Highly variable hearing loss due to POU4F3 (c.37del) is revealed by longitudinal, frequency specific analyses

Genotype-phenotype correlations add value to the management of families with hereditary hearing loss (HL), where age-related typical audiograms (ARTAs) are generated from cross-sectional regression equations and used to predict the audiogram phenotype across the lifespan. A seven-generation kindred with autosomal dominant sensorineural HL (ADSNHL) was recruited and a novel pathogenic variant in POU4F3 (c.37del) was identified by combining linkage analysis with whole exome sequencing (WES). POU4F3 is noted for large intrafamilial variation including the age of onset of HL, audiogram configuration and presence of vestibular impairment. Sequential audiograms and longitudinal analyses reveal highly variable audiogram features among POU4F3 (c.37del) carriers, limiting the utility of ARTAs for clinical prognosis and management of HL. Furthermore, a comparison of ARTAs against three previously published families (1 Israeli Jewish, 2 Dutch) reveals significant interfamilial differences, with earlier onset and slower deterioration. This is the first published report of a North American family with ADSNHL due to POU4F3, the first report of the pathogenic c.37del variant, and the first study to conduct longitudinal analysis, extending the phenotypic spectrum of DFNA15.

Autosomal dominant non-syndromic hearing loss maps to DFNA33 (13q34) and co-segregates with splice and frameshift variants in ATP11A, a phospholipid flippase gene

Sequencing exomes/genomes have been successful for identifying recessive genes; however, discovery of dominant genes including deafness genes (DFNA) remains challenging. We report a new DFNA gene, ATP11A, in a Newfoundland family with a variable form of bilateral sensorineural hearing loss (SNHL). Genome-wide SNP genotyping linked SNHL to DFNA33 (LOD = 4.77), a locus on 13q34 previously mapped in a German family with variable SNHL. Whole-genome sequencing identified 51 unremarkable positional variants on 13q34. Continuous clinical ascertainment identified several key recombination events and reduced the disease interval to 769 kb, excluding all but one variant. ATP11A (NC_000013.11: chr13:113534963G>A) is a novel variant predicted to be a cryptic donor splice site. RNA studies verified in silico predictions, revealing the retention of 153 bp of intron in the 3' UTR of several ATP11A isoforms. Two unresolved families from Israel were subsequently identified with a similar, variable form of SNHL and a novel duplication (NM_032189.3:c.3322_3327+2dupGTCCAGGT) in exon 28 of ATP11A extended exon 28 by 8 bp, leading to a frameshift and premature stop codon (p.Asn1110Valfs43Ter). ATP11A is a type of P4-ATPase that transports (flip) phospholipids from the outer to inner leaflet of cell membranes to maintain asymmetry. Haploinsufficiency of ATP11A, the phospholipid flippase that specially transports phosphatidylserine (PS) and phosphatidylethanolamine (PE), could leave cells with PS/PE at the extracellular side vulnerable to phagocytic degradation. Given that surface PS can be pharmaceutically targeted, hearing loss due to ATP11A could potentially be treated. It is also likely that ATP11A is the gene underlying DFNA33.

A common variant in CLDN14 causes precipitous, prelingual sensorineural hearing loss in multiple families due to founder effect

