High Incidence of GJB2 Mutations During Screening of Newborns for Hearing Loss in Austria

Mutational spectrum in patients with dominant non-syndromic hearing loss in Austria

PURPOSE

Hearing loss (HL) is often monogenic. The clinical importance of genetic testing in HL may further increase when gene therapy products become available. Diagnoses are, however, complicated by a high genetic and allelic heterogeneity, particularly of autosomal dominant (AD) HL. This work aimed to characterize the mutational spectrum of AD HL in Austria.

METHODS

In an ongoing prospective study, 27 consecutive index patients clinically diagnosed with non-syndromic AD HL, including 18 previously unpublished cases, were analyzed using whole-exome sequencing (WES) and gene panels. Novel variants were characterized using literature and bioinformatic means. Two additional Austrian medical centers provided AD HL mutational data obtained with in-house pipelines. Other Austrian cases of AD HL were gathered from literature.

RESULTS

The solve rate (variants graded as likely pathogenic (LP) or pathogenic (P)) within our cohort amounted to 59.26% (16/27). MYO6 variants were the most common cause. One third of LP/P variants were truncating variants in haploinsufficiency genes. Ten novel variants in HL genes were identified, including six graded as LP or P. In one cohort case and one external case, the analysis uncovered previously unrecognized syndromic presentations.

CONCLUSION

More than half of AD HL cases analyzed at our center were solved with WES. Our data demonstrate the importance of genetic testing, especially for the diagnosis of syndromic presentations, enhance the molecular knowledge of genetic HL, and support other laboratories in the interpretation of variants.

High Prevalence of MYO6 Variants in an Austrian Patient Cohort With Autosomal Dominant Hereditary Hearing Loss

INTRODUCTION

Genetic hearing loss (HL) is often monogenic. Whereas more than half of autosomal recessive (AR) cases in Austria are caused by mutations in a single gene, no disproportionately frequent contributing genetic factor has been identified in cases of autosomal dominant (AD) HL. The genetic characterization of HL continues to improve diagnosis, genetic counseling, and lays a foundation for the development of personalized medicine approaches.

METHODS

Diagnostic HL panel screening was performed in an Austrian multiplex family with AD HL, and segregation was tested with polymerase chain reaction and Sanger sequencing. In an independent approach, 18 unrelated patients with AD HL were screened for causative variants in all known HL genes to date and segregation was tested if additional family members were available. The pathogenicity of novel variants was assessed based on previous literature and bioinformatic tools such as prediction software and protein modeling.

RESULTS

In six of the 19 families under study, candidate pathogenic variants were identified in MYO6, including three novel variants (p.Gln441Pro, p.Ser612Tyr, and p.Gln650ValfsTer7). Some patients carried more than one likely pathogenic variant in known deafness genes.

CONCLUSION

These results suggest a potential high prevalence of MYO6 variants in Austrian cases of AD HL. The presence of multiple rare HL variants in some patients highlights the relevance of considering multiple-hit diagnoses for genetic counseling and targeted therapy design.

Genetics of Hearing Impairment in North-Eastern Romania-A Cost-Effective Improved Diagnosis and Literature Review

Background: We have investigated the main genetic causes for non-syndromic hearing impairment (NSHI) in the hearing impairment individuals from the North-Eastern Romania and proposed a cost-effective diagnosis protocol. Methods: MLPA followed by Sanger Sequencing were used for all 291 patients included in this study. Results: MLPA revealed abnormal results in 141 cases (48.45%): 57 (40.5%) were c.35delG homozygous, 26 (18.44%) were c.35delG heterozygous, 14 (9.93%) were compound heterozygous and 16 (11.35%) had other types of variants. The entire coding region of GJB2 was sequenced and out of 150 patients with normal results at MLPA, 29.33% had abnormal results: variants in heterozygous state: c.71G>A (28%), c.457G>A (20%), c.269T>C (12%), c.109G>A (12%), c.100A>T (12%), c.551G>C (8%). Out of 26 patients with c.35delG in heterozygous state, 38.46% were in fact compound heterozygous. Conclusions: We identified two variants: c.109G>A and c.100A>T that have not been reported in any study from Romania. MLPA is an inexpensive, rapid and reliable technique that could be a cost-effective diagnosis method, useful for patients with hearing impairment. It can be adaptable for the mutation spectrum in every population and followed by Sanger sequencing can provide a genetic diagnosis for patients with different degrees of hearing impairment.

TMPRSS3 regulates cell viability and apoptosis processes of HEI-OC1 cells via regulation of the circ-Slc4a2, miR-182 and Akt cascade

BACKGROUND

The present study aimed to investigate the functions and regulation mechanism of the transmembrane protease, serine 3 (TMPRSS3), which plays an important role in sensorineural hearing loss.

