Nonsyndromal profound genetic deafness in childhood

Frequency of GJB2 mutations in patients with nonsyndromic hearing loss from an ethnically characterized Brazilian population

Introduction

In different parts of the world, mutations in the GJB2 gene are associated with nonsyndromic hearing loss, and the homozygous 35delG mutation (p.Gly12Valfs*2) is a major cause of hereditary hearing loss. However, the 35delG mutation is not equally prevalent across ethnicities, making it important to study other mutations, especially in multiethnic countries such as Brazil.

Objective

This study aimed to identify different mutations in the GJB2 gene in patients with severe to profound nonsyndromic sensorineural hearing loss of putative genetic origin, and who were negative or heterozygote for the 35delG mutation.

Methods

Observational study that analyzed 100 ethnically characterized Brazilian patients with nonsyndromic severe to profound sensorineural hearing loss, who were negative or heterozygote for the 35delG mutation. GJB2 mutations were detected by DNA-based sequencing in this population. Participants’ ethnicities were identified as Latin European, Non-Latin European, Jewish, Native, Turkish, Afro-American, Asian and Others.

Results

Sixteen participants were heterozygote for the 35delG mutation; 14 participants, including three 35delG heterozygote's, had nine different alterations in the GJB2 gene. One variant, p.Ser199Glnfs*9, detected in two participants, was previously unreported. Three variants were pathogenic (p.Trp172*, p.Val167Met, and p.Arg75Trp), two were non-pathogenic (p.Val27Ile and p.Ile196Thr), and three variants were indeterminate (p.Met34Thr, p.Arg127Leu, and p.Lys168Arg). Three cases of compound heterozygosity were detected: p.[(Gly12Valfs*2)];[(Trp172*)], p.[(Gly12Valfs*2)](;)[(Met34Thr)], and p.[(Gly12Valfs*2)(;)[(Ser199Glnfs*9)]).

Conclusion

This study detected previously unclassified variants and one case of previously unreported compound heterozygosity.

Genetic basis of hearing loss in Spanish, Hispanic and Latino populations

Hearing loss (HL) is the most common neurosensory disorder affecting humans. The screening, prevention and treatment of HL require a better understanding of the underlying molecular mechanisms. Genetic predisposition is one of the most common factors that leads to HL. Most HL studies include few Spanish, Hispanic and Latino participants, leaving a critical gap in our understanding about the prevalence, impact, unmet health care needs, and genetic factors associated with hearing impairment among Spanish, Hispanic and Latino populations. The few studies which have been performed show that the gene variants commonly associated with HL in non-Spanish and non-Hispanic populations are infrequently responsible for hearing impairment in Spanish as well as Hispanic and Latino populations (hereafter referred to as Hispanic). To design effective screening tools to detect HL in Spanish and Hispanic populations, studies must be conducted to determine the gene variants that are most commonly associated with hearing impairment in this racial/ethnic group. In this review article, we summarize gene variants and loci associated with HL in Spanish and Hispanic populations. Identifying new genetic variants associated with HL in Spanish and Hispanic populations will pave the way to develop effective screening tools and therapeutic strategies for HL.

Progressive hearing loss and degeneration of hair cell stereocilia in taperin gene knockout mice

The TPRN gene encodes taperin, which is prominently present at the taper region of hair cell stereocilia. Mutations in TPRN have been reported to cause autosomal recessive nonsyndromic deafness 79(DFNB 79). To investigate the role of taperin in pathogenesis of hearing loss, we generated TPRN knockout mice using TALEN technique. Sanger sequencing confirmed an 11 bp deletion at nucleotide 177-187 in exon 1 of TPRN, which results in a truncated form of taperin protein. Heterozygous TPRN^+/- mice showed apparently normal auditory phenotypes to their wide-type (WT) littermates. Homozygous TPRN^-/- mice exhibited progressive sensorineural hearing loss as reflected by auditory brainstem response to both click and tone burst stimuli at postnatal days 15 (P15), 30 (P30), and 60 (P60). Alex Fluor-594 phalloidin labeling showed no obvious difference in hair cell numbers in the cochlea between TPRN^-/- mice and WT mice under light microscope. However, scanning electronic microscopy revealed progressive degeneration of inner hair cell stereocilia, from apparently normal at postnatal days 3 (P3) to scattered absence at P15 and further to substantial loss at P30. The outer hair cell stereocilia also showed progressive degeneration, though much less severe, Collectively, we conclude that taperin plays an important role in maintenance of hair cell stereocilia. Establishment of TPRN knockout mice enables further investigation into the function of this gene.