Genetic isolates provide unprecedented opportunities to identify pathogenic mutations and explore the full natural history of clinically heterogeneous phenotypes such as hearing loss. We noticed a unique audioprofile, characterized by prelingual and rapid deterioration of hearing thresholds at frequencies >0.5 kHz in several adults from unrelated families from the island population of Newfoundland. Targeted serial Sanger sequencing of probands for deafness alleles (n = 23) that we previously identified in this founder population was negative. Whole exome sequencing in four members of the largest family (R2010) identified a CLDN14 (DFNB29) variant [c.488C>T; p. (Ala163Val)], likely pathogenic, sensorineural hearing loss, autosomal recessive. Although not associated with deafness or disease, CLDN14 p.(Ala163Val) has been previously reported as a variant of uncertain significance (VUS). Targeted sequencing of 169 deafness probands identified one homozygote and one heterozygous carrier. Genealogical studies, cascade sequencing and haplotype analysis across four unrelated families showed all subjects with the unique audioprofile (n = 12) were also homozygous for p.(Ala163Val) and shared a 1.4 Mb DFNB29-associated haplotype on chromosome 21. Most significantly, sequencing 175 population controls revealed 1% of the population are heterozygous for CLDN14 p.(Ala163Val), consistent with a major founder effect in Newfoundland. The youngest CLDN14 [c.488C>T; p.(Ala163Val)] homozygote passed newborn screening and had normal hearing thresholds up to 3 years of age, which then deteriorated to a precipitous loss >1 kHz during the first decade. Our study suggests that genetic testing may be necessary to identify at-risk children in time to prevent speech, language and developmental delay.

X-linked hearing loss: two gene mutation examples provide generalizable implications for clinical care

PURPOSE

To describe the inheritance patterns and auditory phenotype features of 3 Canadian families with mutations in 2 X-linked "deafness" genes (DFNX).

METHOD

Audiological, medical, and family histories were collected and family members interviewed to compare hearing thresholds and case histories between cases with mutations in SMPX versus POU3F4.

RESULTS

The family pedigrees reveal characteristic X-linked inheritance patterns. Phenotypic features associated with the SMPX (DFNX4) mutation include early onset in males with rapid progression from mild and flat to sloping sensorineural loss, with highly variable onset and hearing loss severity in females. In contrast, phenotypic features associated with the POU3F4 (DFNX2) mutation are characterized by an early onset, mixed hearing loss with fluctuation in males, and a normal hearing phenotype reported for females.

CONCLUSIONS

The study shows how this unique inheritance pattern and both gender and mutation-specific phenotype variations can alert audiologists to the presence of X-linked genetic etiologies in their clinical practice. By incorporating this knowledge into clinical decision making, audiologists can facilitate the early identification of X-linked hearing loss and contribute to the effective team management of affected families.

Identification of a novel in-frame deletion in KCNQ4 (DFNA2A) and evidence of multiple phenocopies of unknown origin in a family with ADSNHL

Autosomal dominant sensorineural hearing loss (ADSNHL) is extremely genetically heterogeneous, making it difficult to molecularly diagnose. We identified a multiplex (n=28 affected) family from the genetic isolate of Newfoundland, Canada with variable SNHL and used a targeted sequencing approach based on population-specific alleles in WFS1, TMPRSS3 and PCDH15; recurrent mutations in GJB2 and GJB6; and frequently mutated exons of KCNQ4, COCH and TECTA. We identified a novel, in-frame deletion (c.806_808delCCT: p.S269del) in the voltage-gated potassium channel KCNQ4 (DFNA2), which in silico modeling predicts to disrupt multimerization of KCNQ4 subunits. Surprisingly, 10/23 deaf relatives are non-carriers of p.S269del. Further molecular characterization of the DFNA2 locus in deletion carriers ruled out the possibility of a pathogenic mutation other than p.S269del at the DFNA2A/B locus and linkage analysis showed significant linkage to DFNA2 (maximum LOD=3.3). Further support of genetic heterogeneity in family 2071 was revealed by comparisons of audio profiles between p.S269del carriers and non-carriers suggesting additional and as yet unknown etiologies. We discuss the serious implications that genetic heterogeneity, in this case observed within a single family, has on molecular diagnostics and genetic counseling.

