Wie-Yen Young

Functional characterization of the mitochondrial 12S rRNA C1494T mutation associated with aminoglycoside-induced and non-syndromic hearing loss

In this study, we report the biochemical characterization of the deafness-associated mitochondrial 12S rRNA C1494T mutation using 27 cybrid cell lines constructed by transferring mitochondria from 9 lymphoblastoid cell lines derived from a Chinese family into human mitochondrial DNA (mtDNA)-less (ρ°) cells. Six cybrids derived from two asymptomatic members, and nine cybrids derived from three symptomatic members of the Chinese family carrying the C1494T mutation exhibited ∼38 and 43% decrease in the rate of mitochondrial protein labeling, respectively, compared with twelve cybrids derived from four Chinese control individuals. These defects are apparently a primary contributor to significant reductions in the rate of overall respiratory capacity or the rate of malate/glutamate promoted respiration, or succinate/G3P-promoted respiration, or TMPD/ascorbate-promoted respiration in mutant cybrid cell lines derived from either symptomatic or asymptomatic individuals. Furthermore, the very significant/nearly identical increase in the ratio of doubling times in DMDM medium in the presence/absence of high concentration of paromomycin was observed in symptomatic or asymptomatic cybrid cell lines carrying the C1494T mutation as compared with the average rate in control cell lines. These observations provide the direct biochemical evidences that the C1494T mutation is a pathogenic mtDNA mutation associated with aminoglycoside-induced and non-syndromic hearing loss. In addition, these data provide the first biochemical evidence that nuclear background plays a critical role in the phenotypic manifestation of non-syndromic hearing loss and aminoglycoside toxicity associated with the C1494T mutation.

Cosegregation of the G7444A Mutation in the Mitochondrial COI/tRNASer(UCN) Genes with the 12S rRNA A1555G Mutation in a Chinese Family with Aminoglycoside-induced and Nonsyndromic Hearing Loss

We report here on the characterization of a three‐generation Chinese family with aminoglycoside‐induced and nonsyndromic hearing impairment. Ten of 17 matrilineal relatives exhibited bilateral and sensorineural hearing impairment. Of these, nine matrilineal relatives, who had a history of exposure to aminoglycosides, exhibited variable severity and audiometric configuration of hearing loss. The dose and age at the time of drug administration seemed to be correlated with the severity of the hearing loss experienced by affected individuals. Sequence analysis of the complete mitochondrial genome in the pedigree showed the presence of homoplasmic A1555G mutation and 37 variants belonging to haplogroup D4a. Of those variants, the G7444A mutation is of special interest as the mutation at this position results in a read‐through of the stop condon AGA of the COI message, thereby adding three amino acids (Lys–Gln–Lys) to the C‐terminal of the polypeptide. Alternatively, the G7444A mutation is adjacent to the site of 3′ end endonucleolytic processing of L‐strand RNA precursor, spanning tRNASer(UCN) and ND6 mRNA. Thus, the G7444A mutation, similar to the deafness‐associated A7445G mutation, may lead to a defect in the processing of the L‐strand RNA precursor, thus influencing the phenotypic expression of the A1555G mutation. These data also imply that nuclear background plays a role in the aminoglycoside ototoxicity associated with the A1555G mutation in this Chinese pedigree.

Variants in mitochondrial tRNAGlu, tRNAArg, and tRNAThr may influence the phenotypic manifestation of deafness-associated 12S rRNA A1555G mutation in three Han Chinese families with hearing loss†

We report here on the clinical, genetic, and molecular characterization of three Han Chinese pedigrees with aminoglycoside‐induced and nonsyndromic hearing loss. Clinical evaluation revealed the variable phenotype of hearing loss including severity, age‐at‐onset, audiometric configuration in these subjects. Penetrances of hearing loss in BJ107, BJ108, and BJ109 pedigrees are 35%, 63%, and 67%, respectively. Mutational analysis of the complete mitochondrial genomes in these pedigrees showed the identical homoplasmic A1555G mutation and distinct sets of mitochondrial DNA (mtDNA) variants belonging to haplogroups N, F, and M, respectively. Of these variants, the A14693G mutation in the tRNAGlu, the T15908C mutation in the tRNAThr, and the T10454C mutation in the tRNAArg are of special interest as these mutations occur at positions which are highly evolutionarily conserved nucleotides of corresponding tRNAs. These homoplasmic mtDNA mutations were absent among 156 unrelated Chinese controls. The A14693G and T10454C mutations occur at the highly conserved bases of the TψC‐loop of tRNAGlu and tRNAArg, respectively. Furthermore, the T15908C mutation in the tRNAThr disrupts a highly conserved A‐U base‐pairing at the D‐stem of this tRNA. The alteration of structure of these tRNAs by these mtDNA mutations may lead to a failure in tRNA metabolism, thereby causing impairment of mitochondrial translation. Thus, mitochondrial dysfunctions, caused by the A1555G mutation, would be worsened by these mtDNA mutations. Therefore, these mtDNA mutations may have a potential modifier role in increasing the penetrance and expressivity of the deafness‐associated 12S rRNA A1555G mutation in those Chinese pedigrees.

