Prevalence of the c.35delG and p.W24X mutations in the GJB2 gene in patients with nonsyndromic hearing loss from North-West Romania

Non-Syndromic Hearing Loss in a Romanian Population: Carrier Status and Frequent Variants in the GJB2 Gene

The genetic causes of autosomal recessive nonsyndromic hearing loss (ARNSHL) are heterogeneous and highly ethnic-specific. We describe GJB2 (connexin 26) variants and carrier frequencies as part of our study and summarize previously reported ones for the Romanian population. In total, 284 unrelated children with bilateral congenital NSHL were enrolled between 2009 and 2018 in northwestern Romania. A tiered diagnostic approach was used: all subjects were tested for c.35delG, c.71G>A and deletions in GJB6 (connexin 30) using PCR-based methods. Furthermore, 124 cases undiagnosed at this stage were analyzed by multiplex-ligation-dependent probe amplifications (MLPA), probe mix P163, and sequencing of GJB2 exon 2. Targeted allele-specific PCR/restriction fragment length polymorphism (RFLP) established definite ethio-pathogenical diagnosis for 72/284 (25.35%) of the cohort. Out of the 124 further analyzed, in 12 cases (9.67%), we found compound heterozygous point mutations in GJB2. We identified one case of deletion of exon 1 of the WFS1 (wolframin) gene. Carrier status evaluation used Illumina Infinium Global Screening Array (GSA) genotyping: the HINT cohort-416 individuals in northwest Romania, and the FUSE cohort-472 individuals in southwest Romania. GSA variants yielded a cumulated risk allele presence of 0.0284. A tiered diagnostic approach may be efficient in diagnosing ARNSHL. The summarized contributions to Romanian descriptive epidemiology of ARNSHL shows that pathogenic variants in the GJB2 gene are frequent among NSHL cases and have high carrier rates, especially for c.35delG and c.71G>A. These findings may serve in health strategy development.

Prevalence of GJB2 gene mutations correlated to presence of clinical and environmental risk factors in the etiology of congenital sensorineural hearing loss of the Romanian population

Although etiologically heterogeneous at least 50% of all early on-set hearing losses have a genetic cause and of these, the large majority, 75-80% are most probably autosomal recessive and 70% are non-syndromic. The rest of the congenital hearing losses are determined by clinical and environmental factors such as ototoxic medication, prematurity, and complications at birth. During the last decade it became clear that 50-80% of all such afflictions result from mutations in a single gene, GJB2, which encodes the protein Connexin 26. In order to, at least partially clarify this problem, especially in an emerging country such as Romania, where the problem is not studied adequately, we developed a comprehensive study of genetic, clinical and environmental risk factors for congenital hearing loss. The two most common variations of this gene, 35delG and W24X in children with positive diagnosis of bilateral severe to profound sensorineural hearing loss were investigated. A cohort of 34 children (20 female and 14 male), ages between 2 and 10 (mean age 4.62 years), coming from 33 non-related families were evaluated. All cases were diagnosed with severe or profound bilateral congenital SNHL. A statistical comparison of genetic and environmental/clinical prevalence was also attempted since the presence of a genetic disorder cannot rule out the role of other documented risk factors in the etiology of SNHL. The results showed that, 29.4% of cases (10/34) were homozygotic for the 35delG mutation 35delG/35delG), also known as genotype Δ/Δ. 5.88% of cases (2/34) belong to the heterozygotic bi-genic group 35delG/W24X. The clinical factors with high statistical significance for SNHL in a non-genetic group have no significance for genetic SNHL patients. Thus, the present study confirms the relatively high prevalence of the 35delG and W24X mutations in cases of congenital non-syndromic severe of profound bilateral SNHL.

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.

Analysis of GJB2 mutations and the clinical manifestation in a large Hungarian cohort

PURPOSE

Pathogenic variants of the gap junction beta 2 (GJB2) gene are responsible for about 50% of hereditary non-syndromic sensorineural hearing loss (NSHL). In this study, we report mutation frequency and phenotype comparison of different GJB2 gene alterations in Hungarian NSHL patients.

METHODS

The total coding region of the GJB2 gene was analyzed with Sanger or NGS sequencing for 239 patients with NSHL and 160 controls.

RESULTS

Homozygous and compound heterozygous GJB2 mutations were associated with early onset serious clinical phenotype in 28 patients. In 24 patients, two deletion or nonsense mutations were detected in individuals with mainly prelingual NSHL. In compound heterozygous cases, a combination of deletion and missense mutations associated with milder postlingual NSHL. A further 25 cases harbored single heterozygous GJB2 mutations mainly associated with later onset, milder clinical phenotype. The most common mutation was the c.35delG deletion, with 12.6% allele frequency. The hearing loss was more severe in the prelingual groups.

CONCLUSION

The mutation frequency of GJB2 in the investigated cohort is lower than in other European cohorts. The most serious cases were associated with homozygous and compound heterozygous mutations. In our cohort the hearing impairment and age of onset was not altered between in cases with only one heterozygous GJB2 mutation and wild type genotype, which may exclude the possibility of autosomal dominant inheritance. In early onset, severe to profound hearing loss cases, if the GJB2 analysis results in only one heterozygous alteration further next generation sequencing is highly recommended.

