12个非综合征型遗传性耳聋家系mtDNA12SrRNA，tRNA^Leu（UUR）,tRNA^Ser（UCN）及16SrRNA基因序列分析

目的 探讨mtDNA突变与遗传性耳聋的关系。以及突变家系对氨基糖甙类抗生素（aminoglycoside antibiotic,AmAn)耳毒敏感性差异的原因。方法 调查了12个非综合征型耳聋家系;抽取外周血,提取DNA;PCR扩增线粒体DNA9mitochondrialDNA,mtDNA)目的片段,分别以Alw26Ⅰ、ApaⅠ及XbaⅠ限制性内切酶检测1555^G、3243^G及7445^G点突变,行mtDNA12SrRNA,tRNA^Leu(UUR)、tRNA^Ser(UCN)及16SrRNA基因序列测定。结果 经酶切及测序证实12个家系具有mtDNA突变,形式为：1555^G突变家系10个,7445^G突变家系2个,示发现3243^G突变家系,基因测序显示mtDNA16SrRNA基因6序列变化形式为：2230^G点突变,2230^AG插入,2243^AG插入及2230^AA插入突变,它们在家族性AmAn耳毒敏感性家系中被发现,且呈母系遗传;在AmAn不敏感家系中未被发现,结论 单纯1555^G或7445^G突变家系表现为无诱因的渐进性遗传性耳聋或先天性聋;1555^G或7445^G突变合并16SrRNA基因突变者对AmAn高度敏感,表现为家族性敏感致聋。ⅠⅠ     

非综合征型遗传性耳聋两家系线粒体基因突变分析

目的 探讨母系遗传非综合征型耳聋发病机理及7445^G点突变在这类家系及散发感音神经性耳聋病例中的发生率，为建立相应的基因诊断方法提供依据。方法 收集两个母系遗传非综合征型耳聋家系和14个感音神经性耳聋散发病例；抽外周血标本，从白细胞中提取DNA；聚合酶链反应扩增线粒体DNA（mitochondrial DNA,mtDNA）目的片段，分别以Alw 26Ⅰ、ApaⅠ及XbaⅠ限制性内切酶检测1555^G、3243^G及7445^G点突变；行mtDNA 12S r RNA、tRNA^Leu(UUR)、tRNA^Ser(UCN)基因测序。结果 经酶切检测，两家系中12例为7445^G点突变阳性，其余6例及14例散发病例均为阴性，所有病例1555^G、3243^G点突变均阴性；7445^G点突变呈母系遗传。mtDNA测序显示，所有病例1555^G、3243^G点突变均阴性；酶切显示为7445^G突变阳性病例经基因测序均发现有（nt)7445A→G替换。结论 7445^G点突变在母系遗传非综合征型耳聋家系中有较高的发生率，而在散发病例中发生率很低；7445^G结合1555^G点7突变筛查对这类耳聋的诊断有重要意义。     

AQP3基因在非综合征型遗传性耳聋家系中的突变筛查

目的:在定位于9号染色体DFNA55基因座位内的常染色体显性遗传性耳聋大家系686家系中进行AQP3基因突变检测,分析基因与该家系表型的关系。方法:686家系共有21人份DNA血样,其中感音神经性听力下降患者9人。AQP3基因共有6个外显子,针对AQP3基因的全部编码序列共设计了5对引物,进行PCR扩增,对扩增产物进行20g/L琼脂糖凝胶电泳,检测其纯度、浓度,应用PCR产物直接测序法进行基因突变检测;使用DNAStar软件进行测序序列的对比分析,检测基因突变。结果:在AQP3基因第4外显子上检测到两个点突变,其中390CT/390CT(F130F)为纯合同义突变,家系所有成员均发生了这种改变;394GA/WT(D132N)为杂合错义突变,家系中有4人发生了这种变化,其中有3人为耳聋患者,1名为听力正常人。结论:在686家系成员中检测到两个点突变均不是686家系的致病突变,但394GA/WT(D132N)引起了氨基酸的改变,该突变对于686家系的表型到底会有怎样的贡献,还需要进一步的研究。686家系的致病基因需进一步研究探索。     

