Prevalence of Deafness-Associated Connexin-26 (GJB2) and Connexin-30 (GJB6) Pathogenic Alleles in a Large Patient Cohort from Eastern Sicily

Probability of high-risk genetic matching with oocyte and semen donors: complete gene analysis or genotyping test?

PURPOSE

To estimate the probability of high-risk genetic matching when assisted reproductive techniques (ART) are applied with double gamete donation, following an NGS carrier test based on a complete study of the genes concerned. We then determine the results that would have been obtained if the genotyping tests most widely used in Spanish gamete banks had been applied.

METHODS

In this descriptive observational study, 1818 gamete donors were characterised by NGS. The pathogenic variants detected were analysed to estimate the probability of high-risk genetic matching and to determine the results that would have been obtained if the three most commonly used genotyping tests in ART had been applied.

RESULTS

The probability of high-risk genetic matching with gamete donation, screened by NGS and complete gene analysis, was 5.5%, versus the 0.6-2.7% that would have been obtained with the genotyping test. A total of 1741 variants were detected, including 607 different variants, of which only 22.6% would have been detected by all three genotyping tests considered and 44.7% of which would not have been detected by any of these tests.

CONCLUSION

Our study highlights the considerable heterogeneity of the genotyping tests, which present significant differences in their ability to detect pathogenic variants. The complete study of the genes by NGS considerably reduces reproductive risks when genetic matching is performed with gamete donors. Accordingly, we recommend that carrier screening in gamete donors be carried out using NGS and a complete study with nontargeted analysis of the variants of the screened genes.

Genetic etiology of non-syndromic hearing loss in Europe

Hearing impairment not etiologically associated with clinical signs in other organs (non-syndromic) is genetically heterogeneous, so that over 120 genes are currently known to be involved. The frequency of mutations in each gene and the most frequent mutations vary throughout populations. Here we review the genetic etiology of non-syndromic hearing impairment (NSHI) in Europe. Over the years, epidemiological data were scarce because of the large number of involved genes, whose screening was not cost-effective until implementation of massively parallel DNA sequencing. In Europe, the most common form of autosomal recessive NSHI is DFNB1, which accounts for 11-57% of the cases. Mutations in STRC account for 16% of the recessive cases, and only a few more (MYO15A, MYO7A, LOXHD1, USH2A, TMPRSS3, CDH23, TMC1, OTOF, OTOA, SLC26A4, ADGRV1 and TECTA) have contributions higher than 2%. As regards autosomal-dominant NSHI, DFNA22 (MYO6) and DFNA8/12 (TECTA) represent the most common forms, accounting for 21% and 18% of elucidated cases, respectively. The contribution of ACTG1 and WFS1 drops to 9% in both cases, followed by POU4F3 (6.5%), MYO7A (5%), MYH14 and COL11A2 (4% each). Four additional genes contribute 2.5% each one (MITF, KCNQ4, EYA4, SOX10) and the remaining are residually represented. X-linked hearing loss and maternally-inherited NSHI have minor contributions in most countries. Further knowledge on the genetic epidemiology of NSHI in Europe needs a standardization of the experimental approaches and a stratification of the results according to clinical features, familial history and patterns of inheritance, to facilitate comparison between studies.

Analyses of del(GJB6-D13S1830) and del(GJB6-D13S1834) deletions in a large cohort with hearing loss: Caveats to interpretation of molecular test results in multiplex families

BACKGROUND

Mutations involving the closely linked GJB2 and GJB6 at the DFNB1 locus are a common genetic cause of profound congenital hearing loss in many populations. In some deaf GJB2 heterozygotes, a 309 kb deletion involving the GJB6 has been found to be the cause for hearing loss when inherited in trans to a GJB2 mutation.

METHODS

We screened 2,376 probands from a National DNA Repository of deaf individuals.

RESULTS

Fifty-two of 318 heterozygous probands with pathogenic GJB2 sequence variants had a GJB6 deletion. Additionally, eight probands had an isolated heterozygous GJB6 deletion that did not explain their hearing loss. In two deaf subjects, including one proband, a homozygous GJB6 deletion was the cause for their hearing loss, a rare occurrence not reported to date.

