| Part One: Study on the second pathogenic factors of large vestibular aqueduct syndrome In nonsyndromic autosomal recessive hearing loss,large vestibular aqueduct syndrome(LVAS)is a widely recognized disease characterized by enlarged vestibular aqueduct,sensorineural hearing loss.The disease has a high incidence rate in people with hearing loss,and it can account for 5～15% of SNHL among children.This project was based on multi-level research,including the auditory phenotype analysis of patients with LVAS,the identification of second pathogenic factors of LVAS,and the pathogenicity analysis of new SLC26A4 variations.Through comprehensive and systematic analysis of the above research contents,we strive to further clarify the molecular etiology of LVAS,enrich the pathogenic spectrum of Chinese LVAS population,and establish a more precise prevention and intervention strategy.Chapter One: Hearing phenotypes of patients with large vestibular aqueduct syndrome The hearing phenotypes of patients with LVAS are diverse,whether it is the severity of hearing loss or the audiogram shape.The hearing phenotypes of 986 patients with LVAS(including 913 patients with SLC26A4 double allelic mutation,54 patients with SLC26A4 single allelic mutation and 19 patients without SLC26A4 mutation)were analyzed,and the difference between hearing phenotypes of patients with different number of SLC26A4 allelic mutation was explored.Of the 1972 ears(986 cases)examined,62.17% presented with profound hearing loss,24.65%with severe hearing loss,and 9.18% with moderate to severe hearing loss.The most common audiogram shapes were descending(51.22%)and flat(15.47%).A total of 755(76.57%)of the 986 patients exhibited asymmetric interaural hearing loss in terms of severity and/or audiogram shape.Type A(asymmetry of hearing loss severity)was evident in 254 of these cases,Type B(asymmetry of audiogram shape)in 318,and Type C(Type A plus Type B)in Patients with SLC26A4 double/single allelic mutation presented with severe to profound hearing loss,accounting for 87.79% and 82.41% respectively;the most common audiogram shape was descending,followed by flat and residual;the rate of asymmetric interaural hearing loss was 76.12% and 79.63% respectively.In contrast,among the patients without SLC26A4 mutation,52.63% presented with severe to profound hearing loss;the most common audiogram shape was flat,followed by descending and ascending;the asymmetric rate of interaural hearing loss was 89.47%.Among patients with SLC26A4 double/single allelic mutation,with the increase of age,hearing loss tended to be aggravated,and the bilateral hearing phenotypes to be symmetric.However,in patients without SLC26A4 mutation,the relationship between age and hearing loss was unclear,and the auditory phenotypes of patients in different ages were multifarious.Hearing loss associated with LVAS shows diverse phenotypes,and a considerable proportion of patients show bilateral hearing loss asymmetry.Compared with patients with SLC26A4double/single allelic mutation,the hearing phenotypes of patients without SLC26A4 mutation are more various.Chapter Two: Identification of the second pathogenic factors of large vestibular aqueduct syndromeIt is generally believed that LVAS is an autosomal recessive disease caused by SLC26A4 gene mutation,that is,it can only cause disease if it carries double allelic mutation.However,10.85% of LVAS patients in China still fail to find double allelic mutation of SLC26A4,suggesting that there are second pathogenic factors in these patients,among which the identification of SLC26A4 gene copy number variations(CNVs)and new pathogenic genes may be the key to solve the problems.In this study,169 patients with LVAS of unknown molecular etiology were subjected to SLC26A4 gene whole sequence capture(including exons and introns)and next generation sequencing to identify CNVs.CNVs was detected in 79 cases(46.75%),among which the detection rate of CNVs was 63.64% in patients with SLC26A4 single allelic mutation,and15.25% in patients without SLC26A4 mutation.There were the following hot spots in the detected CNVs,namely,exon1-3del(40.51%,32/79),exon5-6del(29.11%,23/79)and exon1-2del(12.66%,10/79).67 cases were verified,and 63 cases(94.03%)were consistent with the CNVs detected.CNVs are one of the important second pathogenic factors of LVAS.It is necessary to identify CNVs in patients with unknown molecular etiology,especially those with SLC26A4 single allelic mutation,so as to extend the pathogenic spectrum of LVAS in China.Chapter Three: Pathogenicity analysis of new variations of SLC26A4 gene SLC26A4 gene is the main pathogenic factor of LVAS,which has an extensive spectrum of gene variations.At present,there are still some rare variations in SLC26A4 gene with unknown clinical significance,so it is necessary to identify the pathogenicity of these variations.In this study,we analyzed the pathogenicity of SLC26A4 gene variations(c.223C>G,c.757A>G,and c.1286C>A)found in three Chinese families.The results showed that all three variations were normal polymorphic sites,which enriched the variation spectrum of SLC26A4 gene in China.Part Two: Hearing phenotypes of patients with hearing loss homozygous for the GJB2 c.235delC mutationHereditary hearing loss is characterized by remarkable phenotypic heterogeneity.Patients with the same pathogenic mutations may exhibit various hearing loss phenotypes.In the Chinese population,the c.235 delC mutation is the most common pathogenic mutation of GJB2,the chief deafness gene,and is closely related to hereditary recessive hearing loss.Here,we investigated the hearing phenotypes of patients with hearing loss associated with the homozygous c.235 delC mutation,paying special attention to asymmetric interaural hearing loss.A total of 244 patients with the GJB2 c.235 delC homozygous mutation encountered from2007 to 2015 were enrolled to analyze the auditory phenotypes.Of the 488 ears(244 cases)examined,71.93%(351)presented with profound hearing loss,14.34%(70)with severe hearing loss,and 9.43%(46)with moderate to severe hearing loss.The most common audiogram shapes were descending(31.15%)and flat(24.18%).A total of 156(63.93%)of the 244 patients exhibited asymmetric interaural hearing loss in terms of severity and/or audiogram shape.Type A(asymmetry of hearing loss severity)was evident in 14 of these cases,Type B(asymmetry of audiogram shape)in 106,and Type C(Type A plus Type B)in36.In addition,211 of 312 ears(67.63%)in the interaural hearing asymmetry group showed profound hearing loss,and 59(18.91%)exhibited severe hearing loss,with the most common audiogram shapes being flat(27.88%)and descending(22.12%).By contrast,in the interaural hearing symmetry group,profound hearing loss was observed in 140 ears(79.55%),and the most common audiograms were descending(46.59%)and residual(21.59%).Hearing loss associated with the GJB2 c.235 delC homozygous mutation shows diverse phenotypes,and a considerable proportion of patients show bilateral hearing loss asymmetry. |
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