJB2 and those who are heterozygous for both the 35delG mutation and the deletion encompassing part of GJB6.

Phenotype Description of a Novel DFNA9/COCH Mutation, I109T

Objectives:

This is a report of the audiological and vestibular characteristics of a Dutch DFNA9 family with a novel mutation, I109T, in the LCCL domain of COCH.

Methods:

From the family with the novel I109T COCH mutation, audiometric data were collected and analyzed longitudinally. Results were compared to those obtained in previously identified P51S, G88E, and G87W COCH mutation carriers. Special attention was also given to a comparison of age-related features such as progressive hearing loss and vestibular impairment.

Results:

A novel mutation (I109T) in COCH segregates with hearing impairment and vestibular dysfunction in the present family. Pure tone thresholds, phoneme recognition scores, and vestibular responses of the I109T mutation carriers were essentially similar to those previously established in P51S, G87W, and G88E mutation carriers. Deterioration of hearing in the I109T mutation carriers started at 43 years of age, and vestibular function deteriorated at least 7 years later.

Conclusions:

The phenotype associated with the novel COCH (I109T) mutation is largely similar to that associated with P51S and G88E mutation carriers. However, subtle differences in terms of onset age and rate of progression seem to exist.

A combination of two truncating mutations in USH2A causes more severe and progressive hearing impairment in Usher syndrome type IIa

OBJECTIVES

Usher syndrome is an inherited disorder that is characterized by hearing impairment (HI), retinitis pigmentosa, and in some cases vestibular dysfunction. Usher syndrome type IIa is caused by mutations in USH2A. HI in these patients is highly heterogeneous and the present study evaluates the effects of different types of USH2A mutations on the audiometric phenotype. Data from two large centres of expertise on Usher Syndrome in the Netherlands and Sweden were combined in order to create a large combined sample of patients to identify possible genotype-phenotype correlations.

DESIGN

A retrospective study on HI in 110 patients (65 Dutch and 45 Swedish) genetically diagnosed with Usher syndrome type IIa. We used methods especially designed for characterizing and testing differences in audiological phenotype between patient subgroups. These methods included Age Related Typical Audiograms (ARTA) and a method to evaluate the difference in the degree of HI developed throughout life between subgroups.

RESULTS

Cross-sectional linear regression analysis of last-visit audiograms for the best hearing ear demonstrated a gradual decline of hearing over decades. The congenital level of HI was in the range of 16-33 dB at 0.25-0.5 kHz, and in the range of 51-60 dB at 1-8 kHz. The annual threshold deterioration was in the range of 0.4-0.5 dB/year at 0.25-2 kHz and in the range of 0.7-0.8 dB/year at 4-8 kHz. Patients with two truncating mutations, including homozygotes for the common c.2299delG mutation, developed significantly more severe HI throughout life than patients with one truncating mutation combined with one nontruncating mutation, and patients with two nontruncating mutations.

CONCLUSIONS

The results have direct implications for patient counselling in terms of prognosis of hearing and may serve as baseline measures for future (genetic) therapeutic interventions.

Features of autosomal recessive non-syndromic hearing impairment: a review to serve as a reference

OBJECTIVE

Non-syndromic sensorineural hearing impairment is inherited in an autosomal recessive fashion in 75-85% of cases. To date, 61 genes with this type of inheritance have been identified as related to hearing impairment, and the genetic heterogeneity is accompanied by a large variety of clinical characteristics. Adequate counselling on a patient's hearing prognosis and rehabilitation is part of the diagnosis on the genetic cause of hearing impairment and, in addition, is important for the psychological well-being of the patient.

TYPE OF REVIEW

Traditional literature review.

DATA SOURCE

All articles describing clinical characteristics of the audiovestibular phenotypes of identified genes and related loci have been reviewed.

CONCLUSION

This review aims to serve as a summary and a reference for counselling purposes when a causative gene has been identified in a patient with a non-syndromic autosomal recessively inherited sensorineural hearing impairment.

Audioprofile Surfaces: The 21st Century Audiogram

OBJECTIVE

To present audiometric data in 3 dimensions by considering age as an addition dimension.

METHODS

Audioprofile surfaces (APSs) were fitted to a set of audiograms by plotting each measurement of an audiogram as an independent point in 3 dimensions with the x, y, and z axes representing frequency, hearing loss in dB, and age, respectively.

RESULTS

Using the Java-based APS viewer as a standalone application, APSs were pre-computed for 34 loci. By selecting APSs for the appropriate genetic locus, a clinician can compare this APS-generated average surface to a specific patient's audiogram.

CONCLUSION

Audioprofile surfaces provide an easily interpreted visual representation of a person's hearing acuity relative to others with the same genetic cause of hearing loss. Audioprofile surfaces will support the generation and testing of sophisticated hypotheses to further refine our understanding of the biology of hearing.

HOMER2, a stereociliary scaffolding protein, is essential for normal hearing in humans and mice

Hereditary hearing loss is a clinically and genetically heterogeneous disorder. More than 80 genes have been implicated to date, and with the advent of targeted genomic enrichment and massively parallel sequencing (TGE+MPS) the rate of novel deafness-gene identification has accelerated. Here we report a family segregating post-lingual progressive autosomal dominant non-syndromic hearing loss (ADNSHL). After first excluding plausible variants in known deafness-causing genes using TGE+MPS, we completed whole exome sequencing in three hearing-impaired family members. Only a single variant, p.Arg185Pro in HOMER2, segregated with the hearing-loss phenotype in the extended family. This amino acid change alters a highly conserved residue in the coiled-coil domain of HOMER2 that is essential for protein multimerization and the HOMER2-CDC42 interaction. As a scaffolding protein, HOMER2 is involved in intracellular calcium homeostasis and cytoskeletal organization. Consistent with this function, we found robust expression in stereocilia of hair cells in the murine inner ear and observed that over-expression of mutant p.Pro185 HOMER2 mRNA causes anatomical changes of the inner ear and neuromasts in zebrafish embryos. Furthermore, mouse mutants homozygous for the targeted deletion of Homer2 present with early-onset rapidly progressive hearing loss. These data provide compelling evidence that HOMER2 is required for normal hearing and that its sequence alteration in humans leads to ADNSHL through a dominant-negative mode of action.