N-Acetyl l-cysteine does not protect against premature age-related hearing loss in C57BL/6J mice: A pilot study

A compound capable of preventing age-related hearing loss would be very useful in an aging population. N-acetyl-L-cysteine (L-NAC) has been shown to be protective against noise exposure, a condition that leads to increased oxidative stress. Not withstanding environmental factors, there is evidence that age-related hearing loss (AHL) in the mouse is linked to more than one genetic loci and, by extension, in humans. Our hypothesis is that AHL defect results in increased sensitivity to oxidative stress and L-NAC would be able to protect the hearing of a mouse model of pre-mature AHL, the C57BL/6J (B6) mouse strain. L-NAC was added to the regular water bottle of B6 mice (experimental group) and available ad lib. The other group received normal tap water. Hearing was tested monthly by the ability to generate the auditory brainstem response (ABR). After the final ABR test, mice were sacrificed by an overdose of Avertin, ears were harvested and hair cell loss was quantified. There was no difference in ABR thresholds or in histopathology between the control group and the group receiving L-NAC in their drinking water. In contrast to the protective effects of L-NAC against noise-induced hearing loss, the lack of protective effect in this study may be due to (i) the dosage level; (ii) the duration of treatment; (iii) the biochemical mechanisms underlying age-induced hearing loss; or (iv) how the mouse metabolizes L-NAC.

Hearing screening outcomes in infants of pregestational diabetic mothers

PURPOSE

Hearing screening results for newborns of diabetic mothers were compared with those of nondiabetic controls.

METHOD

This study was a retrospective chart review of mothers with pregestational diabetes mellitus and their neonates (n=73) who received newborn hearing screening between January 1, 2000, and May 1, 2002. A group of nondiabetic mothers and their infants (n=73), with birth dates that matched the diabetic group, served as controls. A 2-tiered hearing screening protocol, employing distortion product otoacoustic emission (DPOAE) and automated auditory brainstem response (A-ABR) screening techniques, was used.

RESULTS

The DPOAE screening failure rate was 5.5% (4/73) for babies in the nondiabetic control group and 11.0% (8/73) for infants of diabetic mothers; this difference was not statistically significant. The A-ABR failure rate was 9.1% (1/11) for the diabetic group compared with 0% (0/4) for the controls, but the A-ABR was measured for only a small number of participants in each group. The frequency of premature birth and abnormal birth weight was significantly greater for the infants of diabetic mothers compared with controls.

CONCLUSIONS

Given the greater frequency of prematurity and abnormal birth weight in the population of neonates born to diabetics, additional research using A-ABR is recommended.

Projections from the medial geniculate body to primary auditory cortex in neonatally deafened cats

In the present study, anatomical projections from the medial geniculate body (MGB) to primary auditory cortex (AI) were investigated in normal adult cats and in animals that were neonatally deafened with the ototoxic drug amikacin. Cochleotopic/tonotopic maps in AI (based on neural response characteristic frequency) were obtained with microelectrode recording techniques, and single or multiple injections of retrograde tracers (horseradish peroxidase and fluorescent dyes) were introduced into AI. The AI maps of the amikacin-treated cats had an abnormal cochleotopic organization, such that deprived cortical areas exhibited an expanded representation of intact regions of the damaged cochlea. However, retrograde tracer injections into different regions of AI produced a normal pattern of labeling in the ventral division of the medial geniculate body (MGBv). In both experimental and control animals, the main mass of labeled thalamic cells was found in the MGBv. Different isofrequency contours in AI receive input from different portions of the MGBv. Thus, cell arrays labeled by anterior AI injections were situated medially in MGBv, and injections into posterior AI labeled MGBv more laterally. Furthermore, the deafened cats did not develop a more divergent thalamocortical projection compared with normal control animals, indicating that an abnormal spread of the thalamocortical afferents across the frequency domain in AI (anterior-posterior axis) is not responsible for the altered cochleotopic map in these neonatally deafened animals. The relatively normal thalamocortical projection pattern suggests that, after neonatal cochlear lesions, the major reorganization of cochleotopic maps occurs at subthalamic levels.