METHODS

House Ear Institute-Organ of Corti 1 (HEI-OC1) cells, comprising auditory-related cells, were used in the present study. An overexpression vector and small hairpin RNA target on TMPRSS3 were designed and transfected into HEI-OC1 cells. Circular RNA (circRNA) sequencing was conducted and expression profiles were obtained. The circular structure of circRNAs was validated with a polymerase chain reaction and Sanger sequencing using convergent and divergent primers.

RESULTS

Overexpression of TMPRSS3 increased cell viability, whereas suppression of TMPRSS3 increased the percentage of apoptotic cells and decreased cell viability, compared to the control group. circRNA sequencing provided expression profiles indicating that the overexpression of TMPRSS3 increased the expression level of 195 circRNAs. Results of GO (Gene Ontology) and KEGG (Kyoto Encyclopedia of Genes and Genomes) studies indicated that the circRNAs are focused on the RAS signaling pathway. The pathway, circ-Slc41a2 (chr10: 82744115|82767120), miR-182 and Akt, might comprise one of the key cascades of TMPRSS3.

CONCLUSIONS

TMPRSS3 is an important molecule in the regulation of cell viability and cell apoptosis of HEI-OC1 cells. Its functions are dependent on the circ-Slc41a2, miR-182 and Akt cascade.

The Analysis of A Frequent TMPRSS3 Allele Containing P.V116M and P.V291L in A Cis Configuration among Deaf Koreans

We performed targeted re-sequencing to identify the genetic etiology of early-onset postlingual deafness and encountered a frequent TMPRSS3 allele harboring two variants in a cis configuration. We aimed to evaluate the pathogenicity of the allele. Among 88 cochlear implantees with autosomal recessive non-syndromic hearing loss, subjects with GJB2 and SLC26A4 mutations were excluded. Thirty-one probands manifesting early-onset postlingual deafness were sorted. Through targeted re-sequencing, we detected two families with a TMPRSS3 mutant allele containing p.V116M and p.V291L in a cis configuration, p.[p.V116M; p.V291L]. A minor allele frequency was calculated and proteolytic activity was measured. A p.[p.V116M; p.V291L] allele demonstrated a significantly higher frequency compared to normal controls and merited attention due to its high frequency (4.84%, 3/62). The first family showed a novel deleterious splice site variant—c.783-1G>A—in a trans allele, while the other showed homozygosity. The progression to deafness was noted within the first decade, suggesting DFNB10. The proteolytic activity was significantly reduced, confirming the severe pathogenicity. This frequent mutant allele significantly contributes to early-onset postlingual deafness in Koreans. For clinical implication and proper auditory rehabilitation, it is important to pay attention to this allele with a severe pathogenic potential.

A Novel Mutation in SLC26A4 Causes Nonsyndromic Autosomal Recessive Hearing Impairment

BACKGROUND

Heterozygous mutations in GJB2 (MIM: 121011) encoding the gap junction protein connexin 26 are overrepresented in patient groups suffering from nonsyndromic sensorineural hearing impairment (HI) implying the involvement of additional genetic factors. Mutations in SLC26A4 (MIM: 605646), encoding the protein pendrin can cause both Pendred syndrome and autosomal recessive, nonsyndromic HI locus 4 type sensorineural HI (MIM: 600791).

OBJECTIVES

Aim of this study was to investigate the role of SLC26A4 coding mutations in a nonsyndromic hearing impairment (NSHI) patient group bearing heterozygous GJB2 35delG mutations.

DESIGN

We analyzed the 20 coding exons of SLC26A4 in a group of patients (n = 15) bearing heterozygous 35delG mutations and exclusively suffering from congenital HI.

RESULTS

In a case of bilateral congenital hearing loss we identified a rare, novel SLC26A4 exon 2 splice donor mutation (c.164+1delG) predicted to truncate pendrin in the first cytoplasmic domain, as a compound heterozygote with the pathogenic missense mutation c.1061T>C (p.354F>S; rs111033243).

CONCLUSIONS

Screening for SLC26A4 mutations may identify the genetic causes of hearing loss in patients bearing heterozygous mutations in GJB2.

HYPOTHESIS

SLC26A4 coding mutations are genetic causes for nonsyndromic HI in patients bearing heterozygous GJB2 35delG mutations.

Delayed auditory pathway maturation and prematurity

BACKGROUND

Hearing loss is the most common sensory disorder in developed countries and leads to a severe reduction in quality of life. In this uncontrolled case series, we evaluated the auditory development in patients suffering from congenital nonsyndromic hearing impairment related to preterm birth.

