A Novel TECTA Mutation in a Dutch DFNA8/12 Family Confirms Genotype–Phenotype Correlation

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

Complex level alterations of the 2<Emphasis Type="Italic">f</Emphasis><Subscript>1</Subscript>−<Emphasis Type="Italic">f</Emphasis><Subscript>2</Subscript> distortion product due to hypoxia in the guinea pig

It is controversially discussed inasmuch acute hearing disorders might originate from impaired cochlear circulation. Hypoxia-specific alterations of inner ear parameters measurable in patients with acute sensorineural hearing loss would therefore be of great interest. Aim of this study was to characterize hypoxia-related alterations of the 2f ₁−f ₂ distortion product. Nine guinea pigs were anaesthetized by i.m. administration of Midazolam, Medetomidin and Fentanyl. For introduction of hypoxia, the spontaneously breathing animals were offered a gas mixture of N₂O and O₂ containing either 21 or 12–13% O₂. Distortion product otoacoustic emissions (DPOAEs) were continuously monitored at f ₂ = 16 kHz; f ₂/f ₁ = 1, 2; DP-definition = 2f ₁−f ₂; L ₁ = 65 dB and L ₂ = 55 dB, while inhaled oxygen was switched from 21 to 12–13% and back. Oxygen saturation (SaO₂) was continuously monitored. Data from an hypoxic interval were only used for further data processing if DPOAE levels were stable before and after hypoxia. Six hypoxic intervals in five animals fulfilled the stability criterion. During the hypoxic interval with the highest measured SaO₂ (75%), no alterations of DPOAE levels were observed. During the remaining five hypoxic intervals, when SaO₂ ranged between 57 and 70%, DPOAE levels were on average lower with an increased standard deviation compared to mean pre-hypoxic levels. Mean decrease correlated with the decrease of SaO₂ (r = 0.90, P = 0.014). Alterations followed a characteristic time course—when hypoxia was started, DPOAE levels exhibited a short increase before they decreased and remarkably destabilized. After re-oxygenation DPOAE levels showed a pronounced level decrease, while SaO₂ already had recovered to pre-hypoxic values. After reaching a minimum, DPOAE levels slowly recovered to pre-hypoxic values. The decrease of DPOAE levels during hypoxia and the post-hypoxic level alterations have similarly been described by other authors before, while the distinct destabilization and transiently increased DPOAE levels have not been explicitly mentioned. A micromechanical mechanism that might explain a transient level increase and the post-hypoxic DPOAE level changes is discussed.     

Despite a lack of otoacoustic emission,word recognition is not seriously influenced in a TECTA DFNA8/12 family

Objectives

Similar to other zona pellucida mutations in the alpha-tectorin (TECTA) gene, the p.Y1870C alteration in DFNA8/12 causes prelingual, nonsyndromic, autosomal dominant hearing loss. Here we investigated the effect of p.Y1870C on reverse transduction by audiometric studies in the family.

Methods

Pure tone audiometry, brainstem evoked response audiometry, the Freiburger test for speech understanding and transient evoked and distortion product otoacoustic emissions were assessed in three available affected members bearing p.Y1870C.

Results

Pure tone audiometry showed U-shaped curves with moderate to severe degrees of hearing impairment confirmed by brainstem evoked response audiometry. Transient evoked and distortion product otoacoustic emissions were completely absent in all affected family members whereas word recognition scores were up to 95%.

Conclusions

Although the missense p.Y1870C TECTA mutation leads to complete failure of the cochlear amplifier in humans, very high speech perception scores can be achieved with appropriate therapy.     

High-Frequency Sensorineural Hearing Loss and Its Underlying Genetics (<Emphasis Type="Italic">Hfhl1</Emphasis> and <Emphasis Type="Italic">Hfhl2</Emphasis>) in NIH Swiss Mice

