The Importance of Early Genetic Diagnostics of Hearing Loss in Children

The known structural variations in hearing loss and their diagnostic approaches: a comprehensive review

Hearing loss (HL) is the most common sensory disorder, characterized by a wide range of causes, including both environmental and genetic factors. While single-nucleotide variants (SNVs) and small insertions/deletions have been extensively studied, the role of structural variations (SVs) in hearing impairment has gained increasing recognition. This review article aims to provide a comprehensive overview of the importance of SVs in HL, by exploring the SVs associated with HL and their underlying pathogenic mechanisms. Additionally, diagnostic methods of SVs have been briefly evaluated and compared in general. Three major mechanisms by which SVs can lead to HL are gene disruption, gene dosage imbalance, and position effect. Furthermore, to facilitate the detection of SVs in HL, this review presents a table highlighting the key genes and genomic regions implicated in SVs and their diagnostic approaches associated with HL patients. In the next step, indications for the use of SV diagnostic techniques are compiled in another table in this article, which will help experts in choosing the most appropriate technique. At last, the comprehensive review presented here underscores the significant role of SVs in HL. Further research is required to fully elucidate the spectrum of SVs in HL and optimize the clinical use of SV detection methods in routine diagnostic procedures.

KMT2D Deficiency Causes Sensorineural Hearing Loss in Mice and Humans

Individuals with Kabuki syndrome type 1 (KS1) often have hearing loss recognized in middle childhood. Current clinical dogma suggests that this phenotype is caused by frequent infections due to the immune deficiency in KS1 and/or secondary to structural abnormalities of the ear. To clarify some aspects of hearing loss, we collected information on hearing status from 21 individuals with KS1 and found that individuals have both sensorineural and conductive hearing loss, with the average age of presentation being 7 years. Our data suggest that while ear infections and structural abnormalities contribute to the observed hearing loss, these factors do not explain all loss. Using a KS1 mouse model, we found hearing abnormalities from hearing onset, as indicated by auditory brainstem response measurements. In contrast to mouse and human data for CHARGE syndrome, a disorder possessing overlapping clinical features with KS and a well-known cause of hearing loss and structural inner ear abnormalities, there are no apparent structural abnormalities of the cochlea in KS1 mice. The KS1 mice also display diminished distortion product otoacoustic emission levels, which suggests outer hair cell dysfunction. Combining these findings, our data suggests that KMT2D dysfunction causes sensorineural hearing loss compounded with external factors, such as infection.

Full etiologic spectrum of pediatric severe to profound hearing loss of consecutive 119 cases

Determining the etiology of severe-to-profound sensorineural hearing loss (SP-SNHL) in pediatric subjects is particularly important in aiding the decision for auditory rehabilitation. We aimed to update the etiologic spectrum of pediatric SP-SNHL by combining internal auditory canal (IAC)-MRI with comprehensive and state-of-the-art genetic testings. From May 2013 to September 2020, 119 cochlear implantees under the age of 15 years with SP-SNHL were all prospectively recruited. They were subjected to genetic tests, including exome sequencing, and IAC-MRI for etiologic diagnosis. Strict interpretation of results were made based on ACMG/AMP guidelines and by an experienced neuroradiologist. The etiology was determined in of 65.5% (78/119) of our cohort. If only one of the two tests was done, the etiologic diagnostic rate would be reduced by at least 21.8%. Notably, cochlear nerve deficiency (n = 20) detected by IAC-MRI topped the etiology list of our cohort, followed by DFNB4 (n = 18), DFNB1 (n = 10), DFNB9 (n = 10) and periventricular leukomalacia associated with congenital CMV infection (n = 8). Simultaneous application of state-of-the-art genetic tests and IAC-MRI is essential for etiologic diagnosis, and if lesions of the auditory nerve or central nerve system are carefully examined on an MRI, we can identify the cause of deafness in more than 65% of pediatric SP-SNHL cases.

Presentation of potential genes and deleterious variants associated with non-syndromic hearing loss: a computational approach

Non-syndromic hearing loss (NSHL) is a common hereditary disorder. Both clinical and genetic heterogeneity has created many obstacles to understanding the causes of NSHL. The present study has attempted to ravel the genetic aetiology in NSHL progression and to screen out potential target genes using computational approaches. The reported NSHL target genes (2009-2020) have been studied by analyzing different biochemical and signaling pathways, interpretation of their functional association network, and discovery of important regulatory interactions with three previously established miRNAs in the human inner ear as well as in NSHL such as miR-183, miR-182, and miR-96. This study has identified SMAD4 and SNAI2 as the most putative target genes of NSHL. But pathogenic and deleterious non-synonymous single nucleotide polymorphisms discovered within SMAD4 is anticipated to have an impact on NSHL progression. Additionally, the identified deleterious variants in the functional domains of SMAD4 added a supportive clue for further study. Thus, the identified deleterious variant i.e., rs377767367 (G491V) in SMAD4 needs further clinical validation. The present outcomes would provide insights into the genetics of NSHL progression.

Hearing Screening Combined with Target Gene Panel Testing Increased Etiological Diagnostic Yield in Deaf Children

Genetic testing is the gold standard for exploring the etiology of congenital hearing loss. Here, we enrolled 137 Chinese patients with congenital hearing loss to describe the molecular epidemiology by using 127 gene panel testing or 159 variant testing. Sixty-three deaf children received 127 gene panel testing, while seventy-four patients received 159 variant testing. By use of 127 gene panel testing, more mutant genes and variants were identified. The most frequent mutant genes were GJB2, SLC26A4, MYO15A, CDH23, and OTOF. By analyzing the patients who received 127 gene panel testing, we found that 51 deaf children carried variants which were not included in 159 variant testing. Therefore, a large number of patients would be misdiagnosed if only 159 variant testing is used. This study highlights the advantage of 127 gene panel testing, and it suggests that broader genetic testing should be done to identify the genetic etiology of congenital hearing loss.

Novel GRHL2 Gene Variant Associated with Hearing Loss: A Case Report and Review of the Literature

In contrast to the recessive form, hearing loss inherited in a dominant manner is more often post-lingual and typically results in a progressive sensorineural hearing loss with variable severity and late onset. Variants in the GRHL2 gene are an extremely rare cause of dominantly inherited hearing loss. Genetic testing is a crucial part of the identification of the etiology of hearing loss in individual patients, especially when performed with next-generation sequencing, enabling simultaneous analysis of numerous genes, including those rarely associated with hearing loss. We aimed to evaluate the genetic etiology of hearing loss in a family with moderate late-onset hearing loss using next-generation sequencing and to conduct a review of reported variants in the GRHL2 gene. We identified a novel disease-causing variant in the GRHL2 gene (NM_024915: c.1510C>T; p.Arg504Ter) in both affected members of the family. They both presented with moderate late-onset hearing loss with no additional clinical characteristics. Reviewing known GRHL2 variants associated with hearing loss, we can conclude that they are more likely to be truncating variants, while the associated onset of hearing loss is variable.