Molecular studies of sudden deaf

Author(s)

Jessica Carvalho Bergmann

• Document type: Master's Dissertation
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Instituto de Biologia
• Defense date: 2008-10-20

Examining board members

Edi Lúcia Sartorato; Mônica Barbosa de Melo; Manoel de Nobrega

• Advisor: Norma de Oliveira Penido; Edi Lúcia Sartorato

Abstract

Several factors have been postulated to elicit the etiology of idiopathic sudden sensorineural hearing loss. Sudden deafness is characterized as a sensorioneural disturb, having an abrupt onset and an unknown cause that can be revealed in any age, occurring suddenly or in a progressive way in a 3 day period, of more than 30dB hearing loss at three consecutive frequencies. It can be unilateral or bilateral with tinnitus present and giddiness. In this work 38 patients were studied with their hearing control. Of all this patients, 22 were originating of Federal University of São Paulo São Paulo forming the group A and 16 were from Fono Audio Clinica in Fortaleza (CE) forming the group B. The main objective of this project was to determine possible genetics causes of sudden deafness in patients who lost suddenly their hearing. The main causes of genetic deafness were researched, initiating for the screening of 35delG mutation in the connexin 26 gene (GJB2), D(GJB6-D13S1830) and _(GJB6-D13S1854) deletions, A1555G, C1494T, A827G, T961G and 961delT/insC mutation present in mitochondrial gene MTRNR1 (12S rRNA) and G7444A, A7445G present in mitochondrial gene COI/MTTS1 (tRNAser(UCN)). Screening for the mutation G28T present in TRMU was also made. Then, complete GJB2 gene was screened for other mutations and polymorphisms. Of all patients analyzed, was not found mutation in genes GJB2 and GJB6. Three patients showed a mutation V27I that is a polymorphism still without relation with hearing loss. The mutation G7444A was found in one individual of the control group. Once that this patient has a normal hearing it is strongly suggestive that this mutation by itself can not cause a hearing loss, even if it is associated with two other mutations, the A827G mutation and G28T (TRMU) mutation. The mutation A827G was found in 6 individuals, 3 from deaf patients and 3 from control individuals, but it is no possible to relation this mutation with the hearing loss. The mutation of the gene TRMU was found in 14 individuals, being 9 deaf patients and 5 control individuals. Despite of this mutation being in a regulation gene, it is unknown the relation between this mutation and the hearing loss. With this results we can conclude that idiopathic sudden deafness can not be caused by a mutation in any of this genes studied. Shall the large clinical heterogeneity and genetic involved on those cases, is still impossible a certain conclusion. We can not exclude the fact that these mutations can be in regions not studied in this work and related with the hearing loss. (AU)