The prevalence and expression of inherited connexin 26 mutations associated with nonsyndromic hearing loss in the Israeli population

Audiological Phenotypes of Connexin Gene Mutation Patterns: A Glance at Different GJB2/GJB6 Gene Mutation Profiles

GJB2 mutations are the most common cause of autosomal-recessive non-syndromic sensorineural hearing loss (SNHL). The available evidence shows large phenotypic variability across different genotypes and allelic variants. The aim of this study was to investigate the clinical and audiological features of a cohort of subjects with different GJB2/GJB6 gene mutation profiles from a tertiary referral center in Northeastern Italy. We considered 57 patients with GJB2/GJB6 mutations presenting with congenital, non-syndromic SNHL, mainly coming from the Veneto region (Italy). The samples were screened for mutations in exons 1 and 2 of the GJB2 gene and for the GJB6 gene deletion del (GJB6-D13S1830). Free-field and air-conduction frequency-specific thresholds and the pure-tone average (PTA) were considered in the statistical analysis. Five patients (8.87%) had connexin gene mutations in simple heterozygosis, 15 (26.31%) in compound heterozygosis, 34 (59.64%) in homozygosis, and 3 (5.26%) with digenic patterns. The frequency-specific air-conduction thresholds showed significantly different mean values across the different genotypes (Roy's largest-root test, p = 0.0473). Despite the evidence already available on genetic SNHL, many new insights are to be expected. Further large-scale prospective studies including different populations are necessary to confirm these preliminary findings about the clinical and audiological features of patients with different GJB2/GJB6 gene mutation patterns.

Prenatal Diagnosis and Pregnancy Termination in Jewish and Muslim Women with a Deaf Child in Israel

Deafness is the most common sensory disability in humans, influencing all aspects of life, However, early diagnosis of hearing impairment and initiating the rehabilitation process are of great importance to enable the development of language and communication as soon as possible. We examined the differences in attitudes towards performing prenatal invasive tests and pregnancy terminations in Jewish and Muslim women in Israel due to deafness. Overall, 953 Israeli women, aged 18-46 years with a mean age of 32.0 (SD = 7.12), were enrolled. Of those, 68.7% were city dwellers and 31.3% were village dwellers, and 60.2% were Muslim women and 39.8% were Jewish women. All participants had a child with a hearing impairment or deafness. The group with no genetic hearing loss performed more prenatal invasive tests and pregnancy terminations than those with genetic hearing loss in both ethnic groups. Jewish women performed more invasive prenatal tests and, consequently, a pregnancy termination. Secular Jewish women more frequently underwent pregnancy terminations due to fetal deafness. Further genetic counseling and information concerning IVF and PGD procedures should be provided to the Muslim population.

Age Estimate of GJB2-p.(Arg143Trp) Founder Variant in Hearing Impairment in Ghana, Suggests Multiple Independent Origins across Populations

Gap junction protein beta 2 (GJB2) (connexin 26) variants are commonly implicated in non-syndromic hearing impairment (NSHI). In Ghana, the GJB2 variant p.(Arg143Trp) is the largest contributor to NSHI and has a reported prevalence of 25.9% in affected multiplex families. To date, in the African continent, GJB2-p.(Arg143Trp) has only been reported in Ghana. Using whole-exome sequencing data from 32 individuals from 16 families segregating NSHI, and 38 unrelated hearing controls with the same ethnolinguistic background, we investigated the date and origin of p.(Arg143Trp) in Ghana using linked markers. With a Bayesian linkage disequilibrium gene mapping method, we estimated GJB2-p.(Arg143Trp) to have originated about 9625 years (385 generations) ago in Ghana. A haplotype analysis comparing data extracted from Ghanaians and those from the 1000 Genomes project revealed that GJB2-p.(Arg143Trp) is carried on different haplotype backgrounds in Ghanaian and Japanese populations, as well as among populations of European ancestry, lending further support to the multiple independent origins of the variant. In addition, we found substantial haplotype conservation in the genetic background of Ghanaian individuals with biallelic GJB2-p.(Arg143Trp) compared to the GJB2-p.(Arg143Trp)-negative group with normal hearing from Ghana, suggesting a strong evolutionary constraint in this genomic region in Ghanaian populations that are homozygous for GJB2-p.(Arg143Trp). The present study evaluates the age of GJB2-p.(Arg143Trp) at 9625 years and supports the multiple independent origins of this variant in the global population.

Deafness in an auditory specialist, the big brown bat (Eptesicus fuscus)

Bats are long-lived animals that show presumed resistance to noise-induced and age-related hearing loss, which has been attributed to their dependence on sound processing for survival. Echolocation and basic auditory functions have been studied extensively in the big brown bat (Eptesicus fuscus), an insectivorous microchiropteran species. We conducted hearing tests and analysis of cochlear sensory cells in a group of big brown bats that exhibited anomalies in behavioral sonar tracking experiments and/or lacked neural responses to acoustic stimulation in subcortical auditory nuclei. We show for the first time the presence of profound deafness and extensive cochlear damage in an echolocating bat species. Auditory brainstem responses were abnormal or absent in these bats, and histological analyses of their cochleae revealed extensive loss of hair cells, supporting cells, and spiral ganglion neurons. The underlying cause of deafness is unknown.

Performance after cochlear implantation in DFNB1 patients

Objective

To evaluate the speech perception and language development with cochlear implants (CI) of DFNB1 children in comparison with non-DFNB1 deaf children.

