中国人群遗传性耳聋研究进展

耳聋有着复杂的病因学特点，遗传和／或环境因素均可致聋。120多个耳聋相关基因的发现为我们了解听觉的病理生理机制提供了新的视点。然而，最近的研究表明在中国相当一部分综合征性和非综合征性耳聋仅由为数不多的几个基因突变引起。本文旨在综述综合征性、非综合征性及线粒体遗传性聋在中国人群感音神经性聋致病机制方面的最新进展。深入了解中国人群耳聋分子病因学特点，对获得准确的耳聋早期诊断和遗传咨询，以便及时干预和治疗至关重要。     

Connexin mutation testing of children with nonsyndromic, autosomal recessive sensorineural hearing loss

OBJECTIVE: The etiology of hearing loss is heterogeneous and falls into the two broad categories of genetic and environmental. In the genetic subgroup, 70% are non syndromic. Fifty percent of nonsyndromic sensorineural deafness is due to a mutation in the connexin 26 gene. This article presents the detection rate of connexin mutations in a multiethnic Canadian population. METHODS: A study of patients with nonsyndromic hearing loss seen over a period of 2 years who had connexin 26 mutation testing. RESULTS: Nine of the 18 patients had connexin 26 mutations. CONCLUSION: The majority of our patients with connexin 26 mutations had moderate to profound hearing loss. Testing for connexin mutations should be standard care because it accounts for a large proportion of individuals with nonsyndromic hearing loss. Reasons for testing include ruling out a syndromic cause, predicting moderate to profound hearing loss, and the need for language intervention, cochlear implants, and genetic counselling.     

Etiology of syndromic and nonsyndromic sensorineural hearing loss

The past 10 years have seen an explosive gain in our understanding of molecular mechanisms of hearing and deafness. This has already resulted in improved diagnosis for the population with hereditary hearing loss. For syndromic hearing loss, we will see a shift from the historical terminology to a more precise genetic definition based on specific genetic abnormality. Functional studies of nonsyndromic deafness genes will elucidate the complex functional and hemostatic mechanisms in the inner ear. Ultimately, availability of gene therapy for the affected patients will bring to closure the circle of detection, identification, and correction of the disease.     

Prevalence of GJB2 mutations in prelingual deafness in the Greek population

OBJECTIVE: Mutations in the gene encoding the gap junction protein connexin 26 (GJB2) have been shown as a major contributor to prelingual, sensorineural, nonsyndromic, recessive deafness. One specific mutation, 35delG, has accounted for the majority of the mutations detected in the GJB2 gene in Caucasian populations. The aim of our study was to determine the prevalence and spectrum of GJB2 mutations in prelingual deafness in the Greek population. METHODS: In a collaboration with the major referral centers for childhood deafness in Greece, patients were examined by an extensive questionnaire to exclude syndromic forms and environmental causes of deafness and by allele-specific polymerase chain reaction (PCR) for the detection of the 35delG mutation. Patients heterozygous for the 35delG mutation were further analyzed by direct genomic sequencing of the coding region of the GJB2 gene. RESULTS: The 35delG mutation was found in 42.2% of the chromosomes in 45 familial cases of prelingual, nonsyndromic deafness (18 homozygotes and 2 heterozygotes) and in 30.6% of the chromosomes in 165 sporadic cases (45 homozygotes and 11 heterozygotes). Direct genomic sequencing in heterozygous patients revealed the L90P (2 alleles), W24X (2 alleles), R184P (2 alleles), and 291insA (1 allele) mutations. CONCLUSION: Mutations in the GJB2 gene are responsible for about one third of prelingual, sensorineural, nonsyndromic deafness in the Greek population, and allele-specific PCR is an easy screening method for the common 35delG mutation.     

