A new autosomal dominant syndrome of idiopathic progressive vestibulo-cochlear dysfunction with middle-age onset

Ultrastructural co-localization of cochlin and type II collagen in the rat semicircular canal

Cochlin and type II collagen are major constituents of the inner ear extracellular matrix. To investigate the morphological relation of cochlin and type II collagen in the rat semicircular canal, immuno-electronmicroscopic analysis was performed using the post-embedding immunogold method. Immunolabeling for cochlin was detected in the fibrillar substance underlying the supporting epithelium of the sensory cells and beneath the epithelial cells facing the endolymph in the semicircular canals. Immunolabeling for type II collagen was observed in the same fibrillar substance in the subepithelial area. The co-localization of cochlin and type II collagen in the fibrillar substance in the subepithelial area indicate that cochlin may play a role in the structural homeostasis of the vestibule acting in concert with the fibrillar type II collagen bundles.

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.

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.

Expression of Cochlin in the Vestibular Organ of Rats

The COCH gene mutated in autosomal dominant sensorineural deafness (DFNA9) encodes cochlin, a major constituent of the inner ear extracellular matrix. Cochlin constitutes 70% of the inner ear protein and cochlin isoforms can be classified into three subgroups, p63s, p44s and p40s. Symptoms of some DFNA9 patients are consistent with those of Ménière's disease. Here, we report the expression of cochlin in the vestibular organ of rats using isoform-specific antibodies that recognize all three isoforms. Cochlin is highly expressed in the stromata of the maculae of otolithic organs and cristae of semicircular canals, and in the channels in the bony labyrinth that transmit the dendritic innervation to the cristae and maculae. Cochlin cannot be detected in the sensory cells, dark cells, nor in the acellular structures, otolithic membrane or in the cupula. These findings support the theory that deposition of acidophilic substance in the inner ear caused by mutation of cochlin can induce a secondary retrograde dendritic degeneration of the vestibular nerves.

Progressive Late-Onset Sensorineural Hearing Loss and Vestibular Impairment with Vertigo (DFNA9/COCH): Longitudinal Analyses in a Belgian Family

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.

Cross-sectional analysis of hearing threshold in relation to age in a large family with cochleovestibular impairment thoroughly genotyped for DFNA9/COCH

Hearing threshold was analyzed for each frequency in relation to age in 88 members of a large Dutch family with cochleovestibular impairment caused by a P51S mutation in the COCH gene within the DFNA9 locus (chromosome 14q12-13). The participants in this study were 34 mutation carriers and 54 relatives without the mutation (control subjects). A sigmoidal dose-response curve with a variable slope was used to fit the mutation carriers' threshold-on-age data. Progression started at about 40 years of age and only lasted for some 20 to 25 years; the associated average progression was 2.9 dB/y for all frequencies. However, some hearing impairment was already present before, predominantly at the high frequencies. The mean thresholds in the young mutation carriers (< 33 years of age) were significantly higher (by 4 to 13 dB) than those in age-matched controls at 2 to 8 kHz. Presumably, mutation carriers have a congenital, stable offset threshold (10 to 29 dB) at these frequencies, and develop progression later in life.

Hereditary cochleovestibular dysfunction due to a COCH gene mutation (DFNA9): a follow-up study of a family

Cochleovestibular impairment was evaluated, in relation to age, in a longitudinal follow-up study on a Dutch family with a DFNA9 trait caused by a Pro51Ser mutation in the COCH gene on chromosome 14q12-q13. Fourteen cases were genotyped. The onset age of progressive impairment reported by the mutation carriers was between age 35 and 45 years. Pure-tone thresholds deteriorated by about 2-7 dB per year (mean 3.8 dB per year) in a variable, often asymmetrical, fashion. One mutation carrier developed recurrent episodes of vertigo accompanied by nausea and vomiting, resembling Ménière's disease. Two others developed special susceptibility for motion sickness and appeared to have a hyperactive vestibulo-ocular reflex. More advanced stages of vestibular impairment, i.e. vestibular hyporeflexia and complete vestibular areflexia, were eventually found in a number of cases. DFNA9/COCH should be considered as a possible cause in patients developing combined progressive cochlear and vestibular impairment, or suspected hereditary Ménière-like disease, from around middle age.