A Novel C-Terminal CIB2 (Calcium and Integrin Binding Protein 2) Mutation Associated with Non-Syndromic Hearing Loss in a Hispanic Family

Hearing loss is a complex disorder caused by both genetic and environmental factors. Previously, mutations in CIB2 have been identified as a common cause of genetic hearing loss in Pakistani and Turkish populations. Here we report a novel (c.556C>T; p.(Arg186Trp)) transition mutation in the CIB2 gene identified through whole exome sequencing (WES) in a Caribbean Hispanic family with non-syndromic hearing loss. CIB2 belongs to the family of calcium-and integrin-binding (CIB) proteins. The carboxy-termini of CIB proteins are associated with calcium binding and intracellular signaling. The p.(Arg186Trp) mutation is localized within predicted type II PDZ binding ligand at the carboxy terminus. Our ex vivo studies revealed that the mutation did not alter the interactions of CIB2 with Whirlin, nor its targeting to the tips of hair cell stereocilia. However, we found that the mutation disrupts inhibition of ATP-induced Ca2+ responses by CIB2 in a heterologous expression system. Our findings support p.(Arg186Trp) mutation as a cause for hearing loss in this Hispanic family. In addition, it further highlights the necessity of the calcium binding property of CIB2 for normal hearing.

Identification of four novel connexin 26 mutations in non-syndromic deaf patients: genotype-phenotype analysis in moderate cases

This paper presents a mutation as well as a genotype-phenotype analysis of the GJB2 and GJB6 genes in 476 samples from non-syndromic unrelated Argentinean deaf patients (104 familial and 372 sporadic cases). Most of them were of prelingual onset (82 %) and 27 % were cochlear implanted. Variation of sequences was detected in 171 of the 474 patients (36 %). Overall, 43 different sequence variations were identified in GJB2 and GJB6. Four of them are reported for the first time in GJB2: c.233dupG, p.Ala78Ser, p.Val190Asp and p.Cys211Tyr. Mutations in GJB6 were detected in 3 % of patients [nine del(GJB6-D13S1830) and three del(GJB6-D13S1854)]. Of the 43 different variations identified in GJB2, 6 were polymorphisms and of the others, 10 (27 %) were truncating and 27 (73 %) were nontruncating. Patients with two truncating mutations had significantly worse hearing impairment than all other groups. Moderate phenotypes were observed in a group of patients carrying biallelic mutations (23 %). This work shows the high prevalence of GJB2 mutations in the Argentinean population and presents an analysis of moderate phenotypes in our cohort.

Audiological and radiological characteristics of a family with T961G mitochondrial mutation

OBJECTIVE

The aim of this study was to describe audiological and radiological characteristics, and other secondary aspects, in a family carrying a T961G mutation in the 12S rRNA mitochondrial gene.

DESIGN

Case report.

STUDY SAMPLE

Six members of a family participated in an audiological evaluation that included pure-tone audiometry, immittance tests, auditory brainstem responses (ABR), and otoacoustic emissions (OAE). The radiological evaluation was conducted through temporal bone CT scans using a Toshiba 16 channels Aquilon Spirale. Neuropsychiatric evaluation was also administered.

RESULTS

Three participants were diagnosed with severe sensorineural hearing loss of cochlear origin and cochlear malformations visible in CT scans. One participant had a mild mixed-hearing loss and no cochlear malformations. Two participants had normal audiological and radiological findings.

CONCLUSIONS

We believe our study can provide helpful insight on the clinical findings of a rare mutation, of which few data have been presented in literature.