The most frequent sensory disorder worldwide is hearing impairment. It impacts over 5% of the world population (360 million persons), and is characterized by extreme genetic heterogeneity. Over 80 genes have been implicated in isolated (also referred to as ‘non-syndromic’) hearing loss, and abundant evidence supports the existence of many more ‘deafness-causing’ genes. In this study, we used a sequential screening strategy to first exclude causal mutations in known deafness-causing genes in a family segregating autosomal dominant non-syndromic hearing loss. We next turned to whole exome sequencing and identified a single variant—p.Arg185Pro in HOMER2—that segregated with the phenotype in the extended family. To validate the pathological significance of this mutation, we studied two animal models. In zebrafish, we overexpressed mutant HOMER2 and observed inner ear defects; and in mice we documented robust expression in stereocilia of cochlear hair cells and demonstrated that its absence causes early-onset progressive deafness. Our data offer novel insights into gene pathways essential for normal auditory function and the maintenance of cochlear hair cells.

Audiometric characteristics of a dutch family with a new mutation in GATA3 causing HDR syndrome

We present the case of a Dutch family with a new mutation (c523_528dup) in GATA3 causing HDR syndrome. HDR syndrome is characterised by hypoparathyroidism, deafness and renal defects. In this study, we describe the audiometric characteristics of 5 patients from this family. Their hearing impairment was congenital, bilateral and symmetric. Audiograms showed mild-to-moderate hearing impairment with a flat audiogram configuration. Higher frequencies tended to be affected more strongly. Cross-sectional analyses showed no progression, and a mean audiogram was established. Psychophysical measurements in 3 HDR patients - including speech reception in noise, loudness scaling, gap detection and difference limen for frequency - were obtained to assess hearing function in greater detail. Overall, the results of the psychophysical measurements indicated characteristics of outer hair cell loss. CT scanning showed no anomalies in 3 of the HDR patients. Although 2 patients displayed vestibular symptoms, no anomalies in the vestibular system were found by vestibulo-ocular examination. Our results are in agreement with the theory that outer hair cell malfunctioning can play a major role in HDR syndrome.

AudioGene: predicting hearing loss genotypes from phenotypes to guide genetic screening

Autosomal dominant nonsyndromic hearing loss (ADNSHL) is a common and often progressive sensory deficit. ADNSHL displays a high degree of genetic heterogeneity and varying rates of progression. Accurate, comprehensive, and cost-effective genetic testing facilitates genetic counseling and provides valuable prognostic information to affected individuals. In this article, we describe the algorithm underlying AudioGene, a software system employing machine-learning techniques that utilizes phenotypic information derived from audiograms to predict the genetic cause of hearing loss in persons segregating ADNSHL. Our data show that AudioGene has an accuracy of 68% in predicting the causative gene within its top three predictions, as compared with 44% for a majority classifier. We also show that AudioGene remains effective for audiograms with high levels of clinical measurement noise. We identify audiometric outliers for each genetic locus and hypothesize that outliers may reflect modifying genetic effects. As personalized genomic medicine becomes more common, AudioGene will be increasingly useful as a phenotypic filter to assess pathogenicity of variants identified by massively parallel sequencing.

Clinical follow-up and histopathology of the temporal bones in Nathalie syndrome

The Nathalie syndrome (OMIM 255990) comprises a combination of features that do not resemble any other known syndrome and is as such an independent, rare entity. It is characterized by sensorineural hearing impairment, juvenile cataract, spinal muscular atrophy, skeletal abnormalities, retardation of growth, underdeveloped secondary gender characteristics and cardiomyopathy. Worldwide, only one family with this syndrome is known. An update of the clinical follow-up in this family and the results of autopsy are given. Audiometry showed a downsloping configuration that corresponded to the findings at histopathological examination of the cochlea: a diffuse atrophy of the organ of Corti, severe and diffuse atrophy of the stria vascularis and moderate loss of cochlear neurons in all turns. Another new striking feature is that individuals with the Nathalie syndrome have a shortened life expectancy with a risk of sudden death or death from heart failure resulting from (dilated) cardiomyopathy.

Optokinetic response in patients with vestibular areflexia

Optokinetic nystagmus (OKN) responses (stimuli 40°/s and 60°/s) were evaluated in 121 patients with vestibular areflexia (VA) and were compared with a control group of 99 control subjects matched by age. The mean response levels were significantly higher in the VA group than in the control group: 1.7°/s at 40°/s stimulation, and 4.4°/s at 60°/s. The VA group showed a significantly wider scattering and greater variances and, as a group, they exhibited higher OKN gains than the control subjects. We suggest that the higher gain of OKN responses in VA patients can be attributed to an increased efficiency in signal processing by the cortical optokinetic system. This enhancement may be similar to the enhancement which, in healthy subjects, is produced by "optokinetic training".

Phenotype analysis of an Australian DFNA9 family with the 1109N COCH mutation

OBJECTIVES

We studied the clinical characteristics of an Australian family with an autosomal dominant sensorineural hearing impairment (DFNA9) caused by an I109N mutation in COCH.

METHODS

Retrospective analyses of audiometric data from 8 mutation carriers of an Australian DFNA9 family with the I109N COCH mutation were performed. Cross-sectional hearing levels related to age, age-related typical audiograms, and speech recognition scores related to age and to the level of hearing impairment were investigated. Data were compared to those obtained in previously identified DFNA9 families with P51S, V66G, G87W, G88E, I109T, and C542F COCH mutations.

RESULTS

Deterioration of hearing in the I109N mutation carriers started before the age of 40 years. The audiometric characteristics of the I109N mutation carriers are essentially similar to those previously established in I109T mutation carriers and, to a lesser extent, in P51S, G87W, and G88E mutation carriers.

CONCLUSIONS

The phenotype associated with the I109N COCH mutation is largely similar to that associated with the I109T, P51S, G87W, and G88E mutation carriers. However, subtle differences seem to exist in terms of age of onset and rate of progression.

Genotype-phenotype correlation in DFNB8/10 families with TMPRSS3 mutations

In the present study, genotype–phenotype correlations in eight Dutch DFNB8/10 families with compound heterozygous mutations in TMPRSS3 were addressed. We compared the phenotypes of the families by focusing on the mutation data. The compound heterozygous variants in the TMPRSS3 gene in the present families included one novel variant, p.Val199Met, and four previously described pathogenic variants, p.Ala306Thr, p.Thr70fs, p.Ala138Glu, and p.Cys107Xfs. In addition, the p.Ala426Thr variant, which had previously been reported as a possible polymorphism, was found in one family. All affected family members reported progressive bilateral hearing impairment, with variable onset ages and progression rates. In general, the hearing impairment affected the high frequencies first, and sooner or later, depending on the mutation, the low frequencies started to deteriorate, which eventually resulted in a flat audiogram configuration. The ski-slope audiogram configuration is suggestive for the involvement of TMPRSS3. Our data suggest that not only the protein truncating mutation p.T70fs has a severe effect but also the amino acid substitutions p.Ala306Thr and p.Val199Met. A combination of two of these three mutations causes prelingual profound hearing impairment. However, in combination with the p.Ala426Thr or p.Ala138Glu mutations, a milder phenotype with postlingual onset of the hearing impairment is seen. Therefore, the latter mutations are likely to be less detrimental for protein function. Further studies are needed to distinguish possible phenotypic differences between different TMPRSS3 mutations. Evaluation of performance of patients with a cochlear implant indicated that this is a good treatment option for patients with TMPRSS3 mutations as satisfactory speech reception was reached after implantation.