线粒体DNA A1555G和961 insC双重突变导致的非综合征型遗传性耳聋

目的探讨一个非综合征型遗传性耳聋大家系线粒体DNA(mitoehondrial DNA，mtDNA)突变类型。方法临床听力测试已明确诊断，并收集非综合征型遗传性耳聋分支家系中33人及6例散发聋患者的外周静脉血样本，从白细胞中提取DNA，聚合酶链反应扩增mtDNA目的片段，分别用BsmA I、Apa I及Xba I限制性内切酶检测1555G、3243G和7445G点突变，对相关的扩增片段进行基因测序。结果酶切检测，家系中17例耳聋患者均为1555G点突变阳性，非母系成员及散发聋病例均为阴性。测序结果：6例酶切显示1555G突变阳性病例均发现(nt)1555A→G转换和(nt)961C插入，3243G、7445G点突变阴性。结论在该非综合征型遗传性耳聋大家系中，mtDNA 12SrRNA基因区域A1555G和961insC的双重突变可能共同参与了听力损害的过程。     

一个母系遗传非综合征耳聋大家系及mtD12SrRNA基因突变

目的 对一个非综合征母系遗传耳聋大家系的分子遗传学进行探讨。方法 采用聚合酶链反应（ＰＣＲ）,扩增ｍｔＤＮＡ与非综合征耳聋相关位点ｎｔ１５５５和ｎｔ７４４５的区域,通过ＰＣＲ－ＳＳＣＰ,ＰＣＲ－ＲＦＬＰ,ＰＣＲ产物克隆序列测定等技术对该家系进行了系统研究。结果 发现该家系中全部患者和４个母系亲属有ｍｔＤＮＡＡ１５５５Ｇ突变,而家系中正常配偶和对照组（１００名正常个体）的ｍｔＤＮＡ１５５５位点均无突     

12个非综合征型遗传性耳聋家系mtDNA12SrRNA,tRNA~(Leu(UUR)),tRNA~(Ser(UCN))及16SrRNA基因序列分析

目的　探讨 mt DNA突变与遗传性耳聋的关系 ,以及突变家系对氨基糖甙类抗生素(aminoglycoside antibiotic,Am An)耳毒敏感性差异的原因。方法　调查了 12个非综合征型耳聋家系 ;抽取外周血 ,提取 DNA;PCR扩增线粒体 DNA(mitochondrial DNA,mt DNA)目的片段 ,分别以 Alw2 6 、Apa 及 Xba 限制性内切酶检测 15 5 5 G、32 43G及 744 5 G 点突变 ;行 mt DNA 12 S r RNA、t RNALeu(UUR) 、t RNASer(UCN)及 16 S r RNA基因序列测定。结果　经酶切及测序证实 12个家系具有 mt DNA突变 ,形式为 :15 5 5 G突变家系 10个 ,744 5 G突变家系 2个 ,未发现 32 43G 突变家系。基因测序显示 mt DNA 16 S r RNA基因序列变化形式为 :2 2 30 G点突变、2 2 30 AG插入、2 2 43AG插入及 2 2 30 AA插入突变 ,它们在家族性 Am An耳毒敏感性家系中被发现 ,且呈母系遗传 ;在 Am An不敏感家系中未被发现。结论　单纯 15 5 5 G或 744 5 G突变家系表现为无诱因的渐进性遗传性耳聋或先天性聋 ;15 5 5 G或 744 5 G突变合并 16 S r RNA基因突变者对Am An高度敏感 ,表现为家族性敏感致聋。     