Studies using inbred strains of mice have been invaluable for identifying alleles that adversely affect hearing. However, the efficacy of those studies is limited by the phenotypes that these strains express and the alleles that they segregate. Here, by selectively breeding phenotypically and genetically heterogeneous NIH Swiss mice, we generated two lines—the all-frequency hearing loss (AFHL) line and the high-frequency hearing loss (HFHL) line—with differential hearing loss. The AFHL line exhibited characteristics typical of severe, early-onset, sensorineural hearing impairment. In contrast, the HFHL line expressed a novel early-onset, mildly progressive, and frequency-specific sensorineural hearing loss. By quantitative trait loci (QTLs) analyses in these two lines, we identified QTLs on chromosomes 7, 8, and 10 that significantly affected hearing function. The loci on chromosomes 7 and 8 (Hfhl1 and Hfhl2, respectively) are novel and appear to adversely affect only high frequencies (≥30 kHz). Mice homozygous for NIH Swiss alleles at either Hfhl1 or Hfhl2 have 32-kHz auditory-evoked brain stem response thresholds that are 8–14 dB SPL higher than the corresponding heterozygotes. DNA sequence analyses suggest that both the Cdh23 ^ahl and Gipc3 ^ahl5 variants contribute to the chromosome 10 QTL detected in the AFHL line. The frequency-specific hearing loss indicates that the Hfhl1 and Hfhl2 alleles may affect tonotopic development. In addition, dissecting the underlying complex genetics of high-frequency hearing loss may prove relevant in identifying less severe and common forms of hearing impairment in the human population.     

Tonsillectomy <Emphasis Type="Italic">à chaud</Emphasis> for quinsy: revisited

In a prospective study involving 16 patients over a 12 month period, we determined whether tonsillectomy à chaud is an acceptable alternative to interval tonsillectomy for patients with quinsy. Guidelines for the acute surgical management of quinsy (or peritonsillar abscess) were established following a departmental audit. Sixteen patients were admitted with a quinsy plus an indication for tonsillectomy; 12 were evaluated prospectively. Each was treated either by incision and drainage or needle aspiration, rehydration, analgesia and intravenous antibiotic therapy, followed by a tonsillectomy à chaud (immediate tonsillectomy) within 30 h of the acute admission. Despite initial drainage, a high incidence of pus was detected intra-operatively. A much larger group of patients had peritonsillitis rather than peritonsillar abscess. Of the 16 patients admitted with a quinsy and indication for tonsillectomy over a 12 month period, 12 consented to tonsillectomy à chaud. Aspiration was used to confirm the presence of a quinsy in seven patients (58%), and incision and drainage in the remaining five. There were no complications, and further hospitalisations were avoided thus reducing patient morbidity and costs. We propose that tonsillectomy à chaud remains a justifiable alternative to interval tonsillectomy for such patients when personnel and theatre facilities permit.     

Mucin in middle ear effusions inhibits attachment of <Emphasis Type="Italic">Haemophilus influenzae</Emphasis> to mucosal epithelial cells

Although otitis media with effusion is often preceded by an infection of the tympanic cavity, when cultured, many effusions show no culturable bacteria. Based on the hypothesis that the effusion might play a protective role in the course of infection, the influence of this fluid on adhesion of H. influenzae (Hi) type-b strain 770235 and nontypeable H. influenzae (NTHi) strains to buccal epithelial cells was investigated. Effusions were classified as mucoid, seromucoid and serous. Mucoid secretions inhibited adhesion to a significantly greater extent (62%) than did seromucous (52%) and serous effusions (47%) ( P<0.001). The glycoprotein and high-molecular-weight fractions showed similar levels of inhibition. Sialic acid concentration, and, to a lesser extent, protein concentration, correlated with the level of inhibition. Desialylated effusions lost their ability to block bacterial attachment. Thus, middle ear effusion fluid exhibits an inhibitory effect that is due to mucins, which determine viscosity and represent the sialylated high-molecular-weight glycoprotein fraction of the effusion.     

Progressive Hearing Loss and Increased Susceptibility to Noise-Induced Hearing Loss in Mice Carrying a <Emphasis Type="Italic">Cdh23</Emphasis> but not a <Emphasis Type="Italic">Myo7a</Emphasis> Mutation

Exposure to intense noise can damage the stereocilia of sensory hair cells in the inner ear. Since stereocilia play a vital role in the transduction of sound from a mechanical stimulus into an electrical one, this pathology is thought to contribute to noise-induced hearing loss. Mice homozygous for null mutations in either the myosin VIIa (Myo7a) or cadherin 23 (Cdh23) genes are deaf and have disorganized stereocilia bundles. We show that mice heterozygous for a presumed null allele of Cdh23 (Cdh23^v) have low- and high-frequency hearing loss at 5–6 weeks of age, the high-frequency component of which worsens with increasing age. We also show that noise-induced hearing loss in 11–12-week-old Cdh23^v heterozygotes is two times greater than for wild-type littermates. Interestingly, these effects are dependent upon the genetic background on which the Cdh23^v mutation is carried. Noise-induced hearing loss in 11–12-week-old mice heterozygous for a null allele of Myo7a (Myo7a^4626SB) is not significantly different from wild-type littermates. CDH23 is the first gene known to cause deafness in the human population to be linked with predisposition to noise-induced hearing loss.     