Audioprofile-directed successful mutation analysis in a DFNA2/KCNQ4 (p.Leu274His) family

OBJECTIVES

We undertook to show that in a family with nonsyndromic autosomal dominant sensorineural hearing loss, genetic analysis can be successful when there is a match with a specific DFNA audioprofile. We also provide an update of relevant DFNA2/KCNQ4 audioprofiles and report the results of automatic audioprofile analysis using the Internet program AudioGene.

METHODS

Audiometric data and blood samples were obtained from the family W08-0384. Based on the audiograms of the affected participants, mutation analysis of KCNQ4 was started. Original audiometric threshold data were collected for all identified KCNQ4-related DFNA2 families. The Internet computer program AudioGene, recently developed for automatic audioprofile analysis, was accessed.

RESULTS

The family's audioprofile and the program AudioGene predicted the DFNA2/KCNQ4 locus. Mutation analysis of KCNQ4 revealed a c.821T>A (p.Leu274His) mutation of the KCNQ4 gene. This mutation has been previously identified in a Dutch family. Genetic analysis revealed a common haplotype in these two families over a region including the KCNQ4 gene.

CONCLUSIONS

Familiarity with the audioprofiles of DFNA traits may lead to successful mutation analysis of the gene involved, even in a small family in which genetic linkage analysis is not an option. Alternatively, the specially developed program AudioGene can be accessed on the Internet to perform automatic audioprofile analysis of a family's (audiological) phenotype.

DFNA8/12 caused by TECTA mutations is the most identified subtype of nonsyndromic autosomal dominant hearing loss

The prevalence of DFNA8/DFNA12 (DFNA8/12), a type of autosomal dominant nonsyndromic hearing loss (ADNSHL), is unknown as comprehensive population-based genetic screening has not been conducted. We therefore completed unbiased screening for TECTA mutations in a Spanish cohort of 372 probands from ADNSHL families. Three additional families (Spanish, Belgian, and English) known to be linked to DFNA8/12 were also included in the screening. In an additional cohort of 835 American ADNSHL families, we preselected 73 probands for TECTA screening based on audiometric data. In aggregate, we identified 23 TECTA mutations in this process. Remarkably, 20 of these mutations are novel, more than doubling the number of reported TECTA ADNSHL mutations from 13 to 33. Mutations lie in all domains of the α-tectorin protein, including those for the first time identified in the entactin domain, as well as the vWFD1, vWFD2, and vWFD3 repeats, and the D1-D2 and TIL2 connectors. Although the majority are private mutations, four of them-p.Cys1036Tyr, p.Cys1837Gly, p.Thr1866Met, and p.Arg1890Cys-were observed in more than one unrelated family. For two of these mutations founder effects were also confirmed. Our data validate previously observed genotype-phenotype correlations in DFNA8/12 and introduce new correlations. Specifically, mutations in the N-terminal region of α-tectorin (entactin domain, vWFD1, and vWFD2) lead to mid-frequency NSHL, a phenotype previously associated only with mutations in the ZP domain. Collectively, our results indicate that DFNA8/12 hearing loss is a frequent type of ADNSHL.

Next-generation sequencing identifies mutations of SMPX, which encodes the small muscle protein, X-linked, as a cause of progressive hearing impairment

In a Dutch family with an X-linked postlingual progressive hearing impairment, a critical linkage interval was determined to span a region of 12.9 Mb flanked by the markers DXS7108 and DXS7110. This interval overlaps with the previously described DFNX4 locus and contains 75 annotated genes. Subsequent next-generation sequencing (NGS) detected one variant within the linkage interval, a nonsense mutation in SMPX. SMPX encodes the small muscle protein, X-linked (SMPX). Further screening was performed on 26 index patients from small families for which X-linked inheritance of nonsyndromic hearing impairment (NSHI) was not excluded. We detected a frameshift mutation in SMPX in one of the patients. Segregation analysis of both mutations in the families in whom they were found revealed that the mutations cosegregated with hearing impairment. Although we show that SMPX is expressed in many different organs, including the human inner ear, no obvious symptoms other than hearing impairment were observed in the patients. SMPX had previously been demonstrated to be specifically expressed in striated muscle and, therefore, seemed an unlikely candidate gene for hearing impairment. We hypothesize that SMPX functions in inner ear development and/or maintenance in the IGF-1 pathway, the integrin pathway through Rac1, or both.

Phenotypes of Two Dutch DFNA3 Families with Mutations in GJB2

Objectives:

We describe the phenotype of 2 Dutch DFNA3 families with mutations in the GJB2 gene.

Methods:

Two patients from family 1 and one isolated patient from family 2 were studied. The audiometric examination consisted of pure tone and speech audiometry. Two patients underwent vestibular testing and high-resolution computed tomographic scanning of the temporal bone. Mutation analysis of GJB2 and GJB6 was performed.

Results:

All 3 patients had severe to profound sensorineural hearing impairment. Cochlear implantation was performed in 2 patients, and their phoneme recognition scores were good. Mutation analyses revealed a p. Arg184Gln mutation in GJB2 in family 1 and a p. Arg75Trp mutation in GJB2 in family 2. No mutations in GJB6 were identified. Vestibular function tests and computed tomographic scans yielded normal findings in the examined subjects.

Conclusions:

Severe to profound sensorineural hearing impairment was found in these DFNA3 patients, and was well rehabilitated with cochlear implantation. A thorough genotype-phenotype correlation is difficult because of the small number of affected patients and the limited clinical data of these patients. More clinical data on DFNA3 families need to be published in order to create a reliable and precise phenotype characterization.

Mutations in TMC1 are a common cause of DFNB7/11 hearing loss in the Iranian population

OBJECTIVES

We investigated the cause of autosomal recessive nonsyndromic hearing loss (ARNSHL) that segregated in 2 consanguineous Iranian families.