Clinical and Molecular Characterization of a Chinese Patient With Auditory Neuropathy Associated With Mitochondrial 12S rRNA T1095C Mutation

Mutations in mitochondrial DNA (mtDNA), particularly those in the 12S rRNA gene, have been shown to be associated with sensorineural hearing loss. Recently, a systematic and extended mutation screening of the mitochondrial 12S rRNA gene has been initiated in the large clinical population of the Otology Clinic at the Chinese PLA General Hospital with the aim of identifying mtDNA mutations associated with hearing loss. Here we report the clinical and molecular characterization of a Chinese patient with auditory neuropathy. Sequence analysis of mtDNA in this patient identified a T‐to‐C transition at position 1095 (T1095C) in the 12S rRNA gene and other nucleotide changes. The T1095C mutation is expected to disrupt an evolutionarily conserved A‐to‐U base‐pair, which is at the highly conserved P‐site of 12S rRNA. The T1095C mutation has also been found to be associated with hearing loss in several unrelated families. Among other nucleotide changes, two novel variants: the I175V mutation in the CO2 and the V112M mutation in the ND6 localize at highly evolutionarily conserved residues from different organisms. Furthermore, the absence of mutation in the otoferlin related to auditory neuropathy showed that otoferlin may not be involved in the phenotypic expression of T1095C mutation in this subject. These data suggest that the T1095C mutation may be associated with auditory neuropathy in this subject, and two novel variants I175V and V112M may play a role in the phenotypic expression of the T1095C mutation.

Coexistence of mitochondrial 12S rRNA C1494T and CO1/tRNASer(UCN) G7444A mutations in two Han Chinese pedigrees with aminoglycoside-induced and non-syndromic hearing loss

Mutations in mitochondrial DNA are one of the important causes of hearing loss. We report here the clinical, genetic, and molecular characterization of two Han Chinese pedigrees with maternally transmitted aminoglycoside-induced and nonsyndromic bilateral hearing loss. Clinical evaluation revealed the wide range of severity, age-at-onset, and audiometric configuration of hearing impairment in matrilineal relatives in these families. The penetrances of hearing loss in these pedigrees were 20% and 18%, when aminoglycoside-induced deafness was included. When the effect of aminoglycosides was excluded, the penetrances of hearing loss in these seven pedigrees were 10% and 15%. Sequence analysis of the complete mitochondrial genomes in these pedigrees showed the presence of the deafness-associated 12S rRNA C1494T and CO1/tRNA(Ser(UCN)) G7444A mutations. Their distinct sets of mtDNA polymorphism belonged to Eastern Asian haplogroup C4a1, while other previously identified six Chinese mitochondrial genomes harboring the C1494T mutation belong to haplogroups D5a2, D, R, and F1, respectively. This suggested that the C1494T or G7444A mutation occurred sporadically and multiplied through evolution of the mitochondrial DNA (mtDNA). The absence of functionally significant mutations in tRNA and rRNAs or secondary LHON mutations in their mtDNA suggest that these mtDNA haplogroup-specific variants may not play an important role in the phenotypic expression of the 12S rRNA C1494T and CO1/tRNA(Ser(UCN)) G7444A mutations in those Chinese families. However, aminoglycosides and other nuclear modifier genes play a modifying role in the phenotypic manifestation of the C1494T mutation in these Chinese families.

Acoustic neuroma surgery for preservation of hearing: technique and experience in the Chinese PLA General Hospital

Abstract Conclusions: Good hearing preservation can be achieved during acoustic neuroma surgery assisted by real-time dynamic auditory monitoring and ear endoscopic techniques. Preservation of the arachnoid and its blood supply are important for hearing preservation, and injury to the internal auditory artery is the most important cause of hearing loss. Objective: To explore techniques to preserve hearing during acoustic neuroma resection. Methods: This was a retrospective case review in a hospital setting. From July 2003 to July 2007, intraoperative auditory monitoring using auditory brainstem response (ABR) and electrocochleography (EcochG) was conducted in 18 of 138 patients undergoing surgery for acoustic neuroma who had preoperative hearing. The retrosigmoid approach was used for 16 complete resections and 2 patients underwent partial resections. Assisted endoscopic surgery was conducted for 10 ears. The main outcome measure was preservation of hearing, assessed using the classification method of the American Institute of Otolaryngology-Head and Neck Surgery. Results: Hearing was preserved in 11 of the 18 patients (61.1%): 2 of 5 patients whose tumors were larger than 20 mm (40%), and 9 of 13 patients with smaller tumors (69.2%). Among the 10 cases of ear endoscope-assisted surgery, hearing was preserved in 8 (80%). Intraoperative monitoring revealed that the waveform was influenced when the posterior labium of the internal acoustic meatus was ground and drilled, or when traction or electrocoagulation was performed near the opening of the internal acoustic meatus, especially when the internal auditory artery was clamped, the tumor in the internal acoustic meatus was treated, and the arachnoid vessels in the inner-most layer of the tumor surface were clamped or electrocoagulated.

Surgical treatment of endolymphatic sac tumor

Abstract The objective of this study was to understand the clinical characteristics of endolymphatic sac tumor and to optimize its diagnosis and treatment. We carried out a retrospective review of 11 patients diagnosed as having endolymphatic sac tumor based on operative findings and pathological features, and their clinical manifestations, differential diagnosis, and surgical approaches are discussed in detail. The lesions of 10 cases were completely surgically resected, two cases via the mastoid approach, 8 cases via the oto-cervical or cranio-oto-cervical combined approach. In one case the tumor was partially removed and the patient received adjuvant radiotherapy. In operation, four cases had facial-hypoglossal neural anastomosis, two cases had great auricular nerve graft, and in four cases the facial nerve integrity remained. Survival follow-up data range from 14 months to 10 years. We conclude that endolymphatic sac tumor is very rare and easily misdiagnosed. Reasonable surgical treatment can provide a good prognosis.