GJB2 and GJB6 genes mutations in children with non-syndromic hearing loss

Introduction. At the moment there is not enough data in Romania about the incidence of the main genetic mutations which can cause hearing loss.

Objective. The current research aims to determine on a representative sample the prevalence of two mutations of genes GJB2 -c.35delG and p.W24X- and two mutations of genes GJB6 -del(GJB6-D13S1830), del(GJB6-D13S1854) respectively - in patients with congenital nonsyndromic sensorineural hearing loss (CNSHL).

Methods: The sample group included 179 children with CNSHL. The evaluation consist in: a.Clinical, laboratory and imagistic examination; b.ENT exam and audiological evaluation. c.Two methods (semi-nested PCR technique followed by RFLP, validated with ARMS-PCR analysis) for detection of c.35delG and pW24X mutations; d.PCR-multiplex technique for detecting del(GJB6-D13S1830) and del (GJB6-D13S1854).

Results: The audiological diagnosis was: profound hearing loss in 116 patients (64.8%), severe hearing loss in 29 children (16.2%) and moderate hearing loss in 34 patients (representing 19% of the trial patients). The prevalence for the three mutations was: 27.3 % for c.35delG, 3.6 % for p.W24X and 0.28% for del(GJB6-D13S1830). The detection of the three mutations (two on GJB2 gene and one on GJB 6 gene) has allowed to establish the genetic cause for deafness in 45 patients, representing 25.14% of the sample group. Our study is reporting the first case in Romania with a mutation of gene GJB6. Mutation del(GJB6-D13S1854) lacked in all 179 patients.

Conclusion: The prevalence data obtained in the current research are comparable to data communicated by studies from other European countries.

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.

Auditory outcome after cochlear implantation in patients with congenital nonsyndromic hearing loss: influence of the GJB2 status

OBJECTIVE

To compare the audiologic outcome after cochlear implantation between 2 groups of patients with congenital nonsyndromic sensorineural hearing loss.

STUDY DESIGN

Retrospective cohort study.

SETTING

Department of Otorhinolaryngology, University hospital (tertiary referral center).

PATIENTS

From a bigger pool of implanted patients, 2 groups, each numbering 30 were enrolled. The patients from the first group were diagnosed with a Connexin 26 mutation (GJB2), whereas all of the patients from the second cohort were with a wild type genotype. Both groups were age matched, 1 to 7 years old at the age of implantation, with diagnosed congenital nonsyndromic sensorineural hearing loss.

MAIN OUTCOME MEASURES

Both groups were evaluated with the help evaluation of auditory responses to speech/EARS/test battery - LiP test (Listening Progress Profile), MTP tests 3,6,12 (Monosyllabic-Trochee-Polysyllabic Test), GASP test (Glendonald Auditory Screening Procedure), and others. Follow-up period was at least 36 months.

RESULTS

Mean test scores were compared at the 1st, 6th, 12th, 24th, and 36th month. LiP outcome was significantly better (p < 0.05) for the GJB2-related cohort for the whole follow-up period except at the first month. MTP3, 6, and 12 tests displayed the same statistically significant outcome in favor of the first group. In the open-set test GASP, the difference was apparent: 1.22, 2.40, 5.59, and 7.40 mean scores at the 6th, 12th, 24, and 36th months for the first cohort versus 0.00, 0.07, 0.81, and 1.74 for the GJB2-unrelated patients.

CONCLUSION

The results from our study suggest that children with GJB2-related deafness show better auditory performance after cochlear implantation than age-matched children with GJB2-nonrelated sensorineural hearing loss.

Lower carrier rate of GJB2 W24X ancestral Indian mutation in Roma samples from Hungary: implication for public health intervention

The purpose of this work was to characterise the W24X mutation of the GJB2 gene in order to provide more representative and geographicaly relevant carrier rates of healthy Roma subisolates and the Hungarian population. 493 Roma and 498 Hungarian healthy subjects were genotyped for the GJB2 c.71G>A (rs104894396, W24X) mutation by PCR-RFLP assay and direct sequencing. This is the first report on GJB2 W24X mutation in geographically subisolated Roma population of Hungary compared to local Hungarians. Comparing the genotype and allele frequencies of GJB2 rs104894396 mutation, significant difference was found in GG (98.4 vs. 99.8 %), GA (1.62 vs. 0.20 %) genotypes and A (0.8 vs. 0.1 %) allele between the Roma and Hungarian populations, respectively (p < 0.02). None of the subjects of Roma and Hungarian samples carried the GJB2 W24X AA genotype. Considerable result of our study, that the proportion of GJB2 W24X GA heterozygotes and the A allele frequency was eight times higher in Roma than in Hungarians. Considering the results, the mutant allele frequency both in Roma (0.8 %) and in Hungarian (0.1 %) populations is lower than expected from previous results, likely reflecting local differentiated subisolates of these populations and a suspected lower risk for GJB2 mutation related deafness. However, the significant difference in GJB2 W24X carrier rates between the Roma and Hungarians may initiate individual diagnostic investigations and effective public health interventions.