METHODS

Otologic and audiometric examinations were performed on affected members of each family. Genome-wide parametric multipoint linkage mapping using a recessive model was performed with Affymetrix 50K GeneChips or short tandem repeat polymorphisms. Direct sequencing was used to confirm the causative mutation in each family.

RESULTS

In 2 Iranian families, L-1651 and L-8600606, with ARNSHL that mapped to the DFNB7/11 locus, homozygosity for a reported splice site mutation (c.776+1G>A), and a novel deletion (c.1589_1590delCT; p.S530*) were identified in the TMC1 gene, respectively.

CONCLUSIONS

Consistent with the previously reported phenotype in DFNB7/11 families, the 2 Iranian families had segregated congenital, profound hearing impairment. However, in family L-1651, one affected family member (IV:3) has milder hearing impairment than expected, suggesting a potential genetic modifier effect. These results indicate that DFNB7/11 is a common form of genetic hearing loss in Iran, because this population is the source of 6 of the 29 TMC1 mutations reported worldwide.

A novel mutation in COCH-implications for genotype-phenotype correlations in DFNA9 hearing loss

OBJECTIVES/HYPOTHESIS

To determine the cause of autosomal dominant hearing loss segregating in an American family.

STUDY DESIGN

Family study.

METHODS

Otologic and audiometric examination was performed on affected family members. Genome wide parametric multipoint linkage mapping using a dominant model was performed with Affymetrix 50K GeneChip data. Direct sequencing was used to confirm the causative mutation.

RESULTS

In American family 467, segregating autosomal dominant nonsyndromic hearing loss, a novel heterozygous missense mutation (c.362T>C; p.F121S) was identified in the COCH gene. This mutation was also associated with vestibular dysfunction typical of other DFNA9 families. However, affected family members also exhibited memory loss and night blindness.

CONCLUSIONS

The novel COCH mutation affects the functionally important limulus factor C, Coch-5b2 and Lgl1 domain where most DFNA9 mutations have been localized. The onset of the hearing loss, in the 2nd or 3rd decade of life, is earlier than in most DFNA9 families. The progression of hearing loss and vestibular dysfunction in the American family is typical of other DFNA9 families with mutations in this domain. Memory loss and night blindness have not been previously reported in DFNA9 families.

Progressive sensorineural hearing loss and normal vestibular function in a Dutch DFNB7/11 family with a novel mutation in TMC1

In a Dutch family with autosomal recessive hearing loss, genome-wide single-nucleotide polymorphism analysis mapped the genetic defect to the DFNB7/11 locus. A novel homozygous A-to-G change in the TMC1 gene was detected near the splice donor site of intron 19 (c.1763+3A→G) segregating with the hearing loss in this family. One of the 6 transmembrane domains and the actual TMC channel domain are predicted to be absent in the mutant protein. The sensorineural hearing impairment in this DFNB7/11 family has a postlingual onset. Audiometric analysis initially showed a steeply downward-sloping threshold configuration. The progressive phenotype in this family resembles the phenotype previously described for families with dominant TMC1 mutations (DFNA36) rather than that of families with recessive TMC1 mutations (DFNB7/11) which invariably cause severe-to-profound prelingual hearing impairment.

Homozygosity mapping reveals mutations of GRXCR1 as a cause of autosomal-recessive nonsyndromic hearing impairment

We identified overlapping homozygous regions within the DFNB25 locus in two Dutch and ten Pakistani families with sensorineural autosomal-recessive nonsyndromic hearing impairment (arNSHI). Only one of the families, W98-053, was not consanguineous, and its sibship pointed toward a reduced critical region of 0.9 Mb. This region contained the GRXCR1 gene, and the orthologous mouse gene was described to be mutated in the pirouette (pi) mutant with resulting hearing loss and circling behavior. Sequence analysis of the GRXCR1 gene in hearing-impaired family members revealed splice-site mutations in two Dutch families and a missense and nonsense mutation, respectively, in two Pakistani families. The splice-site mutations are predicted to cause frameshifts and premature stop codons. In family W98-053, this could be confirmed by cDNA analysis. GRXCR1 is predicted to contain a GRX-like domain. GRX domains are involved in reversible S-glutathionylation of proteins and thereby in the modulation of activity and/or localization of these proteins. The missense mutation is located in this domain, whereas the nonsense and splice-site mutations may result in complete or partial absence of the GRX-like domain or of the complete protein. Hearing loss in patients with GRXCR1 mutations is congenital and is moderate to profound. Progression of the hearing loss was observed in family W98-053. Vestibular dysfunction was observed in some but not all affected individuals. Quantitative analysis of GRXCR1 transcripts in fetal and adult human tissues revealed a preferential expression of the gene in fetal cochlea, which may explain the nonsyndromic nature of the hearing impairment.

Evidence of progression and fluctuation of hearing impairment in branchio-oto-renal syndrome

We retrospectively analysed long-term serial audiometry data from patients with branchio-oto-renal (BOR) syndrome to show the features of progression and fluctuation in hearing impairment and relate the findings to age and magnetic resonance imaging (MRI) findings in the petrosal bones. Thirty-two clinically affected BOR patients from six Dutch families (A-F) were included. Audiograms were available in 24 cases, covering followup intervals of between 3 and 30 years, and suitable for individual statistical analysis in 16 cases: 14 cases also had MRI findings. Significant progression in hearing impairment was found in 10 cases, while findings of significant fluctuation were made in seven cases. These findings did not clearly correlate with MRI findings. Substantial fluctuation occurred only in cases followed at a relatively young age. Patients with an enlarged endolymphatic duct and/or sac showed significantly higher sensorineural hearing thresholds than those with either normal MRI findings or cochlear/labyrinthine hypoplasia with or without enlarged duct or sac. We conclude that progressive, fluctuant hearing loss occurred in some BOR patients; however, only young patients showed substantial threshold fluctuation. BOR patients with an enlarged endolymphatic duct and/or sac on MRI seemed to be predisposed to developing more severe hearing impairment.

Audiometric and Vestibular Features in a Second Dutch DFNA20/26 Family with a Novel Mutation in ACTG1

Objectives:

We analyzed the phenotype in a 5-generation DFNA20/26 family with a novel missense mutation in the ACTG1 gene (c.151G>A) and compared the findings to previous reports on DFNA20/26 families.

Methods:

Audiometric data were collected from the family members of a Dutch kindred with the novel ACTG1 mutation. Cross-sectional and/or longitudinal analyses were performed on pure tone and speech audiometry data of the mutation carriers. Age-related typical audiograms were constructed. Vestibular examination was performed in all mutation carriers.

