Audiological Manifestations and Features of Connexin 26 Deafness

ACEMg Diet Supplement Modifies Progression of Hereditary Deafness

Dietary supplements consisting of beta-carotene (precursor to vitamin A), vitamins C and E and the mineral magnesium (ACEMg) can be beneficial for reducing hearing loss due to aminoglycosides and overstimulation. This regimen also slowed progression of deafness for a boy with GJB2 (CONNEXIN 26) mutations. To assess the potential for treating GJB2 and other forms of hereditary hearing loss with ACEMg, we tested the influence of ACEMg on the cochlea and hearing of mouse models for two human mutations: GJB2, the leading cause of childhood deafness, and DIAPH3, a cause of auditory neuropathy. One group of mice modeling GJB2 (Gjb2-CKO) received ACEMg diet starting shortly after they were weaned (4 weeks) until 16 weeks of age. Another group of Gjb2-CKO mice received ACEMg in utero and after weaning. The ACEMg diet was given to mice modeling DIAPH3 (Diap3-Tg) after weaning (4 weeks) until 12 weeks of age. Control groups received food pellets without the ACEMg supplement. Hearing thresholds measured by auditory brainstem response were significantly better for Gjb2-CKO mice fed ACEMg than for the control diet group. In contrast, Diap3-Tg mice displayed worse thresholds than controls. These results indicate that ACEMg supplementation can influence the progression of genetic hearing loss.

[The application of ultrasound for diagnostics of middle ear pathologies]

The objective of the present work was to summarize the results of the application of ultrasound tests for differential diagnostics of various diseases and lesions affecting the middle ear. Almost 7.000 threshold and suprathreshold studies were carried out in the patients presenting with various forms of sensorineural impairment of hearing. The ultrasound investigations were conducted with the use of the EKHOTEST-02 apparatus (Giperion, Moscow). The results of determination of threshold hearing sensitivity to ultrasound and lateralization of its threshold and suprathreshold values suggest their significance for the detection of even such a minimal disturbance in the cochlear function as the phenomenon of accelerated increase in loudness and the associated enhancement of the severity of the damage to the peripheral sensory system.

ACEMg supplementation ameliorates progressive Connexin 26 hearing loss in a child

Mutations in the gene encoding Connexin 26 are the most common cause of genetic hearing loss. The hearing loss is typically stable but may be progressive. The reason for progression is unknown. Antioxidants have been associated with attenuation of hearing loss from other insults. One antioxidant regimen consists of beta-carotene (metabolized to vitamin A), vitamin C, vitamin E, and magnesium (ACEMg). We present a child with Connexin 26 related hearing loss who experienced progressive hearing loss over 7 years of observation. He was given ACEMg daily for 3 years, during which time his progressive hearing loss was ameliorated.

Connexin 26 and 30 mutations in paediatric patients with congenital, non-syndromic hearing loss treated with cochlear implantation in Mediterranean Turkey

Objective:

Mutations in the genes for connexin 26 (GJB2) and connexin 30 (GJB6) play an important role in autosomal recessive, non-syndromic hearing loss. This study aimed to detect the 35delG and 167delT mutations of theGJB2gene and the del(GJB6-D13S1830) mutation of theGJB6gene in paediatric patients diagnosed with congenital, non-syndromic hearing loss and treated with cochlear implantation in Mediterranean Turkey.

Materials and method:

We included 94 children diagnosed with congenital, non-syndromic hearing loss and treated with cochlear implantation. Blood samples were collected, DNA extracted and an enzyme-linked immunosorbent assay performed to enable molecular diagnosis of mutations.

Results:

Of the 94 children analysed, the 35delG mutation was detected in 12 (12.7 per cent): 10 (83.3 per cent) were homozygous and 2 (16.7 per cent) heterozygous mutant. The 167delT and del(GJB6-D13S1830) mutations were not detected.

Conclusion:

The GJB2-35delG mutation is a major cause of congenital, non-syndromic hearing loss in this study population.

