| Impaired hearing is the most common sensory disorder worldwide.Without appropriate opportunities to learn language,these children will fall behind their heating peers in communication,cognition,reading,and social-emotional development.Such delays may result in lower education and employment levels in adulthood.In 50-60%of them,impairment hearing loss due to a genetic cause (hereditary impaired hearing,HIH)and in 40-50%of the cases acquired due to prematurely,neonatal hypoxia,pre or postnatal infections,ototoxic drugs,or acoustic or cranial trauma.Hereditary impaired heating may occur as part of a muitisystem disease(syndromic HIH)or as disorder restricted to the ear and vestibular system (nonsyndromic HIH).Since nonsyndromic HIH is almost exclusively caused by cochlear defects,affected patients suffer from sensor neural hearing loss.Approxialy autosomal recessive mutations account for the 70-80%of(NSSHI).This study was to investigate of clinical epidemiology and molecular epidemiology of deaf-mutes Students in Gansu Province.This thesis comprised two parts and the details were described as following:The First Part:Clinical Epidemiology Analysis of 801 Deaf-mutes Students in Chinese NorthwestThis study was to investigate the main cause of hearing loss and get more information in Chinese Northwest deaf-mute students;we analyzed the clinical epidemiological data from 801 deaf-mute students in Gansu Province.All patients' medical history were taken by questionnaire and telephone interview from parents and teachers.All patients underwent general physical examination and otolaryngological examination including pure-tone audiometry,acoustic immittanee and auditory-brainstem response(ABR)tests.This study involved 801 deaf-mute students from the Northwest of China.326(326/801=40.69%)had the history of prescribing drugs,in addition 282 of these 801 students had prescribing amino glycosides;85 (85/801;10.61%)students were found to have a family history of deafness.At last, risk factors during pregnancy,disease of newborn and infection constituted a substantial proportion of 23.72%(190/801).The clinical epidemiological analysis identified that it is important to improve the safety of amino glycosides antibiotic therapy and molecular epidemiological studies in Chinese northwest.In addition,the incidence of congenital hearing loss is the highest in newborns,usual screening is necessary.The Second Part:GJB2,SLC26A4 and Mitochondrial DNA A1555G Mutations in Prelingual Deafness in the North West of ChinaThe study was to reveal the spectrum and frequency of the GJB2 gene,SLC26A4 gene and Mitochondrial DNA(mtDNA)A1555G mutations in Chinese northwest by 801 patients with nonsyndromic hearing loss(NSHI).Blood samples were obtained from 801 patients with NSHI in Northwest of China;Genomic DNA was extracted from the isolated leukocytes;PCR and direct sequencing were used to analyze the coding region of GJB2 gene,SLC26A4 gene(exon 7,19)and The mitochondrial DNA target fragments.One hundred and twenty-five of the 801 NSHI(125/801, 15.61%)were found to have GJB2 mutations,8.99%(72/801)had biallelic mutations (homozygous or compound heterozygous).The 235delC mutation was the most common type of GJB2 mutation,with a frequency of 78.79%(156/198)among the GJB2 mutations.101(101/801,12.61%)children were found to carry IVS7-2A>G, H723R and T721M mutations(SLC26A4 gene)and 41(41/801,5.12%)had biallelic mutations(homozygous or compound heterozygous).Conclusion We found that 28.22%of the patients had GJB2 gene and SLC26A4(IVS7-2A>G;H723R,T721M) mutations.The mitochondrial DNA A1555G mutation was found in 67 individuals from 801 patients(8.36%).15 of these 67 patients have family histories.The pattern of results implied that by conducting the necessary DNA tests,about 22.47%(8.99%+5.12%+8.36%)of the nonsyndromic hearing loss population in this region could be effectively detected at younger ages,and thus,early intervention measures could be undertaken to help them in language acquisition.
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