AUNA2: A Novel Type of Non-Syndromic Slowly Progressive Auditory Synaptopathy/Auditory Neuropathy with Autosomal-Dominant Inheritance.

BACKGROUND: Auditory synaptopathy/neuropathy (AS/AN) is a heterogeneous disorder, which may be caused by environmental factors like postnatal hyperbilirubinemia or by genetic factors. The genetic forms are subdivided into syndromic and non-syndromic types, and show different inheritance patterns with a strong preponderance of autosomal-recessive forms. To date, only a single locus for non-syndromic autosomal-dominant AS/AN (AUNA1) has been reported in a single family, in which a non-coding DIAPH3 mutation was subsequently described as causative. MATERIALS AND METHODS: Here, we report detailed clinical data on a large German AS/AN family with slowly progressive postlingual hearing loss. Affected family members developed their first symptoms in their second decade. Moderate hearing loss in the fourth decade then progressed to profound hearing impairment in older family members. Comprehensive audiological and neurological tests were performed in the affected family members. Genetic testing comprised linkage analyses with polymorphic markers and a genome-wide linkage analysis using the Affymetrix GeneChip® Human Mapping 250K. RESULTS AND CONCLUSION: We identified a large family with autosomal-dominant AS/AN. By means of linkage analyses, the AUNA1 locus was excluded, and putatively linked regions on chromosomal bands 12q24 and 13q34 were identified as likely carrying the second locus for autosomal-dominant AS/AN (AUNA2). AUNA2 is associated with a slowly progressive postlingual hearing loss without any evidence for additional symptoms in other organ systems.

Hearing impairment in a female infant with interstitial deletion of 2q24.1q24.3.

Patients with interstitial deletions in 2q24.1q24.3 are rarely reported. These patients manifest a variety of clinical features in addition to intellectual disability, depending on the size and location of the deletion. We report a female patient with interstitial deletion of 5.5 Mb in 2q24.1q24.3, who showed intrauterine growth retardation, hypotonia, global developmental delay, microcephaly, and characteristic facial appearance. In addition, she had hearing impairment, with no auditory brainstem response. Case of 2q24.1q24.3 deletion with hearing impairment is quite rare. We suspect that hearing impairment is caused by bilateral cochlear nerve deficiency due to cochlear nerve canal stenosis. Further studies are necessary to evaluate hearing impairment as a clinical feature in patients with de novo heterozygous 2q24.1q24.3 deletion.

Genetics of peripheral vestibular dysfunction: lessons from mutant mouse strains.

BACKGROUND: A considerable amount of research has been published about genetic hearing impairment. Fifty to sixty percent of hearing loss is thought to have a genetic cause. Genes may also play a significant role in acquired hearing loss due to aging, noise exposure, or ototoxic medications. Between 1995 and 2012, over 100 causative genes have been identified for syndromic and nonsyndromic forms of hereditary hearing loss. Mouse models have been extremely valuable in facilitating the discovery of hearing loss genes and in understanding inner ear pathology due to genetic mutations or elucidating fundamental mechanisms of inner ear development. PURPOSE: Whereas much is being learned about hereditary hearing loss and the genetics of cochlear disorders, relatively little is known about the role genes may play in peripheral vestibular impairment. Here we review the literature with regard to genetics of vestibular dysfunction and discuss what we have learned from studies using mutant mouse models and direct measures of peripheral vestibular neural function. RESULTS: Several genes are considered that when mutated lead to varying degrees of inner ear vestibular dysfunction due to deficits in otoconia, stereocilia, hair cells, or neurons. Behavior often does not reveal the inner ear deficit. Many of the examples presented are also known to cause human disorders. CONCLUSIONS: Knowledge regarding the roles of particular genes in the operation of the vestibular sensory apparatus is growing, and it is clear that gene products co-expressed in the cochlea and vestibule may play different roles in the respective end organs. The discovery of new genes mediating critical inner ear vestibular function carries the promise of new strategies in diagnosing, treating, and managing patients as well as predicting the course and level of morbidity in human vestibular disease.

The genetic basis of auditory neuropathy spectrum disorder (ANSD).

