The varieties of auditory neuropathy

Molecular study of patients with auditory neuropathy

Auditory neuropathy is a type of hearing loss that constitutes a change in the conduct of the auditory stimulus by the involvement of inner hair cells or auditory nerve synapses. It is characterized by the absence or alteration of waves in the examination of brainstem auditory evoked potentials, with otoacoustic and/or cochlear microphonic issues. At present, four loci associated with non‑syndromic auditory neuropathy have been mapped: Autosomal recessive deafness‑9 [DFNB9; the otoferlin (OTOF) gene] and autosomal recessive deafness‑59 [DFNB59; the pejvakin (PJVK) gene], associated with autosomal recessive inheritance; the autosomal dominant auditory neuropathy gene [AUNA1; the diaphanous‑3 (DIAPH3) gene]; and AUNX1, linked to chromosome X. Furthermore, mutations of connexin 26 [the gap junction β2 (GJB2) gene] have also been associated with the disease. OTOF gene mutations exert a significant role in auditory neuropathy. In excess of 80 pathogenic mutations have been identified in individuals with non‑syndromic deafness in populations of different origins, with an emphasis on the p.Q829X mutation, which was found in ~3% of cases of deafness in the Spanish population. The identification of genetic alterations responsible for auditory neuropathy is one of the challenges contributing to understand the molecular bases of the different phenotypes of hearing loss. Thus, the present study aimed to investigate molecular changes in the OTOF gene in patients with auditory neuropathy, and to develop a DNA chip for the molecular diagnosis of auditory neuropathy using mass spectrometry for genotyping. Genetic alterations were investigated in 47 patients with hearing loss and clinical diagnosis of auditory neuropathy, and the c.35delG mutation in the GJB2 gene was identified in three homozygous patients, and the heterozygous parents of one of these cases. Additionally, OTOF gene mutations were tracked by complete sequencing of 48 exons, although these results are still preliminary. Studying the genetic basis of auditory neuropathy is of utmost importance for obtaining a differential diagnosis, developing more specific treatments and more accurate genetic counseling.

High frequency of OTOF mutations in Chinese infants with congenital auditory neuropathy spectrum disorder

Auditory neuropathy spectrum disorder (ANSD) is one of the most common diseases leading to hearing and speech communication barriers in infants and young children. The OTOF gene is the first gene identified for autosomal recessive non-syndromic ANSD, and patients with OTOF mutations have shown marked improvement of auditory functions from the cochlear implantation, but the true involvement of OTOF mutations in Chinese ANSD patients is still unknown which precludes the effective management of this disease. Here, we investigated the contribution of OTOF mutations to congenital ANSD patients in China. In all, 37 infants and young Children with ANSD were screened for all the exons of OTOF gene, of them 34 patients had no neonatal risk factors who were considered as congenital ANSD. The clinical manifestation and audiometric features were also investigated and compared in patients with and without OTOF mutations. In all, 14 of these subjects were shown to carry two or three mutant alleles of OTOF with the high frequency of 41.2% in congenital ANSD patients. In total, 15 novel pathogenic mutations and 10 reported mutations were identified. Our results confirmed that mutations in OTOF gene were a major cause of congenital ANSD in China. Identification of OTOF mutations can facilitate diagnosis, clinical intervention and counseling for congenital ANSD.

Molecular Impairment Mechanisms of Novel OPA1 Mutations Predicted by Molecular Modeling in Patients With Autosomal Dominant Optic Atrophy and Auditory Neuropathy Spectrum Disorder

HYPOTHESIS

Different missense mutations of the optic atrophy 1 gene (OPA1) identified in optic atrophy patients with auditory neuropathy spectrum disorder (ANSD) induce functional impairment through different molecular mechanisms.

BACKGROUND

OPA1 is the gene responsible for autosomal dominant optic atrophy (ADOA), but some of its mutations are also associated with ANSD. OPA1 is a member of the GTPase family of proteins and plays a key role in the maintenance of mitochondrial activities that are dependent on dimer formation of the protein. There are many reports of OPA1 mutations, but the molecular mechanisms of their functional impairments are unclear.

METHODS

The sequences of coding regions in OPA1 were analyzed from blood samples of ADOA patients with ANSD. Molecular modeling of the protein's ability to form dimers and its GTP-binding ability were conducted to study the effects of structural changes in OPA1 caused by two identified mutations and their resultant effects on protein function.

RESULTS

Two heterozygous mutations, p.T414P (c.1240A>C) and p.T540P (c.1618A>C), located in the GTPase and middle domains of OPA1, respectively, were identified in two patients. Molecular modeling indicated decreased dimer formation caused by destabilization of the association structure of the p.T414P mutant, and decreased GTP-binding caused by destabilization of the binding site structure in the p.T540P mutant.

CONCLUSION

These two different conformational changes might result in decreased GTPase activities that trigger ADOA associated with ANSD, and are likely to be associated with mild clinical features. Molecular modeling would provide useful information in clinical practice.

Acoustically evoked auditory change complex in children with auditory neuropathy spectrum disorder: a potential objective tool for identifying cochlear implant candidates

OBJECTIVES

The overall aim of the study was to evaluate the feasibility of using electrophysiological measures of the auditory change complex (ACC) to identify candidates for cochlear implantation in children with auditory neuropathy spectrum disorder (ANSD). To achieve this overall aim, this study (1) assessed the feasibility of measuring the ACC evoked by temporal gaps in a group of children with ANSD across a wide age range and (2) investigated the association between gap detection thresholds (GDTs) measured by the ACC recordings and open-set speech-perception performance in these subjects.

DESIGN

Nineteen children with bilateral ANSD ranging in age between 1.9 and 14.9 years (mean: 7.8 years) participated in this study. Electrophysiological recordings of the auditory event-related potential (ERP), including the onset ERP response and the ACC, were completed in all subjects and open-set speech perception was evaluated for a subgroup of 16 subjects. For the ERP recordings, the stimulus was a Gaussian noise presented through ER-3A insert earphones to the test ear. Two stimulation conditions were used. In the "control condition," the stimulus was an 800-msec Gaussian noise. In the "gapped condition," the stimuli were two noise segments, each being 400 msec in duration, separated by one of five gaps (i.e., 5, 10, 20, 50, or 100 msec). The interstimulation interval was 1200 msec. The aided open-set speech perception ability was assessed using the Phonetically Balanced Kindergarten (PBK) word lists presented at 60 dB SPL using recorded testing material in a sound booth. For speech perception tests, subjects wore their hearing aids at the settings recommended by their clinical audiologists. For a subgroup of five subjects, psychophysical GDTs for the Gaussian noise were also assessed using a three-interval, three-alternative forced-choice procedure.

