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Abstract Introduction Hearing loss etiology depends on the population studied as well as on the ethnicity and the socio-economic condition of the analyzed region. Etiological diagnosis contributes to the improvement of preventive measures and to the early identification of this deficiency. Objective To identify the etiological factors of hearing loss and its prevalence in a tertiary hospital in southern Brazil, to verify the frequency of mutations in GJB2 and GJB6 genes, and to correlate the degree of hearing loss with the etiological factors of deafness. Methods This prevalence study involved 140 children with bilateral sensorineural or mixed hearing loss. Medical history, physical examination, audiometry, and evoked auditory brainstem response were conducted. Imaging and genetic examinations were also performed. Results Etiologies and their prevalence were as follows: (a) indeterminate causes, 31.4%; (b) conditions related to neonatal period, 22.1%; (c) genetic, 22.1%; (d) auditory neuropathy, 10%; (e) other factors (cortical malformation, intracranial hemorrhage, and internal ear malformations), 7.9% and (f) congenital infections, 6.4%. Within the genetic cases, ten homozygous and seven heterozygotes of the 35delG mutation were identified, besides two cases of rare variants of GJB2: p.Try172* and p.Arg184Pro. One case with homozygosis of del(GJB6-D13S1830) was found. Regarding severity of hearing loss, in 78.6% of the cases the degree of hearing loss was profound and there were no significant differences when comparing between etiologies. Conclusion The number of indeterminate etiologies is still high and congenital CMV infection may be a possible cause of undiagnosed etiology for hearing loss. The predominance of etiologies related to neonatal conditions and infectious causes are characteristic of developing countries. The most prevalent mutation was 35delG, the main GJB2 gene, probably because of the European influence in the genotype of our population.
Resumo Introdução A etiologia da perda auditiva depende da população estudada, da etnia e da condição socioeconômica da região analisada. O diagnóstico etiológico contribui para o aprimoramento das medidas preventivas e para a identificação precoce dessa deficiência. Objetivos Identificar os fatores etiológicos da perda auditiva e sua prevalência em um hospital terciário do sul do Brasil, verificar a frequência de mutações nos genes GJB2 e GJB6 e correlacionar o grau da perda auditiva com os fatores etiológicos da deficiência auditiva. Método Este estudo de prevalência avaliou 140 crianças com perda auditiva neurossensorial bilateral ou mista. Foram submetidos a anamnese com histórico médico, exame físico, audiometria e potencial evocado auditivo de tronco encefálico. Exames de imagem e genéticos também foram feitos. Resultados As etiologias e sua prevalência foram as seguintes: (a) causas indeterminadas, 31,4%; (b) condições relacionadas ao período neonatal, 22,1%; (c) genética, 22,1%; (d) neuropatia auditiva, 10%; (e) outros fatores (malformação cortical, hemorragia intracraniana e malformações da orelha interna), 7,9% e (f) infecções congênitas, 6,4%. Entre os casos genéticos, foram identificados dez casos homozigotos e sete heterozigotos da mutação 35delG, além de dois casos de variantes raras do GJB2: p.Try172* e p.Arg184Pro. Foi encontrado um caso homozigoto da mutação del (GJB6‐D13S1830). Em relação à gravidade da perda auditiva, em 78,6% dos casos o grau da perda auditiva foi profundo e não houve diferenças significantes na comparação entre as etiologias. Conclusão O número de etiologias indeterminadas ainda é elevado e a infecção congênita por CMV pode ser uma possível causa de etiologia não diagnosticada para perda auditiva. A predominância das etiologias relacionadas às condições neonatais e às causas infecciosas são características de países em desenvolvimento. A mutação mais prevalente foi a 35delG e o principal gene foi o GJB2, provavelmente devido à influência europeia no genótipo de nossa população.