Performance of speech perception after cochlear implantation in DFNB1 patients

CONCLUSION

There were no apparent differences in speech performance after cochlear implantation between patients with biallelic GJB2 and/or GJB6 mutations and those with deafness of unknown aetiology. These data have important implications for the selection of prognostic indicators of the outcome of cochlear implantation.

OBJECTIVE

To compare performance after cochlear implantation in children with mutations in GJB2 (connexin 26) and/or GJB6 (connexin 30) and children with deafness of unknown aetiology.

SUBJECTS AND METHODS

Genetic analysis and speech performance evaluation was determined in 24 patients with (n=11) and without (n=13) biallelic GJB2 and/or GJB6 mutations who underwent cochlear implantation. Speech perception skills were measured 12 and 24 months after surgery. Each patient was classified in accordance with the speech perception category (SPC).

RESULTS

Overall, the two groups showed similar significant improvement in speech perception after implantation.

Clinical aspects of hereditary hearing loss

Hearing loss is an etiologically diverse condition with many disease-related complications and major clinical, social, and quality of life implications. As the rate of acquired hearing loss secondary to environmental causes decreases and improvements in the diagnosis of abnormalities occur, the significance of genetic factors that lead to deafness increases. Advancements in molecular biology have led to improved detection and earlier intervention in patients with hearing loss. Subsequently, earlier implementation of educational services and cochlear implant technology in patients with profound hearing loss now results in superior communication skills and enhanced language development. The aim of this review is to provide a comprehensive framework underlying the causes of hearing impairment and to detail the clinical management for patients with hereditary hearing loss.

Mutations inGJB2,GJB6, and mitochondrial DNA are rare in African American and Caribbean Hispanic individuals with hearing impairment

Autosomal recessive nonsyndromic sensorineural hearing impairment (ARNSHI) comprises 80% of familial hearing loss cases. Approximately half result from mutations in the connexin 26 (Cx26) gene, GJB2, in Caucasian populations. Heterozygous mutations in GJB2 occasionally co-occur with a deletion of part of GJB6 (connexin 30; Cx30). It is estimated that approximately 1% of deafness is maternally inherited, due to mutations in mitochondrial DNA (mtDNA). Few studies have focused on the frequency of mutations in connexins or mtDNA in African American (AA) and Caribbean Hispanic (CH) admixture populations. In this study, we performed bidirectional sequencing of the GJB2 gene and polymerase chain reaction (PCR) screening for the common GJB6 deletion, as well as PCR/RFLP analysis for three mutations in mtDNA (A1555G, A3243G, A7445G), in 109 predominantly simplex AA and CH individuals. Variations found were a 101T > C (M34T; 1/101 cases), 109G > A (V37I; 1/101), 35delG (mutation; 4/101, (3/4) of non-AA/CH ethnicity), 167delT (mutation; 1/101), 139G > T (mutation; E47X; 1/101 homozygote, consanguineous), -15C > T (1/101), 79G > A (V27I; 9/101), 380G > A (R127H; 4/101; Guyana, India, Pakistan ethnicity), 670A > C (Indeterminate; K224Q; 1/101), 503A > G (novel; K168R; 3/101) and 684C > A (novel; 1/101). All but one of the AA and CH patients had monoallelic variations. There were no hemizygous GJB6 deletions in those with monoallelic GJB2 variations. We also did not identify any patients with the three mutations in mtDNA. Bidirectional sequencing of the GJB2 gene was performed in 187 AA and Hispanic healthy individuals. Our results reveal that GJB2 mutations, GJB6 deletions, and mtDNA mutations may not be significant in these minority admixture populations.

