The Study of Deafness Molecular Diagnosis Technology in Clinical Application
|School||PLA Postgraduate Medical School|
|Course||Department of Otolaryngology - Head and Neck Surgery|
|Keywords||hearing loss GJB2 mtDNA 12S rRNA SLC26A4 POU3F4 non-coding region|
It is well known that heating loss is a common defect of newboms. Approximately one in 1000 newborns is born with hearing loss and 70%have no associated anomalies.50%of congenital hearing loss is caused by genetic etiology, 25%of hearing loss is due to environmental factors,and the etiology is obscure in the remaining 25%.14%of individuals with hearing problems between the ages of 45 and 64 is mainly due to genetic etiology.Sometimes interaction between environmental factors and genetic background can also cause hearing loss. Because different causes can lead to hearing loss,it is difficult to determine the definite cause of hearing loss in individuals without associated anomalies and family history of hearing loss.With much attention paid to environmental factors, improved public health condition,and infections under control,hearing loss caused by genetic etiology increases.In the recent ten years,the relationship between deafness and genetic etiology have been further explored and much process is made.Many genes relating to hearing loss are cloned and located, which makes us understand the mechanism of hearing loss in molecular level.The recerch in molecular epidemiology of deafness advance the advent of deafness molecular diagnosis.The study is to explore the significance of deafness molecular diagnosis in NSHL.Part one:analysis of clinical application of deafness molecular diagnosis in NSHLIn this study we gave initial analysis of etiology for 492 hearing loss patients according to medical records,family history,and high-resolution CT of the temporal bone.GJB2,mtDNA12S rRNA,and SLC26A4 were amplified by PCR. The amplicons of these genes were used to molecular diagnosis.272(55.28%)of all NSHL patients were diagnosed with different etiology including high risk factors of newborns,usage of ototoxicity drug,infection,abnormities or LVAS on CT,and hereditary deafness.220(44.72%)of all NSHL patients had no definite etiology.Twenty-seven patients were found mutations in GJB2 gene or mtDNA12S rRNA of 220 patients without definite etiology.Twenty-eight patients were found mutations in GJB2 gene or mtDNA12S rRNA in 101 hereditary deafness.SLC26A4 gene was screened in sixty-eight LVAS patients on CT. Thirty-two patients were carriers of compound heterozygotes or homozygotes pathologic mutations of SLC26A4 gene,and detection rate was 47.06%. Twenty-six patients were heterozygote carriers of pathologic mutations of SLC26A4 gene,and detection rate was 38.24%.The total detection rate of pathologic mutations was 85.29%in LVAS patients.The deafness molecular diagnosis plays a important role in exploring the cause of deafness.Part two:the medical diagnostic strategy of patient with characteristic clinical phenotypePOU3F4 is the sole cloned gene inⅩchromatosome.The mutations in POU3F4 gene lead to the characteristic temporal bone changes on CT,which is easily recognized by clinicians.The mutations of this gene were reported in different region and race.We paid much attention to this gene.When we analyzed a patient from deafness family,we found the patient with bone-air gaps on low frequencies of pure tone test and characteristic temporal bone changes on CT including bilateral and symmetric bulbous dilatation of the internal auditory canals and incomplete separation of the basal turn of the cochlea from the fundus of the internal auditory canal.Family history is consistent with the diagnosis of X-linked.We screened POU3F4 gene of patients and family members.A novel mutation 499C＞T was found in the male deafnesses.This mutation changes Arg to stop.Mother of the proband and female obligate carriers are normal hearing, and they transmit the mutation to hearing loss patients.Other male with normal hearing has no mutation in POU3F4 gene.This mutation found makes the cause of this family identified and mutations spectrum of POU3F4 abundant.There was no pathologic mutation found in the further study on 125 male deafnesses.This result indicates that the mutation rate is low in male deafnesses and characteristic temporal bone changes on CT is the clue of gene test on POU3F4.Part three:the study of relationship between GJB2 gene non-coding region and deafnessGJB2 gene is first chosen as detected gene in the deaf because of it’s maximum contribution to deafness.We found that 10%of prelingual hearing loss patients was the only one pathologic mutation carriers.This frequencies are higer than that of normal hearing.We could not decide the relationship of one pathologic mutation carriers and deafness in hearing loss patients.Whether there are other mutations in noncoding region,We sequenced exonl and promoter region on the hearing loss patients with one pathologic mutation.We didn’t find significant mutation in twenty hearing loss patients with one pathologic mutation, twenty hearing loss patients without pathologic mutation,and twenty-two normal hearing subjects.This result suggests that:1.there is no relationship between the non-coding region and deafness.2.There are DNA methylation in non-coding region in cochlear.3.There are sequence changes father away from core promoter involving deafness.4.There are other functional genes mutations or modifier genes changes that associates with GJB2 gene causing deafness.All of above need to be further explored.This study shows that the deafness molecular diagnosis is important to explore the cause of deafness.Absence of candidate genes in detection and unexplained problem in gene test at present are badly in need of solutions.