Results:

Overall, high-frequency hearing impairment, most prominent at ages over 30 years, was observed with a progression rate of 1.1 to 2.1 dB/y, increasing with frequency. It ultimately resulted in residual hearing. Speech recognition scores remained good at given pure tone average (1, 2, and 4 kHz) levels, but were slightly poorer than those at similar levels in a group of patients with presbycusis. Vestibular examination did not reveal any consistent, statistically significant abnormalities.

Conclusions:

The audiometric phenotype of the Dutch DFNA20/26 family with a novel mutation in ACTG1 was largely consistent with previous reports on DFNA20/26. Considerable variations were found in audiogram configurations within the family. This is the first known DFNA20/26 family that has experienced tinnitus.

Vestibular impairment in a Dutch DFNA15 family with an L289F mutation in POU4F3

Vestibular examination (electronystagmography with rotatory chair and caloric tests) was performed on 18 carriers and 1 phenocopy carrier in a Dutch family with autosomal dominant nonsyndromic DFNA15. This is the second DFNA15 family worldwide to have a novel L289F mutation in POU4F3. Vestibular involvement appeared to be present in 2 affected individuals according to their medical history. Vestibular examination results in an extended subset of L289F POU4F3 mutation carriers varied from normal to areflexia. DFNA15 is the third cochleovestibular disorder, after DFNA9 and DFNA11, in the autosomal dominant nonsyndromic hearing impairment.

Mild and Variable Audiometric and Vestibular Features in a Third DFNA15 Family with a Novel Mutation in POU4F3

Objectives:

Cochleovestibular characteristics were investigated in a Dutch DFNA15 family with a novel POU4F3 mutation, L223P

Methods:

A 4-generation pedigree was constructed of the Dutch family with the novel L223P POU4F3 mutation. Pure tone audiometric data were collected and analyzed cross-sectionally in mutation carriers. Age-related typical audiograms were derived. Vestibular examination was performed in most of the mutation carriers. The results were compared to those obtained from previously identified 884del8 and L289F POU4F3 mutation carriers.

Results:

A novel mutation (L223P) in POU4F3 segregated with hearing impairment in the present family. Audiometric analysis generally showed an early-adult to midlife onset of hearing impairment. High-frequency hearing impairment was observed most frequently. Age-related typical audiograms showed a down-sloping configuration at ages of more than 30 years, with the fastest rate of progression at the high frequencies. Vestibular function tests revealed hypofunction of the vestibular labyrinth in 2 mutation carriers (not statistically significant).

Conclusions:

The clinical features in the present family with a POU4F3 mutation were fairly similar to those in the 2 previously described DFNA15 families, but the level of hearing impairment was milder, and there was no substantial vestibular dysfunction.

Nijmegen results with application of a bone-anchored hearing aid in children: simplified surgical technique

OBJECTIVES

A retrospective analysis was performed to evaluate the clinical outcome of percutaneous bone-anchored hearing aid (BAHA) application in children with the outcome measures of fixture loss and skin reactions.

METHODS

An analysis was done of 93 of the 101 children 16 years of age or younger who underwent the simplified Nijmegen surgical technique between January 1994 and July 2007.

RESULTS

Twenty-one of 129 fixtures (16.3%) were lost or removed. In 12 cases, osseointegration failed. The majority of the fixture losses (86%) occurred within 1 year after surgery. No differences were found between 3 age groups or between fixture lengths (seven 3-mm implants versus fourteen 4-mm implants). The BAHA fixtures were less stable in children than in adults. In 8 cases, Holgers grade 4 skin reactions were noted at an average (+/-SD) of 5.5 +/- 4.7 months after surgery, ie, significantly sooner than the milder reactions (p = 0.001). In 28 cases (22%), skin reactions of Holgers grades 2 to 4 were observed. Revision surgery to reduce subcutaneous scar tissue was necessary in 22 implants (17%).

CONCLUSIONS

Fixture loss was more frequent in children than in adults. The age of the child and the length of the fixture did not appear to influence fixture stability. Children should undergo frequent checkups at the outpatient clinic.

Hearing impairment in genotyped Wolfram syndrome patients

OBJECTIVES

Wolfram syndrome is a progressive neurodegenerative syndrome characterized by the features "DIDMOAD" (diabetes insipidus, diabetes mellitus, optic atrophy, and deafness). We sought to study the audiometric data of genotyped Wolfram syndrome patients with sensorineural hearing impairment.

METHODS

Pure tone threshold data of 23 Wolfram syndrome patients were used for cross-sectional analysis in subgroups (age less than 16 years or between 19 and 25 years, gender, and origin).

RESULTS

All subgroups, with 1 exception, showed a fairly similar type of hearing impairment with, on average, thresholds of about 25 dB (range, 0 to 65 dB) at 0.25 to 1 kHz, gently sloping downward to about 60 dB (range, 25 to 95 dB) at 8 kHz. The subgroup of Dutch women, which was excluded from the calculations of the average hearing thresholds, showed a higher degree of hearing impairment. Only the latter subgroup showed progression; however, contrary to the previous longitudinal analysis, progression was not significant in the present cross-sectional analysis, presumably because of the high degree of cross-subject variability.

CONCLUSIONS

This unique collection of audiometric data from genotyped Wolfram syndrome patients shows no substantial progression in sensorineural hearing impairment with advancing age, no relation to the types of WFS1 mutations identified, and, with exclusion of the subgroup of Dutch female patients, no significant sex-related differences.

Occupational noise, smoking, and a high body mass index are risk factors for age-related hearing impairment and moderate alcohol consumption is protective: a European population-based multicenter study

A multicenter study was set up to elucidate the environmental and medical risk factors contributing to age-related hearing impairment (ARHI). Nine subsamples, collected by nine audiological centers across Europe, added up to a total of 4,083 subjects between 53 and 67 years. Audiometric data (pure-tone average [PTA]) were collected and the participants filled out a questionnaire on environmental risk factors and medical history. People with a history of disease that could affect hearing were excluded. PTAs were adjusted for age and sex and tested for association with exposure to risk factors. Noise exposure was associated with a significant loss of hearing at high sound frequencies (>1 kHz). Smoking significantly increased high-frequency hearing loss, and the effect was dose-dependent. The effect of smoking remained significant when accounting for cardiovascular disease events. Taller people had better hearing on average with a more pronounced effect at low sound frequencies (<2 kHz). A high body mass index (BMI) correlated with hearing loss across the frequency range tested. Moderate alcohol consumption was inversely correlated with hearing loss. Significant associations were found in the high as well as in the low frequencies. The results suggest that a healthy lifestyle can protect against age-related hearing impairment.