CONCLUSION

This study represents the largest US cohort of deaf individuals harboring GJB2 and GJB6 variants, including unique subsets of families with deaf parents. Testing additional members to clarify the phase of GJB2/GJB6 variants in multiplex families was crucial in interpreting clinical significance of the variants in the proband. It highlights the importance of determining the phase of GJB2/GJB6 variants when interpreting molecular test results especially in multiplex families with assortative mating.

Real ear measurement (REM) and auditory performances with open, tulip and double closed dome in patients using hearing aids

OBJECTIVE

The aim of the study is to evaluate the importance of acoustic modifications generated by different commercially available ear-tips, focused on domes of receiver in the canal hearing aids using Real Ear Measurement (REM).

METHODS

We enrolled 110 people selecting 200 ears bearers of hearing aids. In every patient, we performed REM and audiological tests with three different dome types: Open, Tulip and Double Closed (DC). Data about real-ear occluded gain (REOG), Pure Tone Average (PTA), Word Recognition Score (WRS) with aids switched on in Free Field, Ear and Auditory Comfort were collected and analyzed.

RESULTS

REOG gain was statistically significant different between the three types of dome, with a DC that always closes the external auditory canal (EAC) (p < 0.001). There was no statistically significant difference between the PTA (p = 0.11). Regarding the WRS there were statistically significant differences between Open and DC dome (p < 0.001) and between Tulip and DC dome (p < 0.001), with worse discrimination when using DC. Both auditory and ear comfort are worse in the DC than in the other two domes (p < 0.001). From measured REOG gain values, in 135 cases Tulip dome does not occlude the EAC, with a statistically significant difference compared to DC (p < 0.001; Odd Ratio 0.0012; 95% CI 0.001-0.0196).

CONCLUSION

Our study confirms the necessity to perform REM to evaluate if the prescription target is achieved, especially when tulip domes are used, because they may not occlude the ear canal, causing in some cases the reduction of the vocal discrimination.

Application of Cervical Vestibular-Evoked Myogenic Potentials in Adults with Moderate to Profound Sensorineural Hearing Loss: A Preliminary Study

Introduction  The cochlea and the vestibular receptors are closely related in terms of anatomy and phylogeny. Patients with moderate to profound sensorineural hearing loss (MPSHL) should have their vestibular organ functions tested.

Objective  To evaluate the incidence of vestibular abnormalities in patients with MPSHL and to study the correlation between the etiology of hearing loss (HL) and a possible damage to the labyrinth.

Methods  A case-control retrospective study was performed. In the case group, 20 adults with MPSHL of known etiology were included. The control group was composed of 15 adults with normal hearing. The case group was divided into 4 subgroups based on the etiology (bacterial meningitis, virus, vascular disease, congenital). Cervical vestibular-evoked myogenic potentials (cVEMPs) were used to rate the saccular function and lower vestibular nerve.

Results  The study was performed in 70 ears, and it highlighted the presence of early biphasic P1-N1 complex in 29 (71.5%) out of 40 ears in the study group, and in all of the 30 ears in the control group ( p  = 0.001). Regarding the presence or absence of cVEMPs among the four subgroups of patients with MPSHL, the data were statistically significant ( p  < 0.001). The comparison between the latencies and amplitude of P1-N1 in case and control groups from other studies and in the four subgroups of cases in the present study did not detect statistically significant differences.

Conclusion  The present study demonstrates that patients with MPSHL have a high incidence of damage to the labyrinthine organs, and it increases the current knowledge about the etiopathogenesis of sensorineural HL, which is often of unknown nature.

GJB2 and GJB6 Mutations in Hereditary Recessive Non-Syndromic Hearing Impairment in Cameroon

