Estudo molecular em crianças candidatas e submetidas ao implante coclear

Abstract

Aim: recent progresses in molecular biology have been made in the diagnosis of sensorineural hearing loss. The high prevalence of a connexin 26 gene mutation, and its easy identification have made the diagnosis possible. The most frequent gene mutation is called 35delG. The purpose of this study was to evaluate the prevalence of 35delG mutation in children submitted to cochlear implantation who had severe and profound hearing loss previously diagnosed as idiopathic. Method: The study was done at the Cochlear Implantation Clinic of the Otolaryngology Department and at the Laboratório Genética Humana-CBMEG, UNICAMP-SP. 32 children with severe to profound sensorineural hearing loss were evaluated. The detection of the 35delG mutation was made by a allele -specific PCR, using primers and polymerase chain reaction. Results: 69% had a normal exam, 12% were homozygous for the mutation, 19% of the cases were heterozygous. The 35delG mutation in heterozygousity is not a cause of hearing loss. Conclusion: The data confirm the high prevalence of the 35delG mutation in nonsyndromic bilateral profound sensorineural hearing loss. It was also possible to diagnose the cause of hearing loss as genetic in a significant percentage of patients. That stresses the importance of the molecular investigation in those cases formerly classified as idiopathic.

Associação entre fenótipo, desempenho com próteses auditivas e genótipo da deficiência auditiva infantil em crianças com e sem alteração genética

“…The issue heterozygote and homozygote if often studied by researchers (1,9) . The authors refer that it is necessary that the individual inherits two mutated alleles, one from the father and another from the mother, to express the auditory deficiency (homozygosis).…”

“…The Idea of relating the genetic HI manifestations with the auditory performance with the use of cochlear implant (CI) is also a concern of many researchers (7)(8)(9)(10) . Different from the findings with hearing aids, the children with genetic mutations present, in general, higher benefits with the CI when compared with the children without such mutations.…”

“…Other authors (7)(8)(9)(10) studied the performance of subjects with cochlear implantation, according to their hearing impairments, observing that children with genetic alterations present more benefits with cochlear implantation.…”

Investigação genética da surdez hereditária: mutação do gene da Conexina 26

“…Sendo assim, há impossibilidade da Conexina 26 ser codificada pelo gene GJB2 alterado. Nos casos de heterozigose, quando o paciente apresentar a mutação em apenas um dos alelos, é possível que o outro alelo codifique a proteína, isso implica em um menor número de Conexina 26 codificada (12) .…”

“…A mutação 35delG em heterozigose não diagnostica a causa da surdez, apenas comprova que o paciente é portador da mutação. Portanto, neste estudo foi possível diagnosticar como genética a causa da surdez em uma parcela significativa de crianças (12) .…”