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La hipoacusia congénita o de aparición temprana es un trastorno sensorial muy frecuente en niños. Las causas son diversas, pueden intervenir factores genéticos y/o ambientales. El 80% de la sordera hereditaria es no sindrómica y de herencia autosómica recesiva. Hasta un 50% de estos casos se deben a mutaciones en el locus DFNB1 donde están localizados los genes GJB2 y GJB6, que codifican las conexinas 26 y 30, dos proteínas que se expresan predominantemente en la cóclea. Se han reportado más de 100 mutaciones en el gen GJB2, con una mutación muy frecuente, 35delG, que representa hasta un 85% de los alelos mutados. Una deleción en el gen GJB6, (delGJB6-D13S1830), surge como la segunda mutación más frecuente. La hipoacusia debida a mutaciones en estos genes es de inicio prelocutivo, con un grado de severidad que varía de moderado a profundo, existiendo casos leves en menor proporción, con variaciones inter e intrafamiliares. Es generalmente estable, bilateral, y afecta a todas las frecuencias. El conocimiento de las causas genéticas de la hipoacusia ha permitido contar con nuevas herramientas para el diagnóstico, y como consecuencia, se ha optimizado el asesoramiento genético y facilitado el diagnóstico precoz de los pacientes, incluso en el período prenatal. La detección precoz tiene un impacto inmediato en la implementación de terapias que permiten una estimulación auditiva temprana. En esta revisión se describe el papel de las conexinas en la fisiología auditiva, así como también las características moleculares y audiológicas y el desempeño auditivo con audífonos e implante coclear en pacientes que presentan mutaciones en las conexinas 26 y 30.
Congenital or early appearing hearing loss is a very common sensory disorder in children. The causes for the disorder are diverse and genetic as well as environmental factors may be involved. Overall, 80% of the hereditary deafness is non-syndromic and of autosomal recessive inheritance. Up to 50% of the cases are associated with mutations in the DFNB1 locus that contains the GJB2 and the GJB6 genes encoding connexins 26 and 30, two proteins that are predominantly expressed in the cochlea. More than 100 mutations of the GJB2 have been reported. The 35delG is a common mutation accounting for up to 85% of the mutated alleles. A deletion in the GJB6 gene, (delGJB6-D13S1830), is the second most frequent mutation found. Hearing loss due to mutations in these genes has an onset before speech develops and degree of severity varies from moderate to severe, with a lower incidence of mild cases and inter- and intrafamily variations. The condition is usually stable, bilateral, and affecting all frequencies. Increased knowledge on the genetic causes of hearing loss has allowed for the development of new diagnostic tools and consequently, improvement of genetic counseling and early, even prenatal, diagnosis. Early detection has an immediate impact with implementation of early auditory stimulation therapies. In this review the role of connexins in auditory physiology described, as well as molecular and audiological features and auditory performance with hearing aids and cochlear implants in patients with connexins 26 and 30 mutations.
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Humanos , Recém-Nascido , Lactente , Pré-Escolar , Criança , Adolescente , Implante Coclear , Conexina 26 , Conexina 30 , Conexinas/genética , Perda Auditiva Neurossensorial/congênito , Perda Auditiva Neurossensorial/genética , Argentina/epidemiologia , Mutação , Patologia MolecularRESUMO
Abstract Introduction: Several studies have associated congenital sensorineural hearing loss in children with prolongation of the cardiac parameter QTc. The cause of this association is unknown. At the same time, mutations in GJB2, which encodes connexin 26, are the most common cause of congenital hearing impairment. Objective: To compare electrocardiographic parameters (PR interval, QRS complex, and QTc interval) in patients with hearing loss who were tested for mutations in GJB2 and GJB6 to investigate whether these mutations affect electrical activity of the heart. Methods: 346 patients (176 males, 170 females) with sensorineural hearing loss of 30 dB HL or more, aged 21.8 ± 19.9 years (including 147 children <14 years), underwent both genetic study for GJB2 and GJB6 mutations and electrocardiography. Results: Mutations in GJB2, including homozygotes and heterozygotes, were found in 112 (32%) patients. There were no significant differences in ECG parameters between groups of patients with and without mutations in GJB2. No differences were observed either in men (mean PR with mutation: 155 ± 16.6 vs. 153.6 ± 30.1 without; QRS: 99.9 ± 9.9 vs. 101.1 ± 15.4; QTc: 414.9 ± 29.9 vs. 412.4 ± 25.7) or women (mean PR with: 148.7 ± 21 vs. 143.8 ± 22.8 without; QRS: 94.8 ± 7.6 vs. 92.9 ± 9.6; QTc: 416.8 ± 20.6 vs. 424.9 ± 22.8). In similar fashion, we did we find any significant differences between groups of children with and without GJB2 mutations (mean PR with: 126.3 ± 19.6 vs. 127 ± 19.7 without; QRS: 80.7 ± 9.5 vs. 79.4 ± 11.6; QTc: 419.7 ± 23.5 vs. 419.8 ± 24.8). Conclusion: No association was found between the presence of GJB2 mutations encoding connexin 26 in patients with hearing loss and their ECG parameters (PR, QRS, QTc).