Prevalence of DFNB1 mutations in Slovak patients with non-syndromic hearing loss

OBJECTIVES

Non-syndromic hearing loss is one of the most common genetically determined diseases in human. The incidence is approximately 1:700 and most of the cases are caused by mutations in specific locus - DFNB1, which contains two genes -GJB2 and GJB6. For the GJB2 gene following mutations are most prevalent in specific populations - 35delG, 235delC, W24X and 167delT for Caucasians, Asians, Indians and Ashkenazi Jews, respectively. Large deletions are common in GJB6 gene. Many other mutations and polymorphisms were found in DFNB1 focused non-syndromic hearing loss studies thus the establishment of optimal screening protocol should be based on population specific mutation screening studies and is an objective in our study.

PATIENTS AND METHODS

In our study samples from 273 non-syndromic hearing loss patients were screened for mutations in coding and non-coding part of GJB2 gene and large deletion in GJB6 gene - del(GJB6-D13S1830).

RESULTS

Causal mutation on both chromosomes was detected in 24.57% of patients, another 9.9% carried causal mutation on one chromosome. Totally 7 polymorphisms: V27I, M34T, F83L, 354 C→T, R127H, V153I, 684 C→A and 11 causal mutations: IVS1+1 G→A, 35delG, W24X, V37I, E47X, 167delT, V84M, L90P, 310del14, 333-334delAA, R184Q were detected. No patient carried the GJB6 deletion mutation (del(GJB6-D13S1830)).

CONCLUSION

According to our results sequencing of GJB2 coding regions and IVS1+1G→A specific detection should explain approximately 25% of sporadic NSHL cases and these two tests are relevant for use as routine screening protocol for NSHL in Slovakia. The GJB6 del(GJB6-D13S1830) mutation was not detected in any of NSHL samples therefore it is not necessary to implement it in our routine screening protocol.

Prevalence of mutations located at the dfnb1 locus in a population of cochlear implanted children in eastern Romania

OBJECTIVE

Hearing loss is one of the major public health problems, with a genetic etiology in more than 60% of cases. Connexin 26 and connexin 30 mutations are the most prevalent causes of deafness. The aim of this study is to characterize and to establish the prevalence of the GJB2 and GJB6 gene mutations in a population of cochlear implanted recipients from Eastern Romania, this being the first report of this type in our country.

METHODS

We present a retrospective study that enrolled 45 Caucasian cochlear implanted patients with non-syndromic sensorineural severe to profound, congenital or progressive with early-onset idiopathic hearing loss. We performed sequential analysis of exon 1 and the coding exon 2 of the GJB2 gene including also the splice sites and analysis of the deletions del(GJB6-D13S1830), del(GJB6-D13S1854) and del(chr13:19,837,343-19,968,698).

RESULTS

The genetic analysis of the GJB2 gene identified connexin 26 mutations in 22 patients out of 45 (12 homozygous for c.35delG, 6 compound heterozygous and 4 with mutations only on one allele). We found 6 different mutations, the most prevalent being c.35delG - found on 32 alleles, followed by p.W24* - found on 2 alleles. We did not identify the deletions del(GJB6-D13S1830), del(GJB6-D13S1854) and del(chr13:19,837,343-19,968,698).

CONCLUSIONS

Although the most prevalent mutation was c.35delG (80% from all types of mutations), unexpectedly we identified 5 more different mutations. The presence of 6 different mutations on the GJB2 gene has implications in hearing screening programs development in our region and in genetic counseling.

Prenatal screening for the 35delG GJB2, del (GJB6-D13S1830), and del (GJB6-D13S1854) mutations in the Romanian population

OBJECTIVE

In this study, the aim of prenatal screening was to estimate the carrier frequency of the three mutations 35delG, del (GJB6-D13S1830), and del (GJB6-D13S1854), which are known to be the leading mutations of hereditary hearing loss in European populations.

METHODS

We performed a prenatal screening to assess the carrier frequency of the most common mutations at the DFNB1 gene locus in the general population. Samples of amniotic fluid (n=339) and chorionic villi (n=11) were taken from an unselected group of 350 unrelated pregnant women with normal hearing. Genomic fetal DNA was extracted and analyzed by PCR multiplex assays.

RESULTS

The rate of carriers for the 35delG GJB2 mutation was 3.14%, comparable to that of most Southeastern European populations. All samples were negative for GJB6-D13S1830 and GJB6-D13S1854 deletions. The genetic tests were considered for carrier detection and early diagnosis rather than termination of pregnancy.

CONCLUSIONS

Our study suggests a need for detecting the carriers. This is the first step for the construction of a national database and provides information for health planners and policy makers to help them in planning programs and allocation resources. The molecular testing was well received by pregnant women and appears to be feasible and highly acceptable.