RESULTS

Responses evoked by the onset of the Gaussian noise (i.e., onset responses) were recorded in all stimulation conditions from all subjects tested in this study. The presence/absence, peak latency and amplitude, and response width of the onset response did not correlate with aided PBK word scores. The objective GDTs measured with the ACC recordings from 17 subjects ranged from 10 to 100 msec. The ACC was not recorded from two subjects for any gap durations tested in this study. There was a robust negative correlation between objective GDTs and aided PBK word scores. In general, subjects with prolonged objective GDTs showed low-aided PBK word scores. GDTs measured using electrophysiological recordings of the ACC correlated well with those measured using psychophysical procedures in four of five subjects who were evaluated using both procedures.

CONCLUSIONS

The clinical application of the onset response in predicting open-set speech-perception ability is relatively limited in children with ANSD. The ACC recordings can be used to objectively evaluate temporal resolution abilities in children with ANSD having no severe comorbidities, and who are older than 1.9 years. The ACC can potentially be used as an objective tool to identify poor performers among children with ANSD using properly fit amplification, and who are thus, cochlear implant candidates.

Understanding auditory neuropathy spectrum disorder: a systematic review in transgenic mouse models

Auditory neuropathy spectrum disorder is a unique group of hearing dysfunctions characterized by preserved outer hair cell function and abnormal neural conduction of the auditory pathway. However, the pathogenic mechanism underlying this disorder is not clear. We therefore performed a systematic review of genetic mouse models with different gene mutations to provide a valuable tool for better understanding of the process and the possible molecular mechanisms. Of the 18 articles retrieved, nine met the required criteria. All biochemical, histological, and electrophysiological results were recorded for each of the mouse models, as was the transgenic technology. This review provides a summary of different mouse models that may play an important role in the diagnosis and management of auditory neuropathy spectrum disorder in the future.

Management of children with auditory neuropathy spectrum disorder (ANSD)

INTRODUCTION

ANSD is a challenging problem.

OBJECTIVE

To present our experience on management of the children with ANSD with respect to clinical data.

METHODS

This retrospective study included all children younger than 16 years of age who applied to the department between 2005 and 2013 (with the exception of newborn hearing screening NHS referrals). The data were derived from pure tone, OAEs and ABR tests, and further medical risk factors of the subjects were evaluated.

RESULTS

ANSD was recognized in 74 ears of 40 children (B/U: 34/6) among 1952 children with SNHL (2.04%) detected among 9520 applicants to the department (0.42%). The clinical tests revealed that hearing loss greater than 15dB was present in both ears of 38 cases. The degree of hearing loss was profound in 48% children, severe in 12% children, moderate in 28% children, mild in 10% children and normal in 5% children. ABRs were absent/abnormal in 37/3 ears and CMs were detected in all. Acoustic reflexes were absent in all ears. Rehabilitation was managed by CI and hearing aids in 15 and 23 cases, respectively. FM system was given to two cases displaying normal hearing but poor speech discrimination in noisy environments.

CONCLUSION

ANSD is a relatively challenging problem for the audiology departments because of its various clinical features and difficulties in management. Our patients with ANSD most commonly displayed profound hearing loss. The number of overlooked cases may be minimized by performing ABR and OAE in every case referred with the suspicion of hearing loss.

Synaptopathy in the noise-exposed and aging cochlea: Primary neural degeneration in acquired sensorineural hearing loss

The classic view of sensorineural hearing loss (SNHL) is that the "primary" targets are hair cells, and that cochlear-nerve loss is "secondary" to hair cell degeneration. Our recent work in mouse and guinea pig has challenged that view. In noise-induced hearing loss, exposures causing only reversible threshold shifts (and no hair cell loss) nevertheless cause permanent loss of >50% of cochlear-nerve/hair-cell synapses. Similarly, in age-related hearing loss, degeneration of cochlear synapses precedes both hair cell loss and threshold elevation. This primary neural degeneration has remained hidden for three reasons: 1) the spiral ganglion cells, the cochlear neural elements commonly assessed in studies of SNHL, survive for years despite loss of synaptic connection with hair cells, 2) the synaptic terminals of cochlear nerve fibers are unmyelinated and difficult to see in the light microscope, and 3) the degeneration is selective for cochlear-nerve fibers with high thresholds. Although not required for threshold detection in quiet (e.g. threshold audiometry or auditory brainstem response threshold), these high-threshold fibers are critical for hearing in noisy environments. Our research suggests that 1) primary neural degeneration is an important contributor to the perceptual handicap in SNHL, and 2) in cases where the hair cells survive, neurotrophin therapies can elicit neurite outgrowth from spiral ganglion neurons and re-establishment of their peripheral synapses. This article is part of a Special Issue entitled .

Refinement of Molecular Diagnostic Protocol of Auditory Neuropathy Spectrum Disorder: Disclosure of Significant Level of Etiologic Homogeneity in Koreans and Its Clinical Implications

Auditory neuropathy spectrum disorder (ANSD) is a sensorineural hearing disorder caused by dysfunction of auditory neural conduction. ANSD has a heterogeneous etiology, including genetic factors; the response to cochlear implantation significantly varies depending on the etiology. The results of timely cochlear implantation for OTOF-related ANSD (DFNB9) have been reported to be good. Therefore, identifying the causative gene of ANSD, especially OTOF, is an important issue to rehabilitate these patients.Six sporadic ANSD subjects without anatomical abnormality of the cochlear nerve, including the 4 subjects that were previously reported to be without detectable OTOF mutation, were included. We performed targeted resequencing (TRS) of known deafness genes and multiphasic bioinformatics analyses of the data that ensured detection of capture failure and structural variations. Exclusion of SNP was also double checked. The TRS data previously obtained from 2 subjects were reanalyzed. Through this study, we detected 2 mutant alleles of OTOF from 5 (83.3%) of 6 ANSD subjects. All of the 5 subjects carried at least 1 mutant allele carrying p.R1939Q. This variant was categorized as a simple SNP (rs201326023) in the database and it resided in the exon with frequent capture failures, which previously led to exclusion of this variant from eligible candidacy mistakenly. In addition, we detected a structural variation within OTOF from a previously undiagnosed ANSD subject, which was the second structural variation reported in DFNB9 subjects to date.We identify a strong etiologic homogeneity of prelingual ANSD in case of the anatomically normal cochlear nerve in Koreans and now report DFNB9 as the single overwhelming cause. Multiphasic analysis of TRS data ensuring detection of capture failure and structural variations would be expected to reveal DFNB9 from a substantial portion of previously undiagnosed ANSD subjects in Koreans. Based on our results, we propose a novel strategy that incorporates imaging studies, prevalent mutation screening and multiphasic analysis of TRS data in a stepwise manner to correctly detect DFNB9 in Koreans.