Electrocochleography and gentamicin therapy for Ménière's disease: a preliminary report

OBJECTIVE

It is widely held that an enlarged summating potential (SP) relative to the eighth nerve action potential (AP) is a reflection of endolymphatic hydrops. Aminoglycosides are an accepted treatment for incapacitating Ménière's disease and are known to affect both sensory and secretory cells of the inner ear. The intent of this study was to determine whether this effect on secretory cells could be objectively confirmed by virtue of changes in the electrocochleogram (ECoG) of patients receiving gentamicin therapy for Ménière's disease.

STUDY DESIGN

This was a prospective longitudinal study of repeated ECoG measures in three groups of subjects. Ménière's patients undergoing gentamicin treatment were compared with two control groups: individuals with stable Ménière's disease and normal-hearing control subjects.

SETTING

The study was conducted at a tertiary referral center.

PATIENTS

The sample included 21 normal-hearing subjects, 15 patients with stable unilateral Ménière's disease, and 12 with disabling unilateral Ménière's disease.

INTERVENTIONS

For patients with disabling Ménière's disease, gentamicin was administered transtympanically. Audiograms, impedance tests, and ECoG were performed twice for all subjects.

MAIN OUTCOME MEASURES

The SP and AP amplitudes, AP latency, and SP/AP ratio of the EcoG were measured.

RESULTS

A statistically significant reduction in the SP/AP ratio was observed after gentamicin administration (analysis of variance interaction effect: F2 = 5.64; p = 0.0065).

CONCLUSIONS

The significant reduction in the SP/AP ratio in the gentamicin-treated Ménière's group supports the hypothesis that gentamicin improves the electrophysiologic function of the cochlea, possibly by reducing the severity of the associated endolymphatic hydrops.

Auditory brainstem response. A comparison of different interpretation strategies for detection of cerebellopontine angle tumors

In this retrospective study (111 tumor; 1370 non-tumor patients), the effectiveness of the auditory brainstem response for identifying cerebellopontine angle tumors was studied using different criteria to interpret the test. Individual ABR features were examined. The I-V was best (sensitivity = 82%; specificity = 97%) but present for only 44% of the population; I-III (sensitivity = 50%; specificity = 96%) and III-V (sensitivity = 30%; specificity = 97%) were worst. Ninety-three percent of patients had V and ILDV, with good results (sensitivity = 74% and 81% respectively; specificity = 93% each). Three interpretation strategies were compared: (1) included the latencies of V, ILDV, I-V, III-V and I-III and ILDI-V, (2) excluded III-V and I-III, (3) used I-V and ILDI-V when available; V and ILDV otherwise. When corrected for hearing loss, strategy 3 provided significantly better specificity (91%) than strategy 1 (87%), with no significant difference in sensitivity (92% and 93%, respectively).

Effects of chronic cochlear damage on threshold and frequency tuning of neurons in AI auditory cortex

We describe the effects of long-term cochlear lesions on the frequency response properties of AI cortical neurons in the cat. Young animals were treated with amikacin to produce bilateral, basal to mid-turn cochlear lesions. After 12-24 months the response properties of single neurons or small unit clusters in primary auditory cortex were recorded in anesthetized animals. Responses to stimulus frequency and intensity were mapped in detail and frequency threshold curves (FTCs) and Q10dB values were derived. Subsequent to recording experiments, scanning electron microscopy of the sensory epithelium was used to characterize the degree and extent of the cochlear damage. In normal control animals, Q10dB values were, on average, lower than those derived by others from cochlear nerve fibre recordings in the same species. In amikacin-treated animals, deterioration was evident in the threshold and tuning properties of cortical neurons, particularly in those cells whose input originated in damaged cochlear regions. Often, neurons associated with 'normal' cochlear areas (as assessed by scanning microscopy) also had poor frequency tuning compared with controls. As an animal model of sensorineural hearing loss, we consider the cat with long-term cochlear lesions to be more appropriate than animals with acute or short-term pathology. We also suggest that in making physiological-psychophysical correlations, neural responses from the central auditory system (e.g. cortex) should perhaps be given more consideration than data derived at the cochlear level.