Genetics of hearing and deafness

This article is a review of the genes and genetic disorders that affect hearing in humans and a few selected mouse models of deafness. Genetics is playing an increasingly critical role in the practice of medicine. This is not only in part to the importance that genetic knowledge has on traditional genetic diseases but also in part to the fact that genetic knowledge provides an understanding of the fundamental biological process of most diseases. The proteins coded by the genes related to hearing loss (HL) are involved in many functions in the ear, such as cochlear fluid homeostasis, ionic channels, stereocilia morphology and function, synaptic transmission, gene regulation, and others. Mouse models play a crucial role in understanding of the pathogenesis associated with these genes. Different types of familial HL have been recognized for years; however, in the last two decades, there has been tremendous progress in the discovery of gene mutations that cause deafness. Most of the cases of genetic deafness recognized today are monogenic disorders that can be broadly classified by the mode of inheritance (i.e., autosomal dominant, autosomal recessive, X-linked, and mitochondrial inheritance) and by the presence of associated phenotypic features (i.e., syndromic; and nonsyndromic). In terms of nonsyndromic HL, the chromosomal locations are currently known for ∼ 125 loci (54 for dominant and 71 for recessive deafness), 64 genes have been identified (24 for dominant and 40 for recessive deafness), and there are many more loci for syndromic deafness and X-linked and mitochondrial DNA disorders (http://hereditaryhearingloss.org). Thus, today's clinician must understand the science of medical genetics as this knowledge can lead to more effective disease diagnosis, counseling, treatment, and prevention.

Prevalence of Connexin 26 (GJB2) and Pendred (SLC26A4) mutations in a population of adult cochlear implant candidates

OBJECTIVE

To assess the prevalence of Connexin 26 (GJB2), Connexin 30 (GJB6), and Pendred (SLC26A4) mutations in a population of adult cochlear implant patients with a history of either early idiopathic or hereditary progressive sensorineural deafness.

BACKGROUND

Significant efforts have been applied in defining the epidemiology of Connexin 26 (GJB2)-associated hearing impairment in the pediatric population, yet the issue remains ambiguous for adult patients. Causation is important in this population because there are implications to prognosis, risk of associated medical manifestations, and for genetic counseling purposes.

PATIENTS

Adult patients meeting criteria for cochlear implantation with early-onset hearing loss assessed at an adult cochlear implant center from November 2007 to April 2009.

INTERVENTION

Genomic DNA samples from whole blood were tested with bidirectional sequence analysis for mutations in the coding region of the GJB2 and SLC26A4 genes and tested for large deletions of the GJB6 gene.

RESULTS

Fifty-seven patients were analyzed for GJB2 mutations. Eight patients (14%) were found to have GJB2-related hearing impairment; 5 patients were homozygous for the c.35delG mutation (genotype c.35delG/c.35delG), and 3 additional patients were compound heterozygotes with 2 different GJB2 mutations. Of these 8 patients with GJB2-related hearing impairment, 3 had serviceable hearing into their teenage years. One additional patient had 1 GJB2 variant (p.Met195Ile, heterozygous). None had GJB6 mutations. Of the 57 patients, 30 were also analyzed for SLC26A4 mutations. Three of these patients were compound heterozygotes for disease-causing SLC26A4 mutations, confirming SLC26A4-related hearing impairment. Three additional patients were found to have a single variant in SLC26A4.

CONCLUSION

The prevalence of GJB2- and SLC26A4-related hearing impairment in an adult population with early-onset severe sensorineural hearing loss is significant, suggesting the need for routine assessment for genetic etiologies in this group. We also note 3 individuals with causal connexin 26 mutations with subjective serviceable hearing into adolescence in our cohort.

Imaging correlation of children with DFNB1 vs non-DFNB1 hearing loss

OBJECTIVES

To evaluate temporal bone CT findings in GJB2-related deafness (DFNB1) hearing loss and non-DFNB1 hearing loss children.

STUDY DESIGN

Case-control series.