Pathophysiological mechanisms and functional hearing consequences of auditory neuropathy

The effects of inner ear abnormality on audibility have been explored since the early 20th century when sound detection measures were first used to define and quantify 'hearing loss'. The development in the 1970s of objective measures of cochlear hair cell function (cochlear microphonics, otoacoustic emissions, summating potentials) and auditory nerve/brainstem activity (auditory brainstem responses) have made it possible to distinguish both synaptic and auditory nerve disorders from sensory receptor loss. This distinction is critically important when considering aetiology and management. In this review we address the clinical and pathophysiological features of auditory neuropathy that distinguish site(s) of dysfunction. We describe the diagnostic criteria for: (i) presynaptic disorders affecting inner hair cells and ribbon synapses; (ii) postsynaptic disorders affecting unmyelinated auditory nerve dendrites; (iii) postsynaptic disorders affecting auditory ganglion cells and their myelinated axons and dendrites; and (iv) central neural pathway disorders affecting the auditory brainstem. We review data and principles to identify treatment options for affected patients and explore their benefits as a function of site of lesion.

Perceptual separation of sensorineural hearing loss and auditory neuropathy spectrum disorder

OBJECTIVES/HYPOTHESIS

The present study aimed to examine whether the response patterns to the chimeric lexical tone tokens, combined with their pure tone audiometry (PTA) results, could separate listeners with sensorineural hearing loss (SNHL) from listeners with auditory neuropathy spectrum disorder (ANSD).

STUDY DESIGN

Case-control study.

METHODS

Forty-three SNHL subjects and 46 ANSD subjects participated in a Mandarin lexical tone perception test using original and chimeric tone tokens. Ten sets of monosyllables, with four tone patterns for each, were processed through a 16-channel chimeric synthesizer in which a temporal envelope (E) from a monosyllabic word of one tone was paired with a fine structure (FS) from the same monosyllable of other tones.

RESULTS

Significantly negative correlations were present between tone perception scores and PTA0.5-4 kHz for both SNHL (P < 0.001) and ANSD (P < 0.001) subjects. Overall, 72.4%, 66.4%, and 46.3% of the tone responses were consistent with FS for the SNHL subjects with mild, moderate, and severe degree of hearing loss, respectively; and 28.4%, 23.1%, and 22.7% were consistent with FS for the ANSD subjects, with the equivalent degree of hearing loss. Similarly, 17.6%, 24.2%, and 37.7% of the tone responses were consistent with E for the SNHL subjects with mild, moderate, and severe degree of hearing loss, respectively; and 45.5%, 44.3%, and 36.5% were consistent with E for the ANSD subjects.

CONCLUSION

Subjects with SNHL and ANSD may be separated by representing their FS- and E-consistent tone responses as a function of their pure-tone hearing thresholds.

LEVEL OF EVIDENCE

3b. Laryngoscope, 126:1420-1425, 2016.

Auditory nerve disease and auditory neuropathy spectrum disorders

In 1996, a new type of bilateral hearing disorder was discerned and published almost simultaneously by Kaga et al. [1] and Starr et al. [2]. Although the pathophysiology of this disorder as reported by each author was essentially identical, Kaga used the term "auditory nerve disease" and Starr used the term "auditory neuropathy". Auditory neuropathy (AN) in adults is an acquired disorder characterized by mild-to-moderate pure-tone hearing loss, poor speech discrimination, and absence of the auditory brainstem response (ABR) all in the presence of normal cochlear outer hair cell function as indicated by normal distortion product otoacoustic emissions (DPOAEs) and evoked summating potentials (SPs) by electrocochleography (ECoG). A variety of processes and etiologies are thought to be involved in its pathophysiology including mutations of the OTOF and/or OPA1 genes. Most of the subsequent reports in the literature discuss the various auditory profiles of patients with AN [3,4] and in this report we present the profiles of an additional 17 cases of adult AN. Cochlear implants are useful for the reacquisition of hearing in adult AN although hearing aids are ineffective. In 2008, the new term of Auditory Neuropathy Spectrum Disorders (ANSD) was proposed by the Colorado Children's Hospital group following a comprehensive study of newborn hearing test results. When ABRs were absent and DPOAEs were present in particular cases during newborn screening they were classified as ANSD. In 2013, our group in the Tokyo Medical Center classified ANSD into three types by following changes in ABRs and DPOAEs over time with development. In Type I, there is normalization of hearing over time, Type II shows a change into profound hearing loss and Type III is true auditory neuropathy (AN). We emphasize that, in adults, ANSD is not the same as AN.

Identifying Children With Poor Cochlear Implantation Outcomes Using Massively Parallel Sequencing

Cochlear implantation is currently the treatment of choice for children with severe to profound hearing impairment. However, the outcomes with cochlear implants (CIs) vary significantly among recipients. The purpose of the present study is to identify the genetic determinants of poor CI outcomes. Twelve children with poor CI outcomes (the "cases") and 30 "matched controls" with good CI outcomes were subjected to comprehensive genetic analyses using massively parallel sequencing, which targeted 129 known deafness genes. Audiological features, imaging findings, and auditory/speech performance with CIs were then correlated to the genetic diagnoses. We identified genetic variants which are associated with poor CI outcomes in 7 (58%) of the 12 cases; 4 cases had bi-allelic PCDH15 pathogenic mutations and 3 cases were homozygous for the DFNB59 p.G292R variant. Mutations in the WFS1, GJB3, ESRRB, LRTOMT, MYO3A, and POU3F4 genes were detected in 7 (23%) of the 30 matched controls. The allele frequencies of PCDH15 and DFNB59 variants were significantly higher in the cases than in the matched controls (both P < 0.001). In the 7 CI recipients with PCDH15 or DFNB59 variants, otoacoustic emissions were absent in both ears, and imaging findings were normal in all 7 implanted ears. PCDH15 or DFNB59 variants are associated with poor CI performance, yet children with PCDH15 or DFNB59 variants might show clinical features indistinguishable from those of other typical pediatric CI recipients. Accordingly, genetic examination is indicated in all CI candidates before operation.

Neurological associations in auditory neuropathy spectrum disorder: Results from a tertiary hospital in South India

Aims:

To find out the prevalence and types of neurological abnormalities associated in auditory neuropathy spectrum disorder in a large tertiary referral center.

Settings and Design:

A prospective clinical study was conducted on all patients diagnosed with auditory neuropathy spectrum disorder in the ear, nose, and throat (ENT) and neurology departments during a 17-month period. Patients with neurological abnormalities on history and examination were further assessed by a neurologist to determine the type of disorder present.

Results:

The frequency of auditory neuropathy spectrum disorder was 1.12%. Sixty percent were found to have neurological involvement. This included cerebral palsy in children, peripheral neuropathy (PN), spinocerebellar ataxia, hereditary motor-sensory neuropathy, spastic paresis, and ponto-bulbar palsy. Neurological lesions did not present simultaneously with hearing loss in most patients. Sixty-six percent of patients with auditory neuropathy spectrum disorder were born of consanguineous marriages.

Conclusions:

There is a high prevalence of neurological lesions in auditory neuropathy spectrum disorder which has to be kept in mind while evaluating such patients. Follow-up and counselling regarding the appearance of neuropathies is therefore important in such patients. A hereditary etiology is indicated in a majority of cases of auditory neuropathy spectrum disorder.