Connexin 26基因233delC突变与中国人先天性耳聋的研究

目的 :Connexin2 6基因突变是引起常染色体隐性遗传 DFNB1和常染色体显性遗传 DFNA3的遗传基础 ,其中的 35 del G的突变在欧美人 DFNB1耳聋患者中的检出率为 70～ 80 % ,但在中国耳聋人群中未检到该点突变。本文旨在筛选中国人耳聋相关的 Connexin2 6基因的突变热点。方法 :采用 PCR- RFL P筛选 2 19例不同耳聋类型的患者和 5 0例听力正常人的 Connexin 2 6基因 2 33del C的突变 (2 1.5 % )。结果 :2 19例耳聋患者中共发现了 47例 Connexin 2 6基因2 33del C的突变 (2 1.5 % )。在先天性耳聋患者中 2 33del C的突变率为 33% ,遗传性语前聋患者为 2 6 .7%。 5 0例药物性致聋的患者有 10例发生突变。遗传性及散发性进行性感音神经性耳聋和听力正常人未检测到 2 33delc突变。结论 :Connexin2 6基因 2 33del C突变在中国先天性耳聋人群中发生频率较高 ,与欧美人不同。我们的结果表明 ,Connexin2 6基因异常导致耳聋的突变热点具有种族特异性     

与非综合征型聋相关缝隙连接蛋白31及线粒体12SrRNA基因突变

 耳聋是影响人类健康和造成人类残疾的常见疾病,它主要由遗传因素和环境因素引起。遗传性聋包括综合征型聋和非综合征型聋,其中非综合征型聋约占70%。 GJB3及线粒体12SrRNA基因突变和非综合征型聋密切相关。本文就GJB3及线粒体12SrRNA基因突变与非综合征型聋的相关性进行综述,进一步明确其发病的相关性,在明确部分非综合征型聋病因的同时,更好的为患者及其家族成员提供准确的遗传咨询和指导,为临床防聋治聋提供依据及策略。     

Prelingual nonsyndromic hearing loss in Greece. Molecular and clinical findings

Mutations in the gene encoding the gap-junction protein connexin 26 (GJB2) on chromosome 13q11 have been shown as a major contributor to prelingual, sensorineural, nonsyndromic deafness. One specific mutation, 35delG, has accounted for the majority of the mutations detected in the GJB2 gene in Caucasian populations and is one of the most frequent disease mutations identified so far with highest carrier frequency of 3,5% in the Greek population. In a collaboration with the major referral centers for childhood deafness in Greece, patients were examined by an extensive questionnaire to exclude syndromic forms and environmental causes of deafness and by allele-specific PCR for the detection of the 35delG mutation. The 35delG mutation was found in 32.1% of the alleles in 173 unrelated cases of prelingual deafness: 50 homozygotes and 11 heterozygotes. Individuals heterozygous for the 35delG mutation were further analyzed by direct genomic sequencing of the coding region of the GJB2 gene, which revealed R184P and 486insT mutations in single alleles. We conclude that the 35delG GJB2 mutation is responsible for one third of prelingual, sensorineural deafness in Greece, which is higher than the usually quoted 20% for Caucasian populations.     

国人无综合征性耳聋患者的线粒体基因组7445^A→G突变263 …

OBJECTIVE: To study the Mitochondrial DNA 7445A-->G mutation in nonsyndromic deafness patients in Chinese population. METHOD: Polymerase chain reaction and restriction fragment length polymorphism (PCR-RFLP) were used to screen the mitochondrial DNA 7445A-->G mutation among 128 nonsyndromic deafness individuals from 32 pedigrees, 135 sporadic nonsyndromic deafness patients and 100 normal subjects. RESULT: The 7445A-->G mutation did not appear in the experiment. CONCLUSION: Incidence of the mitochondrial 7445A-->G mutation was lower than that of mtDNA 1555A-->G mutation in nonsyndromic deafness patients in China.     

耳聋-掌跖皮肤角化综合征的连接蛋白基因型和表型分析

目的GJB2、GJB6、GJB3基因与遗传性耳聋及角化病有关，以GJB2、GJB6、GJB3基因为候选基因，研究1例伴有掌跖角化病的综合征型耳聋先证者的分子病因，探讨其表型及遗传特征。方法 采集先证者及其父母外周血并提取DNA，对GJB2、GJB6、GJB3基因编码区进行PCR扩增，以直接测序的方法进行突变分析。结果 先证者及其父母GJB3、GJB6基因测序未发现突变。先证者携带GJB2基因R75W单等位基因突变，其父母未携带此突变，在证实先证者与其父亲的亲子关系后明确先证者携带的R75W为新生突变。301名中国正常对照中未发现GJB2基因R75W突变。结论 在中国首次发现了GJB2基因新生突变R75W，此突变可能以显性方式遗传，导致耳聋-掌跖皮肤角化综合征。在不同种族R75W导致的耳聋多为双侧重度到极重度感音神经性聋。而皮肤表型的严重程度有所不同。     