Resumo Introdução: Vários estudos têm associado a perda auditiva neurossensorial congênita em crianças ao prolongamento do parâmetro cardíaco QTc. A causa dessa associação é desconhecida. Ao mesmo tempo, as mutações no GJB2, que codifica a conexina 26, são a causa mais comum de deficiência auditiva congênita. Objetivo: Comparar parâmetros eletrocardiográficos (intervalo PR, complexos QRS e intervalo QTc) em pacientes com perda auditiva que foram testados para mutações no GJB2 e GJB6 para investigar se essas mutações afetam a atividade elétrica do coração. Método: Foram submetidos a estudo genético para mutações de GJB2 e GJB6 e eletrocardiograma 346 pacientes (176 homens, 170 mulheres) com perda auditiva neurossensorial de 30 dB ou mais, com média de 21,8 ± 19,9 anos (incluindo 147 crianças <14 anos). Resultados: Mutações no GJB2, inclusive homozigóticos e heterozigóticos, foram encontradas em 112 (32%) pacientes. Não houve diferenças significativas nos parâmetros de ECG entre grupos de pacientes com e sem mutações no GJB2. Não foram observadas diferenças em homens (PR médio com mutação: 155 ± 16,6 vs. 153,6 ± 30,1 sem mutação; QRS: 99,9 ± 9,9 vs. 101,1 ± 15,4; QTc: 414,9 ± 29,9 vs. 412,4 ± 25,7) nem em mulheres (PR médio com: 148,7 ± 21 vs. 143,8 ± 22,8, sem; QRS: 94,8 ± 7,6 vs. 92,9 ± 9,6; QTc: 416,8 ± 20,6 vs. 424,9 ± 22,8). Da mesma forma, encontramos diferenças significativas entre os grupos de crianças com e sem mutações de GJB2 (PR médio com: 126,3 ± 19,6 vs. 127 ± 19,7, sem; QRS: 80,7 ± 9,5 vs. 79,4 ± 11,6; QTc: 419,7 ± 23,5 vs. 419,8 ± 24,8). Conclusão: Não foi encontrada associação entre a presença de mutações de GJB2 que codificam conexina 26 em pacientes com perda auditiva e seus parâmetros de ECG (PR, QRS, QTc).
