Tetsuya Tono

Prevalence of mitochondrial gene mutations among hearing impaired patients

The frequency of three mitochondrial point mutations, 1555A→G, 3243A→G, and 7445A→G, known to be associated with hearing impairment, was examined using restriction fragment length polymorphism (RFLP) analysis in two Japanese groups: (1) 319 unrelated SNHL outpatients (including 21 with aminoglycoside antibiotic injection history), and (2) 140 cochlear implantation patients (including 22 with aminoglycoside induced hearing loss). Approximately 3% of the outpatients and 10% of the cochlear implantation patients had the 1555A→G mutation. The frequency was higher in the patients with a history of aminoglycoside injection (outpatient group 33%, cochlear implantation group 59%). One outpatient (0.314%) had the 3243A→G mutation, but no outpatients had the 7445A→G mutation and neither were found in the cochlear implantation group. The significance of the 1555A→G mutation, the most prevalent mitochondrial mutation found in this study of a hearing impaired population in Japan, among subjects with specific backgrounds, such as aminoglycoside induced hearing loss, is evident.

Effect of single-drug treatment on idiopathic sudden sensorineural hearing loss

OBJECTIVES In order to evaluate the effect of a medical administration for the sudden deafness patients, single-drug treatment for idiopathic sudden sensorineural hearing loss (ISSHL) was assessed at multi-centers participating in the Acute Severe Hearing Loss Study Group sponsored by the Ministry of Health, Labor and Welfare of Japan. METHODS The subjects consisted of ISSHL patients who were (1) 20 years of age or older, (2) diagnosed within 2 weeks after the onset of hearing loss, (3) showing a mean hearing level of 40-90 dB at five frequencies from 250 to 4000 Hz, (4) previously untreated, and (5) with normal for age in hearing of the opposite ear. The drugs used in this study were ATP, alprostadil, hydrocortisone and amidotrizoate, which were administered intravenously, and beraprost sodium and betamethasone, which were given orally. Two drugs were assigned to each center, one of which was selected according to the code hidden in envelopes and administered for 1 week. The treatment after the single-drug administration was conducted at the discretion of each center. The hearing gain and recovery rate at 1 week after the initiation of single-drug treatment and at 1 month or over when the hearing level was fixed, were evaluated based on the criteria for hearing recovery prepared by the Acute Severe Hearing Loss Study Group. RESULTS There was no statistically significant difference in the recovery rate among drugs either at 1 week after the initiation of single-drug treatment or at the time of fixed hearing level. At the time when the hearing level was fixed, a statistically significant difference in the complete recovery rate was detected only between amidotrizoate and beraprost sodium. CONCLUSION From these results, we could not find any specific drugs recommended for ISSNHL. In evaluating the effect of the drugs, however, several problems in the clinical trial for ISSHL should be considered.

Correlation between MRI Findings and Second-Look Operation in Cholesteatoma Surgery

Two-staged intact canal wall tympanoplasty is a common operation for treatment of middle ear cholesteatoma. MRI provides better tissue differentiation of the middle ear and/or mastoid, which often become occupied with soft density tissue after the first operation. If MRI was able to detect the presence of a recurrent or residual cholesteatoma with sufficient sensitivity and specificity, this may facilitate a decrease in the number of second-look procedures. This study compared MRI findings to surgical findings at second-look surgery and calculated the correlation rates between the two sets of findings. Thirty ears having undergone intact canal wall tympanoplasty for cholesteatoma at the initial operation were examined by MRI prior to the second look. Otoscopic findings of the tympanic membrane were nonsuspect in all cases. The true positive rate was 11/30 (37%) and the true negative rate was 10/30 (33%), leading to a radiosurgical correlation of 70%, whereas the false positive rate was 6/30 (20%) and the false negative rate was 3/30 (10%). This indicates that 30% of the MRI findings were incorrect. Therefore, at the present time, MRI does not appear as a likely replacement for second-look surgery in cases of intact canal wall tympanoplasty.