Parents' perspectives on the dilemmas with intervention for infants with auditory neuropathy spectrum disorder: A qualitative study

OBJECTIVE

This paper explores parental experiences of choices surrounding auditory management and language and communication development for infants and children with auditory neuropathy spectrum disorder (ANSD) in the light of the heterogeneity of condition, a poor evidence base for best outcomes in relation to management options, and the scarcity of data rooted in parent and family experience.

DESIGN

Qualitative narrative study.

STUDY SAMPLE

Twenty-five parents of 21 children (aged four months to six years) identified with ANSD through the newborn hearing screening programme.

RESULTS

Families identify barriers to early management due to conflicting expert opinions and ANSD-specific challenges with diagnosis and prognosis in infants, and share their accounts on their own evaluations of intervention benefit in their children.

CONCLUSIONS

The results are of relevance to the clinicians and other professionals involved in early intervention, management, and support of infants with ANSD.

Auditory neuropathy

Neural disorders of the auditory nerve are associated with particular disorders of auditory perceptions dependent on processing of acoustic temporal cues. These include: (1) speech perception; (2) localizing a sound's origin in space; and (3) identifying sounds in background noise. Auditory neuropathy (AN) is a consequence of: (1) presynaptic disorders affecting inner hair cell ribbon synapses; (2) postsynaptic disorders of auditory nerve dendrites; and (3) postsynaptic disorders of auditory nerve axons. The etiologies of these disorders are diverse, similar to other cranial or peripheral neuropathies. The pathologies cause attenuated and dyssynchronous auditory nerve discharges. Therapies and management of patients with AN are reviewed.

Psychoacoustic Characteristics of Tinnitus in Individuals with Auditory Neuropathy Spectrum Disorder

The study aimed at understanding the psychoacoustic characteristics of tinnitus in individuals with auditory neuropathy spectrum disorder (ANSD). It attempts to assess the pitch and intensity of loudness of tinnitus matched by individuals with ANSD. Fifty individuals who were diagnosed as having auditory neuropathy spectrum disorder were included in the study. Tinnitus evaluation was carried out where the individuals matched the frequency and intensity of loudness of the tinnitus. The results of the study shows that pitch matched by majority of patients with ANSD is predominantly low pitched (<1000 Hz). The frequency of tinnitus matched by the patients with ANSD also correlated with the degree of maximal hearing loss. The intensity of loudness of the tinnitus was around 10-15 dB higher than their threshold in majority of the patients considered in the study. There was a weak negative correlation for the matched frequency and intensity of loudness. The results of the study suggest that majority of individuals with low frequency hearing loss had low pitched tinnitus. Thus, there could be discordant damage between outer and inner hair cells, abnormal firing of auditory nerve in individuals with ANSD which can lead to tinnitus. Thus, it can help to understand the physiology of tinnitus in individuals with ANSD.

Auditory neuropathy in late preterm infants treated with phototherapy for hyperbilirubinemia

OBJECTIVE

To evaluate the prevalence of auditory neuropathy (AN) in late preterms treated with phototherapy for hyperbilirubinemia.

DESIGN

Prospective observational study comprising late preterms treated with phototherapy for hyperbilirubinemia. Newborns were screened with combined transient-evoked otoacoustic emissions (TEOAEs) / automated auditory brainstem responses (AABR). Infants who failed screening underwent diagnostic (ABR). Infants were all re-evaluated with AABR at one year.

STUDY SAMPLE

Eighty-five infants with a mean serum total bilirubin concentration of 22.3 ± 1.76 mg/dl; severe-hyperbilirubinemia (SH), and 102 infants with a mean serum total bilirubin concentration of 18.6 ± 1.26 mg/dl; non-severe hyperbilirubinemia (NSH) were included.

RESULTS

From 85 late preterms with SH, six (7.1%) failed screening and underwent diagnostic ABR for six weeks. AN was diagnosed in two (2%) infants with SH. Four (3.9%) of the 102 controls with NSH demonstrated failure at TEOAE/AABR. No AN was diagnosed in the control group at the diagnostic ABR. No statistically significant difference was found between infants treated with phototherapy for SH and NSH with regard to AN/AD either in the postnatal period or at one year. No correlation was found between serum bilirubin levels and ABR latencies or thresholds.

CONCLUSIONS

AN (2%) in late preterms treated with phototherapy for severe-hyperbilirubinemia was not higher than in those with non-severe hyperbilirubinemia.

BDNF increases survival and neuronal differentiation of human neural precursor cells cotransplanted with a nanofiber gel to the auditory nerve in a rat model of neuronal damage

Objectives. To study possible nerve regeneration of a damaged auditory nerve by the use of stem cell transplantation. Methods. We transplanted HNPCs to the rat AN trunk by the internal auditory meatus (IAM). Furthermore, we studied if addition of BDNF affects survival and phenotypic differentiation of the grafted HNPCs. A bioactive nanofiber gel (PA gel), in selected groups mixed with BDNF, was applied close to the implanted cells. Before transplantation, all rats had been deafened by a round window niche application of β-bungarotoxin. This neurotoxin causes a selective toxic destruction of the AN while keeping the hair cells intact. Results. Overall, HNPCs survived well for up to six weeks in all groups. However, transplants receiving the BDNF-containing PA gel demonstrated significantly higher numbers of HNPCs and neuronal differentiation. At six weeks, a majority of the HNPCs had migrated into the brain stem and differentiated. Differentiated human cells as well as neurites were observed in the vicinity of the cochlear nucleus. Conclusion. Our results indicate that human neural precursor cells (HNPC) integration with host tissue benefits from additional brain derived neurotrophic factor (BDNF) treatment and that these cells appear to be good candidates for further regenerative studies on the auditory nerve (AN).

Auditory neuropathy spectrum disorder: a review

PURPOSE

Auditory neuropathy spectrum disorder, or ANSD, can be a confusing diagnosis to physicians, clinicians, those diagnosed, and parents of children diagnosed with the condition. The purpose of this review is to provide the reader with an understanding of the disorder, the limitations in current tools to determine site(s) of lesion, and management techniques.

METHOD

This article is a review of what is known about ANSD. It includes descriptions of assessment tools, causes of ANSD, and patient management techniques.

CONCLUSIONS

This review is a guide to audiologists, speech-language pathologists, and early interventionists who work with individuals diagnosed with ANSD and/or their families. It highlights the need for more precise tools to describe the disorder in order to facilitate decisions about interventions and lead to better predictions of outcome.

Preliminary performance of cochlear implants in post-lingual patients with auditory neuropathy

CONCLUSIONS

Auditory restoration can be obtained by using cochlear implants (CIs) in post-lingual patients with auditory neuropathy (AN). However, improvements in postoperative speech recognition for these patients varied.

OBJECTIVES

The primary purpose of this study was to assess the postoperative performances of two post-lingual AN patients after receiving CIs.

METHODS

Two post-lingual AN patients received unilateral CIs and the efficacy of the implants was then evaluated. One patient was female with bilateral mid-severe hearing loss and received an implant at age 28 years. The second patient was male with severe hearing loss and he received an implant at age 15 years. The postoperative performance for both patients was evaluated.