OBJECTIVE: Auditory neuropathy is a hearing disorder where outer hair cell function within the cochlea is normal, but inner hair cell and/or the auditory nerve function is disrupted. It is a heterogeneous disorder which can have either congenital or acquired causes. Furthermore, the aetiology of auditory neuropathy is vast, which may include prematurity, hyperbilirubinaemia, anoxia, hypoxia, congenital brain anomalies, ototoxic drug exposure, and genetic factors. It is estimated that approximately 40% of cases have an underlying genetic basis, which can be inherited in both syndromic and non syndromic conditions. This review paper provides an overview of the genetic conditions associated with auditory neuropathy spectrum disorders (ANSDs) and highlights some of the defective genes that have been found to be linked to the pathological auditory changes. METHOD: Literature search was conducted using a number of resources including textbooks, professional journals and the relevant websites. RESULTS: The largest proportion of auditory neuropathy spectrum disorders (ANSDs) is due to genetic factors which can be syndromic, non-syndromic or mitochondrial related. The inheritance pattern can include all the four main types of inheritances such as autosomal dominant, autosomal recessive, X-linked and mitochondrial. CONCLUSION: This paper has provided an overview of mutation with some of the genes and/or loci discovered to be the cause for auditory neuropathy spectrum disorders (ANSDs). It has been noted that different gene mutations may trigger different pathological changes in patients with this disorder. These discoveries have provided us with vital information as to the sites of pathology in auditory neuropathy spectrum disorders (ANSDs), and the results highlight the heterogeneity of the disorder.

Dystrophic epidermolysis bullosa with one dominant and one recessive mutation of the COL7A1 gene in a child with deafness.

Dystrophic epidermolysis bullosa can be inherited in autosomal dominant and recessive forms, the former usually expressed as a milder phenotype, although mild forms of recessive dystrophic epidermolysis bullosa can occur. We present a patient who was found to be a compound heterozygote, inheriting a dominant mutation from his father and a recessive mutation from his mother, resulting in a clinically severe case of dystrophic epidermolysis bullosa. Mutations in the gene for collagen VII (COL7A1) have been documented in both types of dystrophic epidermolysis bullosa. Our patient has also been diagnosed with bilateral auditory neuropathy, a disorder coincidentally also mapped to a nearby gene on chromosome 3p21 (the transmembrane inner ear expressed gene, TMIE).

Frequency-specific electrocochleography indicates that presynaptic and postsynaptic mechanisms of auditory neuropathy exist.

OBJECTIVES: The physiological mechanisms underlying auditory neuropathy (AN) remain unclear and it is likely that the multiple disruptions are classified under the broadly defined term. Cochlear implantation is being more widely used in this population to bypass the suspected site-of-lesion although a number of cases have been identified within the Sydney Cochlear Implant Centre where this management strategy has been unsuccessful. It is likely that this relates to the different physiological mechanisms underlying AN. DESIGN: To investigate the site-of-lesion in AN, frequency-specific round window electrocochleography (ECochG) was used to assess local hair-cell, dendritic, and axonal currents generated within the cochlea in 14 subjects with AN and compared with responses from two normally hearing subjects. ECochG results were then compared with electrically evoked auditory brain stem response (EABR) measured after cochlear implantation. RESULTS: The results of this study demonstrate that two dominant patterns of ECochG waveforms (produced by a high-frequency alternating tone burst) can be identified in this population of AN subjects: (a) gross waveform showing a prolonged summating potential (SP) latency that, in most cases, is followed by a small compound action potential; and (b) gross waveform showing a normal latency SP waveform followed by a broad negative potential [assumed to reflect the dendritic potential (DP) identified in anaesthetized guinea-pigs]. This study demonstrates that in most subjects (n = 7) with a prolonged latency SP but no DP, normal morphology EABR waveforms were elicited for all electrode channels. On the other hand, all subjects (n = 7) who showed a normal latency SP followed by a broad negative DP, showed EABR waveforms that were absent or having poor wave V morphology. The authors' interpretation of this is that ECochG results may provide a classification of AN into pre- and postsynaptic lesions. CONCLUSIONS: We suggest that a presynaptic and postsynaptic type of AN exist that may have implications for the fitting of cochlear implants.

Recent advances in the genetics of recurrent vertigo and vestibulopathy.