一个母系遗传非综合征耳聋大家系及mtDNA12SrRNA基因突变研究

目的　对一个非综合征母系遗传耳聋大家系的分子遗传学进行探讨。方法　采用聚合酶链反应（ Ｐ Ｃ Ｒ） ,扩增ｍｔ Ｄ Ｎ Ａ 与非综合征耳聋相关位点ｎｔ１５５５ 和ｎｔ７４４５ 的区域,通过 Ｐ Ｃ Ｒ Ｓ Ｓ Ｃ Ｐ, Ｐ Ｃ Ｒ Ｒ Ｆ Ｌ Ｐ, Ｐ Ｃ Ｒ 产物克隆序列测定等技术对该家系进行了系统研究。结果　发现该家系中全部患者和４ 个母系亲属有ｍｔ Ｄ Ｎ Ａ Ａ１５５５ Ｇ 突变,而家系中正常配偶和对照组（１００ 名正常个体） 的ｍｔ Ｄ Ｎ Ａ１５５５ 位点均无突变;该家系ｍｔ Ｄ Ｎ Ａ７４４５ 位点无突变产生。结论　提示ｍｔ Ｄ Ｎ Ａ Ａ１５５５ Ｇ 位点突变可能是导致该家系患者致聋的主要因素之一。     

7个非综合征型耳聋家系患者的mtDNA A1555G突变分析

目的探讨非综合征型耳聋家系患者mtDNA A1555G突变及其临床特征。方法应用聚合酶链反应、限制性核酸内切酶酶切和DNA测序技术对7个非综合征型耳聋家系112个成员的mtDNA A1555G突变进行检测，并分析听力临床资料。结果7个家系中所有受检的母系成员mtDNA A1555G突变均为阳性，突变性质含同质性和异质性二种；非母系成员及配偶该突变为阴性。突变的性质与临床表型的有关。结论mtDNA A1555G突变可导致非综合征型耳聋和氨基糖苷类抗生素致聋，其突变性质含均质性和异质性两种，且与临床表型相关。     

一个母系遗传非综合征型耳聋家系线粒体12S rRNA G709A位点的突变分析

目的 通过对一个母系遗传非综合征型耳聋家系进行线粒体DNA(mitochondrial DNA,mtDNA)12S rRNA、tRNA~(Ser(UCN))以及核基因GJB2突变分析,研究mtDNA突变与遗传性耳聋的相关性.方法 临床听力测试以明确诊断,收集非综合征型遗传性耳聋家系中18例母系成员和53名对照(包括6名父系亲属、7名配偶对照和40名当地无关对照)外周静脉血样本,采用聚合酶链反应和测序技术对mtDNA 12S rRNA、tRNA~(ser(UCN))和GJB2基因进行突变分析,并对发现的基因突变进行计算机辅助的二级结构模拟分析.结果 测序结果表明,此家系线粒体DNA 12S rRNA存在mtDNA G709A点突变,该突变未见报道;无tRNA~(Ser(UCN))基因突变;对GJB2突变分析发现4例具有299-300 delAT.计算机分析显示12SrRNA的二级结构中第8、9茎环结构发生改变.结论 家系中8例耳聋患者都具有线粒体12S rRNAG709A位点的突变,该突变在正常人群中具有高度保守性,提示GT09A点突变与母系遗传家系成员的进行性耳聋具有相关性;10例具有G709A突变的母系遗传家系成员未出现耳聋的临床表现,提示G709A点突变可能在其他核修饰基因的协同作用下参与了听力损害的过程.     

七个非综合征型耳聋家系患者的mtDNA A1555G突变性质与特点

目的 探讨非综合征型耳聋家系患者mtDNA A1555G突变性质及其特点,探索临床表型多样性的分子遗传学基础.方法 应用聚合酶链反应-限制性片段长度多态和实时荧光-扩增阻碍突变系统-定量PCR(real time-amplification refractory mutation system-quantitative PCR,RT-ARMS-qPCR)检测7个非综合征型耳聋家系71个成员的mtDNA A1555G突变,并收集、分析其临床资料.结果 7个家系中所有受检的母系成员mtDNA A1555G突变均为阳性,突变性质含同质性和异质性两种;非母系成员及配偶该突变为阴性.7个家系mtDNA A1555G同质性突变的拷贝数与耳聋轻重程度相关(R=0.341,P=0.022);mtDNA A1555G异质性突变的拷贝数与耳聋轻重程度相关(R=0.85,P=0.015).结论 mtDNA A1555G突变可导致非综合征型耳聋和氨基糖甙类抗生素致聋,其突变性质含同质性和异质性两种,且含mtDNA A1555G位点的突变型与野生型的比例与耳聋的严重程度密切相关.     