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Humanos , Masculino , Feminino , Recém-Nascido , Lactente , Pré-Escolar , Criança , Adolescente , Adulto , Pessoa de Meia-Idade , Idoso , Idoso de 80 Anos ou mais , Adulto Jovem , Síndrome do QT Longo/genética , Conexina 26/genética , Perda Auditiva Neurossensorial/genética , Mutação , Síndrome do QT Longo/complicações , Eletrocardiografia , Genótipo , Perda Auditiva Neurossensorial/complicaçõesRESUMO
Introducción. La sordera congénita es un problema de salud pública. Su incidencia en México es de 2-3 por cada 1000 recién nacidos. El diagnóstico oportuno con el tamiz auditivo neonatal es fundamental para un mejor pronóstico funcional. Aproximadamente 70% de las sorderas congénitas son de origen genético, con herencia autosómica recesiva. La mayoría de estos casos se asocia con mutaciones en el gen GJB2 , que codifica para la proteína conexina 26. Hay tres mutaciones reportadas como las más frecuentes en este gen: c.35delG, c.167delT y c.235delC. Métodos. Previo consentimiento informado de los pacientes, se obtuvo 1 ml de sangre periférica para la extracción de ADN. Mediante las técnicas de PCR-RFLP o PCR seguida de secuenciación, se buscaron las tres mutaciones más frecuentes del gen GJB2 . Resultados. Se realizó el estudio molecular en 11 pacientes: Se encontró un cambio en la secuencia codificante en cinco de ellos. Un paciente fue homocigoto para c.35delG; otro resultó heterocigoto para c.35insG, mutación no reportada previamente; un tercero fue heterocigoto para c.34G>T y dos más fueron heterocigotos para el polimorfismo c.79G>A (p.V27I). En ningún caso se hallaron las mutaciones c.167delT y c.235delC. Conclusiones. Se encontraron cambios de secuencias que correspondieron a dos polimorfismos y a tres mutaciones. La frecuencia de las tres mutaciones investigadas fue menor a lo reportado en la literatura y se encontró una mutación no reportada previamente. Este estudio evidencia la importancia del diagnóstico oportuno con manejo integral, incluyendo el asesoramiento genético con base en estudios moleculares, y resalta la importancia de conocer el perfil genotípico de este grupo de pacientes.
Background. Congenital deafness is a public health problem affecting 2-3:1000 newborns in Mexico. Neonatal audiologic screening allows early detection with important implications for the functional prognosis. About 70% of cases of congenital deafness are associated with a genetic etiology with an autosomal recessive pattern of inheritance. Most cases are caused by mutations in the GJB2 gene, which codifies conexin 26. The three most commonly reported mutations in this gene are c.35delG, c.167delT and c.235delC. Methods. After obtaining informed consent, DNA was extracted from a blood sample, and the three previously mentioned mutations were searched for using PCR-RFLP or PCR followed by sequencing. Results. Molecular analysis was carried out in 11 patients. In five of these patients, a change in sequence was observed. In none of the patients were c.167delT and c.235delC mutations found. One patient was homozygous for c.35delG and another patient was heterozygous for c.35insG, which is a mutation not previously reported. A third patient was heterozygous for c.34G>T. Two additional patients had the c.79G>A (p.V27I) polymorphism. Conclusions. Frequency of the three mutations analyzed was lower compared to other populations. Five sequence changes were observed, two polymorphisms and three mutations, one of them novel. This study also demonstrates the relevance of early diagnosis and multidisciplinary management and the importance of determining the genetic basis of this disease in pediatric patients with congenital deafness.
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La principal causa de hipoacusia no-sindrómica autosómica recesiva (HNSAR) son mutaciones en el locus DFNB1, que contiene los genes GJB2 (conexina 26) y GJB6 (conexina 30). Se han descripto más de 100 mutaciones diferentes en GJB2. Dos deleciones en GJB6, del (GJB6-D13S1830) y del(GJB6-D13S1854) mostraron ser prevalentes en España. El objetivo de este trabajo fue determinar la prevalencia de mutaciones en los genes GJB2 y GJB6, en niños con HNSAR de Argentina. Este estudio incluyó 113 niños no relacionados con hipoacusia neurosensorial no-sindrómica moderada a profunda. Para el análisis molecular se utilizó una estrategia en etapas. La mutación 35delG (gen GJB2) se analizó mediante PCR-RFLP. La presencia de deleciones en GJB6 se investigó por PCR múltiple. Las muestras no resueltas en las dos primeras etapas fueron analizadas por secuenciación directa del gen GJB2. En 58 pacientes se encontraron alteraciones en la secuencia de los genes GJB2/GJB6. La mutación 35delG se detectó en 52 de los 84 alelos con mutaciones patogénicas. Se identificaron 16 variantes de secuencia diferentes; entre ellas una mutación no descripta previamente, 262G>C (A88P). La deleción del (GJB6-D13S1830) fue identificada en 7 alelos. La frecuencia de mutaciones en GJB2/GJB6 encontrada en este trabajo está en concordancia con la de otras poblaciones caucásicas. La mutación más prevalente fue 35delG y la segunda mutación más común la deleción del (GJB6-D13S1830), con frecuencias similares a las encontradas en España, desde donde Argentina recibió una de sus mayores olas inmigratorias. Estos resultados destacan la importancia del estudio de los genes GJB2/GJB6 en el diagnóstico etiológico de sordera permitiendo un tratamiento precoz y un asesoramiento genético oportuno.