Phenotype description of a Dutch otosclerosis family with suggestive linkage toOTSC7

This study reports on a clinical investigation of a Dutch family that shows suggestive linkage to OTSC7. Cross-sectional as well as longitudinal analyses of audiometric data were performed. Also, high-resolution computed tomography (CT) images of the temporal bones from genetically affected family members were obtained to study the incidence and extent of otospongiotic foci. Audiometric data showed a considerable degree of phenotypic variability. Cross-sectional regression analysis did not show age-dependent progression of bone conduction (BC), air conduction (AC), and air-bone gap (ABG) levels. Longitudinal analysis of audiometric follow-up data of one family member showed age-dependent progression of AC, BC, and ABG levels. High-resolution CT images revealed an otospongiotic focus in six of six (100%) clinically affected individuals that carried the disease haplotype. In none of the clinically unaffected family members that showed linkage to OTSC7, an otospongiotic focus was detected by CT. In conclusion, hearing impairment in the present otosclerosis family seems to be variable in terms of onset age and level of progression. Long-term audiometric data of one patient proved to be valuable in understanding progression of hearing impairment in this individual. The detection rate of otospongiotic foci in our study group is similar compared to previous reports on CT data in consecutive otosclerosis patients who had stapes replacing surgery.

Vertical corneal striae in families with autosomal dominant hearing loss: DFNA9/COCH

PURPOSE

Investigation of a possible association between vertical corneal striae and mutations in the COCH gene, observed in four DFNA9 families with autosomal dominant hearing loss and vestibular dysfunction.

DESIGN

Prospective case series.

METHODS

Ophthalmologic examinations with photography of the cornea after instillation of fluorescein were performed in 98 family members with 61 mutation carriers of four DFNA9 families at the Radboud University Nijmegen Medical Centre. Families 1 and 2 harbor the Pro51Ser mutation, and families 3 and 4 harbor the Gly88Glu and the Gly87Trp mutation, respectively. Statistical analysis was performed to find an association between the vertical corneal striae and the COCH mutation for each family and to test whether the four families were different in this respect.

RESULTS

The vertical corneal striae were exclusively visible after instillation of fluorescein. They caused minor problems, as dry eye symptoms, and were not present in the general Dutch ophthalmologic population. The striae were present from an age of 47 years in 32 individuals, of whom 27 individuals had a COCH mutation. Statistical analysis on the striae and the COCH mutations showed a significant association in families 1, 2, and 3 (P = .0006), but not in family 4 (P = .63).

CONCLUSIONS

Data analysis demonstrated a significant association between vertical corneal striae and the Pro51Ser and Gly88Glu mutations in the COCH gene in DFNA9 families 1, 2, and 3 with cochleovestibular dysfunction. Our findings suggest that the vertical corneal striae and cochleovestibular dysfunction may be caused by the same COCH mutations.

Familial aggregation of tinnitus: a European multicentre study

INTRODUCTION AND AIM

Tinnitus is a common condition affecting approximately 20% of the older population. There is increasing evidence that changes in the central auditory system following cochlear malfunctioning are responsible for tinnitus. To date, few investigators have studied the influence of genetic factors on tinnitus. The present report investigates the presence of a familial effect in tinnitus subjects.

METHODS

In a European multicentre study, 198 families were recruited in seven European countries. Each family had at least 3 siblings. Subjects were screened for causes of hearing loss other than presbyacusis by clinical examination and a questionnaire. The presence of tinnitus was evaluated with the question "Nowadays, do you ever get noises in your head or ear (tinnitus) which usually last longer than five minutes". Familial aggregation was tested using three methods: a mixed model approach, calculating familial correlations, and estimating the risk of a subject having tinnitus if the disorder is present in another family member.

RESULTS

All methods demonstrated a significant familial effect for tinnitus. The effect persisted after correction for the effect of other risk factors such as hearing loss, gender and age. The size of the familial effect is smaller than that for age-related hearing impairment, with a familial correlation of 0.15.

CONCLUSION

The presence of a familial effect for tinnitus opens the door to specific studies that can determine whether this effect is due to a shared familial environment or the involvement of genetic factors. Subsequent association studies may result in the identification of the factors responsible. In addition, more emphasis should be placed on the effect of role models in the treatment of tinnitus.

Clinical Characteristics of a Dutch DFNA9 Family with a Novel COCH Mutation, G87W

The present study aims to report audiological and vestibular characteristics of a Dutch DFNA9 family with a novel mutation, G87W, in the LCCL domain of COCH. From the family with the novel G87W COCH mutation audiometric data were collected and analyzed longitudinally. Results were compared with those obtained in previously identified P51S COCH mutation carriers (n = 74) and with those obtained in G88E mutation carriers. Special attention was also given to a comparison of age-related features, such as progressive hearing loss and vestibular impairment. A novel mutation (G87W) in COCH is indicative of hearing impairment and vestibular dysfunction in the present family. Pure-tone thresholds, phoneme recognition scores, and vestibular responses of the G87W mutation carriers were essentially similar to those previously established in the P51S and G88E mutation carriers. Deterioration of hearing and vestibular function in the G87W mutation carriers started at the age of 43 years. Remarkably, similar to G88E mutation carriers, the proportion of patients over 40 years of age who developed complete vestibular areflexia was significantly lower for the G87W mutation carriers than for the P51S mutation carriers. In conclusion, the phenotype associated with the novel COCH (G87W) mutation is largely similar to that associated with the P51S and G88E mutation carriers. However, subtle differences in terms of onset age and rate of progression seem to exist.

Progressive sensorineural hearing impairment in maternally inherited diabetes mellitus and deafness (MIDD)

OBJECTIVE

To study the progression of hearing impairment (HI) and audiological features in patients with the mitochondrial A to G mutation in the tRNA(LEU(RUU)) gene at position 3,243 associated with maternally inherited diabetes and deafness.

DESIGN

Retrospective phenotype genotype family study.

SETTING

Tertiary referral center.

PATIENTS

Six adult family members with the mitochondrial tRNA(LEU(RUU)) gene mutation at location 3,243. Data were obtained on medical history, otological examination, and pure tone and speech audiometry. Peripheral leukocytes were analyzed for the presence of the mutation, and heteroplasmy levels were determined. Selected patients underwent vestibular testing, brainstem-evoked response audiometry and neurological examination.