Dynamic Expression of <Emphasis Type="Italic">Lgr5</Emphasis>, a Wnt Target Gene,in the Developing and Mature Mouse Cochlea

The Wnt signaling pathway is a recurring theme in tissue development and homeostasis. Its specific roles during inner ear development are just emerging, but few studies have characterized Wnt target genes. Lgr5, a member of the G protein-coupled receptor family, is a Wnt target in the gastrointestinal and integumentary systems. Although its function is unknown, its deficiency leads to perinatal lethality due to gastrointestinal distension. In this study, we used a knock-in reporter mouse to examine the spatiotemporal expression of Lgr5 in the cochlear duct during embryonic and postnatal periods. In the embryonic day 15.5 (E15.5) cochlear duct, Lgr5-EGFP is expressed in the floor epithelium and overlapped with the prosensory markers Sox2, Jagged1, and p27(Kip1). Nascent hair cells and supporting cells in the apical turn of the E18.5 cochlear duct express Lgr5-EGFP, which becomes downregulated in hair cells and subsets of supporting cells in more mature stages. In situ hybridization experiments validated the reporter expression, which gradually decreases until the second postnatal week. Only the third row of Deiters’ cells expresses Lgr5-EGFP in the mature organ of Corti. Normal cochlear development was observed in Lgr5^EGFP/EGFP and Lgr5^EGFP/+ mice, which exhibited normal auditory thresholds. The expression pattern of Lgr5 contrasts with another Wnt target gene, Axin2, a feedback inhibitor of the Wnt pathway. Robust Axin2 expression was found in cells surrounding the embryonic cochlear duct and becomes restricted to tympanic border cells below the basilar membrane in the postnatal cochlea. Both Lgr5 and Axin2 act as Wnt targets in the cochlea because purified Wnt3a promoted and Wnt antagonist suppressed their expression. Their differential expression among cell populations highlights the dynamic but complex distribution of Wnt-activated cells in and around the embryonic and postnatal cochlea.     

Concurrent Development of the Head and Pinnae and the Acoustical Cues to Sound Location in a Precocious Species,the Chinchilla (<Emphasis Type="Italic">Chinchilla lanigera)</Emphasis>

Sounds are filtered in a spatial- and frequency-dependent manner by the head and pinna giving rise to the acoustical cues to sound source location. These spectral and temporal transformations are dependent on the physical dimensions of the head and pinna. Therefore, the magnitudes of binaural sound location cues—the interaural time (ITD) and level (ILD) differences—are hypothesized to systematically increase while the lower frequency limit of substantial ILD production is expected to decrease due to the increase in head and pinna size during development. The frequency ranges of the monaural spectral notch cues to source elevation are also expected to decrease. This hypothesis was tested here by measuring directional transfer functions (DTFs), the directional components of head-related transfer functions, and the linear dimensions of the head and pinnae for chinchillas from birth through adulthood. Dimensions of the head and pinna increased by factors of 1.8 and 2.42, respectively, reaching adult values by ~6 weeks. From the DTFs, the ITDs, ILDs, and spectral shape cues were computed. Maximum ITDs increased by a factor of 1.75, from ~160 μs at birth (P0-1, first postnatal day) to 280 μs in adults. ILDs depended on source location and frequency exhibiting a shift in the frequency range of substantial ILD (>10 dB) from higher to lower frequencies with increasing head and pinnae size. Similar trends were observed for the spectral notch frequencies which ranged from 14.7–33.4 kHz at P0-1 to 5.3–19.1 kHz in adults. The development of the spectral notch cues, the spatial- and frequency-dependent distributions of DTF amplitude gain, acoustic directionality, maximum gain, and the acoustic axis were systematically related to the dimensions of the head and pinnae. The dimension of the head and pinnae in the chinchilla as well as the acoustical properties associated with them are mature by ~6 weeks.     