RESULTS

After using the CI for 6 months, the hearing ability of both subjects was improved by the CI with an average post-implant threshold of 35 dB and 44 dB, respectively. The woman made significant progress in speech recognition with an open-set spondee recognition score of 55% and sentence recognition in quiet score of 90%. Sentence recognition in noise scores were 94% (SNR = +10 dB), 88% (SNR = +5 dB), and 80% (SNR = 0 dB). The boy achieved improved recognition scores for monosyllables (40%) and disyllables (26%), but poor sentence recognition both in quiet (0%) and in noise (0%).

A homozygous SLITRK6 nonsense mutation is associated with progressive auditory neuropathy in humans

OBJECTIVES/HYPOTHESIS

SLITRK family proteins control neurite outgrowth and regulate synaptic development. In mice, Slitrk6 plays a role in the survival and innervation of sensory neurons in the inner ear, vestibular apparatus, and retina, and also influences axial eye length. We provide the first detailed description of the auditory phenotype in humans with recessive SLITRK6 deficiency.

STUDY DESIGN

Prospective observational case study.

METHODS

Nine closely related Amish subjects from an endogamous Amish community of Pennsylvania underwent audiologic and vestibular testing. Single nucleotide polymorphism microarrays were used to map the chromosome locus, and Sanger sequencing or high-resolution melt analysis were used to confirm the allelic variant.

RESULTS

All nine subjects were homozygous for a novel nonsense variant of SLITRK6 (c.1240C>T, p.Gln414Ter). Adult patients had high myopia. The 4 oldest SLITRK6 c.1240C>T homozygotes had absent ipsilateral middle ear muscle reflexes (MEMRs). Distortion product otoacoustic emissions (DPOAEs) were absent in all ears tested and the cochlear microphonic (CM) was increased in amplitude and duration in young patients and absent in the two oldest subjects. Auditory brainstem responses (ABRs) were dys-synchronised bilaterally with no reproducible waves I, III, or V at high intensities. Hearing loss and speech reception thresholds deteriorated symmetrically with age, which resulted in severe-to-profound hearing impairment by early adulthood. Vestibular evoked myogenic potentials were normal in three ears and absent in one.

CONCLUSION

Homozygous SLITRK6 c.1240C>T (p.Gln414Ter) nonsense mutations are associated with high myopia, cochlear dysfunction attributed to outer hair cell disease, and progressive auditory neuropathy.

Prevalence of auditory neuropathy spectrum disorder in an auditory health care service

Auditory neuropathy spectrum disorder (ANSD) is characterized by impairment of the auditory nerve associated with preservation of outer hair cell function.

Objective

To establish the prevalence of ANSD in subjects with sensorineural hearing loss (SNHL).

Method

This retrospective study was carried out between 2010 and 2012 and included the charts of 2,292 individuals with SNHL. Data from otolaryngological and audiological examinations based on pure-tone and speech audiometry, impedance tests, otoacoustic emissions (OAEs), and brainstem auditory evoked potentials (BAEPs) were collected. Inclusion criteria: presence of OAEs and/or cochlear microphonic (CM); absent or altered BAEPs, and normal MRI scans of the brain.

Results

Twenty-seven (1.2%) of the 2,292 subjects with SNHL had ANSD (37% males; 63% females). Mild SNHL was seen in 29.6% of the individuals with ANSD; 55.5% had moderate SNHL; 7.4% had severe SNHL; and 7.5% had profound SNHL. In terms of age, 14.8% were aged between zero and 20 years, 44.1% were 41 to 60 years old, and 7.4% were above the age of 60.

Conclusion

ANSD was seen in 1.2% of the individuals with SNHL included in this study.

OTOF mutation screening in Japanese severe to profound recessive hearing loss patients

BACKGROUND

Auditory neuropathy spectrum disorder (ANSD) is a unique form of hearing loss that involves absence or severe abnormality of auditory brainstem response (ABR), but also the presence of otoacoustic emissions (OAEs). However, with age, the OAEs disappear, making it difficult to distinguish this condition from other nonsyndromic hearing loss. Therefore, the frequency of ANSD may be underestimated. The aim of this study was to determine what portion of nonsyndromic hearing loss is caused by mutations of OTOF, the major responsible gene for nonsyndromic ANSD.

METHODS

We screened 160 unrelated Japanese with severe to profound recessive nonsyndromic hearing loss (ARNSHL) without GJB2 or SLC26A4 mutations, and 192 controls with normal hearing.

RESULTS

We identified five pathogenic OTOF mutations (p.D398E, p.Y474X, p.N727S, p.R1856Q and p.R1939Q) and six novel, possibly pathogenic variants (p.D450E, p.W717X, p.S1368X, p.R1583H, p.V1778I, and p.E1803A).

CONCLUSIONS

The present study showed that OTOF mutations accounted for 3.2-7.3% of severe to profound ARNSHL patients in Japan. OTOF mutations are thus a frequent cause in the Japanese deafness population and mutation screening should be considered regardless of the presence/absence of OAEs.

Dysmyelination of auditory afferent axons increases the jitter of action potential timing during high-frequency firing

Auditory neuropathies are linked to loss of temporal acuity of sound-evoked signals, which may be related to myelin loss. However, it is not known how myelin loss affects the waveform and temporal precision of action potentials (APs) in auditory CNS nerve terminals. Here we investigated the excitability of the calyx of Held nerve terminal in dysmyelinated auditory brainstems using the Long-Evans Shaker (LES) rat, a spontaneous mutant where compact myelin wrapping does not occur due to a genetic deletion of myelin basic protein. We found at relatively mature postnatal ages (15-17 d after birth) LES rat calyces showed prolonged spike latencies, indicative of a threefold reduction in the AP propagation velocity. Furthermore, LES rat afferent fiber-evoked APs showed a pronounced loss of temporal precision, even at low stimulation frequencies (10 Hz). While normal calyces were able to fire APs without failures at impressive rates of up to 1 kHz, LES calyces were unable to do so. Direct recordings of the presynaptic calyx terminal AP waveform revealed that myelin loss does not affect the AP spike upstroke and downstroke kinetics, but dysmyelination reduces the after-depolarization and enhances the fast after-hyperpolarization peak following the AP spike in the LES rat. Together these findings show that proper myelination is essential not only for fast AP propagation, but also for precise presynaptic AP firing that minimizes both spike jitter and failures, two characteristics critically important for the accurate processing of sound signals in the auditory brainstem.

