Deafness resulting from mutations in the GJB2 (connexin 26) gene in Brazilian patients

Abstract

Congenital deafness occurs in approximately 1 in 1000 live births. In developed countries about 60% of hearing loss is genetic. However, in Brazil most cases of hearing loss are due to environmental factors, such as congenital infections (mainly rubella), perinatal anoxia, kernicterus and meningitis. Recently, it has been demonstrated that the GJB2 gene is a major gene underlying congenital sensorial deafness. Mutations in this gene cause 10-20% of all genetic sensory hearing loss. One specific mutation, 35delG, accounts for the majority of mutant alleles. The extent of the hearing impairment varies from mild/moderate to profound, even within the patients homozygous for the common 35delG mutation. There may also be progression with age. Mutation analysis in the GJB2 gene was performed on 36 families (group A) presenting with at least one individual with non-syndromic deafness (NSD). An unselected series of 26 deaf individuals referred by other services where the environmental factors were not completely excluded was also part of the study (group B). Mutations in the GJB2 gene were found in 22% (eight patients) of the families tested in group A, and 11.5% (three patients) of individuals within group B. This finding should facilitate diagnosis of congenital deafness and allow early treatment of the affected subjects.

Prevalence of GJB2 (Connexin-26) and GJB6 (Connexin-30) Mutations in a Cohort of 300 Brazilian Hearing-Impaired Individuals: Implications for Diagnosis and Genetic Counseling

“…In spite of the difference in sample selection criteria, the frequency of individuals presenting c.35delG mutation in the GJB2 gene (12.4%) in our study was similar to that found (13.9%) in the report of de Oliveira et al (2007). Our study agrees with these previous reports (de Oliveira, et al, 2007;Oliveira, et al, 2002;Piatto, et al, 2004), showing that the c.35delG mutation is the most frequent among causative mutations of hearing impairment in the Brazilian population. This is a common mutation causing HL in Caucasian populations, mainly from Mediterranean Europe and the United States, and seems to be rare in the Asian and African populations.…”

“…(de Oliveira, et al, 2007;Oliveira, et al, 2002;Piatto, et al, 2004). Our study comprises a sample that included sporadic and familial cases, and individuals presenting only with known deafness-related syndromes were excluded.…”

Estudo molecular em crianças candidatas e submetidas ao implante coclear

“…This is particularly true for cases of family hearing loss, among which the frequence of mutations in this gene was found to be of 50%, but also for sporadic cases, among which the frequence was a bit higher than 11% (approximately 1:9) (Oliveira et al, 2002). In Brazil, the prevalence of 0.97% of 35delG mutation carriers was found to be approximately 1:103 heterozigotes, in a survey carried out with 620 newborns in the region of Campinas-SP (Oliveira et al, 2004).…”

“…In order to detect the 35delG mutation we used the allele specific PCR method (AS-PCR), using primers and the aforementioned polymerase chain reaction -modification patented by CBMEG -UNICAMP. (Oliveira et al, 2002). This method easily differentiates the normal allele from the mutant and through two reactions it is possible to distinguish normal homozygotes, 35delG homozygote and heterozygote carriers of the 35delG mutation.…”

Correlação entre dados audiométricos e mutação 35delG em dez pacientes

“…In another study, performed in patients with hearing loss, mutations in the GJB2 gene were found in 33.5% of cases, and only the 35delG mutation was identified in 84.2% of mutant alleles 14 . The methodology used in the current study, AS-PCR and automated sequencing, was similar to the three above mentioned researches, but a variation was found in the frequency of the alleles with the 35delG mutation.…”