RESULTS

One patient showed relatively normal hearing, whereas in the others, HI had started at 27 to 79 years of age. All the patients showed progression in HI of approximately 1.4 dB/yr on average at 0.25 and 8 kHz. In the frequency range 0.5 to 2 kHz, progression was approximately 2 dB/yr; at 4 kHz, progression was 2.4 dB/yr. Vestibular and brainstem-evoked response audiometry test results were normal. All the patients achieved the maximum speech recognition score, as was expected based on their pure-tone average at 1, 2, and 4 kHz.

CONCLUSION

Our six adult patients with the mitochondrial tRNA(LEU(RUU)) gene mutation at location 3,243 showed almost normal to severe HI which was progressive beyond presbyacusis. Data from the literature and our findings suggest a cochlear localization of the HI.

Vestibular deterioration precedes hearing deterioration in the P51S COCH mutation (DFNA9): an analysis in 74 mutation carriers

OBJECTIVES

To analyze cochleovestibular impairment features in P51S COCH mutation carriers (n = 22) in a new, large Dutch family and to compare the results to those obtained in previously identified similar mutation carriers (n = 52). To evaluate age-related features between progressive hearing and vestibular impairment of all mutation carriers (n = 74).

STUDY DESIGN

Family study.

METHODS

Regression analysis was performed in relation to age to outline the development of hearing thresholds, speech recognition scores, and vestibulo-ocular reflex time constant as the key vestibular response parameter.

RESULTS

Pure tone thresholds, phoneme recognition scores, and vestibular responses of the mutation carriers in the new family were essentially similar to those previously established in all other mutation carriers. Hearing started to deteriorate in all mutation carriers from 43 years of age onwards, whereas deterioration of vestibular function started from age 34.

CONCLUSION

Vestibular impairment starts earlier, progresses more rapidly, and, eventually, is more complete than hearing impairment in P51S COCH mutation carriers.

A novel TECTA mutation in a Dutch DFNA8/12 family confirms genotype-phenotype correlation

A novel TECTA mutation, p.R1890C, was found in a Dutch family with nonsyndromic autosomal dominant sensorineural hearing impairment. In early life, presumably congenital, hearing impairment occurred in the midfrequency range, amounting to about 40 dB at 1 kHz. Speech recognition was good with all phoneme recognition scores exceeding 90%. An intact horizontal vestibuloocular reflex was found in four tested patients. The missense mutation is located in the zona pellucida (ZP) domain of alpha-tectorin. Mutations affecting the ZP domain of alpha-tectorin are significantly associated with midfrequency hearing impairment. Substitutions affecting other amino acid residues than cysteines show a significant association with hearing impairment without progression. Indeed, in the present family progression seemed to be absent. In addition, the presently identified mutation affecting the ZP domain resulted in a substantially lesser degree of hearing impairment than was previously reported for DFNA8/12 traits with mutations affecting the ZP domain of alpha-tectorin.

Cochleovestibular and Ocular Features in a Dutch DFNA11 Family

OBJECTIVES

To report hearing impairment and vestibular and ocular features in a Dutch DFNA11 family and to compare these results to reported data on three other DFNA11 families.

STUDY DESIGN

Family study.

METHODS

Regression analysis was performed in relation to age to outline the development of hearing thresholds and speech recognition scores. Vestibular and ocular functions were examined.

RESULTS

First symptoms of hearing impairment started between the ages of 4 and 43 years. Most of the audiograms were symmetric and flat or downsloping. The annual threshold deterioration increased from 0.2 to 2.6 dB per year at 0.25 to 8 kHz in the longitudinal analyses and in the cross-sectional analysis from 0.3 to 0.9 dB per year. The speech recognition score was quite good, deteriorating by 0.9% per year from a 90% score at the age of 36 years onward. Remarkably, extensive ocular examination including corrected visual acuity and refraction measurements, slit-lamp examination, ophthalmoscopy, Goldmann perimetry, electroretinography and electro-oculography revealed signs of subclinical retinal dysfunction. None of the patients showed the classic triad of retinitis pigmentosa. Pure-tone thresholds, phoneme recognition scores, and vestibular responses of the mutation carriers were fairly similar to previously described DFNA11 families.

CONCLUSION

Even though the diverse mutations are located in different regions of the myosin VIIa gene, the cochleovestibular phenotype is fairly similar in all DFNA11 families. Surprisingly, only in this family was subclinical retinal dysfunction detected.

The Phenotype of the First Otosclerosis Family Linked to OTSC5

OBJECTIVE

To report the audiometric and radiologic findings in the first otosclerosis family linked to OTSC5.

STUDY DESIGN

A clinical investigation of a family linked to OTSC5, including analyses of audiometric data and of high-resolution computed tomography (CT) images of the temporal bones from genetically affected family members.

SETTING

Tertiary referral center.

PATIENTS

Family members from a four-generation pedigree with otosclerosis segregating as an autosomal dominant trait.

MAIN OUTCOME MEASURE(S)

Pre-surgery pure tone audiometric data. Classification of otosclerotic foci on high-resolution spiral CT images of the temporal bones of genetically affected individuals.

RESULTS

Audiometric data showed a considerable degree of phenotypic variability. Cross-sectional regression analysis did not disclose any clear age dependence of threshold-related data. Systematic differences between mean parameter values relating to the thresholds in the best or the worst ear were found. High-resolution CT images revealed a fenestral otosclerotic focus in seven of nine (78%) clinically affected individuals and cochlear foci in one of these seven patients.

CONCLUSION

The phenotype of OTSC5 seems to be variable. Additional long-term audiometric data are needed to construct age-related typical audiograms, which may also facilitate the comparison between phenotypes of the different otosclerosis loci. The detection rate of otospongiotic foci in our study group is similar or lower compared with previous reports on CT data in consecutive otosclerosis patients who had stapes replacing surgery.

Visual impairment in Finnish Usher syndrome type III

PURPOSE

To evaluate visual impairment in Finnish Usher syndrome type 3 (USH3) and compare this with visual impairment in Usher syndrome types 1b (USH1b) and 2a (USH2a).

METHODS

We carried out a retrospective study of 28 Finnish USH3 patients, 24 Dutch USH2a patients and 17 Dutch USH1b patients. Cross-sectional regression analyses of the functional acuity score (FAS), functional field score (FFS*) and functional vision score (FVS*) related to age were performed for all patients. The FFS* and FVS* were calculated using the isoptre V-4 test target instead of the usual III-4 target. Statistical tests relating to regression lines and Student's t-test were used to compare between USH3 patients and the other genetic subtypes of Usher syndrome.