The main cause of autosomal recessive nonsyndromic hear-ing loss (ARNSHL) are mutations in genes GJB2 (connexin 26) and GJB6 (connexin 30) at the DFNB1 locus. More than 100 different mutations in GJB2 have been described. Two dele-tions in GJB6, of (GJB6-D13S1830) and of (GJB6-D13S1854) have been found prevalent in Spain. The aim of this study was to determine the prevalence of GJB2 and GJB6 gene muta-tions in children with ARNSHL in Argentina. In the study, 113 non-related children with moderate to profound nonsyndromic sensorineural hearing loss were included. A staging strategy was used for molecular analysis. The 35delG mutation (gene GJB2) was analyzed using PCR-RFLP. The presence of de-letions in GJB6 was tested by multiplex PCR. Samples that were not resolved in the first two stages were subsequently assessed by direct sequencing of the GJB2 gene. In 58 patients abnormal patterns were found in the GJB2/GJB6 sequences. The 35delG mutation was detected in 52 of the 84 alleles with pathogenic mutations. Sixteen different sequence variants were identified of which one, 262G>C (A88P), was not previously described. Deletion of (GJB6-D13S1830) was identified in 7 alleles. The rate of mutations in GJB2/GJB6 found in this study is similar to that reported in other Caucasian populations. The most prevalent mutation was 35delG followed by a deletion of (GJB6-D13S1830), with a rate similar to that found in Spain from which Argentina received one of the largest waves of immigrants. These results emphasize the need to study GJB2/GJB6 genes in the etiological diagnosis of hearing loss allowing for early treatment and adequate genetic counseling.
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Humanos , Masculino , Feminino , Lactente , Pré-Escolar , Criança , Adolescente , Conexinas/genética , Genes , Mutação/genética , Perda Auditiva/congênito , Perda Auditiva/diagnóstico , Perda Auditiva/etiologia , Surdez/diagnóstico , Surdez/etiologia , ArgentinaRESUMO
Introducción: Se estima que 1 de cada 1.000 niños presenta hipoacusia severa al nacimiento o en los primeros meses de vida y el 50 por ciento de las hipoacusias congénitas se relacionan con el gen de la conexina 26 (GJB2). En poblaciones caucásicas la variante patogénica 35delG del gen GJB2, que es la más frecuente, se encuentra en 30 por ciento de los pacientes con hipoacusia congénita no sindrómica. En Chile, la frecuencia de esta variante en escolares sordos no está descrita. Objetivos: Estimar la frecuencia de la mutación 35delG del gen GJB2 en niños con sordera congénita no sindrómica y no atribuible a causas ambientales conocidas, de colegios especiales de Santiago. Correlacionar la presencia de 35delG con los antecedentes clínicos de estos niños. Material y método: Se determinó la presencia de la mutación 35delG mediante PCR alelo específico y secuenciación automatizada en 81 escolares. Se buscó asociar la presencia de 35delG y los antecedentes clínicos de los niños mediante la prueba exacta de Fisher. Resultados: En el grupo estudiado, el 11,25 por ciento de los casos presentaron la variante 35delG, siendo ésta más frecuente en los casos en que había antecedentes familiares de sordera. En 8 casos se encontró una variante considerada no patogénica V27I. Conclusión: La frecuencia de la mutación 35delG fue inferior a lo esperado, probablemente debido al método de selección de los niños a estudiar (aquellos cuyos padres no referían causa conocida de sordera, lo cual no fue refrendado por exámenes de laboratorio que permitieran descartar enfermedades infecciosas u otras condiciones causantes de sordera).