This study aimed to investigate GJB2 (connexin 26) and GJB6 (connexin 30) mutations associated with familial non-syndromic childhood hearing impairment (HI) in Cameroon. We selected only families segregating HI, with at least two affected individuals and with strong evidence of non-environmental causes. DNA was extracted from peripheral blood, and the entire coding region of GJB2 was interrogated using Sanger sequencing. Multiplex PCR and Sanger sequencing were used to analyze the prevalence of the GJB6-D3S1830 deletion. A total of 93 patients, belonging to 41 families, were included in the analysis. Hearing impairment was sensorineural in 51 out of 54 (94.4%) patients. Pedigree analysis suggested autosomal recessive inheritance in 85.4% (35/41) of families. Hearing impairment was inherited in an autosomal dominant and mitochondrial mode in 12.2% (5/41) and 2.4% (1/41) of families, respectively. Most HI participants were non-syndromic (92.5%; 86/93). Four patients from two families presented with type 2 Waardenburg syndrome, and three cases of type 2 Usher syndrome were identified in one family. No GJB2 mutations were found in any of the 29 families with non-syndromic HI. Additionally, the GJB6-D3S1830 deletion was not identified in any of the HI patients. This study confirms that mutations in the GJB2 gene and the del(GJB6-D13S1830) mutation do not contribute to familial HI in Cameroon.

Use of 3D Volume Rendering Based on High-Resolution Computed Tomography Temporal Bone in Patients with Cochlear Implants

Case series

Patients: Male, 50 • Male, 3 • Female, 55

Final Diagnosis: Malposition of the array

Symptoms: Deafness

Medication: —

Clinical Procedure: Cochlear Implant 3D rendering

Specialty: Audiology

A novel mutation of the EYA4 gene associated with post-lingual hearing loss in a proband is co-segregating with a novel PAX3 mutation in two congenitally deaf family members

OBJECTIVES

This work was aimed at establishing the molecular etiology of hearing loss in a 9-year old girl with post-lingual non-syndromic mild sensorineural hearing loss with a complex family history of clinically heterogeneous deafness.

METHODS

The proband's DNA was subjected to NGS analysis of a 59-targeted gene panel, with the use of the Ion Torrent PGM platform. Conventional Sanger sequencing was used for segregation analysis in all the affected relatives. The proband and all the other hearing impaired members of the family underwent a thorough clinical and audiological evaluation.

RESULTS

A new likely pathogenic mutation in the EYA4 gene (c.1154C > T; p.Ser385Leu) was identified in the proband and in her 42-year-old father with post-lingual non-syndromic profound sensorineural hearing loss. The EYA4 mutation was also found in the proband's grandfather and uncle, both showing clinical features of Waardenburg syndrome type 1. A novel pathogenic splice-site mutation (c.321+1G > A) of the PAX3 gene was found to co-segregate with the EYA4 mutation in these two subjects.

CONCLUSION

The identified novel EYA4 mutation can be considered responsible of the hearing loss observed in the proband and her father, while a dual molecular diagnosis was reached in the relatives co-segregating the EYA4 and the PAX3 mutations. In these two subjects the DFNA10 phenotype was masked by Waardenburg syndrome. The use of NGS targeted gene-panel, in combination with an extensive clinical and audiological examination led us to identify the genetic cause of the hearing loss in members of a family in which different forms of autosomal dominant deafness segregate. These results provide precise and especially important prognostic and follow-up information for the future audiologic management in the youngest affected member.

Spectrum and Frequency of the GJB2 Gene Pathogenic Variants in a Large Cohort of Patients with Hearing Impairment Living in a Subarctic Region of Russia (the Sakha Republic)

Pathogenic variants in the GJB2 gene, encoding connexin 26, are known to be a major cause of hearing impairment (HI). More than 300 allelic variants have been identified in the GJB2 gene. Spectrum and allelic frequencies of the GJB2 gene vary significantly among different ethnic groups worldwide. Until now, the spectrum and frequency of the pathogenic variants in exon 1, exon 2 and the flanking intronic regions of the GJB2 gene have not been described thoroughly in the Sakha Republic (Yakutia), which is located in a subarctic region in Russia. The complete sequencing of the non-coding and coding regions of the GJB2 gene was performed in 393 patients with HI (Yakuts—296, Russians—51, mixed and other ethnicities—46) and in 187 normal hearing individuals of Yakut (n = 107) and Russian (n = 80) populations. In the total sample (n = 580), we revealed 12 allelic variants of the GJB2 gene, 8 of which were recessive pathogenic variants. Ten genotypes with biallelic recessive pathogenic variants in the GJB2 gene (in a homozygous or a compound heterozygous state) were found in 192 out of 393 patients (48.85%). We found that the most frequent GJB2 pathogenic variant in the Yakut patients was c.-23+1G>A (51.82%) and that the second most frequent was c.109G>A (2.37%), followed by c.35delG (1.64%). Pathogenic variants с.35delG (22.34%), c.-23+1G>A (5.31%), and c.313_326del14 (2.12%) were found to be the most frequent among the Russian patients. The carrier frequencies of the c.-23+1G>A and с.109G>A pathogenic variants in the Yakut control group were 10.20% and 2.80%, respectively. The carrier frequencies of с.35delG and c.101T>C were identical (2.5%) in the Russian control group. We found that the contribution of the GJB2 gene pathogenic variants in HI in the population of the Sakha Republic (48.85%) was the highest among all of the previously studied regions of Asia. We suggest that extensive accumulation of the c.-23+1G>A pathogenic variant in the indigenous Yakut population (92.20% of all mutant chromosomes in patients) and an extremely high (10.20%) carrier frequency in the control group may indicate a possible selective advantage for the c.-23+1G>A carriers living in subarctic climate.