Protection from Acoustic Trauma Is <Emphasis Type="Italic">Not</Emphasis> a Primary Function of the Medial Olivocochlear Efferent System

The medial olivocochlear (MOC) efferent system is an important component of an active mechanical outer hair cell system in mammals. An extensive neurophysiological literature demonstrates that the MOC system attenuates the response of the cochlea to sound by reducing the gain of the outer hair cell mechanical response to stimulation. Despite a growing understanding of MOC physiology, the biological role of the MOC system in mammalian audition remains uncertain. Some evidence suggests that the MOC system functions in a protective role by acting to reduce receptor damage during intense acoustic exposure. For the MOC system to have evolved as a protective mechanism, however, the inner ears of mammals must be exposed to potentially damaging sources of noise that can elicit MOC-mediated protective effects under natural conditions. In this review, we evaluate the possibility that the MOC system evolved to protect the inner ear from naturally occurring environmental noise. Our survey of nonanthropogenic noise levels shows that while sustained sources of broadband noise are found in nearly all natural acoustic environments, frequency-averaged ambient noise levels in these environments rarely exceed 70 dB SPL. Similarly, sources reporting ambient noise spectra in natural acoustic environments suggest that noise levels within narrow frequency bands are typically low in intensity (<40 dB SPL). Only in rare instances (e.g., during frog choruses) are ambient noise levels sustained at moderately high intensities (~70–90 dB SPL). By contrast, all experiments in which an MOC-mediated protective effect was demonstrated used much higher sound intensities to traumatize the cochlea (100–150 dB SPL). This substantial difference between natural ambient noise levels and the experimental conditions necessary to evoke MOC-mediated protection suggests that even the noisiest natural acoustic environments are not sufficiently intense to have selected for the evolution of the MOC system as a protective mechanism. Furthermore, although relatively intense noise environments do exist in nature, they are insufficiently distributed to account for the widespread distribution of the MOC system in mammals. The paucity of high-intensity noise and the near ubiquity of low-level noise in natural environments supports the hypothesis that the MOC system evolved as a mechanism for unmasking biologically significant acoustic stimuli by reducing the response of the cochlea to simultaneous low-level noise. This suggested role enjoys widespread experimental support.     

Age-Dependent Changes of Gap Detection in the Mongolian Gerbil (<Emphasis Type="Italic">Meriones unguiculatus</Emphasis>)

Gap detection using broadband noise was characterized in a group of young gerbils from the breeding colony of the University of Regensburg (RB gerbils), old RB gerbils, and old gerbils from the breeding colony of the University of South Carolina (SC gerbils). Data from old RB and old SC gerbils were not significantly different and were subsequently combined for a comparison with data from the group of young RB gerbils. Level dependence of gap-detection thresholds in young and old domesticated gerbils resembled the typical mammalian pattern of level dependence. Gap-detection thresholds of old gerbils were significantly elevated at 30 dB SL and 50 dB SPL as compared with young gerbils. Compared with young gerbils tested at 30 dB SL and 50 dB SPL, the distribution of gap-detection thresholds in old gerbils was broader with a spread to higher gap-detection thresholds. Some old animals retained excellent temporal resolution, while some showed impaired gap detection. The gap-detection data collected in young and old gerbils resemble previously published data from humans of different age and confirm that gerbils are a useful model to study age-dependent changes in temporal processing.     

The Deaf Mouse Mutant <Emphasis Type="Italic">Jeff</Emphasis> (<Emphasis Type="Italic">Jf</Emphasis>) is a Single Gene Model of Otitis Media

Otitis media is the most common cause of hearing impairment in children and is primarily characterized by inflammation of the middle ear mucosa. Yet nothing is known of the underlying genetic pathways predisposing to otitis media in the human population. Increasingly, large-scale mouse mutagenesis programs have undertaken systematic and genome-wide efforts to recover large numbers of novel mutations affecting a diverse array of phenotypic areas involved with genetic disease including deafness. As part of the UK mutagenesis program, we have identified a novel deaf mouse mutant, Jeff (Jf). Jeff maps to the distal region of mouse chromosome 17 and presents with fluid and pus in the middle ear cavity. Jeff mutants are 21% smaller than wild-type littermates, have a mild craniofacial abnormality, and have elevated hearing thresholds. Middle ear epithelia of Jeff mice show evidence of a chronic proliferative otitis media. The Jeff mutant should prove valuable in elucidating the underlying genetic pathways predisposing to otitis media. REH and AE contributed equally to this study. SDMB AND KPS are joint senior authors.     

