Graça Fialho

GJB2 Mutations and Degree of Hearing Loss: A Multicenter Study

Hearing impairment (HI) affects 1 in 650 newborns, which makes it the most common congenital sensory impairment. Despite extraordinary genetic heterogeneity, mutations in one gene, GJB2, which encodes the connexin 26 protein and is involved in inner ear homeostasis, are found in up to 50% of patients with autosomal recessive nonsyndromic hearing loss. Because of the high frequency of GJB2 mutations, mutation analysis of this gene is widely available as a diagnostic test. In this study, we assessed the association between genotype and degree of hearing loss in persons with HI and biallelic GJB2 mutations. We performed cross-sectional analyses of GJB2 genotype and audiometric data from 1,531 persons, from 16 different countries, with autosomal recessive, mild-to-profound nonsyndromic HI. The median age of all participants was 8 years; 90% of persons were within the age range of 0-26 years. Of the 83 different mutations identified, 47 were classified as nontruncating, and 36 as truncating. A total of 153 different genotypes were found, of which 56 were homozygous truncating (T/T), 30 were homozygous nontruncating (NT/NT), and 67 were compound heterozygous truncating/nontruncating (T/NT). The degree of HI associated with biallelic truncating mutations was significantly more severe than the HI associated with biallelic nontruncating mutations (P<.0001). The HI of 48 different genotypes was less severe than that of 35delG homozygotes. Several common mutations (M34T, V37I, and L90P) were associated with mild-to-moderate HI (median 25-40 dB). Two genotypes--35delG/R143W (median 105 dB) and 35delG/dela(GJB6-D13S1830) (median 108 dB)--had significantly more-severe HI than that of 35delG homozygotes.

Phenotypic variability of patients homozygous for the GJB2 mutation 35delG cannot be explained by the influence of one major modifier gene

Hereditary hearing loss (HL) is a very heterogeneous trait, with 46 gene identifications for non-syndromic HL. Mutations in GJB2 cause up to half of all cases of severe-to-profound congenital autosomal recessive non-syndromic HL, with 35delG being the most frequent mutation in Caucasians. Although a genotype–phenotype correlation has been established for most GJB2 genotypes, the HL of 35delG homozygous patients is mild to profound. We hypothesise that this phenotypic variability is at least partly caused by the influence of modifier genes. By performing a whole-genome association (WGA) study on 35delG homozygotes, we sought to identify modifier genes. The association study was performed by comparing the genotypes of mild/moderate cases and profound cases. The first analysis included a pooling-based WGA study of a first set of 255 samples by using both the Illumina 550K and Affymetrix 500K chips. This analysis resulted in a ranking of all analysed single-nucleotide polymorphisms (SNPs) according to their P-values. The top 250 most significantly associated SNPs were genotyped individually in the same sample set. All 192 SNPs that still had significant P-values were genotyped in a second independent set of 297 samples for replication. The significant P-values were replicated in nine SNPs, with combined P-values between 3 × 10−3 and 1 × 10−4. This study suggests that the phenotypic variability in 35delG homozygous patients cannot be explained by the effect of one major modifier gene. Significantly associated SNPs may reflect a small modifying effect on the phenotype. Increasing the power of the study will be of greatest importance to confirm these results.

A novel hearing loss-related mutation occurring in the GJB2 basal promoter

Mutations in the GJB2 gene are a major cause of non-syndromic recessive hearing loss in many countries. In a significant fraction of patients, only monoallelic GJB2 mutations known to be either recessive or of unclear pathogenicity are identified. This paper reports a novel GJB2 mutation, −3438C→T, found in the basal promoter of the gene, in trans with V84M, in a patient with profound hearing impairment. This novel mutation can abolish the basal promoter activity of GJB2. These results highlight the importance of extending the mutational screening to regions outside the coding region of GJB2.

A novel M163L mutation in connexin 26 causing cell death and associated with autosomal dominant hearing loss

Mutations in GJB2 gene (encoding connexin 26) are the most common cause of hereditary non-syndromic sensorineural hearing loss (NSSHL) in different populations. The majority of GJB2 mutations are recessive, but a few dominant mutations have been associated with hearing loss either isolated or associated with skin disease. We describe a novel dominant pathogenic GJB2 mutation, identified in a Portuguese family affected with bilateral mild/moderate high-frequency NSSHL. In vitro functional studies demonstrate that the mutant protein (p.M163L) has defective trafficking to the plasma membrane and is associated with increased cell death.