Regulation of conduction time along axons

Timely delivery of information is essential for proper functioning of the nervous system. Precise regulation of nerve conduction velocity is needed for correct exertion of motor skills, sensory integration and cognitive functions. In vertebrates, the rapid transmission of signals along nerve fibers is made possible by the myelination of axons and the resulting saltatory conduction in between nodes of Ranvier. Myelin is a specialization of glia cells and is provided by oligodendrocytes in the central nervous system. Myelination not only maximizes conduction velocity, but also provides a means to systematically regulate conduction times in the nervous system. Systematic regulation of conduction velocity along axons, and thus systematic regulation of conduction time in between neural areas, is a common occurrence in the nervous system. To date, little is understood about the mechanism that underlies systematic conduction velocity regulation and conduction time synchrony. Node assembly, internode distance (node spacing) and axon diameter - all parameters determining the speed of signal propagation along axons - are controlled by myelinating glia. Therefore, an interaction between glial cells and neurons has been suggested. This review summarizes examples of neural systems in which conduction velocity is regulated by anatomical variations along axons. While functional implications in these systems are not always clear, recent studies on the auditory system of birds and mammals present examples of conduction velocity regulation in systems with high temporal precision and a defined biological function. Together these findings suggest an active process that shapes the interaction between axons and myelinating glia to control conduction velocity along axons. Future studies involving these systems may provide further insight into how specific conduction times in the brain are established and maintained in development. Throughout the text, conduction velocity is used for the speed of signal propagation, i.e. the speed at which an action potential travels. Conduction time refers to the time it takes for a specific signal to travel from its origin to its target, i.e. neuronal cell body to axonal terminal.

Generation of inner ear sensory cells from bone marrow-derived human mesenchymal stem cells

AIM

Hearing loss is the most common sensory disorder in humans, its main cause being the loss of cochlear hair cells. We studied the potential of human mesenchymal stem cells (hMSCs) to differentiate towards hair cells and auditory neurons.

MATERIALS & METHODS

hMSCs were first differentiated to neural progenitors and subsequently to hair cell- or auditory neuron-like cells using in vitro culture methods.

RESULTS

Differentiation of hMSCs to an intermediate neural progenitor stage was critical for obtaining inner ear sensory lineages. hMSCs generated hair cell-like cells only when neural progenitors derived from nonadherent hMSC cultures grown in serum-free medium were exposed to EGF and retinoic acid. Auditory neuron-like cells were obtained when treated with retinoic acid, and in the presence of defined growth factor combinations containing Sonic Hedgehog.

CONCLUSION

The results show the potential of hMSCs to give rise to inner ear sensory cells.

Genetic analysis of auditory neuropathy spectrum disorder in the Korean population

Auditory neuropathy spectrum disorder (ANSD) is caused by dys-synchronous auditory neural response as a result of impairment of the functions of the auditory nerve or inner hair cells, or synapses between inner hair cells and the auditory nerve. To identify a causative gene causing ANSD in the Korean population, we conducted gene screening of the OTOF, DIAPH3, and PJVK genes in 19 unrelated Korean patients with ANSD. A novel nonsense mutation (p.Y1064X) and a known pathogenic mutation (p.R1939Q) of the OTOF gene were identified in a patient as compound heterozygote. Pedigree analysis for these mutations showed co-segregation of mutation genotype and the disease in the family, and it supported that the p.Y1064X might be a novel genetic cause of autosomal recessive ANSD. A novel missense variant p.K1017R (c.3050A>G) in the DIAPH3 gene was also identified in the heterozygous state. In contrast, no mutation was detected in the PJVK gene. These results indicate that no major causative gene has been reported to date in the Korean population and that pathogenic mutations in undiscovered candidate genes may have an effect on ANSD.

Auditory neuropathy in a low-risk population: a review of the literature

OBJECTIVE

Collect all available published evidence on the prevalence of auditory neuropathy in the well baby population and calculate the contribution of this to the false negative rate of oto-acoustic emission based newborn hearing screening programs.

METHOD

PubMed and EMBASE were searched for relevant articles published between 1996 and 2010. Medical Subject Headings terms included 'Auditory disease', 'Prevalence' and 'Child' and their relevant synonyms. Included were original studies, which focused on well babies and reported the prevalence of auditory neuropathy.

RESULTS

Of 519 citations 4 articles met the inclusion criteria. The population based prevalence of auditory neuropathy in children in population hearing screening was found to vary between 0.006% (SD 0.006) and 0.03% (SD 0.02). The false negative rate, caused by missed children with auditory neuropathy, is between 4 and 17%.

CONCLUSION

The available information on the prevalence of auditory neuropathy in the well baby population is poor. However, if oto-acoustic emission screening is used in the first stage of a neonatal hearing screening program, children with auditory neuropathy are missed. The cost-effectiveness of population-based screening using auditory brainstem response should be studied.

Auditory neuropathy spectrum disorder: its prevalence and audiological characteristics in an Indian tertiary care hospital

OBJECTIVE

Auditory neuropathy spectrum disorder (ANSD) has become a well accepted clinical entity. ANSD has now become easy to recognize with advent of test battery approach for hearing loss evaluation. However, little is known about its epidemiology and aetiology, especially its prevalence and incidence in India. This study was conducted to determine the prevalence and audiological characteristics of ANSD in our tertiary care hospital at New Delhi, India.

METHODS

We prospectively enrolled all the paediatric cases i.e. less than 12years of age referred to our outpatient department for hearing evaluation. All the cases were evaluated using complete audiological test battery consisting of pure tone audiometry (PTA), impedance audiometry, acoustic reflexes, otoacoustic emissions (OAE), and brain stem evoked response audiometry (BERA). The instrument used was GSI Audera. BERA with both condensation and rarefaction polarity was performed in cases with absent wave V even at highest intensity levels. The criteria used for diagnosis of ANSD was normal or near normal cochlear hair cells (sensory) function (preservation of otoacoustic emissions and/or cochlear microphonics) and absent or abnormal auditory nerve function (absent or severely abnormal auditory brainstem potentials). A repeat test battery was performed after 3months on the diagnosed cases of auditory neuropathy. Based on their behavioural findings the appropriate management programme was formulated.

RESULTS

A total of 487 paediatric cases were referred for hearing evaluation. 183 (37.6%) cases showed absent BERA and 26(5.3%) cases fulfilled the diagnostic criteria for ANSD. Repeat examination after 3months revealed presence of OAE's in 57.6% (15/26) cases while cochlear microphonics were present in all the 26 cases.

CONCLUSION

The prevalence of ANSD in our study is 5.3% and in children diagnosed with severe to profound hearing loss is 14%. Presence of cochlear microphonics with absent BERA seems to be reliable criteria for diagnosing ANSD.

Language outcomes and service provision of preschool children with congenital hearing loss

BACKGROUND

Children with congenital hearing loss (HL) are at increased risk of speech and language delays and require increased resource needs.

METHODS

Assessments of language, adaptive behavior, and resource needs at mean age of 60±5 months. Effects of age of enrollment in Early Intervention (EI) and degree of HL were evaluated.