SUBJECTS AND METHODS

Children with nonsyndromic hearing loss diagnosed as DFNB1 or non-DFNB1 after screening GJB2 allele variants and the large GJB6 deletion. Temporal bone CT images compared in a cohort of nine DFNB1 children with 10 non-DFNB1 children. Visual criteria and absolute measurements were compared against established normative values.

RESULTS

Visual inspection failed to identify two patients with abnormalities identified by using absolute measurements. Only one of nine DFNB1 children had an ear anomaly versus seven of 10 non-DFNB1 (odds ratio 16.33; 95% CI, 1.35, 197.78; P = 0.050). The non-DFNB1 group had a mean vestibule width that was significantly larger, and a mean lateral semicircular canal island width and vestibular aqueduct that were significantly smaller than the DFNB1 group.

CONCLUSIONS

Visual inspection of temporal bone CT images alone may not identify all anomalies and should be used with absolute CT measurements. Abnormal temporal bone CT findings are significantly less likely in children with DFNB1 compared with non-DFNB1 children despite similar age and degree of hearing loss.

Assessing parental attitudes toward genetic testing for childhood hearing loss: Before and after genetic consultation

We report on the development of a Genetic Attitude Assessment Tool (GAAT) to measure parental attitudes in contemplating genetic testing for childhood hearing loss, and to examine the differences in assessments made before and after genetic counseling. The GAAT tool was administered to a convenient sample of 119 parents of children with bilateral sensorineural hearing loss. The respondents completed the survey either before (n = 77) or after (n = 42) genetic counseling. Exploratory Factor Analysis was applied to identify and quantify the underlying psychosocial structure. Our results showed the validated 54-item GAAT instrument contains six subscales: (1) "test intention," (2) "beliefs in non-genetic causes of hearing loss," (3) "deferral of decision to undergo genetic testing," (4) "appropriate use of genetic testing results," (5) "beliefs in the benefits," and (6) "concerns about stigma." The respondents who answered the survey after genetic counseling had higher "test intention" (P = 0.017) and endorsed to a greater extent "beliefs in the benefits" (P < 0.001). They believed to a lesser extent that childhood hearing loss was due to "non-genetic causes" (P < 0.001) and were less inclined to prefer "decision deferral" (P = 0.031). Respondents who themselves had a hearing loss expressed a significantly weaker belief in "non-genetic causes" of hearing loss (P < 0.0001). In conclusion the validated GAAT instrument is responsive to changes in parental attitudes after genetic counseling. The GAAT may be used to monitor parental attitudes serially, to further understand how parental attitudes change from pre genetic counseling, post genetic counseling, to post test result disclosure.

Temporal bone imaging in GJB2 deafness

OBJECTIVE

To describe temporal bone findings on computed tomography (CT) imaging in GJB2-related hearing loss (HL). We asked whether evaluation of the temporal bone is required in individuals with biallelic GJB2 mutations.

STUDY DESIGN

Randomized, blinded, controlled, prospective measurement.

METHODS

Blood from 264 pediatric cochlear implant users was analyzed for mutations in the GJB2 gene. Thirty-six aspects of the temporal bone on CT imaging were evaluated in 53 individuals (106 ears) with biallelic disease causing GJB2 mutations. A subset of patients was age matched and compared with normally hearing individuals. Subjects with biallelic GJB2 mutations were tested for mutations in the SLC26A4 gene to rule out Pendred syndrome as a confounding cause of large vestibular aqueduct syndrome.

RESULTS

Approximately 53% of ears of subjects (72% of subjects) with biallelic GJB2 mutations had at least one temporal bone anomaly. The most common findings were 1) dilated endolymphatic fossa (28%); 2) hypoplastic modiolus (25%); 3) large vestibular aqueduct (8%); 4) hypoplastic horizontal semicircular canal (8%); 5) hypoplastic cochlea (4%). Compared with normally hearing individuals, the GJB2 group had hypoplasia of the cochlear nerve canal, lateral semicircular canal vestibule, internal auditory canal (t tests, P < .001), and were 11 times more likely to have a hypoplastic modiolus. Dilated endolymphatic fossae were 1.4 times more common in the GJB2 group, and large vestibular aqueducts were 3 times more common in the GJB2 group, as compared with normally hearing controls.