PURPOSE OF REVIEW: To focus on recent advances in the genetics of recurrent vertigo, with an overview on episodic ataxia, benign recurrent vertigo (mainly migraine-associated vertigo), bilateral vestibulopathy, and Ménière's disease. RECENT FINDINGS: Since the identification more than a decade ago of the genetic causes of episodic ataxia type 1 with myokymia caused by KCNA1 mutations and episodic ataxia type 2 with nystagmus caused by CACNA1A mutations, the list of episodic ataxia syndromes with distinct clinical features and genetic loci is slowly expanding, now up to episodic ataxia type 7. There is growing recognition for a correlation between benign recurrent vertigo and migraine, and acceptance for vertigo as a manifestation of migraine; efforts to identify susceptibility loci for migraine and migraine-associated vertigo are underway. A handful of families with vestibulopathy spanning several generations have been identified. Although no gene has yet been found, vestibulopathy with normal hearing variably associated with migraine is likely monogenic and heterogeneous, similar to nonsydromic deafness. There is also continuing effort to identify genetic causes of familial Ménière's disease. SUMMARY: Overlapping clinical features among different familial syndromes of recurrent vertigo and strong association with migraine suggest shared mechanisms. Collaborative efforts in patient identification and recruitment will facilitate progress in understanding disease mechanisms to improve diagnosis and treatment of recurrent vertigo.

[Sequence analysis of DFNB59 gene in a Chinese family with dominantly inherited auditory neuropathy].

OBJECTIVE: To investigate if the DFNB59 gene contributes to the hearing loss of a Chinese pedigree with dominantly inherited auditory neuropathy (AN). METHOD: Nine members in four generations of the family were selected for this study. Genomic DNA was isolated from the peripheral leukocytes of the patients using the pure gene DNA isolation kits. Firstly, the subjects DNA fragment was PCR amplified using specific primers corresponding to exon 2 and 4 of the DFNB59 gene. Each fragment was purified and subsequently analyzed by direct sequencing in an applied biosystems 3730 automated DNA sequencer. The whole coding sequence of DFNB59 gene of one family patient were then PCR amplified and submitted for sequence analysis as described above. The resultant sequence data were compared with the standard sequence to identify deafness-associated mutations. RESULT: PCR amplifications were successfully conducted in all the subjects. We failed to detect the presence either of mutations T54I and R183W in the exon 2 and exon 4 that have been reported, or any other deafness-associated mutations in the whole DFNB59 gene, by sequence analysis. CONCLUSION: The DFNB59 gene seems not contribute to the pathogenesis of this Chinese AN family, which suggesting new gene(s) involvement.

[Sequence analysis of OTOF gene in a Chinese pedigree with autosomal dominant auditory neuropathy].

OBJECTIVE: To investigate if the OTOF gene contributes to the non-syndromic hearing loss of a Chinese pedigree with dominantly inherited auditory neuropathy (AN). METHOD: The subjects included were 9 live individuals in an autosomal dominant AN pedigree, 3 sporadic AN patients and 3 normal-hearing controls. Genomic DNA was isolated from the peripheral leukocytes of the subjects using the Pure gene DNA Isolation Kits. Firstly, the whole coding sequence of OTOF gene of one family patient were PCR amplified using specific primers. Each fragment was purified and subsequently analyzed by direct sequencing in an Applied Biosystems 3 730 automated DNA sequencer. The resultant sequence data were compared with the standard sequence to identify deafness-associated mutations. Other DNA samples were then screened for these mutations by PCR amplification and sequence analysis. RESULT: PCR amplifications were successfully conducted in all the subjects. Comparison of the resultant OTOF sequence in one family patient with the standard sequence identified 10 nucleotide variants which do not lead to amino acid change. These mutations were also detectable in other family individuals, 3 sporadic AN patients and 3 normal-hearing controls. CONCLUSION: The OTOF does not seem to contribute to the pathogenesis of this Chinese AN family, which suggest new gene(s) involvement.

Cyclin D1 expression and histopathologic features in vestibular schwannomas.