Treatment of tripod fracture of zygomatic bone by <Emphasis Type="Italic">N</Emphasis>-2-butyl cyanoacrylate glue fixation,and its effects on the tissues

The standard treatment of zygomatic bone fractures is fixation by microplates or miniplates and screws today. It is very difficult to place plates and screws into thin bones or small bone fragments especially in the facial bones and bones adjacent to important structures. Cyanoacrylate is used as a hemostatic agent, an embolic agent, in retinal tears, in corneal ulcers, in fixation of mandibular osteotomies and in craniofacial surgery. N-2-Butyl cyanoacrylate is a form of cyanoacrylate which is bioabsorbable and biocompatible. It is easily applied to the tissues. We aimed to determine the effect of N-2-butyl cyanoacrylate in the fixation of displaced zygomatic bone fractures. We examined the histotoxicity and the effects on healing and foreign body reaction of N-2-butyl cyanoacrylate. Eight New Zealand white rabbits underwent zygomatic osteotomies bilaterally. The fractures on left sides of the rabbits were determined as study site and right sides as control site. Knight and North classification of zygomatic bone fractures were used and group 4 fractures were made bilaterally. Open reduction of fractures was performed bilaterally and N-2-butyl cyanoacrylate was applied only on left sides. No fixation was made on right sides representing the control group. Postoperatively in the first, second, third and fourth weeks, two rabbits were sacrificed and the fracture sites were examined macroscopically and histopathologically. In the glued study group, fixation was obtained in all cases whereas in the control group, all the fractures were seen to be displaced. Tissue reaction was similar in the study and the control groups.     

The efficacy of <Emphasis Type="Italic">N</Emphasis>-2-butyl cyanoacrylate in the fixation of nasal septum to the anterior nasal spine in rabbits: experimental study

In nasal septal surgery, fixing the caudal portion of the nasal septum to the anterior nasal spine is difficult with the present techniques. N-2-butyl cyanoacrylate is a form of cyanoacrylate which is bioabsorbable and biocompatible. The feasibility and efficacy of the compound, which is easy to apply to the tissues, for the above purpose is investigated in this experimental study. Fourteen New Zealand rabbits were included in the study. The nasal septum was exposed with the open approach (transcolumellar). In the study group (n = 10), the septum was detached from the nasal floor and attached to a point 3 mm lateral to the nasal spine on the right side, using 2-butyl cyanoacrylate. In control group (n = 4) it was deviated 3 mm to the right side and left for spontaneous healing without using any fixation method. Beginning on the third postoperative week, one animal was sacrificed under general anesthesia, every week in the study group and every third week in the control group, and the septum was analysed. Foreign body reaction, histotoxicity, and the structure of the regenerative tissue in the junction of bone and cartilage were analysed with histopathology. The success of stabilization in the study group, where the septum was attached with N-2-butyl cyanoacrylate, was significantly superior to the control group where no fixation method was used (P < 0.05). Histopathologically, there were no differences between the two groups with respect to foreign body reaction, histotoxicity, and the tissue that formed between the bone and cartilage (P > 0.05). This study demonstrated that N-2-Butyl cyanoacrylate was successful in the fixation of the caudal edge of the nasal septum to the anterior nasal spine. No serious infections, foreign body reaction, necrosis or histotoxicity were observed.     

Neomycin-Induced Hair Cell Death and Rapid Regeneration in the Lateral Line of Zebrafish (<Emphasis Type="Italic">Danio rerio</Emphasis>)

Mechanoreceptive hair cells are extremely sensitive to aminoglycoside antibiotics, including neomycin. Hair cell survival was assessed in larval wild-type zebrafish lateral line neuromasts 4 h after initial exposure to a range of neomycin concentrations for 1 h. Each of the lateral line neuromasts was scored in live fish for the presence or absence of hair cells using the fluorescent vital dye DASPEI to selectively label hair cells. All neuromasts were devoid of DASPEI-labeled hair cells 4 h after 500 µM neomycin exposure. Vital DASPEI staining was proportional to the number of hair cells per neuromast identified in fixed larvae using immunocytochemistry for acetylated tubulin and phalloidin labeling. The time course of hair cell regeneration in the lateral line neuromasts was also analyzed following neomycin-induced damage. Regenerated hair cells were first observed using live DASPEI staining 12 and 24 h following neomycin treatment. The potential role of proliferation in regenerating hair cells was analyzed. A 1 h pulse-fix protocol using bromodeoxyuridine (BrdU) incorporation was used to identify S-phase cells in neuromasts. BrdU incorporation in neomycin-damaged neuromasts did not differ from control neuromasts 4 h after drug exposure but was dramatically upregulated after 12 h. The proliferative cells identified during a 1 h period at 12 h after neomycin treatment were able to give rise to new hair cells by 24–48 h after drug treatment. The results presented here provide a standardized preparation for studying and identifying genes that influence vertebrate hair cell death, survival, and regeneration following ototoxic insults.