Causes of deafness in British Bangladeshi children: a prevalence twice that of the UK population cannot be accounted for by consanguinity alone

Objective: To study the causes and prevalence of sensorineural deafness in Bangladeshi children resident in East London. Methods: This was a cross sectional survey of children of Bangladeshi origin living in East London with bilateral sensorineural hearing loss of 40 db HL or more. In this study, 134 patients were included. The study looked primarily at the causes of sensorineural hearing loss in this population. Results: The prevalence of deafness in Bangladeshi children in East London is approximately 3.86 per 1000 [95% confidence intervals (CI) 3.20, 4.65] which is significantly greater than the average UK prevalence of 1.65 per 1000. The prevalence of deafness in these Bangladeshi children belonging to non‐consanguineous families only, the prevalence falls to 2.73 per 1000 (95% CI 2.19, 3.41). In 60% cases the cause of deafness was genetic. The single most common cause of sensorineural hearing loss in this population was mutations in the GJB2 gene (Connexin 26) in 20 of these patients (17%). Parents were consanguineous in 33% of the families. Conclusion: This study concludes that prevalence of sensorineural deafness in Bangladeshi children is at least 2.3 times the national average. This study also concludes that genetic causes are the common cause of deafness in this ethnic group, with nearly 30% of children with non‐syndromic deafness having mutations in GJB2. Although parental consanguinity was very high in this population it did not account for the whole increase in prevalence.     

GJB2 gene mutations in childhood deafness

The frequency of childhood deafness is estimated at 1:1,000 and at least half of these cases are genetic. Recently, mutations in the GJB2 gene have been found in a great number of familial and sporadic cases of congenital deafness in Caucasians. The most common mutation (70%) is the frameshift mutation of a single guanine in position 35 (35delG). More than 20 mutations in the GJB2 gene are associated with DFNB1, a prevalent type of autosomal recessive non-syndromic neurosensory deafness. Last year we initiated a systematic screening programme to evaluate the causes of deafness in the population of prelingually deaf children who are referred to our cochlear implant programme. All of the deaf children and their parents undergo a comprehensive medical review, directed to identify causes of acquired deafness and manifestations of syndromic hearing impairment. DNA is extracted from the blood of all of the children. The technique AS-PCR (allele-specific polymerase chain reaction) is used for the identification of the mutation 35delG. Screening for other GJB2 gene mutations is carried out by single-strand conformation polymorphisms (SSCP). Our results on the identification of DFNB1 will be presented, as well as a discussion on the implications of an aetiological diagnosis in cochlear implantation.     

Prognostic evaluation of electrocochleography in idiopathic sudden sensorineural hearing loss

The frequency of childhood deafness is estimated at 1:1,000 and at least half of these cases are genetic. Recently, mutations in the GJB2 gene have been found in a great number of familial and sporadic cases of congenital deafness in Caucasians. The most common mutation (70%) is the frameshift mutation of a single guanine in position 35 (35delG). More than 20 mutations in the GJB2 gene are associated with DFNB1, a prevalent type of autosomal recessive non-syndromic neurosensory deafness. Last year we initiated a systematic screening programme to evaluate the causes of deafness in the population of prelingually deaf children who are referred to our cochlear implant programme. All of the deaf children and their parents undergo a comprehensive medical review, directed to identify causes of acquired deafness and manifestations of syndromic hearing impairment. DNA is extracted from the blood of all of the children. The technique AS-PCR (allele-specific polymerase chain reaction) is used for the identification of the mutation 35delG. Screening for other GJB2 gene mutations is carried out by single-strand conformation polymorphisms (SSCP). Our results on the identification of DFNB1 will be presented, as well as a discussion on the implications of an aetiological diagnosis in cochlear implantation.     

