Search

Objective: the aim of this work was to evaluate the possible different impacts of genetic and environmental factors in childhood deafness in northern Cameroon. GJB2 mutations are responsible for more than half of all cases of prelingual nonsyndromic recessive deafness in Caucasians, representing the most important deafness-causing factor in the industrialized world. Other genes such as MTRNR1 are also involved. In sub-Saharan Africa, environmental factors seem to dominate genetic contributions, but few studies on the etiology of deafness in Africa are available for comparison., Design: prospective cross sectional study., Study Sample: we performed a molecular screen of the GJB2 and MTRNR1 genes in 70 deaf children and 67 unaffected controls in Maroua (Cameroon) and a literature analysis focused on deafness epidemiology in developing countries., Results: no GJB2 mutations emerged, and only a single MTRNR1 variant that may be pathogenic was found., Conclusion: environmental factors turn out to be more relevant than genetic factor in the Maroua population.

Mutations in the GJB2 gene, which encodes the gap-junction protein connexin 26, are the most common cause of nonsyndromic hearing loss (NSHL) and account for about 32% of cases. We analyzed 734 patients and identified mutations in 474/1468 chromosomes. Thirty-six different mutations and five polymorphisms were found in 269 NSHL subjects. Our data confirm 35delG as the most frequent GJB2 mutation in the Italian population, accounting for about 68% of all the mutated GJB2 alleles analyzed. We also identified two novel variants: the V156I mutation and the C>A change at nucleotide 684 in the 3'UTR of the gene. The GJB6 gene deletion, del(GJB6-D13S1830), which can cause HL in combination with GJB2 mutations in trans, was identified in three patients, while the del(GJB6-D13S1854) was not observed in our cohort of patients. We collected audiometric data from 200 patients with biallelic DFNB1 mutations or with dominant mutation in GJB2 to determine the degree of HL to correlate the genotypes with the audiological phenotypes.

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 x 10(-3) and 1 x 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.

Objectives: Mutations in the GJB2 gene, encoding Connexin 26, can cause nonsyndromic recessive deafness or dominant hearing loss (HL) with or without keratoderma. The objective was to perform a molecular evaluation to establish the inherited pattern of deafness in the sporadic cases afferent to our center., Methods: The subject was a 2-year-old Italian girl with nonsyndromic early onset HL. We performed DNA sequencing of the GJB2 gene and deletion analysis of the GJB6 gene in all family members., Results: Direct sequencing of the gene showed a heterozygous C-->G transition at nucleotide 172 resulting in a proline to alanine amino acid substitution at codon 58 (P58A). The analyses indicate that the P58A mutation appeared de novo in the proband with a possible dominant effect., Conclusions: This mutation occurs in the first extracellular domain (EC1), which seems to be very important for connexon-connexon interaction and for the control of voltage gating of the channel. The de novo occurrence of an EC1 mutation in a sporadic case of deafness is consistent with the assumption that P58A can cause dominant HL.

Mutations of the GJB2 gene, encoding Connexin 26, are the most common cause of hereditary congenital hearing loss in many countries, and account for up to 50% of cases of autosomal-recessive non-syndromic deafness. By contrast, only a few GJB2 mutations have been reported to cause an autosomal-dominant form of non-syndromic deafness. We report on a family from southern Italy in whom dominant, non-syndromic, post-lingual hearing loss is associated with a novel missense mutation in the GJB2 gene. Direct sequencing of the gene showed a heterozygous G-->A transition at nucleotide 535, resulting in an aspartic acid to asparagine amino acid substitution at codon 179 (D179N). This mutation occurred in the second extracellular domain (EC2), which would seem to be very important for connexon-connexon interaction.