WFS1andGJB2mutations in patients with bilateral low-frequency sensorineural hearing loss

Autosomal Dominant Non-Syndromic Hearing Loss (DFNA): A Comprehensive Narrative Review

Autosomal dominant non-syndromic hearing loss (HL) typically occurs when only one dominant allele within the disease gene is sufficient to express the phenotype. Therefore, most patients diagnosed with autosomal dominant non-syndromic HL have a hearing-impaired parent, although de novo mutations should be considered in all cases of negative family history. To date, more than 50 genes and 80 loci have been identified for autosomal dominant non-syndromic HL. DFNA22 (MYO6 gene), DFNA8/12 (TECTA gene), DFNA20/26 (ACTG1 gene), DFNA6/14/38 (WFS1 gene), DFNA15 (POU4F3 gene), DFNA2A (KCNQ4 gene), and DFNA10 (EYA4 gene) are some of the most common forms of autosomal dominant non-syndromic HL. The characteristics of autosomal dominant non-syndromic HL are heterogenous. However, in most cases, HL tends to be bilateral, post-lingual in onset (childhood to early adulthood), high-frequency (sloping audiometric configuration), progressive, and variable in severity (mild to profound degree). DFNA1 (DIAPH1 gene) and DFNA6/14/38 (WFS1 gene) are the most common forms of autosomal dominant non-syndromic HL affecting low frequencies, while DFNA16 (unknown gene) is characterized by fluctuating HL. A long audiological follow-up is of paramount importance to identify hearing threshold deteriorations early and ensure prompt treatment with hearing aids or cochlear implants.

Monogenic Causes of Low-Frequency Non-Syndromic Hearing Loss

BACKGROUND

Low-frequency non-syndromic hearing loss (LFNSHL) is a rare form of hearing loss (HL). It is defined as HL at low frequencies (≤2,000 Hz) resulting in a characteristic ascending audiogram. LFNSHL is usually diagnosed postlingually and is progressive, leading to HL affecting other frequencies as well. Sometimes it occurs with tinnitus. Around half of the diagnosed prelingual HL cases have a genetic cause and it is usually inherited in an autosomal recessive mode. Postlingual HL caused by genetic changes generally has an autosomal dominant pattern of inheritance and its incidence remains unknown.

SUMMARY

To date, only a handful of genes have been found as causing LFNSHL: well-established WFS1 and, reported in some cases, DIAPH1, MYO7A, TNC, and CCDC50 (respectively, responsible for DFNA6/14/38, DFNA1, DFNA11, DFNA56, and DFNA44). In this review, we set out audiological phenotypes, causative genetic changes, and molecular mechanisms leading to the development of LFNSHL.

KEY MESSAGES

LFNSHL is most commonly caused by pathogenic variants in the WFS1 gene, but it is also important to consider changes in other HL genes, which may result in similar audiological phenotype.

A Novel Missense WFS1 Variant: Expanding the Mutational Spectrum Associated with Nonsyndromic Low-Frequency Sensorineural Hearing Loss

Background. Nonsyndromic low-frequency sensorineural hearing loss (LFSNHL) is an uncommon form of hearing loss (HL) that typically affects frequencies at 2000 Hz and below. Heterozygous variants in the WFS1 gene at the DFNA6/14/38 locus are considered a common cause of LFSNHL. To date, 34 different pathogenic genetic variants have been reported to cause LFSNHL with seven of these variants identified in the Chinese population. However, limited reports are available on the association between WFS1 gene and LFSNHL. Here, we report a five-generation Chinese family with an autosomal dominant inheritance pattern of postlingual and progressive LFSNHL. Methods. Routine clinical and audiological examinations were performed on 16 affected and 7 healthy members in this family. The targeted next-generation sequencing of 127 known deafness genes was performed to identify variants in affected individuals. Sanger sequencing were further employed to confirm the pathogenic variant identified. Results. A novel heterozygous pathogenic genetic variant c.2530G > T (p.Ala844Ser) was identified in the WFS1 gene in all patients of this family. The mutated Ala residue is evolutionarily conserved and cosegregated with HL. The variant was predicted to be deleterious by MutationTaster, PolyPhen-2, LRT, and Fathmm software. Conservation analysis and 3D protein structure model indicated that the variant caused a structural change in the protein. Conclusions. Our present study identifies a novel heterozygous WFS1 variant associated with LFSNHL in a Chinese family.