Study Design

Retrospective case series.

Setting

Academic tertiary center.

Results

Thirty-one congenitally deafened children, screened for GJB2 allele variants, were followed for an average 32 months after CI. With the use of age-appropriate testing, 75% of DFNB1 and 53% of non-DFNB1 children achieved open set word recognition (speech perception category [SPC] level 6). Multivariate analysis showed that SPC was primarily dependent on duration of CI use, but not on the cause of hearing loss. In Reynell language tests, DFNB1 children showed more consistent and quicker gains than non-DFNB1 children.

Conclusion

Although children with CI with DFNB1 show faster gains in Reynell scores, duration of CI use appears to have a greater effect on speech perception than DFNB1 status. SIGNIFICANCE: Identification of DFNB1 children is useful in counseling of CI outcomes.

Survey on Infant Hearing Loss at Caritas Baby Hospital in Bethlehem-Palestine

This study describes the epidemiology of infants’ hearing loss (IHL) among patients under 3 months of age at Caritas Baby Hospital, the only pediatric hospital in Palestine. It was aimed to demonstrate that IHL is a major health problem in Palestine and to assess the first available data of the newborn hearing screening program conducted between September 25, 2006 and December 31, 2011. Data was uploaded and analyzed using Microsoft Excel and the Statistical Package for the Social Sciences software (SPSS version 21). A total of 8144 infants were tested, 4812 (59%) were males and 3332 (41%) were females. As to their origin, 72% (5886) came from the Bethlehem district, 25% (2044) from the Hebron district, while 3% (214) from the other Palestinian districts (Jericho, Ramallah, Nablus, Jenin and Jerusalem). The transient evoked otoacoustic emissions (TEOAEs) and the automated auditory brainstem response were used according to the manufacturer guidelines. The results were interpreted according to the indications of the American Academy of Pediatrics, the National Institutes of Health, and the European Consensus Development Conference on Neonatal Hearing Screening. Out of the 8144 infants tested, 1507 (14.6%) did not pass the 1^st test, 477 (32.8%) of these 1507 infants failed retesting, while 498 (33%) patients were lost to follow-up. Only 152 (31.9%) patients that failed retesting went to an audiologist. The audiologist evaluation revealed that 101 (66.4%) patients presented with a mild-moderate or profound hearing loss according to the Bureau International of Audiophonologie standards, 44 (28.9%) patients had otitis media, whereas 7 cases (4.7%) had no hearing disorders. The overall unadjusted percentage of hearing loss was 1.24%, and the adjusted overall percentage was 1.85%. The chart review showed that jaundice, sepsis, prematurity, lung disease were more common among the affected patients. The high prevalence of childhood deafness in Palestine is of utmost importance and deserves immediate attention on the part of the Palestinian government. Meanwhile, Caritas Baby Hospital undertook to set up a newborn hearing screening unit utilizing the TEOAE method.

Molecular analysis of the GJB2, GJB6 and SLC26A4 genes in Korean deafness patients

OBJECTIVES

Mutations in the GJB2, GJB6 and SLC26A4 genes are a frequent cause of hearing loss in a number of populations. However, little is known about the genetic causes of hearing loss in the Korean population.

METHODS

We sequenced the GJB2 and GJB6 genes to examine the role of mutations in these genes in 22 hearing loss patients. We also sequenced the SLC26A4 gene in seven patients with inner ear malformations, including enlarged vestibular aqueduct (EVA) revealed by computer tomography.

RESULTS

Coding sequence mutations in GJB2 were identified in 13.6% of the patients screened. Two different mutations, 235delC and T86R were found in three unrelated patients. The 235delC was the most prevalent mutation with an allele frequency of 6.9% in our patient group. No mutations, including 342-kb deletion, were found in GJB6 gene. Three different variants of SLC26A4 were identified in the EVA patients, including one novel mutation. Four EVA patients carried two mutant alleles of SLC26A4, and at least one allele in all patients was the H723R mutation, which accounted for 75% of all mutant alleles.

CONCLUSIONS

Our results suggest that GJB2 and SLC26A4 mutations together make up a major cause of congenital hearing loss in the Korean population. Further studies may be able to identify other common variants that account for a significant fraction of hearing loss in the Korean population.

Müllerian anomalies, hearing loss, and connexin 26 mutations

In a study of the possible inter-relationship among müllerian anomalies, hearing loss, and connexin 26 mutations, we evaluated all women in whom müllerian anomalies were diagnosed on hysterosalpingography during a 6-year period (n = 24/519). Audiometric testing revealed five (22.7%) with unrecognized sensorineural hearing loss; however, on genetic evaluation, none harbored a connexin 26 mutation.

Frequency of the 35delG mutation in the connexin 26 gene in Turkish hearing-impaired patients

The 35delG mutation in the connexin 26 gene (GJB2) at the DFNB1 locus is the most common mutation in patients with autosomal-recessive sensorineural deafness. Genetic diagnosis is crucial for genetic counseling. We have developed an easy and simple method and screened a total of 235 unrelated hearing-impaired children. We found 48 of the subjects to be homozygous for the mutation, including 27 of 83 familial cases, 15 of 101 singletons, 4 of 9 subjects born to assortative marriages (deaf married to deaf), and 2 of 42 subjects for whom the parents claimed an environmental factor as the etiology of the condition. The high ratio of individuals homozygous for the mutation indicated that the 35delG mutation in the connexin gene accounts for more than 90% of the mutations at this locus.