Screening For Deafness Gene In Cochlear Implant Recipients

Severe deafness or hearing impairment affecting about 1 in 1,000 children,half of that is genetic.Non-syndromic autosomal recessive deafness is the most common form of genetic hearing loss,accounts for approximately 80 percent of cases of hereditary deafness.So far more that 100 genes associated with Non-syndromic hearing loss(including dominant and recessive autosomal,X-linked,Y-linked and mitochondrial types of transmission) have been cloned(The Hereditary Hearing loss Homepage, http://wehh01.ua.ac.be/hhh/).To determine the molecular etiology of cochlear implant recipients, this study focused on the prevalence of candidate genes:GJB2, mitochondrial 12S rRNA and SLC26A4(PDS) gene mutations in patients undergoing cochlear implantation.Part1:The Methods of Collecting Clinical Date and Screening the Genes of Deafness in Cochlear Implant RecipientsCases Collection:We enrolled 100 non-syndromic deafness cochlear implant recipients and 109 healthy controls from November,2004 to June,2006 in PUMCH for mutation screening of GJB2 and mitochondrial 12S rRNA gene.We enrolled another 48 Cochlear Implant Recipients with inner ear malformation and 50 healthy controls for mutation screening of SLC26A4(PDS) gene.Materials and Methods:This part demonstrate detailedly the methods and material used in collecting clinical date and screening the genes of deafness in cochlear implant recipients,including the mathods of collecting genetic resource of the cochlear implant recipients and establishing the database of the hereditary hearing imparement;the facility,software and reagent used in this study;and the analysis strategy of the date in the study.Part2:Screening of the GJB2(Connexin-26) geneObjective:To determine the prevalence of GJB2 gene mutations in patients undergoing cochlear implantation.Methods:We enrolled 100 cochlear implant recipients for mutation screening.Genomic DNA was extracted from the blood of all patients, amplified in PCR and analyzed for single strand conformation polymorphism (SSCP) or direct sequencing to detect mutations of GJB2 gene.Results:The result shows that the GJB2 mutationsare detected in 41.0% (41/100) of the cochlear implant recipients.This study found 11 different variations in the GJB2 gene.The 235de1C mutation was the most prevalent mutation accounting for 21.0%(42/200) in all cochlear implant recipients. 187G＞T and 230G＞A mutations were novel mutation of GJB2 gene in the Chinese population.Conclusion:Mutations in the GJB2 gene were a major cause of deafness in cochlear implant recipients;the carrier frequency of 235delC mutation was highest.Part 3:Screening of the Mitochondrial 12SrRNA GeneObjective To investigate the prevalence of the mitochondrial 12S rRNA gene mutation in Chinese patients received cochlear implantation.Methods The 100 Chinese patients received cochlear implantation were analyzed in the present study(96 with pre-lingual hearing loss,4 with post-lingual hearing loss).Genomic DNA was extracted from peripheral blood obtained.After PCR amplication,each fragments of the mitochondrial 12S rRNA gene was sequenced in automated DNA sequencer. Results Only two cases was identified with the mitochondrial 1555 A＞G mutation and One occurrences of the de1T961Cn mutation in the mitochondrial 12S rRNA gene out of 16 patients received aminoglycosides.The deafness mutation was accounting for 3%in all cochlear implant recipients.Conclution In this study,mutations of the mitochondrial 12S rRNA gene were not the major cause of deafness in cochlear implant recipients.Part 4:Screening of SLC26A4(PDS) Gene in patients with EVA or others Inner Ear MalformationObjective:To determine the prevalence of SLC26A4(PDS) gene mutations in Cochlear Implant Recipients with inner ear malformation,and the correlation between SLC26A4(PDS) gene mutations and inner ear malformation and intra-operative testing of the electrically evoked auditory nerve compound action potentials(ECAP).Methods:48 Cochlear Implant Recipients with temporal bone malformation and 50 health control were enrolled for mutation screening.Genomic DNA was extracted from the blood,amplified in PCR and analyzed for direct sequencing to detect mutations of SLC26A4(PDS) gene.48 Cochlear Implant Recipients were tested intraoperative neural response telemetry(NRT), which measures the electrically evoked auditory nerve compound action potentials(ECAP).Results:The result shows that the SLC26A4(PDS) mutations are detected in 70.3%(26/37) of the patients with EVA(enlarged vestibular aqueduct), and 18.2%(2/11) of the patients with others malformation of inner ear. Fifteen different mutations were identified,8 of which had never been previously reported.The IVS7-2A＞G mutation was the most prevalent mutation of SLC26A4(PDS) gene accounting for 45.9%(17/37) in the patients with EVA(enlarged vestibular aqueduct).There was no association implied between SLC26A4 mutations ECAP in Cochlear Implant Recipients with inner ear malformation.Conclusion:In Cochlear Implant Recipients,mutations in the SLC26A4 (PDS) gene was a major cause of EVA,the most common mutation was IVS7-2A＞G.