Genetic Evaluation of Prelingual Hearing Impairment: Recommendations of an European Network for Genetic Hearing Impairment

Novel genetic determinants contribute to hearing loss in a central European cohort with enlarged vestibular aqueduct

BACKGROUND

The enlarged vestibular aqueduct (EVA) is the most commonly detected inner ear malformation. Biallelic pathogenic variants in the SLC26A4 gene, coding for the anion exchanger pendrin, are frequently involved in determining Pendred syndrome and nonsyndromic autosomal recessive hearing loss DFNB4 in EVA patients. In Caucasian cohorts, the genetic determinants of EVA remain unknown in approximately 50% of cases. We have recruited a cohort of 32 Austrian patients with hearing loss and EVA to define the prevalence and type of pathogenic sequence alterations in SLC26A4 and discover novel EVA-associated genes.

METHODS

Sanger sequencing, single nucleotide polymorphism (SNP) assays, copy number variation (CNV) testing, and Exome Sequencing (ES) were employed for gene analysis. Cell-based functional and molecular assays were used to discriminate between gene variants with and without impact on protein function.

RESULTS

SLC26A4 biallelic variants were detected in 5/32 patients (16%) and monoallelic variants in 5/32 patients (16%). The pathogenicity of the uncharacterized SLC26A4 protein variants was assigned or excluded based on their ion transport function and cellular abundance. The monoallelic or biallelic Caucasian EVA haplotype was detected in 7/32 (22%) patients, but its pathogenicity could not be confirmed. X-linked pathogenic variants in POU3F4 (2/32, 6%) and biallelic pathogenic variants in GJB2 (2/32, 6%) were also found. No CNV of SLC26A4 and STRC genes was detected. ES of eleven undiagnosed patients with bilateral EVA detected rare sequence variants in six EVA-unrelated genes (monoallelic variants in SCD5, REST, EDNRB, TJP2, TMC1, and two variants in CDH23) in five patients (5/11, 45%). Cell-based assays showed that the TJP2 variant leads to a mislocalized protein product forming dimers with the wild-type, supporting autosomal dominant pathogenicity. The genetic causes of hearing loss and EVA remained unidentified in (14/32) 44% of patients.

CONCLUSIONS

The present investigation confirms the role of SLC26A4 in determining hearing loss with EVA, identifies novel genes in this pathophysiological context, highlights the importance of functional testing to exclude or assign pathogenicity of a given gene variant, proposes a possible diagnostic workflow, suggests a novel pathomechanism of disease for TJP2, and highlights voids of knowledge that deserve further investigation.

Zebrafish in-vivo study reveals deleterious activity of human TBC1D24 genetic variants linked with autosomal dominant hearing loss

Hearing loss is a common sensory impairment with a heterogeneous genetic etiology. Genetic variants in the TBC1D24 gene have recently emerged as an important cause of the non-syndromic autosomal dominant hearing loss (ADHL). However, the molecular mechanism behind the TBC1D24-associated ADHL is unknown. Using a zebrafish model, we investigated involvement of TBC1D24 in hearing and the functional effects of the associated ADHL-causing genetic variants. We show that the morpholino-mediated knock-down of Tbc1d24 resulted in defective ear kinocilia structure and reduced locomotor activity of the embryos. The observed phenotypes were rescued by a wild-type TBC1D24 mRNA but not by a mutant mRNA carrying the ADHL-causing variant c.553G>A (p.Asp185Asn), supporting its pathogenic potential. CRISPR-Cas9-mediated knock-out of tbc1d24 led to mechanosensory deficiency of lateral line neuromasts. Overexpression of TBC1D24 mRNA resulted in developmental abnormalities associated with ciliary dysfunction and mesendodermal mispatterning. We observed that the ADHL-causing TBC1D24 variants: c.553G>A (p.Asp185Asn); c.1460A>T (p.His487Leu), c.1461C>G (p.His487Gln) or a novel variant c.905T>G (p.Leu302Arg) alleviated the effect of overexpression, indicating that these variants disrupt the TBC1D24 function. Furthermore, the zebrafish phenotypes correspond to the severity of ADHL. Specific changes in ear structures upon TBC1D24 overexpression further highlighted its tissue-specific role in ciliary function and inner ear development. Our findings provide functional evidence for the pathogenic potential of the ADHL-causing TBC1D24 variants and lead to new insights into the function of TBC1D24 in cilia morphogenesis.

[Update on diagnostic procedures in third window syndromes. German version]

BACKGROUND

The diagnosis of third window syndromes often poses a challenge in clinical practice.

OBJECTIVE

This paper provides an up-to-date overview of diagnostic procedures in third window syndromes, with special emphasis on superior canal dehiscence syndrome (SCDS), large vestibular aqueduct syndrome (LVAS), and X-chromosomal malformation of the cochlea.

MATERIALS AND METHODS

A literature search was performed in PubMed up to December 2023. Furthermore, a selection of the authors' own cases is presented.

RESULTS

Audiovestibular tests for the diagnosis of third window syndromes are most often reported for patients with SCDS in the literature. In this context, cut-off values with different sensitivities and specificities have been defined for different outcome parameters of vestibular evoked myogenic potentials. Current developments include the application of electrocochleography, broadband tympanometry, video head impulse testing, and vibration-induced nystagmus. Genetic analyses are increasingly applied in LVAS.

CONCLUSION

The diagnosis of third window syndromes is always based on the synthesis of patients' symptoms, clinical signs, audiovestibular test results, and imaging.