The high frequency of GJB2 gene mutation c.313_326del14 suggests its possible origin in ancestors of Lithuanian population

Background

Congenital hearing loss (CHL) is diagnosed in 1 – 2 newborns in 1000, genetic factors contribute to two thirds of CHL cases in industrialised countries. Mutations of the GJB2 gene located in the DFNB1 locus (13q11-12) are a major cause of CHL worldwide.

The aim of this cross-sectional study was to assess the contribution of the DFNB1 locus containing the GJB2 and GJB6 genes in the development of early onset hearing loss in the affected group of participants, to determine the population-specific mutational profile and DFNB1-related HL burden in Lithuanian population.

Methods

Clinical data were obtained from a collection of 158 affected participants (146 unrelated probands) with early onset non-syndromic HL. GJB2 and GJB6 gene sequencing and GJB6 gene deletion testing were performed. The data of GJB2 and GJB6 gene sequencing in 98 participants in group of self-reported healthy Lithuanian inhabitants were analysed.

Statistic summary, homogeneity tests, and logistic regression analysis were used for the assessment of genotype-phenotype correlation.

Results

Our findings show 57.5 % of affected participants with two pathogenic GJB2 gene mutations identified. The most prevalent GJB2 mutations were c.35delG, p. (Gly12Valfs*2) (rs80338939) and c.313_326del14, p. (Lys105Glyfs*5) (rs111033253) with allele frequencies 64.7 % and 28.3 % respectively. GJB6 gene mutations were not identified in the affected group of participants. The statistical analysis revealed significant differences between GJB2(−) and GJB2(+) groups in disease severity (p = 0.001), and family history (p = 0.01). The probability of identification of GJB2 mutations in patients with various HL characteristics was estimated. The carrier rate of GJB2 gene mutations – 7.1 % (~1 in 14) was identified in the group of healthy participants and a high frequency of GJB2-related hearing loss was estimated in our population.

Discussion

The results show a very high proportion of GJB2-positive individuals in the research group affected with sensorineural HL. The allele frequency of c.35delG mutation (64.7 %) is consistent with many previously published studies in groups of affected individuals of Caucasian populations. The high frequency of the c.313_326del14 (28.3 % of pathogenic alleles) mutation in affected group of participants was an unexpected finding in our study suggesting not only a high frequency of carriers of this mutation in our population but also its possible origin in Lithuanian ancestors. The high frequency of carriers of the c.313_326del14 mutation in the entire Lithuanian population is supported by it being identified twice in the ethnic Lithuanian group of healthy participants (a frequency 2.0 % of carriers in the study group).

Conclusion

Analysis of the allele frequency of GJB2 gene mutations revealed a high proportion of c. 313_326del14 (rs111033253) mutations in the GJB2-positive group suggesting its possible origin in Lithuanian forebears. The high frequency of carriers of GJB2 gene mutations in the group of healthy participants corresponds to the substantial frequency of GJB2-associated HL in Lithuania. The observations of the study indicate the significant contribution of GJB2 gene mutations to the pathogenesis of the disorder in the Lithuanian population and will contribute to introducing principles to predict the characteristics of the disease in patients.

Electronic supplementary material

The online version of this article (doi:10.1186/s12863-016-0354-9) contains supplementary material, which is available to authorized users.