Cochlear Implantation Outcomes in Patients with Auditory Neuropathy Spectrum Disorder of Genetic and Non-Genetic Etiologies: A Multicenter Study

With diverse etiologies and clinical features, the management of pediatric auditory neuropathy spectrum disorder (ANSD) is often challenging, and the outcomes of cochlear implants (CIs) are variable. This study aimed to investigate CI outcomes in pediatric patients with ANSD of different etiologies. Thirty-six children with ANSD who underwent cochlear implantation between 2001 and 2021 were included. Comprehensive etiological analyses were conducted, including a history review, next-generation sequencing-based genetic examinations, and imaging studies using high-resolution computed tomography and magnetic resonance imaging. Serial behavioral and speech audiometry were performed before and after surgery, and the outcomes with CI were evaluated using the Categories of Auditory Performance (CAP) and Speech Intelligibility Rating (SIR) scores. By etiology, 18, 1, 1, and 10 patients had OTOF-related, WFS1-related, OPA1-related, and cochlear nerve deficiency (CND)-related ANSD, respectively. Six patients had no definite etiology. The average CI-aided behavioral threshold was 28.3 ± 7.8 dBHL, and those with CND-related ANSD were significantly worse than OTOF-related ANSD. The patients’ median CAP and SIR scores were 6 and 4, respectively. Favorable CI outcomes were observed in patients with certain etiologies of ANSD, particularly those with OTOF (CAP/SIR scores 5–7/2–5), WFS1 (CAP/SIR score 6/5), and OPA1 variants (CAP/SIR score 7/5). Patients with CND had suboptimal CI outcomes (CAP/SIR scores 2–6/1–3). Identifying the etiologies in ANSD patients is crucial before surgery and can aid in predicting prognoses.

GJB2 Is a Major Cause of Non-Syndromic Hearing Impairment in Senegal

This study aimed to investigate GJB2 (MIM: 121011) and GJB6 (MIM: 604418) variants associated with familial non-syndromic hearing impairment (HI) in Senegal. We investigated a total of 129 affected and 143 unaffected individuals from 44 multiplex families by segregating autosomal recessive non-syndromic HI, 9 sporadic HI cases of putative genetic origin, and 148 control individuals without personal or family history of HI. The DNA samples were screened for GJB2 coding-region variants and GJB6-D3S1830 deletions. The mean age at the medical diagnosis of the affected individuals was 2.93 ± 2.53 years [range: 1−15 years]. Consanguinity was present in 40 out of 53 families (75.47%). Variants in GJB2 explained HI in 34.1% (n = 15/44) of multiplex families. A bi-allelic pathogenic variant, GJB2: c.94C>T: p.(Arg32Cys) accounted for 25% (n = 11/44 families) of familial cases, of which 80% (n = 12/15) were consanguineous. Interestingly, the previously reported “Ghanaian” founder variant, GJB2: c.427C>T: p.(Arg143Trp), accounted for 4.5% (n = 2/44 families) of the families investigated. Among the normal controls, the allele frequency of GJB2: c.94C>T and GJB2: c.427C>T was estimated at 1% (2/148 ∗ 2) and 2% (4/148 ∗ 2), respectively. No GJB6-D3S1830 deletion was identified in any of the HI patients. This is the first report of a genetic investigation of HI in Senegal, and suggests that GJB2: c.94C>T: p.(Arg32Cys) and GJB2: c.427C>T: p.(Arg143Trp) should be tested in clinical practice for congenital HI in Senegal.

[Childhood hearing screening: achievements, difficulties, and possible ways to improve]

Hearing impairment is the most common sensory impairment that is seen among adults and children. The frequency of congenital hearing loss is well-known due to implementation of newborn hearing screening. Hearing may change throughout a lifetime due to different factors and, therefore, the number of hearing impaired children increases with age. Introduction of universal newborn hearing screening has enabled earlier detection of hearing loss including unilateral and minimal disorders. Nevertheless, despite significant progress made in this field, there is still a group of hearing impairments that stay undiagnosed timely. Auditory neuropathy spectrum disorders, late-onset hearing loss, low-frequency and minimal hearing impairment are sometimes missed in newborn hearing screening or they manifest later. These types of hearing disorders are covered in detail in this review as well as possible ways of increasing the effectiveness of early diagnosis.

Autosomal-dominant WFS1-related disorder-Report of a novel WFS1 variant and review of the phenotypic spectrum of autosomal recessive and dominant forms

Wolfram syndrome was initially reported as an autosomal recessive (AR), progressive neurodegenerative disorder that leads to diabetes insipidus, childhood onset diabetes mellitus (DM), optic atrophy, and deafness (D) also known as DIDMOAD. However, heterozygous dominant pathogenic variants in Wolfram syndrome type 1 (WFS1) may lead to distinct, allelic conditions, described as isolated sensorineural hearing loss (SNHL), syndromic SNHL, congenital cataracts, or early onset DM. We report a family with a novel dominant, likely pathogenic variant in WFS1 (NM_006005.3) c.2605_2616del12 (p.Ser869_His872del), resulting in cataracts, SNHL, and DM in a female and her mother. A maternal aunt had cataracts, DM, and SNHL but was not tested for the familial WFS1 mutation. Both the mother and maternal aunt had early menopause by age 43 years and infertility which may be a coincidental finding that has not been associated with autosomal dominant AD WFS1-related disorder to the best of our knowledge. Screening at risk individuals in families with the AR Wolfram syndrome, for DM, SNHL, and for cataracts is indicated.