RESULTS

Cross-sectional analyses revealed significant deterioration in the FAS (1.3% per year), FFS* (1.4% per year) and FVS* (1.8% per year) with advancing age in the USH3 patient group. At a given age the USH3 patients showed significantly poorer visual field function than the USH2a patients.

CONCLUSIONS

The rate of deterioration in visual function in Finnish USH3 patients was fairly similar to that in Dutch USH1b or USH2a patients. At a given age, visual field impairment in USH3 patients was similar to that in USH1b patients but poorer than in USH2a patients.

Cochlin immunostaining of inner ear pathologic deposits and proteomic analysis in DFNA9 deafness and vestibular dysfunction

Seven missense mutations and one in-frame deletion mutation have been reported in the coagulation factor C homology (COCH) gene, causing the adult-onset, progressive sensorineural hearing loss and vestibular disorder at the DFNA9 locus. Prevalence of COCH mutations worldwide is unknown, as there is no systematic screening effort for late-onset hearing disorders; however, to date, COCH mutations have been found on four continents and the possibility of COCH playing an important role in presbycusis and disorders of imbalance has been considered. Cochlin (encoded by COCH) has also been shown as a major target antigen for autoimmune sensorineural hearing loss. In this report, we present histopathology, immunohistochemistry and proteomic analyses of inner ear tissues from post-mortem DFNA9 temporal bone samples of an individual from a large Dutch kindred segregating the P51S mutation and adult human unaffected controls, and wild-type (+/+) and Coch null (-/-) knock-out mice. DFNA9 is an inner ear disorder with a unique histopathology showing loss of cellularity and aggregation of abundant homogeneous acellular eosinophilic deposits in the cochlear and vestibular labyrinths, similar to protein aggregation in well-known neurodegenerative disorders. By immunohistochemistry on the DFNA9 temporal bone sections, we have shown cochlin staining of the characteristic cochlear and vestibular deposits, indicating aggregation of cochlin in the same structures in which it is normally expressed. Proteomic analysis identified cochlin as the most abundant protein in mouse and human cochleae. The high-level expression and stability of cochlin in the inner ear, even in the absence and severe atrophy of the fibrocytes that normally express COCH, are shown through these studies and further elucidate the pathobiologic events occurring in DFNA9 leading to hearing loss and vestibular dysfunction.

GJB2 mutations and degree of hearing loss: a multicenter study

Hearing impairment (HI) affects 1 in 650 newborns, which makes it the most common congenital sensory impairment. Despite extraordinary genetic heterogeneity, mutations in one gene, GJB2, which encodes the connexin 26 protein and is involved in inner ear homeostasis, are found in up to 50% of patients with autosomal recessive nonsyndromic hearing loss. Because of the high frequency of GJB2 mutations, mutation analysis of this gene is widely available as a diagnostic test. In this study, we assessed the association between genotype and degree of hearing loss in persons with HI and biallelic GJB2 mutations. We performed cross-sectional analyses of GJB2 genotype and audiometric data from 1,531 persons, from 16 different countries, with autosomal recessive, mild-to-profound nonsyndromic HI. The median age of all participants was 8 years; 90% of persons were within the age range of 0-26 years. Of the 83 different mutations identified, 47 were classified as nontruncating, and 36 as truncating. A total of 153 different genotypes were found, of which 56 were homozygous truncating (T/T), 30 were homozygous nontruncating (NT/NT), and 67 were compound heterozygous truncating/nontruncating (T/NT). The degree of HI associated with biallelic truncating mutations was significantly more severe than the HI associated with biallelic nontruncating mutations (P<.0001). The HI of 48 different genotypes was less severe than that of 35delG homozygotes. Several common mutations (M34T, V37I, and L90P) were associated with mild-to-moderate HI (median 25-40 dB). Two genotypes--35delG/R143W (median 105 dB) and 35delG/dela(GJB6-D13S1830) (median 108 dB)--had significantly more-severe HI than that of 35delG homozygotes.

[From gene to disease; a progressive cochlear-vestibular dysfunction with onset in middle-age (DFNA9)]

DFNA9 is an autosomal dominant genetic inner-ear hearing impairment that starts to show itself in the 3rd and 4th decades of life. This hearing impairment may be of a different degree of severity in each ear. Progression of hearing loss is about 3 dB/year. In about one in three patients severe vestibular symptoms similar to those in Ménière's disease are present as a result of a progressive impairment of the vestibular system. Several mutations were found in the COCH-gene on chromosome 14. There are indications that some of the mutations disrupt the folding of the cochlin protein, an important component of the extracellular matrix in the inner ear. DNA-diagnostics confirming the diagnosis ofDFNA9 are possible.

Audiometric, Vestibular, and Genetic Aspects of a DFNA9 Family with a G88E COCH Mutation

OBJECTIVES

To perform genetic analysis and to analyze cochleovestibular impairment features in a newly identified Dutch family with nonsyndromic autosomal dominant hearing impairment (DFNA9).

STUDY DESIGN

Genetic analysis was performed using microsatellite markers and single nucleotide polymorphisms. Audiometric data were collected and analyzed longitudinally. Results were compared with those obtained in previously identified P51S COCH mutation carriers (n = 74). Special attention was also given to a comparison of age-related features such as progressive hearing loss and vestibular impairment.

SETTING

Tertiary referral center.

PATIENTS

G88E COCH mutation carriers from a Dutch family.

MAIN OUTCOME MEASURES

The study of clinical features of a DFNA9 family carrying a G88E COCH mutation and to compare this to the symptoms of those carrying a P51S/COCH mutation.

RESULTS

Pure-tone thresholds, phoneme recognition scores, and vestibular responses of the G88E mutation carriers were essentially similar to those previously established in the P51S mutation carriers. Hearing started to deteriorate in G88E mutation carriers from age 46 to 49 years and onward, whereas deterioration of vestibular function started from approximately age 46 years. In the P51S mutation carriers, vestibular impairment started earlier, at approximately age 34 years. However, the difference in age of onset with the G88E mutation carriers was not significant. Remarkably, the proportion of patients who developed complete vestibular areflexia within the age range of 40 to 56 years was significantly lower for the G88E mutation carriers than for the P51S mutation carriers.

CONCLUSION

Apart from a significantly lower frequency of vestibular areflexia between the ages of 40 and 56 years, there are no phenotypic differences between carriers of the G88E and P51S mutations in the COCH gene.