RESULTS

Children with HL had lower Reynell verbal comprehension scores (77.6±18 versus 94.8±15; p=0.0001) and expressive language scores (85.9±19 versus 97.4±15; p=0.0051) than hearing children. Children with HL enrolled in EI ≤3 months versus >3 months had higher verbal comprehension (86.6±21 versus 70.3±12; p=0.0143) and expressive language scores (92.1±12 versus 80.5±21; p=0.0601), respectively. Children with bilateral moderate to profound HL and children with unilateral or bilateral mild HL were more likely to have low verbal comprehension scores versus children with hearing (75.8±17 and 81.0±22 versus 94.8±15; p=0.001), and receive more special educational services (100% and 100% versus 42%) respectively. After adjusting for degree of HL and Vineland adaptive scores <70, entry to EI ≤3 months was associated with a 13.8 point higher verbal comprehension score (p=0.047) for children with HL. The model accounted for 26% of variance.

CONCLUSIONS

Persistent beneficial effects of early age of entry to EI on verbal comprehension scores are observed for children with congenital HL at preschool age. Children with HL continue to need comprehensive education services.

Aiding and occluding the contralateral ear in implanted children with auditory neuropathy spectrum disorder

BACKGROUND

The challenges associated with auditory neuropathy spectrum disorder (ANSD) are due primarily to temporal impairment and therefore tend to affect perception of low- to midfrequency sounds. A common treatment option for severe impairment in ANSD is cochlear implantation, and because the degree of impairment is unrelated to degree of hearing loss by audiometric thresholds, this population may have significant acoustic sensitivity in the contralateral ear. Clinically, the question arises as to how we should treat the contralateral ear in this population when there is acoustic hearing-should we plug it, amplify it, implant it, or leave it alone?

PURPOSE

The purpose of this study was to examine the effects of acute amplification and plugging of the contralateral ear compared to no intervention in implanted children with ANSD and aidable contralateral hearing. It was hypothesized that due to impaired temporal processing in ANSD, contralateral acoustic input would interfere with speech perception achieved with the cochlear implant (CI) alone; therefore, speech perception performance will decline with amplification and improve with occlusion.

RESEARCH DESIGN

Prospective within-subject comparison. Adaptive speech recognition thresholds (SRTs) for monosyllable and spondee word stimuli were measured in quiet and in noise for the intervention configurations.

STUDY SAMPLE

Nine children treated at the Medical College of Wisconsin Koss Cochlear Implant Program participated in the study. Inclusion criteria for this study were children diagnosed with ANSD who were unilaterally implanted, had aidable hearing in the contralateral ear (defined as a three-frequency pure-tone average of ≤80 dB HL), had at least 1 yr of cochlear implant experience, and were able to perform the speech perception task.

INTERVENTION

We compared SRT with the CI alone to SRTs with interventions of cochlear implant with a contralateral hearing aid (CI+HA) and cochlear implant with a contralateral earplug (CI+plug).

DATA COLLECTION AND ANALYSIS

SRTs were measured and compared within subjects across listening conditions. Within-subject comparisons were analyzed using paired t-tests, and analyses of predictive variables for effects of contralateral intervention were analyzed using linear regression.

RESULTS

Contrary to the hypothesis, the bimodal CI+HA configuration showed a significant improvement in mean performance over the CI-alone configuration in quiet (p = .04). In noise, SRTs were obtained for six subjects, and no significant bimodal benefit was observed (p = .09). There were no consistent effects of occlusion observed across subjects and stimulus conditions. Degree of bimodal benefit showed a significant relationship with performance with the CI alone, with greater bimodal benefit associated with poorer CI-alone performance (p = .01). This finding, however, was limited by floor effects.

CONCLUSIONS

The results of this study indicate that children with ANSD who are experienced cochlear implant users may benefit from contralateral amplification, particularly for moderate cochlear implant performers. It is unclear from these data whether long-term contralateral hearing aid use in real-world situations would ultimately benefit this population; however, a hearing aid trial is recommended with assessment of bimodal benefit over time. These data may help inform clinical guidelines for determining optimal hearing configurations for unilaterally implanted children with ANSD, particularly when considering candidacy for sequential cochlear implantation.

Unilateral auditory neuropathy spectrum disorder

CONCLUSIONS

The majority of the patients with unilateral auditory neuropathy spectrum disorder (UANSD) were pediatric and mostly showed a great degree of hearing loss when diagnosed. Abnormal auditory brainstem response (ABR) and preserved otoacoustic emissions (OAEs) and/or cochlear microphonics (CM) were important features to differentiate it from common sensorineural deafness and central nerve hearing loss.

OBJECTIVE

To identify the clinical characteristics of patients with UANSD.

METHODS

This was a retrospective study involving 14 patients diagnosed as having UANSD between 2004 and 2010 in the Chinese PLA Hospital.

RESULTS

In all, 50% of the cases were males (1:1 sex ratio) and the average age of onset was 4.1 years. Of the 14 affected ears with UANSD in these cases, 6 were left-sided, while 8 were right-sided. Of the 14 contralateral ears, 4 presented with sensorineural hearing loss, while the other 10 showed normal hearing. The degree of hearing loss in the 14 affected ears varied, including moderate in 1, moderately severe in 4, severe in 5, and profound in 4. ABRs were absent in the 14 affected ears, while the OAEs, and/or CM were present.

Auditory and optic neuropathy in Kjer's disease: case report

OBJECTIVE

Description of a female patient with diagnosed Kjer's disease and sensorineural hearing loss, who specifically complained of a progressive inability to understand speech in noisy situations.

DESIGN

Case report.

SUBJECT

A 30-year-old, Caucasian woman with Kjer's disease.

RESULTS

Audiological assessment showed low-frequency sensorineural hearing loss and a disproportionate deterioration in speech discrimination. This inconsistency gave rise to suspicion of possible aggravation. Follow-up testing showed that brainstem responses were absent, while clear otoacoustic emissions and cochlear microphonics were present. Hearing aids were fitted but no improvement was shown.

CONCLUSION

This case shows a combination of auditory neuropathy and Kjer's optic neuropathy. It also illustrates that the combination of unexplained hearing loss and apparently inconsistent audiometric outcomes may be associated with auditory neuropathy. Such unexpected hearing evaluation outcomes may be due to other neurological conditions, such as Kjer's disease.

[Auditory synaptopathy/neuropathy: clinical findings and diagnosis]

Auditory synaptopathy/neuropathy (AS/AN) is a special subtype of sensorineural hearing disorders with heterogeneous phenotypes and underestimated incidence. AS/AN generally develops in infancy, occasionally in adulthood. Symptoms include fluctuating, mostly bilateral hearing loss and abnormally reduced speech comprehension, especially in noisy environments. Within audiological assessments, patients with AS/AN present otoacoustic emissions (TEOAE; DPOAE) and cochlear microphonics (CM), absence of stapedius reflexes (SR) as well as absent or pathologically altered auditory evoked brainstem potentials (ABR). Children with AS/AN cannot be identified within OAE-based newborn hearing screening programs. Clinical findings, transtympanic electrocochleography (ECoG) and further diagnostic tools permit further identification of individual characteristics. In individual cases conventional amplification and the use of FM systems may improve hearing and communication skills. If these interventions, accompanied by intensive hearing, speech and language therapy are unsuccessful, cochlear implants (CI) or alternative forms of communication may be useful options for rehabilitation.