DFNA9 is a progressive audiovestibular dysfunction with a microfibrillar deposit in the inner ear

OBJECTIVES

Several mutations in the COCH gene were recently identified in American and European families with DFNA9, an autosomal dominant progressive sensorineural hearing loss with onset in high frequencies. Our preliminary vestibular studies in one American family indicated progressive vestibular dysfunction. More complete vestibular studies in European families have shown vestibular abnormalities in the affected individuals. Our temporal bone studies on two families with DFNA9 revealed, in addition to neurosensory degeneration, a unique acidophilic deposit in the membranous labyrinths of the affected individuals. The purposes of this study were 1) to further investigate the vestibular abnormalities in members of one American family for the purposes of genotype-phenotype correlation and 2) to investigate the electron microscopic structure of the acidophilic deposit to obtain further insights into the pathogenesis of DFNA9.

STUDY DESIGN

Prospective analysis.

METHODS

Extensive vestibular testing was performed in some unaffected and affected members of a family with DFNA9. One temporal bone was analyzed by electron microscopy of celloidin-embedded tissue.

RESULTS AND CONCLUSIONS

The findings indicate progressive vestibular dysfunction in many of the patients affected with hearing loss. Thus, despite different mutations in the COCH gene, the American and European families manifest auditory and vestibular dysfunction. Electron microscopic analysis shows the spiral ligament to be enriched for a highly branched non-banded microfibrillar substance that is decorated with glycosaminoglycan granules. Additionally, the spiral ligament lacks the 67-nm-thick straight periodically banded bundles of type II collagen that are normally abundant in this structure. A speculative pathogenetic model is proposed for this unique disease and its relationship with other late-onset or adult-onset audiovestibular diseases and Meniere's disease is investigated.

Non-syndromal autosomal dominant hearing impairment: ongoing phenotypical characterization of genotypes

This review is concerned with the present state of phenotypical characterization of known genotypes of non-syndromal autosomal dominant hearing impairment. A brief outline of history and context of phenotyping and genotyping of hearing impairment is given with particular reference to the most recent developments in this field, followed by descriptions of DFNA1, DFNA2, DFNA5, DFNA6/14, DFNA8/12, DFNA9, DFNA 13, DFNA17 and DFNA21. Phenotyping those known genotypes may support the ongoing search for mutations in the corresponding gene and enhance genetic counselling. It is recommended that sufficient attention is given to a detailed description of the phenotype in each (newly) described hereditary hearing impairment disorder.

Progressive cochleovestibular impairment caused by a point mutation in the COCH gene at DFNA9

OBJECTIVES

Analysis of phenotype-genotype correlation.

STUDY DESIGN

Family study.

METHODS

Auditory and vestibulo-ocular functions were examined in a Dutch family with autosomal dominantly inherited sensorineural hearing impairment caused by a 208C > T mutation in the COCH gene, located in chromosome 14q12-q13 (DFNA9). Linear regression analysis of individual longitudinal hearing threshold data (n = 11) on age was performed.

RESULTS

Fifteen of the 16 genetically affected persons could be evaluated. They all developed hearing and vestibular impairment symptoms--and in many cases also cardiovascular disease--in the fourth to fifth decade. At the low frequencies (0.25-2 kHz), hearing loss started at the age of about 40 years and showed an average annual progression of approximately 3 dB, finally resulting in profound hearing losses. In two exceptional cases, annual progression attained levels of up to 24 dB. At the high frequencies (4-8 kHz), the average threshold increased from about 50 dB at the age of 35 years to about 120 dB at the age of 75 years (which amounts to 1.8 dB annual threshold increase). All affected individuals tested showed normal ocular motor functions. The patients older than 46 years generally showed absence of the vestibulo-ocular reflex, but their cervico-ocular reflex was enhanced compared with normal subjects, whereas those aged 40 to 46 years showed either severe vestibular hyporeflexia or unilateral caloric areflexia.

CONCLUSION

These findings suggest a gradual development of cochleovestibular impairment caused by the new mutation found.