CONCLUSIONS

Temporal bone anomalies are common in GJB2-related HL, and imaging of the temporal bone should be included in routine evaluation of these individuals.

The use of buccal smears for a non-invasive screening of the 35delG mutation of the Connexin-26 gene in hearing impaired young children

OBJECTIVES

Recent advances in genetic research indicate that about 50% of congenital deaf patients have a genetic background, with mutations in the Connexin-26 gene being the most frequent one. Screening methods for the genetic cause of deafness have so far mostly been based on the use of peripheral whole blood as DNA source. The use of buccal smears for the genetic screening of deaf patients presents an interesting alternative to drawing blood, especially in young children. In order to validate this method, we compared results from buccal smears from very young deaf children (age<or=3 years) and deaf patients older than 3 years with the results from blood samples deriving from the same patients.

METHODS

The detection of the 35delG mutation in the Connexin-26 gene was chosen to demonstrate the method's feasibility. Blood and buccal smears were collected for genetic analysis from 29 very young deaf children (Group 1: age<or=3 years) and 31 deaf patients older than 3 years (Group 2) during their clinical pre-evaluation for cochlear implantation. Genomic DNA was isolated from blood as well as from buccal smears. Yield of both sources was determined by photometric evaluation of the isolated DNA concentration. Genomic DNA isolated from blood and buccal smears was then submitted to PCR-mediated site-directed mutagenesis followed by BS1 YI restriction and electrophoresis. The results for 35delG detection in DNA originating from blood were compared to those of buccal smears.

RESULTS

Quantitative DNA analysis showed that both sources provided adequate amounts of DNA for PCR. No significant difference was found between Group 1 and Group 2 considering either the DNA amount isolated from blood or from buccal smears. In all 60 patients, DNA isolated from blood revealed the same results concerning the presence of the 35delG mutation as DNA originating from buccal smears.

CONCLUSIONS

This study demonstrates that buccal smears are an adequate, reliable source of genomic DNA providing material for genetic tests that can especially help to avoid drawing blood from very young children for the genetic screening of deafness.

Clinical application of genetic testing for deafness

Advances in the molecular biology of hearing and deafness have identified many genes essential for normal auditory function. Allele variants of these genes cause nonsyndromic deafness, making mutation screening a valuable test to unequivocally diagnose many different forms of inherited deafness. In this study, genetic testing of GJB2, SLC26A4 and WFS1 is reviewed.

GJB2: the spectrum of deafness-causing allele variants and their phenotype

Genetic testing was completed on 1,294 persons with deafness referred to the Molecular Otolaryngology Research Laboratories to establish a diagnosis of DFNB1. Exon 2 of GJB2 was screened for coding sequence allele variants by denaturing high-performance liquid chromatography (DHPLC) complemented by bidirectional sequencing. If two deafness-causing mutations of GJB2 (encoding Connexin 26) were identified, further screening was not performed. If only a single deafness-causing mutation was identified, we screened for the g.1777179_2085947del (hereafter called del(GJB6-D13S1830); GenBank NT_024524.13) and mutations in the noncoding region of GJB2. Phenotype-genotype correlations were evaluated by categorizing mutations as either protein truncating or nontruncating. A total of 205 persons carried two GJB2 exon 2 mutations and were diagnosed as having DFNB1; 100 persons carried only a single deafness-causing allele variant of exon 2. A total of 37 of these persons were c.35delG carriers, and 51 carried other allele variants of GJB2. Persons diagnosed with DFNB1 segregating two truncating/nonsense mutations had a more severe phenotype than persons carrying two missense mutations, with mean hearing impairments being 88 and 37%, respectively (P < 0.05). The number of deaf c.35delG carriers was greater than expected when compared to the c.35delG carrier frequency in normal-hearing controls (P < 0.05), suggesting the existence of at least one other mutation outside the GJB2 coding region that does not complement GJB2 deafness-causing allele variants.