METHODS

Six patients delivered preterm (25th-35th gestational weeks) suffering from mild to profound congenital nonsyndromic hearing impairment, descending from healthy, nonconsanguineous parents and were evaluated by otoacoustic emissions, tympanometry, brainstem-evoked response audiometry, and genetic testing. All patients were treated with hearing aids, and one patient required cochlear implantation.

RESULTS

One preterm infant (32nd gestational week) initially presented with a 70 dB hearing loss, accompanied by negative otoacoustic emissions and normal tympanometric findings. The patient was treated with hearing aids and displayed a gradual improvement in bilateral hearing that completely normalized by 14 months of age accompanied by the development of otoacoustic emission responses. Conclusions We present here for the first time a fully documented preterm patient with delayed auditory pathway maturation and normalization of hearing within 14 months of birth. Although rare, postpartum development of the auditory system should, therefore, be considered in the initial stages for treating preterm hearing impaired patients.

The promoter mutation c.-259C>T (-3438C>T) is not a common cause of non-syndromic hearing impairment in Austria

The objective of this study was to investigate the relevance of routine assessment of c.-259C>T in the Austrian newborn screening program. Homozygous and compound heterozygous mutations in the coding region of the human gene encoding gap junction protein GJB2 (Connexin 26) cause up to 50 % of neonatal autosomal recessive non-syndromic hearing impairment identified in Caucasian newborn screening programs. More recently, a null mutation in the GC box of the GJB2 basal promoter c.-259C>T has been described which causes hearing impairment by completely suppressing GJB2 promoter activity. We determined the occurrence of c.-259C>T in cases of non-syndromic hearing impairment lacking known pathogenic alterations in GJB2 (n = 43), a non-syndromic hearing impaired patient group (n = 15) bearing the heterozygous GJB2 mutations c.35delG, c.[79G>A];[341A>G] (p. [V27I];[E114G]), c.109G>A (p.V37I), c.154G>C (p.V52L), c.262G>T (p.A88S), c.269T>C (p.L90P) and c.551G>C (p.R184P) and in a normal hearing group lacking alterations in GJB2 (n = 50). In the analyzed groups, no occurrence of c.-259C>T was found. The c.-259C>T mutation, previously described as -3438C>T, is not a common cause of non-syndromic hearing impairment alone or together with heterozygous pathogenic GJB2 mutations that are statistically overrepresented in non-syndromic hearing impaired patient groups. Screening of newborns for c.-259C>T is therefore unlikely to be commonly found in Austrian NSHI patients but could make a significant contribution to non-syndromic hearing impairment in other populations.

Connexin 26 gene mutations in non-syndromic hearing loss among Kuwaiti patients

OBJECTIVE

To study connexin 26 (Cx26) gene mutations among autosomal recessive non-syndromal hearing loss in Kuwaiti patients and evaluate their effect on phenotypes.

SUBJECTS AND METHODS

This cross sectional study included 100 patients aged between 6 months and 18 years, who were referred to the Sheikh Salem Al-Ali Centre for audiology and speech evaluation of autosomal recessive non-syndromic sensorineural hearing loss confirmed by clinico-genetic evaluation and a battery of diagnostic tests. Gene profiling and sequencing were performed to detect the presence and nature of Cx26 mutation.

RESULTS

Of the 100 patients, mutation of Cx26 gene was detected in 15 patients (15%) of which 9 (60%) cases were heterozygous and 6 cases (40%) were homozygous. Eighty per cent of the 15 Cx26 positive cases resulted from the 35delG mutation. Among the heterozygous cases, 6 (66.6%) were positive for 35delG. All 6 homozygous patients were positive for the 35delG mutation. A significant correlation was found between genetic findings (p = 0.013) and family history (p = 0.029), as well as the onset (p = 0.015), course (p = 0.033), degree and configuration of hearing loss (p = 0.001).

CONCLUSION

Among the selected Kuwaiti population sample, the Cx26 gene mutation was responsible for 15% of autosomal recessive non-syndromic sensorineural hearing loss. We recommend that screening for Cx26 gene mutation be considered in the screening strategy of patients with non-syndromic childhood hearing loss for counselling and management purposes. .

Compound heterozygosity for dominant and recessive GJB2 mutations in a Tunisian family and association with successful cochlear implant outcome

OBJECTIVES

Mutations of GJB2 encoding connexin 26 are the most common cause of hearing loss. They are responsible for up to 50% of ARNSHL. The pathogenic mutations in this gene are generally inherited recessively. Dominant mutations in GJB2 also cause hearing loss, either in isolated non-syndromic form or as part of a syndrome associated with various skin disorders.

METHODS

We screened a Tunisian child affected by congenital, bilateral, profound, sensorineural hearing loss for mutations in GJB2 gene using PCR and direct sequencing.