Cochlear implantation in an intralabyrinthine acoustic neuroma patient after resection of an intracanalicular tumour

This case study describes a therapeutic strategy using a cochlear implant for a bilateral acoustic neuroma deafened patient. The cochlear nerve had previously been sacrificed on one side during tumour removal, but on the remaining side a functioning cochlear nerve was assessed by electric promontory stimulation in spite of a neuroma extending into the vestibular labyrinth. The patient was successfully stimulated with a Nucleus 22-channel implant after removal of the intracanalicular portion of the neuroma via a middle fossa approach.

Different Clinical Characteristics of Aminoglycoside-Induced Profound Deafness with and without the 1555 A→G Mitochondrial Mutation

Recent genetic studies have shown that hereditary susceptibility to aminoglycoside antibiotics is caused by the 1555 A→G mitochondrial mutation. We found the 1555 mutation in 4 out of 68 postlingual deaf patients who were candidates for cochlear implantation. All 4 patients developed bilateral profound hearing loss following administration of aminoglycosides. The pedigree of the family shows exclusively maternal transmission of hearing impairment in each case. On comparison with neuro-otological findings from aminoglycoside-induced deaf patients without the 1555 mutation, four distinct characteristics were noted: (1) a progressive nature of hearing loss; (2) better residual pure-tone thresholds; (3) lower thresholds for electrical promontory stimulation, and (4) well-preserved vestibular function. Although other factors such as differing dosages and/or administration routes may also be involved, profound hearing loss associated with the 1555 mutation may be due to a different pathogenic mechanism, i.e., strial dysfunction rather than a direct insult to the hair cells.

Massively Parallel DNA Sequencing Facilitates Diagnosis of Patients with Usher Syndrome Type 1

Usher syndrome is an autosomal recessive disorder manifesting hearing loss, retinitis pigmentosa and vestibular dysfunction, and having three clinical subtypes. Usher syndrome type 1 is the most severe subtype due to its profound hearing loss, lack of vestibular responses, and retinitis pigmentosa that appears in prepuberty. Six of the corresponding genes have been identified, making early diagnosis through DNA testing possible, with many immediate and several long-term advantages for patients and their families. However, the conventional genetic techniques, such as direct sequence analysis, are both time-consuming and expensive. Targeted exon sequencing of selected genes using the massively parallel DNA sequencing technology will potentially enable us to systematically tackle previously intractable monogenic disorders and improve molecular diagnosis. Using this technique combined with direct sequence analysis, we screened 17 unrelated Usher syndrome type 1 patients and detected probable pathogenic variants in the 16 of them (94.1%) who carried at least one mutation. Seven patients had the MYO7A mutation (41.2%), which is the most common type in Japanese. Most of the mutations were detected by only the massively parallel DNA sequencing. We report here four patients, who had probable pathogenic mutations in two different Usher syndrome type 1 genes, and one case of MYO7A/PCDH15 digenic inheritance. This is the first report of Usher syndrome mutation analysis using massively parallel DNA sequencing and the frequency of Usher syndrome type 1 genes in Japanese. Mutation screening using this technique has the power to quickly identify mutations of many causative genes while maintaining cost-benefit performance. In addition, the simultaneous mutation analysis of large numbers of genes is useful for detecting mutations in different genes that are possibly disease modifiers or of digenic inheritance.

Hearing preservation and clinical outcome of 32 consecutive electric acoustic stimulation (EAS) surgeries

Abstract Conclusions: Our results indicated that electric acoustic stimulation (EAS) is beneficial for Japanese-speaking patients, including those with less residual hearing at lower frequencies. Comparable outcomes for the patients with less residual hearing indicated that current audiological criteria for EAS could be expanded. Successful hearing preservation results, together with the progressive nature of loss of residual hearing in these patients, mean that minimally invasive full insertion of medium/long electrodes in cochlear implantation (CI) surgery is a desirable solution. The minimally invasive concepts that have been obtained through EAS surgery are, in fact, crucial for all CI patients. Objectives: This study was conducted to evaluate hearing preservation results and speech discrimination outcomes of hearing preservation surgeries using medium/long electrodes. Methods: A total of 32 consecutive minimally invasive hearing preservation CIs (using a round window approach with deep insertion of a flexible electrode) were performed in 30 Japanese patients (two were bilateral cases), including patients with less residual hearing. Hearing preservation rates as well as speech discrimination/perception scores were investigated on a multicenter basis. Results: Postoperative evaluation after full insertion of the flexible electrodes (24 mm, 31.5 mm) showed that residual hearing was well preserved in all 32 ears. In all patients, speech discrimination and perception scores were improved postoperatively.