Spectrum and frequency of GJB2 mutations in a cohort of 264 Portuguese nonsyndromic sensorineural hearing loss patients

Abstract Objective: To assess the spectrum and prevalence of mutations in the GJB2 gene in Portuguese nonsyndromic sensorineural hearing loss (NSSHL) patients. Design: Sequencing of the coding region, basal promoter, exon 1, and donor splice site of the GJB2 gene; screening for the presence of the two common GJB6 deletions. Study sample: A cohort of 264 Portuguese NSSHL patients. Results: At least one out of 21 different GJB2 variants was identified in 80 (30.2%) of the 264 patients analysed. Two mutant alleles were found in 53 (20%) of these probands, of which 83% (44/53) harboured at least one c.35delG allele. Twenty-seven (10.2%) of the probands harboured only one mutant allele. Subsequent analysis revealed that the GJB6 deletion del(GJB6-D13S1854) was present in at least 7.4% (2/27) of the patients carrying only one mutant GJB2 allele. Overall, one in five (55/264) of the patients were diagnosed as having DFNB1-related NSSHL, of which the vast majority (53/55) harboured only GJB2 mutations. Conclusions: This study provides clear demonstration that mutations in the GJB2 gene are an important cause of NSSHL in Portugal, thus representing a valuable indicator as regards therapeutical and rehabilitation options, as well as genetic counseling of these patients and their families.

The Controversial p.Arg127His Mutation in GJB2: Report on Three Portuguese Hearing Loss Family Cases

Mutations in the GJB2 gene account for up to 50% of hereditary nonsyndromic hearing loss in several populations. Over 200 mutations are already described in this gene, and three of them, c.35delG, c.167delT, and c.235delC, are the most frequent in Caucasians, Ashkenazi Jews, and Asians, respectively. Most of GJB2 hearing loss-related mutations are recessive, but a few dominant alleles have also been described. Apart from the clearly pathogenic mutations, there are some other variants whose pathogenicity is still controversial, such as p.Met34Thr, p.Val37Ile, p.Arg127His, and p.Val153Ile. The p.Arg127His allele has been found in some mono- and biallelic hearing-impaired patients from several countries. In this article we report on some Portuguese patients harboring this mutation. Taking into consideration the analysis of these Portuguese cases as well as the genetic and functional data regarding p.Arg127His available in the literature, we conclude that this variant may be a cause of hearing loss depending on environmental factors and/or genetic background.

Novel splice-site mutation c.1615-2A>G (IVS14-2A>G) in the SLC26A4 gene causing Pendred syndrome in a consanguineous Portuguese family.

Novel Splice-Site Mutation c.1615-2A>G (IVS14-2A>G) in the SLC26A4 Gene Causing Pendred Syndrome in a Consanguineous Portuguese Family Helena Sim~oes-Teixeira, Tiago D. Matos, Marta Canas Marques, Óscar Dias, M ario Andrea, Eduardo Barreiros, Lu ıs Barreiros, Felipe Moreno, Graça Fialho, Helena Caria, and Ignacio del Castillo* Faculty of Science, Centre for Biodiversity, Functional and Integrative Genomics (BioFIG), University of Lisbon, Lisbon, Portugal Unidad de Gen etica Molecular, Hospital Universitario Ram on y Cajal, IRYCIS, Madrid, Spain ORL Service, Hospital de Santa Maria, Centro Hospitalar Lisboa Norte, EPE, Lisbon, Portugal Endocrinology Department, Hospital de Santa Maria, Centro Hospitalar Lisboa Norte, EPE, Lisbon, Portugal Centro de Investigaci on Biom edica en Red de Enfermedades Raras (CIBERER), Madrid, Spain Higher School of Health, Polytechnic Institute of Set ubal, Set ubal, Portugal

A novel p.Leu213X mutation in GJB2 gene in a Portuguese family

INTRODUCTION Hearing loss is the most common sensory disability and is present in about 1.9 per 1000 infants at birth. The DFNB1 locus (13q11-q12) includes the genes GJB2, coding for connexin 26, and GJB6, encoding connexin 30. More than 100 mutations have been identified associated with autosomal dominant and recessive hearing loss in the GJB2 gene. OBJECTIVES The aim of the present study was to identify the genetic aetiology of deafness in two Portuguese individuals, presenting nonsyndromic sensorineural moderate and severe hearing loss, respectively. PATIENTS AND METHODS The individuals were evaluated in both ears by pure tone audiometry and blood samples were collected after written informed consent was signed. DNA extraction and PCR amplification of GJB2 coding region followed standard methodologies. PCR products were automatically sequenced in both directions. RESULTS We identified a novel mutation, c.638T>A (p.Leu213X), in GJB2 gene. This nonsense mutation was found in both siblings, and was inherited from their hearing father. Molecular analysis showed that the two siblings were also heterozygous for c.333-334delAA, a previously described GJB2 deletion. This novel mutation was not found in a random control sample of 480 individuals that were screened for coding region of GJB2 gene. p.Leu213X mutation identified in this study for the first time changes the codon 213, coding for a highly conserved and slowly evolving residue of connexin 26, localised to the C-terminus domain of the protein, to a STOP codon, leading to the deletion of the last 14 amino acids of the protein. CONCLUSION We can conclude that the aetiology of deafness in these individuals is due to the GJB2 genotype involving the c.333-334delAA deletion and the novel p.Leu213X mutation in compound heterozygosity.