RESULTS

The proband was found to be compound heterozygous for recessive and dominant GJB2 mutations respectively p.V37I (c.109G > A) and p.R143Q (c.428G > A). Surprisingly the hearing mother is a carrier for this dominant GJB2 mutation. This proband underwent a cochlear implant at four years old. The evaluation using APCEI and IT-MAIS tests at six months post implantation indicates a successful cochlear implant outcome since the deaf child began to acquire language abilities and auditory sensation.

CONCLUSIONS

The p.R143Q mutation was described for the first time in Tunisia. We confirm the low penetrance of this mutation since the proband mother is a carrier despite her normal hearing. We show the effectiveness of cochlear implant to restore the communication abilities and auditory sensation for our patient.

Identification of a p.R143Q dominant mutation in the gap junction beta-2 gene in three Chinese patients with different hearing phenotypes

CONCLUSIONS

p.R143Q mutation in GJB2 can cause mild to profound bilateral sensorineural hearing impairment. Although not common in Chinese patients with hearing loss, it is important to identify the specific phenotype and genotype correlations of the dominant mutation in GJB2.

OBJECTIVE

Mutations in the GJB2 gene are the most common cause of nonsyndromic autosomal recessive sensorineural hearing loss. A few mutations in GJB2 have also been reported to cause dominant nonsyndromic or syndromic hearing loss. However, dominant mutation in GJB2 is not common in Chinese populations.

METHODS

Three patients with hearing impairment from Chinese families are reported here. Temporal CT scan, complete physical (including skin and hair) and otoscopic examinations, and an audiological study, including tympanometry, auditory brainstem response (ABR), auditory steady-state response (ASSR), and 40 Hz auditory event-related potential (40 Hz-AERP), were carried out. The two exons of GJB2, the coding exons of SLC26A4, and mitochondrial 12S rRNA were sequenced.

RESULTS

Sequencing of GJB2 in two patients showed a heterozygous c.428G>A (p.R143Q) mutation, and the third patient was identified with c.299delAT and c.428G>A compound heterozygous mutation. Sequence analysis of the coding exons of SLC26A4 and mitochondrial 12S rRNA was performed but no sequence aberration or deletion was found.

Genetics of congenital hearing impairment: a clinical approach

Hearing impairment (HI) is the most frequent sensory disorder, with a genetic etiology in >50% of all cases, due to mutations in >44 identified genes. Autosomal recessive inheritance explains the majority, with GJB2 (connexin 26) mutations accounting for 15-50% of paediatric HI. Delayed presentation of HI to 11-60 months in cases of biallelic GJB2 mutations is a concern, necessitating a good audiological follow-up in addition to neonatal hearing screening. Providing a genetic diagnosis in congenital HI has implications for the prognosis, the possible risk of associated medical manifestations, and precise genetic counseling of the family, and should be integrated into the medical examinations done in order to diagnose syndromic features. Large-scale mutation detection methods, such as micro arrays, are promising for wider genetic testing, but few studies on their clinical utility have been published, so far. Limitations of interpretation of genetic test results, combined with significant ethical issues, currently do not justify to institute genetic screening for GJB2 mutations in neonates before a diagnosis of HI is established.

Infant hearing loss and connexin testing in a diverse population

PURPOSE

Previous studies of connexin-related hearing loss have typically reported on mixed age groups or adults. To further address epidemiology and natural history of connexin-related hearing loss, we conducted a longitudinal study in an ethnically diverse cohort of infants and toddlers under 3 years of age. Our study compares infants with and without connexin-related hearing loss to examine differences in the prevalence of connexin and non-connexin-related hearing loss by ethnic origin, detection by newborn hearing screening, phenotype, neonatal risk factors, and family history. This is the first study to differentiate infants with and without connexin-related hearing loss.

METHODS

We enrolled 95 infants with hearing loss from whom both exons of Cx26 were sequenced and the Cx30 deletion was assayed. Demographic, family history, newborn hearing screening data, perinatal, and audiologic records were analyzed.

RESULTS

Genetic testing identified biallelic Cx26/30 hearing loss-associated variants in 24.7% of infants with a significantly lower prevalence in Hispanic infants (9.1%). Eighty-two infants underwent newborn hearing screening; 12 infants passed, 3 had connexin-related hearing loss. No differences in newborn hearing screening pass rate, neonatal complications, or hearing loss severity were detected between infants with and without connexin-related hearing loss. Family history correlates with connexin-related hearing loss.

CONCLUSIONS

Connexin-related hearing loss occurs in one quarter of infants in an ethnically diverse hearing loss population but with a lower prevalence in Hispanic infants. Not all infants with connexin-related hearing loss fail newborn hearing screening. Family history correlates significantly with connexin-related hearing loss. Genetic testing should not be deferred because of newborn complications. These results will have an impact on genetic testing for infant hearing loss.