Potential Implications of Slim Modiolar Electrodes for Severely Malformed Cochleae: A Comparison With the Straight Array With Circumferential Electrodes

Structural analysis of pathogenic TMPRSS3 variants and their cochlear implantation outcomes of sensorineural hearing loss

TMPRSS3, a type II transmembrane serine protease, is involved in various biological processes including the development and maintenance of the inner ear. Biallelic variants in TMPRSS3 typically result in altered protease activity, causing autosomal recessive non-syndromic hearing loss (ARNSHL). Structural modeling has been conducted to predict the pathogenicity of TMPRSS3 variants and to gain a better understanding of their prognostic correlation. The mutant-driven changes in TMPRSS3 had substantial impacts on neighboring residues, and the pathogenicity of variants was predicted based on their distance from the active site. However, a more in-depth analysis of other factors, such as intramolecular interactions and protein stability, which affect proteolytic activities is yet to be conducted for TMPRSS3 variants. Among 620 probands who provided genomic DNA for molecular genetic testing, eight families with biallelic TMPRSS3 variants that were segregated in a trans configuration were included. Seven different mutant alleles, either homozygous or compound heterozygous, contributed to TMPRSS3-associated ARNSHL, expanding the genotypic spectrum of disease-causing TMPRSS3 variants. Through three-dimensional modeling and structural analysis, TMPRSS3 variants compromise protein stability by altering intramolecular interactions, and each mutant differently interacts with the serine protease active site. Furthermore, the changes in intramolecular interactions leading to regional instability correlate with the results of functional assay and residual hearing function, but overall stability predictions do not. Our findings also build on previous evidence indicating that most recipients with TMPRSS3 variants have favorable cochlear implantation (CI) outcomes. We found that age at CI was significantly correlated with speech performance outcomes; genotype was not correlated with these outcomes. Collectively, the results of this study contribute to a more structural understanding of the underlying mechanisms of ARNSHL caused by TMPRSS3 variants.

WFS1 autosomal dominant variants linked with hearing loss: update on structural analysis and cochlear implant outcome

BACKGROUND

Wolfram syndrome type 1 gene (WFS1), which encodes a transmembrane structural protein (wolframin), is essential for several biological processes, including proper inner ear function. Unlike the recessively inherited Wolfram syndrome, WFS1 heterozygous variants cause DFNA6/14/38 and wolfram-like syndrome, characterized by autosomal dominant nonsyndromic hearing loss, optic atrophy, and diabetes mellitus. Here, we identified two WFS1 heterozygous variants in three DFNA6/14/38 families using exome sequencing. We reveal the pathogenicity of the WFS1 variants based on three-dimensional (3D) modeling and structural analysis. Furthermore, we present cochlear implantation (CI) outcomes in WFS1-associated DFNA6/14/38 and suggest a genotype-phenotype correlation based on our results and a systematic review.

METHODS

We performed molecular genetic test and evaluated clinical phenotypes of three WFS1-associated DFNA6/14/38 families. A putative WFS1-NCS1 interaction model was generated, and the impacts of WFS1 variants on stability were predicted by comparing intramolecular interactions. A total of 62 WFS1 variants associated with DFNA6/14/38 were included in a systematic review.

RESULTS

One variant is a known mutational hotspot variant in the endoplasmic reticulum (ER)-luminal domain WFS1(NM_006005.3) (c.2051 C > T:p.Ala684Val), and the other is a novel frameshift variant in transmembrane domain 6 (c.1544_1545insA:p.Phe515LeufsTer28). The two variants were pathogenic, based on the ACMG/AMP guidelines. Three-dimensional modeling and structural analysis show that non-polar, hydrophobic substitution of Ala684 (p.Ala684Val) destabilizes the alpha helix and contributes to the loss of WFS1-NCS1 interaction. Also, the p.Phe515LeufsTer28 variant truncates transmembrane domain 7-9 and the ER-luminal domain, possibly impairing membrane localization and C-terminal signal transduction. The systematic review demonstrates favorable outcomes of CI. Remarkably, p.Ala684Val in WFS1 is associated with early-onset severe-to-profound deafness, revealing a strong candidate variant for CI.

CONCLUSIONS

We expanded the genotypic spectrum of WFS1 heterozygous variants underlying DFNA6/14/38 and revealed the pathogenicity of mutant WFS1, providing a theoretical basis for WFS1-NCS1 interactions. We presented a range of phenotypic traits for WFS1 heterozygous variants and demonstrated favorable functional CI outcomes, proposing p.Ala684Val a strong potential marker for CI candidates.