Variants of OTOF and PJVK genes in Chinese patients with auditory neuropathy spectrum disorder

Background

Mutations in OTOF and PJVK genes cause DFNB9 and DFNB59 types of hearing loss, respectively. The patients carrying pathogenic mutations in either of these genes may show the typical phenotype of auditory neuropathy spectrum disorder (ANSD). The aim of the present study was to identify OTOF and PJVK mutations in sporadic ANSD patients.

Methods and Findings

A total of 76 unrelated Chinese non-syndromic ANSD patients were sequenced on the gene OTOF and PJVK exon by exon. Variants were valued in 105 controls with normal hearing to verify the carrying rate. We identified one pathogenic mutation (c.1194T>A) and three novel, possibly pathogenic, variants (c.3570+2T>C, c.4023+1 G>A, and c.1102G>A) in the OTOF gene, and one novel, possibly pathogenic, variant (c.548G>A) in PJVK. Moreover, we found three novel missense mutations within the exons of OTOF.

Conclusions

As we identified 4 and 1 possible pathogenic variants of the OTOF gene and the PJVK gene, respectively, we believe that screening in these genes are important in sporadic ANSD patients. The pathogenicity of these novel mutations needs further study because of their single heterozygous nature. Knowledge on the mutation spectra of these genes in Chinese would be beneficial in understanding the genetic character of this worldwide disease.

Auditory brainstem response (ABR) abnormalities across the life span of rats prenatally exposed to alcohol

BACKGROUND

Fetal alcohol syndrome (FAS) is a leading cause of neurodevelopmental impairments (NDIs) in developed countries. Sensory deficits can play a major role in NDI, yet few studies have investigated the effects of prenatal alcohol exposure on sensory function. In addition, there is a paucity of information on the lifelong effects of prenatal alcohol exposure. Thus, we sought to investigate the effects of prenatal alcohol exposure on auditory function across the life span in an animal model. Based on prior findings with prenatal alcohol exposure and other forms of adverse prenatal environments, we hypothesized that animals prenatally exposed to alcohol would show an age-dependent pattern of (i) hearing and neurological abnormalities as postweanling pups, (ii) a substantial dissipation of such abnormalities in young adulthood, and (iii) a resurgence of such abnormalities in middle-aged adulthood.

METHODS

Pregnant rats were randomly assigned to an untreated control (CON), a pair-fed control (PFC), or an alcohol-treated (ALC) group. The ALC dams were gavaged with 6 mg/kg alcohol daily from gestation day (GD) 6 to 21. The PFC dams were gavaged daily from GD6 to GD21 with an isocaloric and isovolumetric water-based solution of maltose-dextrins and pair-fed to the ALC dams. The CON dams were the untreated group to which the ALC and CON groups were compared. Hearing and neurological functions in the offspring were assessed with the auditory brainstem response (ABR) at the postnatal ages of 22, 220, and 520 days.

RESULTS

In accord with our hypothesis, ABR abnormalities were first observed in the postweanling pups, largely dissipated in young adulthood, and then resurged in middle-aged adulthood. This age-related pattern suggests that the ALC pups had a developmental delay that dissipated in young adulthood and an enhanced age-related deterioration that occurred in middle-aged adulthood. Such a pattern is consistent with the fetal programming hypothesis of adult-onset diseases (the Barker hypothesis).

CONCLUSIONS

Our findings have important clinical implications for the assessment and management of (i) childhood hearing disorders and their comorbidities (i.e., speech-and-language, learning, and attention deficit disorders) and (ii) enhanced age-related hearing and neurological degeneration in middle-aged adulthood that can result from prenatal alcohol exposure. We recommend hearing evaluation be a part of any long-term follow-up for FAS patients and patients exposed to any adverse prenatal environment.

Recovery function of electrically evoked compound action potential in implanted children with auditory neuropathy: preliminary results

CONCLUSION

The results of this study show that the temporal processing ability in children with auditory neuropathy (AN) can be restored to some degree by electrical stimulation through a cochlear implant. In addition, the electrically evoked compound action potential (ECAP) may be a useful index to predict outcomes in implanted children with AN.

OBJECTIVES

The purpose of this study was to evaluate restoration of the temporal processing abilities in implanted children with AN using ECAP recovery function and speech perception.

METHODS

Ten children who had received cochlear implantations participated in this study, including six with AN and four with sensorineural hearing loss (SNHL). ECAP recovery functions were measured, and the slopes of ECAP recovery functions in implanted children with AN were compared with those of implanted children with SNHL. Open-set speech perception test scores of implanted children with AN were compared with those of 78 implanted children with SNHL.

RESULTS

The slopes of the ECAP recovery function in children with AN did not differ significantly from those in children with SNHL. The group of children with robust ECAPs showed good postoperative performance. However, the group with no ECAPs showed poor performance.

Selective inner hair cell loss in prematurity: a temporal bone study of infants from a neonatal intensive care unit

Premature birth is a well-known risk factor for sensorineural hearing loss in general and auditory neuropathy in particular. However, relatively little is known about the underlying causes, in part because there are so few relevant histopathological studies. Here, we report on the analysis of hair cell loss patterns in 54 temporal bones from premature infants and a control group of 46 bones from full-term infants, all of whom spent time in the neonatal intensive care unit at the Hospital de Niños in San Jose, Costa Rica, between 1977 and 1993. The prevalence of significant hair cell loss was higher in the preterm group than the full-term group (41% vs. 28%, respectively). The most striking finding was the frequency of selective inner hair cell loss, an extremely rare histopathological pattern, in the preterm vs. the full-term babies (27% vs. 3%, respectively). The findings suggest that a common cause of non-genetic auditory neuropathy is selective loss of inner hair cells rather than primary damage to the cochlear nerve.

Transplantation of neural differentiated human mesenchymal stem cells into the cochlea of an auditory-neuropathy guinea pig model

The aim of this study was to determine the effects of transplanted neural differentiated human mesenchymal stem cells (hMSCs) in a guinea pig model of auditory neuropathy. In this study, hMSCs were pretreated with a neural-induction protocol and transplanted into the scala tympani of the guinea pig cochlea 7 days after ouabain injury. A control model was made by injection of Hanks balanced salt solution alone into the scala tympani of the guinea pig cochlea 7 days after ouabain injury. We established the auditory neuropathy guinea pig model using 1 mM ouabain application to the round window niche. After application of ouabain to the round window niche, degeneration of most spiral ganglion neurons (SGNs) without the loss of hair cells within the organ of Corti and increasing the auditory brain responses (ABR) threshold were found. After transplantation of neural differentiated hMSCs, the number of SGNs was increased, and some of the SGNs expressed immunoreactivity with human nuclear antibody under confocal laser scanning microscopy. ABR results showed mild hearing recovery after transplantation. Based on an auditory neuropathy animal model, these findings suggest that it may be possible to replace degenerated SGNs by grafting stem cells into the scala tympani.

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.