Introduction: Congenital hearing loss occurs in 1 in 1000 live births and 50 percent of these cases are related with mutations in the connexin26 gene (GJB2). The 35delG variant is the most common of the known pathogenic alleles in Caucasian populations, reaching a frequency of 30 percent among the non syndromic congenital deaf people. The frequency of this variant has not been described in Chilean deaf children. Aim: To estimate the frequency of the 35delG GJB2 gene mutation in children with non syndromic congenital hearing loss of unknown etiology from deaf schools in Santiago, and to evaluate the association between clinical features of these children and the presence of the 35delG allele. Material and method: The presence of the 35delG mutation was studied by allele specific PCR and automatical sequencing in 81 children. The association between clinical issues and genotypes was explored by Fisher exact test. Results: We found the 35delG variant in 11,25 percent of the children, this mutation was more frequent in familial cases than sporadic cases of deafness. We also found the V27I non pathogenic variant in 8 cases. Conclusion: The frequency of the 35delG mutation was lower than the expected, probably due to the criterion used to select the school children to be studied.
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Humanos , Criança , Conexinas/genética , Estudantes , Mutação , Surdez/genética , DNA , Chile , Frequência do Gene , Genótipo , Reação em Cadeia da PolimeraseRESUMO
Las pérdidas auditivas pueden ser atribuidas a factores genéticos o ambientales. Las mutaciones en el gen de la proteína Cx26 (conexina 26) son responsables de un 30-80% de los casos de pérdida auditiva profunda no sindrómica. La variante 35delG es la prevalente en la población caucásica. Entre los factores ambientales, el citomegalovirus (CMV) es la principal causa de infección congénita. Objetivos. Determinar la prevalencia de infección congénita por CMV y la frecuencia de la mutación 35delG en recién nacidos. Identifcar aquellos con riesgo de pérdida de audición con el fn de realizar un seguimiento audiológico para detectar precozmente las hipoacusias. Material y métodos. Se analizaron 1020 muestras de sangre seca, en papel, de recién nacidos, por PCR convencional y en tiempo real. Se efectuaron las otoemisiones acústicas antes del alta hospitalaria a todos los niños. El seguimiento audiológico se realizó tanto a los portadores de 35delG como a los que tuvieron infección congénita por CMV. Resultados. De los pacientes estudiados, 15 fueron heterocigotas para la mutación 35delG. No se detectaron homocigotas. Seis de las muestras fueron positivas para CMV (resultados confirmados en orina); de ellos, solo un neonato fue sintomático. A todos estos niños se les realizaron las evaluaciones audiológicas; presentaron hipoacusia tres niños con infección congénita por CMV y dos portadores de la mutación 35delG. Conclusión. Se detectó un 1,3% de portadores de la mutación 35delG y una frecuencia de infección congénita por CMV del 0,6%. El seguimiento audiológico de estas dos poblaciones permitió la detección de hipoacusias tardías.
Introduction. Hearing loss may be attributed to genetic and environmental factors. Mutations in the gene of the CX26 protein (connexin 26), are responsible for 30-80% of all cases of non-syndromic profound hearing loss. The 35delG is the most frequent variant in the caucasian population. As to environmental factors, the cytomegalovirus (CMV) is the main cause of congenital infection. Objetives. To determine the prevalence of congenital CMV infection and the frequency of the 35delG mutation in newborns. To identify those at risk of suffering hearing loss in order to do an audiologic follow-up of detected cases. Materials y methods. One thousand and twenty samples of dry blood spots corresponding to newborns were tested using conventional and real time PCR. Audiologic screening was performed to all newborns before hospital discharge. Results. Fifteen out of 1020 subjects were heterozygous for the mutation. No homozygous patients were found. Six out of the samples tested positive for CMV (confrmed by a urine sample), out of which only one newborn was symptomatic. The auditory brainstem response was recorded in all these children. Hearing loss was found in three children with congenital CMV infection and two with 35delG mutation. Conclusion. The frecuency of 35delG mutation carriers in our population was 1.3% and the CMV congenital infection prevalence was 0.6%. Audiologic monitoring of these two populations allowed detection of hearing loss of late onset.