OBJECTIVE: To evaluate cyclin D1 expression in vestibular schwannoma and its relationship with histologic, clinical, and radiologic features. PATIENTS: Twenty-one patients with histologically confirmed vestibular schwannoma. INTERVENTION: Immunohistochemistry analysis was performed with anticyclin D1. Histopathologic features studied included Antoni pattern and nuclear and stromal degenerative changes. Clinical charts, audiometric data, and magnetic resonance imaging characteristics were reviewed. MAIN OUTCOME MEASURES: Cyclin D1 expression and its association with histologic, clinical, and radiologic findings. RESULTS: Cyclin D1 expression was found in 52% of cases. Cyclin D1 expression was more frequent in right-sided tumors (p = 0.02) and in tumors with nuclear degenerative changes (p < 0.0001). Patients with negative cyclin D1 expression had longer duration of deafness (p = 0.02) and higher 2,000-Hz hearing thresholds (p = 0.04) than cyclin D1+ patients. CONCLUSION: Cyclin D1 expression, present in nearly half of the cases, may play a role in the development of these tumors. Further studies are needed to fully understand the contributions of histopathologic and immunohistochemical factors to vestibular schwannoma biological activity.

[Auditory neuropathy due to the Q829X mutation in the gene encoding otoferlin (OTOF) in an infant screened for newborn hearing impairment]. / Neuropatia auditiva secundaria a la mutación Q829X en el gen de la otoferlina (OTOF) en un lactante sometido a screening neonatal de hipoacusia.

We report an infant with auditory neuropathy secondary to the Q829X mutation in the gene encoding otoferlin (OTOF). Included in a universal newborn hearing screening program, the subject passed the otoacoustic emission (OAEs) test. Given that the infant had a familial history of deafness auditory brainstem response (ABR) testing was performed, revealing a profound hearing impairment. The genetic study confirmed that the subject was homozygous for the Q829X mutation in OTOF. The patient underwent a cochlear implant, obtaining satisfactory results. The moderately high prevalence of this mutation in the Spanish population could produce a significant false negative rate in newborn hearing screening programs using OAEs.

Progressive auditory neuropathy in patients with Leber's hereditary optic neuropathy.

OBJECTIVE: To investigate auditory neural involvement in patients with Leber's hereditary optic neuropathy (LHON). METHODS: Auditory assessment was undertaken in two patients with LHON. One was a 45 year old woman with Harding disease (multiple-sclerosis-like illness and positive 11778mtDNA mutation) and mild auditory symptoms, whose auditory function was monitored over five years. The other was a 59 year old man with positive 11778mtDNA mutation, who presented with a long standing progressive bilateral hearing loss, moderate on one side and severe to profound on the other. Standard pure tone audiometry, tympanometry, stapedial reflex threshold measurements, stapedial reflex decay, otoacoustic emissions with olivo-cochlear suppression, auditory brain stem responses, and vestibular function tests were undertaken. RESULTS: Both patients had good cochlear function, as judged by otoacoustic emissions (intact outer hair cells) and normal stapedial reflexes (intact inner hair cells). A brain stem lesion was excluded by negative findings on imaging, recordable stapedial reflex thresholds, and, in one of the patients, olivocochlear suppression of otoacoustic emissions. The deterioration of auditory function implied a progressive course in both cases. Vestibular function was unaffected. CONCLUSIONS: The findings are consistent with auditory neuropathy-a lesion of the cochlear nerve presenting with abnormal auditory brain stem responses and with normal inner hair cells and the cochlear nucleus (lower brain stem). The association of auditory neuropathy, or any other auditory dysfunction, with LHON has not been recognised previously. Further studies are necessary to establish whether this is a consistent finding.

Familial auditory neuropathy.