近亲结婚所致非综合征型耳聋家系的线粒体基因突变分析

目的对一个呈母系遗传的非综合征型耳聋大家系进行线粒体DNA的突变检测。方法收集湖南省一个非综合征型遗传性耳聋家系成员外周静脉血，提取基因组DNA（含线粒体DNA），设计特异性引物对目的片段进行PCR扩增，直接测序检测突变类型。结果测序结果显示，线粒体12S rRNA基因A1555G突变为该家系的致病突变，非母系成员不存在这一突变。结论该家系中部分成员使用氨基糖甙类抗生素后出现耳聋，可能是因为药物与线粒体12S rRNA基因的A1555G突变共同参与了听力损伤过程。     

Maternally inherited nonsyndromic hearing loss

In this study we characterized clinically and evaluated molecularly a large family with maternally inherited hearing impairment. Relatives were evaluated audiologically and clinically, the most likely pattern of inheritance was deduced, and molecular DNA analysis for the known mitochondrial mutations associated with hearing impairment was performed. Clinical examination of several relatives showed a normal general state of health, but in 14 of the members tested variable degrees of sensorineural hearing loss were noted. The pedigree was established and demonstrated a clear pattern of maternal inheritance, with 34 of 38 offspring of deaf mothers being hearing impaired, but none of 22 offspring of deaf fathers having any hearing impairment. Since by far the most likely explanation of such a maternal inheritance pattern is a mitochondrial mutation, molecular testing for the three known mitochondrial mutations, A1555G, A7445G, and Cins7472, was performed on 27 of the relatives. All of the individuals tested had the normal sequence at the sites tested. This family with nonsyndromic sensorineural hearing loss has an inheritance pattern strongly suggestive of a mitochondrial mutation. However, molecular testing for the three known mitochondrial mutations associated with nonsyndromic hearing impairment was negative, implying that additional molecular defects can lead to the same phenotype. The search for this novel molecular defect is underway. Am. J. Med. Genet. 84:369–372, 1999. © 1999 Wiley-Liss, Inc.     

Update of spectrum c.35delG and c.‐23+1G>A mutations on the GJB2 gene in individuals with autosomal recessive nonsyndromic hearing loss

Hearing loss (HL) is the most common birth defect and the most prevalent sensorineural condition worldwide. It is associated with more than 1,000 mutations in at least 90 genes. Mutations of the gap junction beta‐2 protein (GJB2) gene located in the nonsyndromic hearing loss and deafness (DFNB1) locus (chromosome 13q11‐12) are the main causes of autosomal recessive nonsyndromic hearing loss worldwide, but important differences exist between various populations. In the present article, two common mutations of the GJB2 gene are compared for ethnic‐specific allele frequency, their function, and their contribution to genetic HL in different populations. The results indicated that mutations of the GJB2 gene could have arisen during human migration. Updates on the spectrum of mutations clearly show that frequent mutations in the GJB2 gene are consistent with the founder mutation hypothesis.     

Different functional consequences of two missense mutations in the GJB2 gene associated with non‐syndromic hearing loss

Mutations in the GJB2 gene, which encodes the gap junction (GJ) protein connexin26 (Cx26), are the most common cause of inherited non‐syndromic hearing loss (NSHL). We identified two missense mutations, p.D46E (c.138T>G) and p.T86R (c.257C>G), of GJB2 in Korean HL families. The novel p.D46E mutation exhibited autosomal dominant inheritance, while the p.T86R mutation, which is exclusively found in Asians, segregated with an autosomal recessive pattern. Thus, we sought to elucidate the pathogenic nature of such different inherited patterns of HL. We studied protein localization and gap junction functions in cells transfected with wild‐type or mutant Cx26 tagged with fluorescent proteins, which allowed visual confirmation of homozygous or heterozygous mutant GJs. The Cx26‐D46E mutant was targeted to the plasma membrane, but this mutant protein failed to transfer Ca²⁺ or propidium iodide intercellularly, suggesting disruption of both ionic and biochemical coupling. Heterozygous GJs also showed dysfunctional intercellular couplings and hemichannel opening, confirming the dominant‐negative nature of the p.D46E mutation. The Cx26‐T86R mutant protein did not form GJs, since the mutated protein was confined in the cytoplasm and not transported to the cell membrane. When Cx26‐T86R was co‐expressed with Cx26‐WT, ionic and biochemical coupling was normal, consistent with the recessive nature of the mutation. These studies revealed distinct pathogenic mechanisms of two GJB2 mutations identified in Korean families. © 2009 Wiley‐Liss, Inc.     