The Otoacoustic Emissions in the Universal Neonatal Hearing Screening: An Update on the European Data (2004 to 2024)

Background: The reported data on European universal neonatal hearing screening (UNHS) practices tend to be scarce, despite the fact that the European Union project, EUScreen, collected unofficial data from 38 collaborating European institutions. The objectives of this systematic review were as follows: (a) to identify the most recent (in a 20-year span) literature information about UNHS programs in Europe and (b) to provide data on the procedures used to assess the population, the intervention policies, and on the estimated prevalence of congenital hearing loss with emphasis on the bilateral hearing loss cases. Methods: Queries were conducted via the Pubmed, Scopus and Google Scholar databases for the time period of 2004-2024. The Mesh terms used were "OAE", "Universal Neonatal Hearing Screening", "congenital hearing loss" and "well babies". Only research articles and review papers of European origin were considered good candidates. The standard English language filter was not used, in order to identify information from non-English-speaking scientific communities and groups. Results: Very few data and reports were identified in the literature search. Eleven manuscripts were identified corresponding to eight UNHS programs. Except in Poland, most of the data refer to regional and not national programs. The screening coverage estimates of all programs exceed 90%; infants were mostly assessed by a three-stage protocol (TEOAE + TEOAE + AABR), followed by a clinical ABR test. The average prevalence (i.e., from well babies AND NICU infants) of bilateral hearing loss ranged from 0.5 to 20.94 per 1000 (Zurich sample). Infants presenting unilateral or bilateral hearing losses were first rehabilitated by hearing aids and consequently (>15 mo) by cochlear implants. Conclusions: Even though UNHS programs are well-established clinical practices in the European States, the amount of information in the literature about these programs is surprising low. The existing data in the timespan 2004-2024 corroborate the international UNHS data in terms of coverage and bilateral hearing loss prevalence, but there is a strong need to supplement the existing information with the latest developments, especially in the area of hearing loss rehabilitation.

Investigation of Deficits in Auditory Emotional Content Recognition by Adult Cochlear Implant Users through the Study of Electroencephalographic Gamma and Alpha Asymmetry and Alexithymia Assessment

BACKGROUND/OBJECTIVES

Given the importance of emotion recognition for communication purposes, and the impairment for such skill in CI users despite impressive language performances, the aim of the present study was to investigate the neural correlates of emotion recognition skills, apart from language, in adult unilateral CI (UCI) users during a music in noise (happy/sad) recognition task. Furthermore, asymmetry was investigated through electroencephalographic (EEG) rhythm, given the traditional concept of hemispheric lateralization for emotional processing, and the intrinsic asymmetry due to the clinical UCI condition.

METHODS

Twenty adult UCI users and eight normal hearing (NH) controls were recruited. EEG gamma and alpha band power was assessed as there is evidence of a relationship between gamma and emotional response and between alpha asymmetry and tendency to approach or withdraw from stimuli. The TAS-20 questionnaire (alexithymia) was completed by the participants.

RESULTS

The results showed no effect of background noise, while supporting that gamma activity related to emotion processing shows alterations in the UCI group compared to the NH group, and that these alterations are also modulated by the etiology of deafness. In particular, relative higher gamma activity in the CI side corresponds to positive processes, correlated with higher emotion recognition abilities, whereas gamma activity in the non-CI side may be related to positive processes inversely correlated with alexithymia and also inversely correlated with age; a correlation between TAS-20 scores and age was found only in the NH group.

CONCLUSIONS

EEG gamma activity appears to be fundamental to the processing of the emotional aspect of music and also to the psychocognitive emotion-related component in adults with CI.

Contiguous Gene Syndromes and Hearing Loss: A Clinical Report of Xq21 Deletion and Comprehensive Literature Review

Given the crucial role of the personalized management and treatment of hearing loss (HL), etiological investigations are performed early on, and genetic analysis significantly contributes to the determination of most syndromic and nonsyndromic HL cases. Knowing hundreds of syndromic associations with HL, little comprehensive data about HL in genomic disorders due to microdeletion or microduplications of contiguous genes is available. Together with the description of a new patient with a novel 3.7 Mb deletion of the Xq21 critical locus, we propose an unreported literature review about clinical findings in patients and their family members with Xq21 deletion syndrome. We finally propose a comprehensive review of HL in contiguous gene syndromes in order to confirm the role of cytogenomic microarray analysis to investigate the etiology of unexplained HL.

Congenital Deafness and Deaf-Mutism: A Historical Perspective

Hearing loss is the most common sensory deficit and one of the most common congenital abnormalities. The estimated prevalence of moderate and severe hearing loss in a normal newborn is 0.1-0.3%, while the prevalence is 2-4% in newborns admitted to the newborn intensive care unit. Therefore, early detection and prompt treatment are of utmost importance in preventing the unwanted sequel of hearing loss on normal language development. The problem of congenital deafness is today addressed on the one hand with hearing screening at birth, on the other with the early (at around 3 months of age) application of hearing aids or, in case of lack of benefit, by the cochlear implant. Molecular genetics, antibody tests for some viruses, and diagnostic imaging have largely contributed to an effective etiological classification. A correct diagnosis and timely fitting of hearing aids or cochlear implants is useful for deaf children. The association between congenital deafness and "mutism", with all the consequences on/the consideration that deaf mutes have had since ancient times, not only from a social point of view but also from a legislative point of view, continued until the end of the nineteenth century, with the development on one side of new methods for the rehabilitation of language and on the other of sign language. But we need to get to the last decades of the last century to have, on the one hand, the diffusion of "universal newborn hearing screening", the discovery of the genetic causes of over half of congenital deafness, and on the other hand the cochlear implants that have allowed thousands of children born deaf the development of normal speech. Below, we will analyze the evolution of the problem between deafness and deaf-mutism over the centuries, with particular attention to the nineteenth century.