非综合征性学语前聋患者肌球蛋白7a基因部分外显子突变的检测

目的　探讨中国人非综合征性学语前聋患者肌球蛋白 7a基因的突变频率和特性。方法　收集非综合征性学语前聋家系 34个 ,大部分来自湖南地区 ,共计 6 5例 ;散发患者 31例 ;健康对照组 10 0例。聚合酶链反应扩增肌球蛋白 7a基因的部分外显子 ,单链构象多态性分析初筛可疑突变者 ,发现异常构象带后再行DNA测序确定是否突变。结果　在 2个患者中检测出肌球蛋白 7a基因 7号外显子的 6 17号核苷酸G→A杂合突变 ,在同一家族的正常人中未发现该突变。该突变发生在肌球蛋白 7a分子的一个保守区段 ,可导致 2 0 6位上的精氨酸改变为谷氨酰胺 (R2 0 6Q )。结论　肌球蛋白 7a基因的R2 0 6Q突变很可能是导致非综合征性学语前聋的一个新突变 ,这一基因7号外显子是遗传性聋的一个突变热点区     

云南3所特教学校聋生临床资料分析

目的对云南3所特殊教育学校聋生人群进行系统性的耳聋临床资料分析,为开展耳聋基因的分子流行病学研究提供参考依据。方法了解聋生详细的耳聋病史;进行全身及耳鼻咽喉常规检查;进行纯音听阂测试及声导抗测试,了解聋生双耳听功能和中耳功能状况。结果聋生耳聋前有耳毒性药物用药史者占8．2％,有家族史者占19．5％,综合征性耳聋占5．3％,耳聋病因不明者亦占较大比例;汉族与非汉族聋生在综合征性耳聋和聋前用药史方面无显著差异,汉族聋生有家族史的比例高于非汉族聋生。结论云南省聋生可能的致聋原因有遗传性聋、药物性聋,但大部分聋生病因不明,尚需借助分子生物学理论和技术,从基因水平进行耳聋病因学的深入研究。。     

无综合征耳聋与线粒体DNA1555^A→C突变

目的：分析４个无综合征耳聋家系是存在线粒体ＤＮＡ１５５５＾Ａ→Ｃ的突变。方法：以ＰＣＲ－ＲＦＬＰ方法进行线粒体ＤＮＡ１５５５＾Ａ→Ｃ突变筛查。结果 仅１个无综合征耳聋家系中的５个成员有４个存在该突变。结论：线粒体ＤＮＡ１５５５＾Ａ→Ｃ点突变与部分无综合征耳聋有一定关系。     

Genes in the ear: what have we learned over the last years?

In developed countries 50% of childhood hearing impairment is attributable to genetic causes. In a limited number of cases, the hearing impairment is part of a syndrome, and several genes for syndromic deafness have been identified over the last 10 years. In the majority of cases, the hearing impairment occurs without additional clinical abnormalities (non-syndromic). Progressive hearing loss is very frequent in adults. By the age of 80 approximately 50% of the population is affected by age-related hearing loss, which is due partly to genetic factors. Before 1994, little was known about the genes responsible for non-syndromic hearing impairment, although epidemiological studies have suggested that more than 100 genes might be involved. Over the last 6 years, extremely rapid progress was realized in the field of the molecular genetics of hearing and deafness. More than 70 genes for non-syndromic hearing impairment have been localized to the human genome, and 18 of these have been identified.     

Nuclear and mitochondrial genes mutated in nonsyndromic impaired hearing

Half of the cases with congenital impaired hearing are hereditary (HIH). HIH may occur as part of a multisystem 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 sensorineural hearing loss. One percent of the total human genes, i.e. 300-500, are estimated to cause syndromic and nonsyndromic HIH. Of these, approximately 120 genes have been cloned thus far, approximately 80 for syndromic HIH and 42 for nonsyndromic HIH. In the majority of the cases, HIH manifests before (prelingual), and rarely after (postlingual) development of speech. Prelingual, nonsyndromic HIH follows an autosomal recessive trait (75-80%), an autosomal dominant trait (10-20%), an X-chromosomal, recessive trait (1-5%), or is maternally inherited (0-20%). Postlingual nonsyndromic HIH usually follows an autosomal dominant trait. Of the 41 mutated genes that cause nonsyndromic HIH, 15 cause autosomal dominant HIH, 15 autosomal recessive HIH, 6 both autosomal dominant and recessive HIH, 2 X-linked HIH, and 3 maternally inherited HIH. Mutations in a single gene may not only cause autosomal dominant, nonsyndromic HIH, but also autosomal recessive, nonsyndromic HIH (GJB2, GJB6, MYO6, MYO7A, TECTA, TMC1), and even syndromic HIH (CDH23, COL11A2, DPP1, DSPP, GJB2, GJB3, GJB6, MYO7A, MYH9, PCDH15, POU3F4, SLC26A4, USH1C, WFS1). Different mutations in the same gene may cause variable phenotypes within a family and between families. Most cases of recessive HIH result from mutations in a single locus, but an increasing number of disorders is recognized, in which mutations in two different genes (GJB2/GJB6, TECTA/KCNQ4), or two different mutations in a single allele (GJB2) are involved. This overview focuses on recent advances in the genetic background of nonsyndromic HIH.     

