Screening for mutations in the GJB3 gene in Brazilian patients with nonsyndromic deafness

Abstract. Deafness is a complex disorder that is affected by a high number of genes and environmental factors. Recently, enormous progress has been made in nonsyndromic deafness research, with the identification of 90 loci and 33 nuclear and 2 mitochondrial genes involved (http://dnalab-www.uia.ac.be/dnalab/hhh/). Mutations in the GJB3 gene, encoding the gap junction protein connexin 31 (Cx31), have been pathogenically linked to erythrokeratodermia variabilis and nonsyndromic autosomal recessive or dominant hereditary hearing impairment. To determine the contribution of the GJB3 gene to sporadic deafness, we analysed the GJB3 gene in 67 families with nonsyndromic hearing impairment. A single coding exon of the GJB3 gene was amplified from genomic DNA and then sequenced. Here we report on three amino acid changes: Y177D (c.529T > G), 49delK (c.1227C > T), and R32W (c.144-146delGAA). The latter substitution has been previously described, but its involvement in hearing impairment remains uncertain. We hypothesize that mutations in the GJB3 gene are an infrequent cause of nonsyndromic deafness

Perspectivas para triagem da deficiência auditiva genética: rastreamento da mutação 35delG em neonatos Prospects for genetic hearing loss screening: 35delG mutation tracking in a newborn population

OBJETIVO: Investigar a prevalência da mutação 35delG em amostra de recém-nascidos, com teste molecular específico; avaliar as perspectivas para a triagem neonatal genética para a deficiência auditiva. CASUÍSTICA E MÉTODO: Foram avaliados 223 recém-nascidos no Hospital de Base de São José do Rio Preto, em São Paulo, para análise molecular da mutação 35delG, no gene da conexina 26, com a técnica da reação em cadeia da polimerase alelo-específico, após extração do DNA genômico de sangue de cordão umbilical. RESULTADOS: Foram identificados cinco heterozigotos, obtendo-se prevalência de 2,24% de portadores da mutação 35delG, na população do estudo. CONCLUSÃO: O uso do teste molecular permitiu a identificação da mutação 35delG na população do estudo, podendo ser utilizado como complemento aos rastreamentos audiométricos neonatais por ser simples, rápido, de fácil execução e de baixo custo.<br>OBJECTIVES: To investigate the prevalence of the 35delG mutation in a newborn population, with specific molecular testing, and to evaluate the prospects for genetic neonatal screening for hearing impairment. POPULATION AND METHOD: 233 newborn were evaluated at the Hospital de Base de São José do Rio Preto, SP, for molecular analysis of the 35delG mutation in the connexin 26 gene, with the reaction technique in allele-specific polymerase chain reaction, after genomic DNA extraction from umbilical cord blood. RESULTS: Five heterozygotes were identified, obtaining a prevalence of 2.24% of 35delG mutation carriers in the study population. CONCLUSION: Using the molecular test allowed for the identification of the 35delG mutation in the study population with the possibility of being used as a complement to neonatal audiometric screening as being simple, fast, and easily to perform with low costs

Molecular Findings In Brazilian Patients With Osteogenesis Imperfecta.

Osteogenesis imperfecta (OI) is a genetic disorder of increased bone fragility and low bone mass. Severity varies widely, ranging from intrauterine fractures and perinatal lethality to very mild forms without fractures. Most patients with a clinical diagnosis of OI have a mutation in the COL1A1 or COL1A2 genes that encode the a chains of type I procollagen, the major protein in bones. Hence, the aim of the present study was to identify mutations in the COL1A1 gene in 13 unrelated Brazilian OI patients. This is the first molecular study of OI in Brazil. We found 6 mutations, 4 of them novel (c.1885delG, p.P239A, p.G592S, p.G649D) and 2 previously described (p.R237X and p.G382S). Thus, the findings show that there are no prevalent mutations in our sample, and that their distribution is similar to that reported by other authors, with preponderance of substitutions for glycine in the triple helix domain, causing OI types II, III and IV.46105-

Somatic and germ cell cytogenetic studies and AZF microdeletion screening in infertile men

Clinical and cytogenetic studies were performed in 65 infertile individuals, and 56 of them were also screened for microdeletions in Yq11 (AZF region). Relevant environmental etiological factors were identified in 10 cases (15.4%). Sertoli-cell-only syndrome was diagnosed in six patients (9,2%). Karyotype abnormalities were detected in six individuals, and five other patients presented desynapsis of bivalents in meiosis. Three out of the 56 patients studied were carriers of microdeletions in the AZF region, one of them also presenting a chromosomal mosaicism for an extra i(22p)

Reduction of Cellular Expression Levels Is a Common Feature of Functionally Affected Pendrin (SLC26A4) Protein Variants

Abstract Sequence alterations in the pendrin gene (SLC26A4) leading to functionally affected protein variants are frequently involved in the pathogenesis of syndromic and nonsyndromic deafness. Considering the high number of SLC26A4 sequence alterations reported to date, discriminating between functionally affected and unaffected pendrin protein variants is essential in contributing to determine the genetic cause of deafness in a given patient. In addition, identifying molecular features common to the functionally affected protein variants can be extremely useful to design future molecule-directed therapeutic approaches. Here we show the functional and molecular characterization of six previously uncharacterized pendrin protein variants found in a cohort of 58 Brazilian deaf patients. Two variants (p.T193I and p.L445W) were undetectable in the plasma membrane, completely retained in the endoplasmic reticulum and showed no transport function; four (p.P142L, p.G149R, p.C282Y and p.Q413R) showed reduced function and significant, although heterogeneous, expression levels in the plasma membrane. Importantly, total expression levels of all of the functionally affected protein variants were significantly reduced with respect to the wild-type and a fully functional variant (p.R776C), regardless of their subcellular localization. Interestingly, reduction of expression may also reduce the transport activity of variants with an intrinsic gain of function (p.Q413R). As reduction of overall cellular abundance was identified as a common molecular feature of pendrin variants with affected function, the identification of strategies to prevent reduction in expression levels may represent a crucial step of potential future therapeutic interventions aimed at restoring the transport activity of dysfunctional pendrin variants

Prevalence and Evolutionary Origins of the del(GJB6-D13S1830) Mutation in the DFNB1 Locus in Hearing-Impaired Subjects: a Multicenter Study

Mutations in GJB2, the gene encoding connexin-26 at the DFNB1 locus on 13q12, are found in as many as 50% of subjects with autosomal recessive, nonsyndromic prelingual hearing impairment. However, genetic diagnosis is complicated by the fact that 10%–50% of affected subjects with GJB2 mutations carry only one mutant allele. Recently, a deletion truncating the GJB6 gene (encoding connexin-30), near GJB2 on 13q12, was shown to be the accompanying mutation in ∼50% of these deaf GJB2 heterozygotes in a cohort of Spanish patients, thus becoming second only to 35delG at GJB2 as the most frequent mutation causing prelingual hearing impairment in Spain. Here, we present data from a multicenter study in nine countries that shows that the deletion is present in most of the screened populations, with higher frequencies in France, Spain, and Israel, where the percentages of unexplained GJB2 heterozygotes fell to 16.0%–20.9% after screening for the del(GJB6-D13S1830) mutation. Our results also suggest that additional mutations remain to be identified, either in DFNB1 or in other unlinked genes involved in epistatic interactions with GJB2. Analysis of haplotypes associated with the deletion revealed a founder effect in Ashkenazi Jews and also suggested a common founder for countries in Western Europe. These results have important implications for the diagnosis and counseling of families with DFNB1 deafness