A role of glutamate in drug-induced ototoxicity: in vivo microdialysis study combined with on-line enzyme fluorometric detection of glutamate in the guinea pig cochlea.

The time course of the changes in perilymphatic glutamate was determined during the application of kanamycin and ethacrynic acid, which are known to damage the hair cells in the inner ear. For the continuous recording of glutamate, the microdialysis technique combined with an enzyme-linked fluorometric assay was used. In guinea pigs receiving a loading dose of 800 mg/kg of kanamycin subcutaneously followed 3 h later by an i.v. injection of 40 mg/kg of ethacrynic acid, a marked glutamate release was clearly found about 2 h after the injection of ethacrynic acid. Injection of kanamycin or ethacrynic acid alone did not produce any change in the perilymphatic glutamate. The morphological changes induced by the administration of both drugs indicated that the collapsing hair cells might release glutamate into the perilymphatic space. The present findings provide additional evidence that glutamate acts as an aggravating factor in aminoglycoside-induced ototoxicity.

Efficacy of diffusion-weighted magnetic resonance imaging in the diagnosis of middle ear cholesteatoma

OBJECTIVE This study evaluated the usefulness of diffusion-weighted magnetic resonance imaging (DWI) in the diagnosis of middle ear cholesteatoma. METHODS We performed DWI on 73 patients suspected of having middle ear cholesteatoma, including 21 revision cases. Magnetic resonance imaging was performed with 1.5T units using diffusion-weighted spin-echo-type echo planar imaging (DWI). RESULTS Of 73 subjects, 59 had cholesteatoma that consisted of 41 primary acquired cholesteatoma, 13 had residual and/or recurrent cholesteatoma, four had congenital cholesteatoma, and one had iatrogenic cholesteatoma. Positive DWI findings were observed in 42 subjects and negative findings in 31 subjects. The sensitivity, specificity, and positive and negative predictive values of DWI for cholesteatoma were 69.4%, 92.8%, 97.5%, and 41.9%, respectively. In the case of 34 patients who were positive for cholesteatoma on both otoscopic and CT examinations, 33 were diagnosed with cholesteatoma. Of the remaining 39 subjects with one or both negative results for cholesteatoma, the sensitivity, specificity, positive predictive value, and negative predictive value of DWI were 57.6%, 92.3%, 93.7%, and 52.1%, respectively. Cholesteatoma mass diameters were less than 5mm in 10 out of 18 subjects with both cholesteatoma and negative DWI findings. Of the 21 subjects who received revision surgery, the sensitivity, specificity, and positive and negative predictive values of DWI for residual or recurrent acquired cholesteatoma were 71.4%, 100%, 100%, and 63.6%, respectively. CONCLUSIONS Since DWI clearly showed high specificity and positive predictive value, it is useful for diagnosing middle ear cholesteatoma, including postoperative recurrent cholesteatoma of 5mm diameter or larger. DWI could sufficiently detect cholesteatoma with one or both negative results on otoscopic and CT examinations, but it was difficult to detect cholesteatoma of less than 5mm diameter using DWI owing to the tiny mass and small volume of debris.

Increase in glutamate-aspartate transporter (GLAST) mRNA during kanamycin-induced cochlear insult in rats

Kanamycin (KM)-induced changes in expression of the gene for glutamate-aspartate transporter (GLAST) in the rat cochlea were analyzed by Northern blotting. With the administration of KM (600 mg/kg/day) once daily for 20 days, the expression of GLAST mRNA gradually increased and reached a peak on day 20. Although the expression of GLAST mRNA remained at a high level until 12 days after the completion of the KM treatment, it then fell to the normal level within 2 months. Such KM treatment resulted in loss of both inner and outer hair cells and a concomitant profound permanent threshold shift. The present findings suggest that during KM administration, high concentrations of extracellular glutamate released by collapsing hair cells induced GLAST mRNA expression. Increased GLAST mRNA might play an important role in the prevention of the secondary death of spiral ganglion neurons from glutamate neurotoxicity.