Hearing preservation in acoustic neuroma surgery: value of monitoring cochlear nerve action potentials

This study reviews the hearing results in 80 consecutive patients who underwent complete removal of histologically proven acoustic neuromas by use of the suboccipital approach. Of these, 56 patients had successful monitoring of cochlear compound action potentials; 20 were not monitored because their surgery predated monitoring; and 4 had unsuccessful monitoring. A significant difference was found in hearing preservation rates between the group in whom compound action potential monitoring was performed and those in whom monitoring was either unavailable or failed (p = 0.02). Overall, 38% (30 of 80) had preserved hearing. There were 51 patients in whom the click threshold for the cochlear compound action potential was measured during surgery. Twenty-one patients had a threshold shift of 20 dB or less, 15 (71%) of these retained serviceable hearing (speech reception threshold < or = 50 dB; speech discrimination score > or = 60%). Of 12 patients in whom the threshold shift was 30 to 60 dB, none had serviceable hearing after surgery. The click threshold shift was predictive of a significant postoperative hearing change (p < 0.001).

Neonatal cochlear hearing loss results in developmental abnormalities of the central auditory pathways

We have used animal models of long term neonatal cochlear hearing loss to study developmental plasticity of the central auditory pathways. Newborn chinchilla pups and feline kittens were treated with the ototoxic drug amikacin, so as to induce basal lesions in the cochlea. At maturity these animals were used in single unit electrophysiological mapping studies, in which the cochleotopic organization of primary auditory cortex (of the cat) and the inferior colliculus of the midbrain (in the chinchilla) were mapped. We have observed, both in the midbrain and auditory cortex, massive reorganization of frequency representation. Most striking were the presence of large monotonic regions (i.e. large areas in which all neurons have similar tuning properties). Cochlear lesions which involve inner hair cells clearly modify the normal development of cochleotopic representation in the midbrain and cortical regions. We suggest that similar abnormal patterns of frequency representation will exist in human subjects with long term neonatal hearing loss.

The effects of long-term cochlear hearing loss on the functional organization of central auditory pathways

We have developed an animal model of neonatal high-frequency cochlear hearing loss to investigate the long-term effects on the central auditory pathways. Specifically, we have induced basal cochlear lesions in newborn kittens using the ototoxic aminoglycoside, amikacin. We have monitored the consequent auditory threshold elevations using auditory brainstem evoked responses (ABR) to tone pip stimuli. In the mature animal we have mapped tonotopic (cochleotopic) representation in primary auditory cortex (AI) using standard micro-electrode recording techniques, and we show that this map becomes massively re-organized. In particular, one frequency area that corresponds to the high frequency cut-off slope of the subject's audiogram appears to become greatly expanded, in some cases to take up 75% of AI surface. In general, the development of normal cochleotopic or tonotopic representation in cortex appears to depend upon the integrity of ascending sensory input from the cochlea particularly during early stages of development. With the clinician in mind, we discuss our findings in relation to practical issues.

The effect of hearing loss on ABR interpretation: use of a correction factor

Patients suspected of retrocochlear disorders often have abnormal ABRs in the presence of high-frequency hearing loss, making clinical decisions difficult. In a retrospective study of the ABR test results of 1539 patients, the false-positive and false-negative rates for ABR are presented as a function of hearing loss at 4000 Hz, both before and after using Selters and Brackmann's correction factor for hearing loss. For patients with more than 50 db HL at 4000 Hz the false-positive and false-negative rates, uncorrected for hearing loss, were 25.0% and 2.9% respectively, and when the correction factor was used were 12.5% and 5.8%. When hearing loss at 4000 Hz was over 90 dB the ABR was abnormal in 75% of nontumor patients. Conclusions are that a correction factor for hearing loss is helpful with reservations, and that ABR is not a useful test when 4000 Hz hearing loss is greater than 90 dB HL and 2000 Hz is greater than 75 dB HL.