GJB2 and GJB6 Mutations in Non-Syndromic Childhood Hearing Impairment in Ghana

Our study aimed to investigate GJB2 (connexin 26) and GJB6 (connexin 30) mutations associated with non-syndromic childhood hearing impairment (HI) as well as the environmental causes of HI in Ghana. Medical reports of 1,104 students attending schools for the deaf were analyzed. Families segregating HI, as well as isolated cases of HI of putative genetic origin were recruited. DNA was extracted from peripheral blood followed by Sanger sequencing of the entire coding region of GJB2. Multiplex PCR and Sanger sequencing were used to analyze the prevalence of GJB6-D3S1830 deletion. Ninety-seven families segregating HI were identified, with 235 affected individuals; and a total of 166 isolated cases of putative genetic causes, were sampled from 11 schools for the deaf in Ghana. The environmental factors, particularly meningitis, remain a major cause of HI impairment in Ghana. The male/female ratio was 1.49. Only 59.6% of the patients had their first comprehensive HI test between 6 to 11 years of age. Nearly all the participants had sensorineural HI (99.5%; n = 639). The majority had pre-lingual HI (68.3%, n = 754), of which 92.8% were congenital. Pedigree analysis suggested autosomal recessive inheritance in 96.9% of the familial cases. GJB2-R143W mutation, previously reported as founder a mutation in Ghana accounted for 25.9% (21/81) in the homozygous state in familial cases, and in 7.9% (11/140) of non-familial non-syndromic congenital HI cases, of putative genetic origin. In a control population without HI, we found a prevalent of GJB2-R143W carriers of 1.4% (2/145), in the heterozygous state. No GJB6-D3S1830 deletion was identified in any of the HI patients. GJB2-R143W mutation accounted for over a quarter of familial non-syndromic HI in Ghana and should be investigated in clinical practice. The large connexin 30 gene deletion (GJB6-D3S1830 deletion) does not account for of congenital non-syndromic HI in Ghana. There is a need to employ next generation sequencing approaches and functional genomics studies to identify the other genes involved in most families and isolated cases of HI in Ghana.

Heterozygous missense variants of LMX1A lead to nonsyndromic hearing impairment and vestibular dysfunction

Unraveling the causes and pathomechanisms of progressive disorders is essential for the development of therapeutic strategies. Here, we identified heterozygous pathogenic missense variants of LMX1A in two families of Dutch origin with progressive nonsyndromic hearing impairment (HI), using whole exome sequencing. One variant, c.721G > C (p.Val241Leu), occurred de novo and is predicted to affect the homeodomain of LMX1A, which is essential for DNA binding. The second variant, c.290G > C (p.Cys97Ser), predicted to affect a zinc-binding residue of the second LIM domain that is involved in protein–protein interactions. Bi-allelic deleterious variants of Lmx1a are associated with a complex phenotype in mice, including deafness and vestibular defects, due to arrest of inner ear development. Although Lmx1a mouse mutants demonstrate neurological, skeletal, pigmentation and reproductive system abnormalities, no syndromic features were present in the participating subjects of either family. LMX1A has previously been suggested as a candidate gene for intellectual disability, but our data do not support this, as affected subjects displayed normal cognition. Large variability was observed in the age of onset (a)symmetry, severity and progression rate of HI. About half of the affected individuals displayed vestibular dysfunction and experienced symptoms thereof. The late-onset progressive phenotype and the absence of cochleovestibular malformations on computed tomography scans indicate that heterozygous defects of LMX1A do not result in severe developmental abnormalities in humans. We propose that a single LMX1A wild-type copy is sufficient for normal development but insufficient for maintenance of cochleovestibular function. Alternatively, minor cochleovestibular developmental abnormalities could eventually lead to the progressive phenotype seen in the families.

Time-controllable Nkcc1 knockdown replicates reversible hearing loss in postnatal mice

Identification of the causal effects of specific proteins on recurrent and partially reversible hearing loss has been difficult because of the lack of an animal model that provides reversible gene knockdown. We have developed the transgenic mouse line Actin-tTS::Nkcc1 tetO/tetO for manipulatable expression of the cochlear K+ circulation protein, NKCC1. Nkcc1 transcription was blocked by the binding of a tetracycline-dependent transcriptional silencer to the tetracycline operator sequences inserted upstream of the Nkcc1 translation initiation site. Administration of the tetracycline derivative doxycycline reversibly regulated Nkcc1 knockdown. Progeny from pregnant/lactating mothers fed doxycycline-free chow from embryonic day 0 showed strong suppression of Nkcc1 expression (~90% downregulation) and Nkcc1 null phenotypes at postnatal day 35 (P35). P35 transgenic mice from mothers fed doxycycline-free chow starting at P0 (delivery) showed weaker suppression of Nkcc1 expression (~70% downregulation) and less hearing loss with mild cochlear structural changes. Treatment of these mice at P35 with doxycycline for 2 weeks reactivated Nkcc1 transcription to control levels and improved hearing level at high frequency; i.e., these doxycycline-treated mice exhibited partially reversible hearing loss. Thus, development of the Actin-tTS::Nkcc1 tetO/tetO transgenic mouse line provides a mouse model for the study of variable hearing loss through reversible knockdown of Nkcc1.