Functional Outcomes of Cochlear Implantation in Children with Bilateral Cochlear Nerve Aplasia

Background and Objectives: Many otologists face a dilemma in the decision-making process of surgical management of patients with cochlear nerve (CN) aplasia. The goal of this study is to provide fresh evidence on cochlear implantation (CI) results in patients with CN aplasia. Materials and Methods: We scrutinized functional outcomes in 37 ears of 21 children with bilateral CN aplasia who underwent unilateral or bilateral CI based on cross-sectional and longitudinal assessments. Results: The Categories of Auditory Performance (CAP) scores gradually improved throughout the 3-year follow-up; however, variable outcomes existed between individuals. Specifically, 90% of recipients with a 1-year postoperative CAP score ≤1 could not achieve a CAP score over 1 even at 3-year postoperative evaluation, while the recipients with a 1-year postoperative CAP score >1 had improved auditory performance, and 72.7% of them were able to achieve a CAP score of 4 or higher. Meanwhile, intraoperative electrically evoked compound action potential was not correlated with postoperative CAP score. Conclusions: Our results further refine previous studies on the clinical feasibility of CI as the first treatment modality to elicit favorable auditory performance in children with CN aplasia. However, special attention should be paid to pediatric patients with an early postoperative CAP score ≤1 for identification of unsuccessful cochlear implants and switching to auditory brainstem implants.

Effects of CoQ10 Replacement Therapy on the Audiological Characteristics of Pediatric Patients with COQ6 Variants

Primary coenzyme Q10 (CoQ10) deficiency refers to a group of mitochondrial cytopathies caused by genetic defects in CoQ10 biosynthesis. Primary coenzyme Q10 deficiency-6 (COQ10D6) is an autosomal recessive disorder attributable to biallelic COQ6 variants; the cardinal phenotypes are steroid-resistant nephrotic syndrome (SRNS), which inevitably progresses to kidney failure, and sensorineural hearing loss (SNHL). Here, we describe the phenotypes and genotypes of 12 children with COQ10D6 from 11 unrelated Korean families and quantitatively explore the beneficial effects of CoQ10 replacement therapy on SNHL. A diagnosis of SRNS generally precedes SNHL documentation. COQ10D6 is associated with progressive SNHL. Four causative COQ6 variants were identified in either homozygotes or compound heterozygotes: c.189_191delGAA, c.484C>T, c.686A>C, and c.782C>T. The response rate (no further hearing loss or improvement) was 42.9%; CoQ10 replacement therapy may thus limit and even improve hearing loss. Notably, the audiological benefit appeared to be genotype-specific, suggesting a genotype–phenotype correlation. The results of cochlear implantation were generally favorable, and the effects were sustained over time. Our results thus propose the beneficial effects of CoQ10 replacement therapy on hearing loss. Our work with COQ10D6 patients is a good example of personalized, genetically tailored, audiological rehabilitation of patients with syndromic deafness.

Genetic Load of Alternations of Transcription Factor Genes in Non-Syndromic Deafness and the Associated Clinical Phenotypes: Experience from Two Tertiary Referral Centers

Sensorineural hearing loss is one of the most common inherited sensory disorders. Functional classifications of deafness genes have shed light on genotype- and mechanism-based pharmacological approaches and on gene therapy strategies. In this study, we characterized the clinical phenotypes and genotypes of non-syndromic deafness caused by transcription factor (TF) gene variants, one of the functional classifications of genetic hearing loss. Of 1280 probands whose genomic DNA was subjected to molecular genetic testing, TF genes were responsible for hearing loss in 2.6%. Thirty-three pathogenic variants, including nine novel variants, accounting for non-syndromic deafness were clustered in only four TF genes (POU3F4, POU4F3, LMX1A, and EYA4), which is indicative of a narrow molecular etiologic spectrum of TF genes, and the functional redundancy of many other TF genes, in the context of non-syndromic deafness. The audiological and radiological characteristics associated with the four TF genes differed significantly, with a wide phenotypic spectrum. The results of this study reveal the genetic load of TF gene alterations among a cohort with non-syndromic hearing loss. Additionally, we have further refined the clinical profiles associated with TF gene variants as a basis for a personalized, genetically tailored approach to audiological rehabilitation.