The congenital hearing phenotype in GJB2 in Queensland, Australia: V37I and mild hearing loss predominates

GJB2 was originally identified in severe, non-syndromic sensorineural hearing loss (SNHL), but was subsequently associated with mild and moderate SNHL. Given the increasing utilisation of genetic testing pre-conceptually, prenatally, and neonatally, it is crucial to understand genotype-phenotype correlations. This study evaluated the nature and frequency of GJB2 variants in an Australian paediatric population with varying degrees of SNHL ascertained through newborn hearing screening. Audiograms from individuals with GJB2 variants and/or a GJB6 deletion (GJB6-D13S11830) were retrospectively reviewed (n = 127). Two-thirds were biallelic (homozygous/compound heterozygous) for pathogenic/likely pathogenic variants of GJB2 and/or GJB6 (n = 80). The most frequent variant was c.109 G > A, followed by c.35delG and c.101 T > C. Compared to biallelic carriage of other GJB2 variants, c.109 G > A positive individuals (homozygous/compound heterozygous) were more likely to have mild HL at their initial and latest audiograms (p = 0.0004). Biallelic carriage of c.35delG was associated with moderately-severe or greater SNHL at both initial and latest audiograms (p = 0.007). The c.101 T > C variant presented with milder SNHL and U-shaped audiograms (p = 0.02). In this agnostically identified cohort, mild SNHL predominated in GJB2/GJB6 carriers in contrast to previous studies targeting individuals with significant loss. Consequently, c.109 G > A, associated with milder phenotypes, was the most frequent. This study provides valuable data to support prognostic confidence in genetic counselling.

Comparative analysis of allele frequencies of 15 deafness gene variants between hearing-loss and normal populations in Henan, China

Background

Hearing loss is found in more than 5 % of cases worldwide. Hearing loss is divided into three types: Sensorineural hearing loss, Combined hearing loss and Conductive hearing loss. Among them, no less than 50 % of pediatric cases of sensorineural hearing loss are genetic. In Henan, China, there are no statistics on the allele frequency of deafness gene variants.

Methods

We divided 2178 subjects enrolled at the Third Affiliated Hospital of Zhengzhou College from January 2019 to March 2021 into a hearing loss group and a normal control group. We performed array and pathogenicity classification for screening the 15 deafness gene variants, calculated and compared the allele frequency of the deafness gene variants, and then compared the hearing loss diagnosis rate between the hearing loss group and the normal control group.

Results

We found that in the hearing loss group, the overall allele frequency of all detected variants was 16.6 %. Comparative analysis showed that the allele frequencies of GJB2 c.235delC variant, GJB3 c.538C > T variant and SLC26A4 c.919-2A > G variant were significantly higher than those of the East Asian population average in the gnomAD database. At the same time, our study confirmed that GJB3 c.538C > T variant may not be the disease-causing variant of hearing loss.

Conclusions

These results support genetic counseling and rational prediction of risk for deafness.

Confirmation of COL4A6 variants in X-linked nonsyndromic hearing loss and its clinical implications

Hearing loss (HL) is one of the most common sensory defects, of which X-linked nonsyndromic hearing loss (NSHL) accounts for only 1-2%. While a COL4A6 variant has been reported in a single Hungarian family with NSHL associated with inner ear malformation, causative role of COL4A6 variants and their phenotypic consequences in NSHL remain elusive. Here we report two families in which we identified a male member with X-linked HL. Each has inherited a rare hemizygous COL4A6 variant from their respective mothers, NM_001287758.1: c.3272 G > C (p.Gly1091Ala) and c.951 + 1 G > C. An in vitro minigene splicing assay revealed that c.951 + 1 G > T leads to skipping of exon 15, strongly suggesting a pathogenic role for this variant in the HL phenotype. The p.Gly1091Ala variant is classified as a variant of unknown significance based on the variant interpretation guidelines. This report provides evidence for variants in the COL4A6 gene resulting in X-linked NSHL. It highlights the importance of in-depth genetic studies in all family members in addition to the proband, especially in multiplex families, to determine the precise etiology of HL.

Comparison of the Motor Performance and Vestibular Function in Infants with a Congenital Cytomegalovirus Infection or a Connexin 26 Mutation: A Preliminary Study

OBJECTIVES

Hearing-impaired children are at risk for vestibular damage and delayed motor development. Two major causes of congenital hearing loss are cytomegalovirus (CMV) infection and connexin (Cx) 26 mutations. Comparison of the motor performance and vestibular function between these specific groups is still underexplored. The objective of this study was to investigate the impact of congenital (c)CMV and Cx26 on the motor performance and vestibular function in 6 months old infants.