Audiometric evaluation of carriers of the connexin 26 mutation 35delG

Mutation in a gap junction protein gene (GJB2 also named connexin 26) is a major cause of autosomal recessive congenital deafness, which is responsible for about 80% of the cases in Mediterranean families, but actually little is known about the influence of GJB2 mutations on the hearing of obligate carriers. We examined GJB2 35delG mutation carrier individuals to test the possible presence and incidence of audiometric abnormalities among carriers of 35delG mutations. Tonal audiometric analysis was performed on a 35delG mutation carrier group (H) and on a non-carrier control group (N). Audiometric evaluations in the control group showed the presence of thresholds within normal limits at all frequencies, while carriers of 35delG mutations presented a decrease of hearing principally at 6,000 and 8,000 Hz. The difference at 6,000 and 8,000 Hz between groups H and N is statistically significant.

Use of a multiplex PCR/sequencing strategy to detect both connexin 30 (GJB6) 342 kb deletion and connexin 26 (GJB2) mutations in cases of childhood deafness

Hearing loss is a common congenital disorder that is frequently associated with mutations in the Cx26 gene (GJB2). Three recent reports that found a large deletion in another DFNB1 gene, Cx30 (GJB6), suggest that this defect may cause nonsyndromic recessive hearing loss through either a homozygous deletion of Cx30, or digenic inheritance of a Cx30 deletion and a Cx26 mutation in trans. We designed a simple diagnostic strategy with multiplex PCR followed by direct sequencing to allow for the simultaneous detection of Cx26 mutations and Cx30 deletions, and evaluated its effectiveness as a clinical genetic test by examining 200 DNA samples. In the 108 samples from deaf subjects, two digenic mutations were identified in Cx26 and Cx30 (E47X/342 kb deletion and 167delT/342 kb deletion); 69 had only Cx26 mutations (29 biallelic, 40 singleton), including two novel frameshift mutations 511-512insAACG and 358-360delAG; and 37 had no detectable mutation in either Cx26 or Cx30. Our deletion mapping suggested that the proximal breakpoint of all reported Cx30 large deletions are between the nucleotide 444 and 627 at the Cx30 coding region within a maximal interval of 78 or 184 bp. This simultaneous examination of Cx26 and Cx30 is a practical and efficient diagnostic approach for patients with nonsyndromic congenital deafness.

Effectiveness of sequencing connexin 26 (GJB2) in cases of familial or sporadic childhood deafness referred for molecular diagnostic testing

PURPOSE

Hearing loss is a common congenital disorder that is frequently associated with mutations in the GJB2 gene encoding the connexin 26 protein (Cx26). We sought to evaluate the effectiveness of direct DNA sequencing for detection of Cx26 mutations as a clinical diagnostic test.

METHODS

We designed a clinical assay using a three-step polymerase chain reaction (PCR)-based DNA sequencing strategy to detect all possible mutations in the open reading frame and flanking sequences of Cx26. The results of the first 324 cases of childhood deafness referred for diagnostic testing were analyzed.

RESULTS

A total of 127 of the 324 (39.2%) cases had at least one mutant Cx26 allele (36.1% of sporadic cases, 70% of familial cases). Of these 127 case, 57 (44.8%) were homozygotes or compound heterozygotes. Thirty-four different mutations were identified, including 10 novel mutations, 6 of which (T8M, K15T, R32L, M93I, N206S, and 511-512insAACG) may be pathogenic. We also provide new evidence on the pathogenicity or nonpathogenicity of 12 previously reported mutations, and clarify the confusing nomenclature of the 313-326del14 mutation.

CONCLUSION

A simple and rigorous method for efficient PCR-based sequence analysis of Cx26 is a sensitive clinical assay for evaluating deaf children. Its widespread use is likely to identify additional pathogenic mutations and lead to a better understanding of the clinical significance of previously identified mutations.

Low intensities and 1.3 ratio produce distortion product otoacoustic emissions which are larger in heterozygous (+/dn) than homozygous (+/+) mice

The f2/f1 frequency ratio of 1.3 in combination with stimulus levels of L1/L2 = 50/60 and 50/50 dB SPL produced a higher level of distortion product otoacoustic emissions (DPOAE) in the heterozygous (+/dn) mice than in the homozygous (+/+) mice. These results suggest that the dn gene carriers have a unique cochlear trait which may be related to the dn gene locus and expressed via a frequency- and intensity-dependent DPOAE function.