OBJECTIVES/HYPOTHESIS: Auditory neuropathy is a sensorineural hearing disorder characterized by absent or abnormal auditory brainstem responses and normal cochlear outer hair cell function as measured by otoacoustic emission recordings. Many risk factors are thought to be involved in its etiology and pathophysiology. Four Chinese pedigrees with familial auditory neuropathy were presented to demonstrate involvement of genetic factors in the etiology of auditory neuropathy. STUDY DESIGN: Probands of the above-mentioned pedigrees, who had been diagnosed with auditory neuropathy, were evaluated and followed in the Department of Otolaryngology-Head and Neck Surgery, China People Liberation Army General Hospital (Beijing, China). Their family members were studied, and the pedigree maps established. METHODS: History of illness, physical examination, pure-tone audiometry, acoustic reflex, auditory brainstem responses, and transient evoked and distortion-product otoacoustic emissions were obtained from members of these families. Some subjects received vestibular caloric testing, computed tomography scan of the temporal bone, and electrocardiography to exclude other possible neuropathic disorders. RESULTS: In most affected patients, hearing loss of various degrees and speech discrimination difficulties started at 10 to 16 years of age. Their audiological evaluation showed absence of acoustic reflex and auditory brainstem responses. As expected in auditory neuropathy, these patients exhibited near-normal cochlear outer hair cell function as shown in distortion product otoacoustic emission recordings. Pure-tone audiometry revealed hearing loss ranging from mild to profound in these patients. Different inheritance patterns were observed in the four families. In Pedigree I, 7 male patients were identified among 43 family members, exhibiting an X-linked recessive pattern. Affected brothers were found in Pedigrees II and III, whereas in pedigree IV, two sisters were affected. All the patients were otherwise normal without evidence of peripheral neuropathy at the time of writing. CONCLUSION: Patients with characteristics of nonsyndromic hereditary auditory neuropathy were identified in one large and three smaller Chinese families. Pedigree analysis suggested an X-linked, recessive hereditary pattern in one pedigree and autosomal recessive inheritances in the other three pedigrees. The phenotypes in the study were typical of auditory neuropathy; they were transmitted in different inheritance patterns, indicating clinical and genetic heterogeneity of this disorder. The observed inheritance and clinical audiological findings are different from those previously described for nonsyndromic low-frequency sensorineural hearing loss. This information should facilitate future molecular linkage analyses and positional cloning for the relative genes contributing to auditory neuropathy.

[A report on a large family with X-linked recessive nonsyndromic hereditary low frequency neuropathic hearing impairment].

OBJECTIVE: To analyze the genetic causes of low frequency neuropathic hearing impairment. METHODS: Using the network established by our institute, the proband of the low frequency neuropathic hearing loss pedigree was found. Then, investigation was carried out in the family from the proband. Cyrillic 2.1 software was set up to draw the pedigree and genetic characterization and phenotypes were analyzed in this family. RESULTS: One-hundred and one alive family members were investigated and the clinic audiologic examinations were performed in 43 of 101 individuals. Six of forty-three individuals appeared to be low frequency neuropathic hearing loss and all patients were males without systemic disorders except hearing loss. The clinic phenotypes were mild, middle, severe and profound hearing loss with disappearing of the auditory brainstem response(ABR) and partial normal results of distortion product otoacoustic emission (DPOAE) in the affected individuals. The onset of hearing loss was at 10-16 years old and the age of all patients was arranged from 18 to 26 years old. CONCLUSION: A large five generations family with hereditary low frequency neuropathic hearing impairment was found in our study. The genetic pattern in this family is male dominant X-linked recessive (XR) nonsyndromic hearing loss. Our findings suggest that some low frequency neuropathic disorders might be attributed to genetic factors.

Familial progressive vestibulocochlear dysfunction caused by a COCH mutation (DFNA9).

OBJECTIVE: To describe the decline of vestibulocochlear function in a man with vestibulocochlear dysfunction caused by a Pro51Ser mutation within the COCH gene on chromosome 14q12-13 (DFNA9). METHODS: A follow-up of more than 15 years was performed in a single case. Clinical investigations were supplemented by oculomotor, vestibular, and auditory tests. RESULTS: A 50-year-old man had had progressive sensorineural hearing loss and dysequilibrium for 15 years; he had been asymptomatic at the age of 35 years. He suffered from instability in the dark, head movement-dependent oscillopsia, paroxysmal positional vertigo, and vertigo with and without nausea. Hearing impairment started unilaterally, predominantly in the high frequencies. He also reported tinnitus. Disease progressed to severe bilateral high-frequency hearing impairment and vestibular areflexia. Fluctuation of vestibulocochlear function was documented and mentioned by the patient. CONCLUSIONS: Our patient proved to suffer from an autosomal dominant vestibulocochlear disorder caused by a COCH gene mutation. The remarkable medical history has some features in common with Meniere disease; however, there are also different clinical and neurophysiological features. In the family, phenotypic variability is present.