DESIGN

Forty children (mean age 6.7 months; range 4.8 to 8.9 months) participated in this cross-sectional design and were recruited from the Flemish CMV registry. They were divided into five age-matched groups: normal-hearing control, asymptomatic cCMV, normal-hearing symptomatic cCMV, hearing-impaired symptomatic cCMV, and hearing-impaired Cx26. Children were examined with the Peabody Developmental Motor Scales-2 and cervical vestibular-evoked myogenic potential (cVEMP) test.

RESULTS

Symptomatic hearing-impaired cCMV children demonstrated a significantly lower gross motor performance compared with the control group (p = 0.005), the asymptomatic cCMV group (p = 0.034), and the Cx26 group (0.016). In this symptomatic hearing-impaired cCMV group, 4 out of 8 children had absent cVEMP responses that were related to the weakest gross motor performance. The Cx26 children showed no significant delay in motor development compared with the control children and none of these children had absent cVEMP responses.

CONCLUSIONS

The weakest gross motor performance was found in symptomatic hearing-impaired cCMV-infected children with absent cVEMP responses. These results suggest that abnormal saccular responses are a major factor for this delayed motor development, although more work is needed including comprehensive vestibular function testing to verify this.

Rare compound heterozygosity involving dominant and recessive mutations of GJB2 gene in an assortative mating hearing impaired Indian family

Connexin 26 (Cx-26), a gap junction protein coded by GJB2 gene, plays a very important role in recycling of potassium ions, one of the vital steps in the mechanotransduction process of hearing. Mutations in the GJB2 gene have been associated with both autosomal recessive as well as dominant nonsyndromic hearing loss. As Cx-26 is linked with skin homeostasis, mutations in this gene are sometimes associated with syndromic forms of hearing loss showing skin anomalies. We report here a non consanguineous assortatively mating hearing impaired family with one of the hearing impaired partners, their hearing impaired sibling and hearing impaired offspring showing compound heterozygosity in the GJB2 gene, involving a dominant mutation p.R184Q and two recessive mutations p.Q124X and c.IVS 1+1G>A in a unique triallelic combination. To the best of our knowledge, this is the first report from India on p.R184Q mutation in the GJB2 gene associated with rare compound heterozygosity showing nonsyndromic presentation.

Autosomal dominant hearing loss resulting from p.R75Q mutation in the GJB2 gene: nonsyndromic presentation in a South Indian family

Mutations in the GJB2 gene encoding the gap junction protein Connexin 26 have been associated with autosomal recessive as well as dominant nonsyndromic hearing loss. Owing to the involvement of connexins in skin homeostasis, GJB2 mutations have also been associated with syndromic forms of hearing loss showing various skin manifestations. We report an assortatively mating hearing impaired family of south Indian origin with three affected members spread over two generations, having p.R75Q mutation in the GJB2 gene in the heterozygous condition. The inheritance pattern was autosomal dominant with mother and son being affected. Dermatological and histopathologic examinations showed absence of palmoplantar keratoderma. To the best of our knowledge, this is the first report from India on p.R75Q mutation in the GJB2 gene with nonsyndromic hearing loss.

Prediction of cochlear implant performance by genetic mutation: the spiral ganglion hypothesis

BACKGROUND

Up to 7% of patients with severe-to-profound deafness do not benefit from cochlear implantation. Given the high surgical implantation and clinical management cost of cochlear implantation (>$1 million lifetime cost), prospective identification of the worst performers would reduce unnecessary procedures and healthcare costs. Because cochlear implants bypass the membranous labyrinth but rely on the spiral ganglion for functionality, we hypothesize that cochlear implant (CI) performance is dictated in part by the anatomic location of the cochlear pathology that underlies the hearing loss. As a corollary, we hypothesize that because genetic testing can identify sites of cochlear pathology, it may be useful in predicting CI performance.

METHODS

29 adult CI recipients with idiopathic adult-onset severe-to-profound hearing loss were studied. DNA samples were subjected to solution-based sequence capture and massively parallel sequencing using the OtoSCOPE(®) platform. The cohort was divided into three CI performance groups (good, intermediate, poor) and genetic causes of deafness were correlated with audiometric data to determine whether there was a gene-specific impact on CI performance.

RESULTS

The genetic cause of deafness was determined in 3/29 (10%) individuals. The two poor performers segregated mutations in TMPRSS3, a gene expressed in the spiral ganglion, while the good performer segregated mutations in LOXHD1, a gene expressed in the membranous labyrinth. Comprehensive literature review identified other good performers with mutations in membranous labyrinth-expressed genes; poor performance was associated with spiral ganglion-expressed genes.

CONCLUSIONS

Our data support the underlying hypothesis that mutations in genes preferentially expressed in the spiral ganglion portend poor CI performance while mutations in genes expressed in the membranous labyrinth portend good CI performance. Although the low mutation rate in known deafness genes in this cohort likely relates to the ascertainment characteristics (postlingual hearing loss in adult CI recipients), these data suggest that genetic testing should be implemented as part of the CI evaluation to test this association prospectively.