Spectrum of GJB2 mutations causing deafness in the British Bangladeshi population

Objective: Mutations in Gap Junction Beta 2 (GJB2) (the gene encoding the protein Connexin 26) have been found to be a major cause of non‐syndromic sensorineural recessive deafness. The mutations in GJB2 causing hearing impairment vary in different populations. The aim of this study was to determine the prevalence and spectrum of GJB2 mutations in prelingual deafness in a population of Bangladeshi origin in the UK. Design: Cross‐sectional survey. Setting: Community based audiology clinic and tertiary level genetics department. Methods: Fifty‐three families (67 patients) with sensorineural hearing loss of unknown cause were included in the study. Detailed history and examination excluded syndromic and environmental causes of hearing loss in the subjects as far as possible. Genetic analysis was performed, specifically looking for mutations in the GJB2 gene. Results: Of the 53 families, 14 were confirmed to have biallelic pathogenic mutations in GJB2 (26%). The most common mutations of GJB2 in this population were W24X, IVS1+1, M1V, W77X and Q124X, W24X being the most common mutation seen in 57% of patients. Conclusion: Mutations in GJB2 are responsible for over one quarter of non‐syndromic sensorineural deafness in the British Bangladeshi population. It is recommended that all Bangladeshi patients with non‐syndromic hearing loss should be first tested for GJB2 mutations before requesting other aetiological investigations.     

A histologic study of nonmorphogenetic forms of hereditary hearing impairment.

It appears that many forms of syndromic and nonsyndromic hereditary hearing impairment are secondary to either neuroepithelial or cochleosaccular dysfunction. Making this distinction can be difficult in human temporal bone specimens; however, this added knowledge may ultimately provide prognostic and therapeutic information in hearing habilitation. Fundamental studies using animal models of different types of hereditary deafness may also prove useful in this respect.     

MYO1F as a candidate gene for nonsyndromic deafness, DFNB15

BACKGROUND: Earlier studies have mapped the autosomal recessive nonsyndromic deafness locus, DFNB15, to chromosomes 3q21.3-q25.2 and 19p13.3-13.1, identifying one of these chromosomal regions (or possibly both) as the site of a deafness-causing gene. Mutations in unconventional myosins cause deafness in mice and humans. One unconventional myosin, myosin 1F (MYO1F), is expressed in the cochlea and maps to chromosome 19p13.3-13.2. OBJECTIVE: To evaluate MYO1F as a candidate gene for deafness at the DFNB15 locus by determining its genomic structure and screening each exon for deafness-causing mutations to identify possible allele variants of MYO1F segregating in the DFNB15 family. METHODS: We used radiation hybrid mapping to localize MYO1F on chromosome arm 19p. We next determined its genomic structure using multiple long-range polymerase chain reaction experiments. Using these data, we completed mutation screening using single-stranded conformational polymorphism analysis and direct sequencing of affected and nonaffected persons in the original DFNB15 family. RESULTS: Radiation hybrid mapping placed MYO1F in the DFNB15 interval, establishing it as a positional candidate gene. Its genomic structure consists of 24 coding exons. No mutations or genomic rearrangements were found in the original DFNB15 family, making it unlikely that MYO1F is the disease-causing gene in this kindred. CONCLUSIONS: Although we did not find MYO1F allele variants in one family with autosomal recessive nonsyndromic hearing loss, the gene remains an excellent candidate for hereditary hearing impairment. Given its wide tissue expression, MYO1F might cause syndromic deafness.