Addition of an affected family member to a previously ascertained autosomal recessive nonsyndromic hearing loss pedigree and systematic phenotype-genotype analysis of splice-site variants in MYO15A

The 133-kDa N-terminal region of myosin XVa is critical for normal structure and function of auditory and hair cells

BACKGROUND

MYO15A is a commonly implicated gene in severe to profound sensorineural hearing loss. Numerous studies have identified mutations in MYO15A in humans, analyzed their presence and co-segregation, and predicted their pathogenicity using software tools. However, few have investigated the pathogenic mechanisms of these mutations using mouse models. In a prior study, we identified the MYO15A c.2482 C > T mutation as a potential causative gene for deafness in a Uygur family from Xinjiang. To further explore the pathogenicity and mechanisms of this mutation, we constructed a mouse model harboring the Myo15a c.2455A > T mutation. This study demonstrates that mice with the Myo15a c.2455A > T spot knock-in exhibit the abnormal hair cell morphology, dysfunction, and hearing loss phenotype observed in humans.

OBJECTIVES

To investigate the pathogenic mechanism of deafness caused by MYO15A c.2482C > T mutation.

MATERIAL AND METHODS

To assess the impact of the MYO15A mutation on hair cell morphology and function, mice underwent audiological tests, quantitative real-time PCR, scanning electron microscopy, immunofluorescence, and Western blot analysis.

RESULTS

The p.Arg819* mutation located in the N-terminal domain of MYO15A showed marked differences in hair cell morphology and function between homozygous mutant mice and normal controls. Notably, the homozygous mutant mice retained residual hearing up to approximately five weeks of age.

CONCLUSIONS AND SIGNIFICANCE

Our findings confirm that Myo15a c.2455A > T spot knock-in mice replicate the abnormal hair cell morphology and dysfunction, as well as the hearing loss phenotype. Additionally, our results indicate that the novel c.2482C > T variant in the MYO15A gene can cause inner ear hair cell dysfunction and audiological disorders in this family.

The clinical and genetic spectrum of twenty-six individuals with hearing loss affected by MYO15A variants

Myosin XVA (MYO15A) is a member of the myosin superfamily that, as a motor protein, plays an essential role in actin polymerization at the tip of the stereocilia in hair cells. Variants in MYO15A are known to be the third most common reason for autosomal recessive non-syndromic hearing loss (ARNSHL). Here, we present twenty-six unrelated families with MYO15A variants from an Iranian cohort. Whole exome sequencing (WES) was performed following a comprehensive medical evaluation. The identified variants were assessed based on the American College of Medical Genetics and Genomics guidelines. Twenty-seven distinct variants linked to MYO15A were identified as contributors to profound ARNSHL. These included ten novel variants and seventeen previously documented variants that co-segregated. Most variants were truncating, with an equal distribution of missense and splicing variants. This research expands the mutational spectrum of MYO15A by introducing ten novel variants and highlights its importance in profound ARNSHL. Moreover, comparing the variants in different domains of MYO15A with previously reported variants in these domains provides more information about the MYO15A protein's role in the hearing process. This information can enhance understanding of the genetic basis of hearing loss and improve future management strategies, including prognosis, prevention, and treatment based on gene modification.

Novel compound heterozygous MYO15A splicing variants in autosomal recessive non-syndromic hearing loss

BACKGROUND

Hereditary hearing loss is a highly heterogeneous disorder. This study aimed to identify the genetic cause of a Chinese family with autosomal recessive non-syndromic sensorineural hearing loss (ARNSHL).

METHODS

Clinical information and peripheral blood samples were collected from the proband and its parents. Two-step high-throughput next-generation sequencing on the Ion Torrent platform was applied to detect variants as follows. First, long-range PCR was performed to amplify all the regions of the GJB2, GJB3, SLC26A4, and MT-RNR1 genes, followed by next-generation sequencing. If no candidate pathogenetic variants were found, the targeted exon sequencing with AmpliSeq technology was employed to examine another 64 deafness-associated genes. Sanger sequencing was used to identify variants and the lineage co-segregation. The splicing of the MYO15A gene was assessed by in silico bioinformatics prediction and minigene assays.

RESULTS

Two candidate MYO15A gene (OMIM, #602,666) heterozygous splicing variants, NG_011634.2 (NM_016239.3): c.6177 + 1G > T and c.9690 + 1G > A, were identified in the proband, and these two variants were both annotated as pathogenic according to the American College of Medical Genetics and Genomics (ACMG) guidelines. Further bioinformatic analysis predicted that the c.6177 + 1G > T variant might cause exon skipping and that the c.9690 + 1G > A variant might activate a cryptic splicing donor site in the downstream intronic region. An in vitro minigene assay confirmed the above predictions.

CONCLUSIONS

We identified a compound heterozygous splicing variant in the MYO15A gene in a Han Chinese family with ARNSHL. Our results broaden the spectrum of MYO15A variants, potentially benefiting the early diagnosis, prevention, and treatment of the disease.

A Novel EYA1 Mutation Causing Alternative RNA Splicing in a Chinese Family With Branchio-Oto Syndrome: Implications for Molecular Diagnosis and Clinical Application

OBJECTIVES

Branchio-oto syndrome (BOS) primarily manifests as hearing loss, preauricular pits, and branchial defects. EYA1 is the most common pathogenic gene, and splicing mutations account for a substantial proportion of cases. However, few studies have addressed the structural changes in the protein caused by splicing mutations and potential pathogenic factors, and several studies have shown that middle-ear surgery has limited effectiveness in improving hearing in these patients. BOS has also been relatively infrequently reported in the Chinese population. This study explored the genetic etiology in the family of a proband with BOS and provided clinical treatment to improve the patient's hearing.

METHODS

We collected detailed clinical features and peripheral blood samples from the patients and unaffected individuals within the family. Pathogenic mutations were identified by whole-exome sequencing and cosegregation analysis and classified according to the American College of Medical Genetics and Genomics guidelines. Alternative splicing was verified through a minigene assay. The predicted three-dimensional protein structure and biochemical experiments were used to investigate the pathogenicity of the mutation. The proband underwent middle-ear surgery and was followed up at 1 month and 6 months postoperatively to monitor auditory improvement.

RESULTS

A novel heterozygous EYA1 splicing variant (c.1050+4 A>C) was identified and classified as pathogenic (PVS1(RNA), PM2, PP1). Skipping of exon 11 of the EYA1 pre-mRNA was confirmed using a minigene assay. This mutation may impair EYA1-SIX1 interactions, as shown by an immunoprecipitation assay. The EYA1-Mut protein exhibited cellular mislocalization and decreased protein expression in cytological experiments. Middle-ear surgery significantly improved hearing loss caused by bone-conduction abnormalities in the proband.

CONCLUSION

We reported a novel splicing variant of EYA1 in a Chinese family with BOS and revealed the potential molecular pathogenic mechanism. The significant hearing improvement observed in the proband after middle-ear surgery provides a reference for auditory rehabilitation in similar patients.