Prevalence of mitochondrial DNA mutations in childhood/congenital onset non-syndromal sensorineural hearing impairment

Genetic factors are the major causes of childhood hearing impairment. Whereas autosomal recessive mutations account for the majority of prelingual non-syndromic sensorineural hearing impairment (NSSHI), the relative contribution of mitochondrial DNA (mtDNA) mutations to childhood onset NSSHI has not been established.
We screened 202 subjects with congenital/childhood onset NSSHI, consisting of 110 sporadic cases, 75 sib pairs, and 17 families with affected subjects in more than one generation, in order to determine the prevalence of mtDNA mutations associated with NSSHI.
mtDNA mutations were found in three of 10 families (30%) in whom the affected members were related through the maternal lineage. One sporadic case (0.9%) was also found to have a known mtDNA mutation but none was found in the sib pairs.
Although the prevalence of mtDNA mutations was low in the group as a whole (2%), we suggest that screening should be considered in cases of childhood hearing impairment when it is progressive and particularly in families where transmission is compatible with maternal inheritance.


Keywords: mitochondrial DNA; point mutation; hearing impairment     

Functional consequences of novel connexin 26 mutations associated with hereditary hearing loss

In a study of 530 individuals with non-syndromic, sensorineural hearing loss, we identified 18 mutations at connexin 26 (Cx26), four of which are novel (-23G>T, I33T, 377_383dupTCCGCAT, W172R) and the remaining 14 (ivs1+1G>A, M1V, 35delG, W24X, I35S, V37I, R75W, W77X, 312del14, E120del, Q124X, Y136X, R143W, R184P) being mutations previously described. To gain insight into functional consequences of these mutations, cellular localization of the mutant proteins and their ability to permit lucifer yellow transfer between cells was studied in seven of them (W24X, I33T, I35S, R75W, E120del, W172R and R184P). I35S and R184P showed impaired trafficking of the protein to the plasma membrane. I33T, R75W, E120del and W172R showed predominantly membrane localization but did not form functional gap junction channels. Surprisingly, W24X, a protein-truncating mutation, apparently permits formation of a full-length protein, perhaps due to a stop codon read-through mechanism. These results provide further evidence that Cx26 mutations affect gap junction activity by mis-regulation at multiple levels.     

Maternally inherited hearing impairment

Mitochondria are intracellular organelles responsible for the majority of a cell's energy production. They have their own small maternally inherited genome which, when mutated, can give rise to a large spectrum of diseases. The phenotype most commonly includes neurological and muscular symptoms, although hearing impairment is an additional feature in some mitochondrial syndromes. Often, syndromic mutations affect only a fraction of all mitochondrial DNA molecules, a condition referred to as heteroplasmy. It is believed that the degree of heteroplasmy in different tissues contributes to the phenotypic heterogeneity that is a hallmark of these syndromes. Five homoplasmic mutations leading to nonsyndromic hearing impairment have been reported (1555A-->G, 7445A-->G, 7472insC, 7510T-->C, 7511T-->C). The 1555A-->G is in the 12S rRNA gene, and in some populations, appears to be a frequent cause of hearing impairment. Carriers of the mutation are abnormally sensitive to aminoglycoside-induced ototoxicity even at 'appropriate' drug levels; in addition, even without aminoglycoside exposure, these persons can develop hearing impairment. The other four nonsyndromic mutations are located in the tRNA(Ser(UCN)) gene. In addition to hearing impairment, with two of these mutations (7445A-->G, 7472insC), other symptoms can be present in some patients. However, why these five mutations preferentially affect the inner ear, despite the crucial role of mitochondria in nearly all cells of the body, is unknown.