Correlation of cochlear pathology with auditory brainstem and cortical responses in cats with high frequency hearing loss

Newborn kittens were treated with the aminoglycoside amikacin to produce a bilateral high frequency cochlear hearing loss. The degree and stability of hearing loss were confirmed by recording auditory brainstem evoked potentials (ABR audiograms). After maturation, cochleotopic frequency representation within primary auditory cortex (AI) was mapped using standard microelectrode recording techniques. The cochlear sensory epithelium was assessed with SEM and the pattern of damage compared with the ABR audiograms and cortical frequency maps. Amikacin treatment resulted in various patterns of haircell damage towards the base of the cochlea. A relatively abrupt transition between damaged and undamaged haircell regions resulted in an ABR audiogram with normal threshold to low frequencies and a high frequency elevation with a steep cut-off slope. In the cortical map, low frequency representation was normal, but anterior areas contained only neurons tuned to a common frequency which corresponded to the frequency-place position of the boundary of the haircell lesion and to the cut-off frequency of the audiogram. A large transitional zone of the cochlear lesion correlated with a gradual cut-off slope to the audiogram and again a remapping of the anterior and normally high frequency area to a common lower frequency. Haircell loss or damage (i.e. disarray of stereocilia) in lower frequency regions of the cochlea correlated with a significant reorganization of the lower frequency bands in the cortical map. We conclude from this study that the pattern of cochleotopic organization of the cortex is dependent on the pattern of activity in the ascending sensory pathway during early stages of development.

Cochlear nerve action potentials during cerebellopontine angle surgery: relationship of latency, amplitude, and threshold measurements to hearing

The cochlear nerve action potential (AP) was monitored during two types of hearing preservation surgery: (1) removal of small cerebellopontine angle tumors and (2) retrolabyrinthine vestibular nerve section. The purpose of this investigation was to study the relationship between changes in intraoperative AP latency, amplitude, and threshold, and changes in audiometric hearing subsequent to surgery. The presence or absence of a cochlear nerve AP toward the end of surgery accurately predicted the presence or absence of postoperative hearing (93%). Regression analyses were performed to explore the relationship between audiometric pre- and postoperative thresholds and intraoperative AP threshold changes. Statistically significant relationships were found for (1) pre-operative audiometric thresholds and initial AP click thresholds (p = 0.0068); (2) final AP click thresholds and postoperative audiometric thresholds (p = 0.0003); (3) AP click (p = 0.0001) and 1 kHz (p = 0.0006) threshold shifts and pre- to postoperative audiometric threshold shifts. No relationship was found between either AP latency or amplitude values and postoperative hearing. Intraoperative threshold measurements can be used as an indicator of hearing change. If amplitude or latency indices are also monitored it may be better to use stimulus levels close to the evoked potential threshold.

Location and dynamics of a membrane-bound fluorescent hapten. A spectroscopic study

In the preceding paper (Petrossian, A. and Owicki, J.C. (1984), Biochim. Biophys. Acta 776, 217-227), we describe the binding of a monoclonal anti-fluorescein antibody to a membrane bound fluorescein-lipid hapten. Those results suggest that some of the hapten fluorescein moiety is extended away from the membrane surface and is available for antibody binding, while some of the hapten is sequestered and not immediately available for antibody binding. In this paper, we carry out a spectroscopic study of the membrane-bound hapten and show that there is more than one physically distinct fluorophore environment, with the sequestered hapten associated with the phospholipid headgroup region. The amount of membrane-associated fluorophore depends upon the membrane lipid composition: most of the fluorophore is associated when the lipid is unsaturated or branched-chain phosphatidylcholines (PC), whereas the hapten is largely extended for PC/cholesterol mixtures. The effect of cholesterol on the availability of membrane-bound hapten to antibody binding is not unique to this system. The conversion between sequestered and extended hapten is slow (minutes).