Biomarkers of presbycusis and tinnitus in a Portuguese older population

Introduction: Presbycusis or age-related hearing loss (ARHL) is a ubiquitous health problem. It is estimated that it will affect up to 1.5 billion people by 2025. In addition, tinnitus occurs in a large majority of cases with presbycusis. Glutamate metabotropic receptor 7 (GRM7) and N-acetyltransferase 2 (NAT2) are some of the genetic markers for presbycusis. Objectives: To explore patterns of hearing loss and the role of GRM7 and NAT2 as possible markers of presbycusis and tinnitus in a Portuguese population sample. Materials and Methods: Tonal and speech audiometry, tinnitus assessment, clinical interview, and DNA samples were obtained from patients aged from 55 to 75 with or without tinnitus. GRM7 analysis was performed by qPCR. Genotyping of single nucleotide polymorphisms (SNPs) in NAT2 was performed by PCR amplification followed by Sanger sequencing or by qPCR. Results: We screened samples from 78 individuals (33 men and 45 women). T allele at GRM7 gene was the most observed (60.3% T/T and 33.3% A/T). Individuals with a T/T genotype have a higher risk for ARHL and 33% lower risk for tinnitus, compared to individuals with A/A and A/T genotype, respectively. Being a slow acetylator (53%) was the most common NAT2 phenotype, more common in men (55.8%). Intermediate acetylator was the second most common phenotype (35.9%) also more frequent in men (82.6%). Noise exposed individuals and individuals with ‘high frequency’ hearing loss seem to have a higher risk for tinnitus. Our data suggests that allele AT of GRM7 can have a statistically significant influence toward the severity of tinnitus. Conclusion: For each increasing year of age the chance of HL increases by 9%. The risk for ARHL was not significantly associated with GRM7 neither NAT2. However, we cannot conclude from our data whether the presence of T allele at GRM7 increases the odds for ARHL or whether the A allele has a protective effect. Genotype A/T at GRM7 could potentially be considered a biomarker of tinnitus severity. This is the first study evaluating the effect of GRM7 and NAT2 gene in tinnitus.

The controversial p.Met34Thr variant in GJB2 gene: Two siblings, one genotype, two phenotypes

INTRODUCTION Recent advances in molecular genetics have increased the identification of genes and mutations responsible for inherited forms of hearing loss (HL), enabling early detection of these cases. Approximately, 60% of early-onset HL cases are due to genetic causes, of which 70% are non-syndromic. Of these, 75-80% are inherited in an autosomal recessive pattern (DFNB). Mutations in GJB2 gene, coding for connexin 26 (Cx26), are the major cause of autosomal recessive hereditary HL, but some GJB2 mutations are yet of unclear or controversial significance. OBJECTIVES The aim of the present study was to identify the etiology of hearing loss, and correlate genotype-phenotype, in two Portuguese siblings with profound and moderate non-syndromic sensorineural bilateral HL. MATERIAL AND METHODS The affected subjects and their parents underwent audiological and genetic study. Molecular analysis of GJB2 gene was performed, searching for mutations in the coding region and receptor splicing site by automated sequencing. RESULTS The onset and the degree of HL were different in the two affected subjects. However, the same GJB2 genotype [p.Met34Thr]+[p.Arg184Pro] was identified in both siblings. The c.551G>C (p.Arg184Pro) and c.101T>C (p.Met34Thr) missense variants were inherited from the father and mother, respectively, both heterozygous carriers of these variants. CONCLUSION The clinical and genetic data here presented suggest that the non-syndromic sensorineural HL of these two Portuguese siblings might be due to the presence of p.Met34Thr and p.Arg184Pro variants in compound heterozygosity. If so, p.Met34Thr variant could have function as a hypomorphic allele that may cause HL depending on the opposing GJB2 allele. The observed phenotypic variability may not, however, be solely explained by variable expression of this genotype. A putative modifier gene or mutations in another HL-associated gene could probably be contributing to the severe HL in one of the siblings.