与耳聋相关的线粒体12S rRNA突变

线粒体DNA突变是引起听力损伤的重要原因之一. 其中,线粒体12S rRNA基因突变与综合征型耳聋和非综合征型耳聋相关. 导致综合征型耳聋的线粒体DNA突变多为异质性,然 而对于非综合征型耳聋突变则多以同质性或高度异质性存在,说明这种分子致病性需要较高的阈值. 位于12S rRNA解码区的A1555G和C1494T突变是造成氨基糖甙类抗生素耳毒性和 非综合征型耳聋常见的分子机制. 这些突变可能造成12S rRNA二级结构的改变,影响线粒体蛋白质的合成,降低细胞内ATP的产生,由此引起的线粒体功能障碍导致耳聋. 但是多数 基因突变的致病机制还仅处于推测阶段. 其它修饰因子如氨基糖甙类抗生素、线粒体单体型、核修饰基因参与了线粒体12S rRNA基因A1555G和C1494T突变相关的耳聋表型表达.     

线粒体DNA G7444A突变可能影响A1555G突变的表型表达

线粒体12S rRNA和tRNASer(UCN) 基因是导致非综合征型听力损失的两个突变热点区域。作者收集了1个母系遗传感音神经性聋家系, 该家系同时携带线粒体DNA (mtDNA) A1555G和G7444A突变。临床资料分析表明, 该家系包括药物致聋的耳聋外显率(所有耳聋患者/所有母系成员)为58%, 而非药物致聋的耳聋外显率(非药物性聋患者/所有母系成员)为25%, 明显高于其他携带A1555G突变的耳聋家系。先证者的线粒体全序列分析表明, 该线粒体基因组共有28个多态位点, 属于东亚人群B4c1单体型。在这些多态位点中, 除A1555G和G7444A突变外, 未发现其他有功能意义的突变。这表明mtDNA G7444A突变可能加重由A1555G突变造成的线粒体功能缺失, 从而增加耳聋的外显率。     

线粒体tRNAThr G15927A突变可能影响耳聋相关的12S rRNA A1555G突变的表型表达

摘要: 对1个中国汉族耳聋家系进行了临床和分子遗传学特征分析。家系中听力下降的母系成员表现为程度不等、听力图形态不同的听力损害, 但同为双侧对称的感觉神经性耳聋。该家系耳聋外显率很高, 包括药物致聋的耳聋外显率为75%, 而非药物致聋的外显率为41.7%。对母系成员进行线粒体DNA(mtDNA)全序列扩增分析, 发现了耳聋相关12S rRNA A1555G同质性突变位点和多态性位点, 属于东亚人群B5b单体型。在这些变异位点中, mtDNA 15927位点的G-A碱基变化破坏tRNA^Thr反密码子结构上十分保守的C-G碱基对, 这可能加重由A1555G突变造成的线粒体功能缺陷。这表明tRNAThrG15927A突变可能增强携带12S rRNA A1555G的中国汉族耳聋家系的外显率和表现度。     

25个携带线粒体12S rRNA A1555G 突变的中国汉族非综合征型耳聋家系

线粒体12S rRNA A1555G突变是引起氨基糖甙类药物诱导的非综合征型耳聋的重要原因之一。文章对收集的25个携带A1555G突变的中国汉族非综合征型耳聋家系进行了临床和分子遗传学评估。结果表明,这25个家系的母系成员在耳聋外显率、听力损失严重程度和发病年龄上存在较大差异。当包括和不包括氨基糖甙类药物使用史时,耳聋的平均外显率分别为28.1%和21.5%,排除氨基糖甙类药物时,耳聋的平均发病年龄从1~15岁不等。线粒体全序列分析发现了16个新变异,不同的线粒体DNA多态性位点显示这25个家系分别属于东亚人群A、B、D、F、G、M、N和R单倍型,其中线粒体单倍型B的家系耳聋外显率和表现度较其他单倍型高。此外,7个继发突变位点和21个高保守性位点突变可能增加了这些家系的耳聋外显率。GJB2基因上未检测到与耳聋相关的突变,表明在本研究的耳聋家系中,GJB2基因可能没有参与A1555G突变的表型表达。以上各方面提示,线粒体单倍型和其他因素可能参与了这25个家系耳聋患者的表型修饰。     

应用基因芯片技术检测非综合征型耳聋基因突变

目的:应用遗传性耳聋基因芯片对散发性聋患者进行分子病因学检测,评估其在遗传性耳聋快速基因诊断中的可靠性。方法:门诊收集散发性聋患者10例,取外周血,提取基因组DNA,用遗传性耳聋基因芯片检测4个中国人中常见的耳聋相关基因中的9个热点突变,包括GJB2(35delG、176del16bp、235delC及299delAT)、GJB3(C538T)、SLC26A4(IVS7-2AG、A2168G)和线粒体DNA 12S rRNA(A1555G、C1494T)。同时,PCR扩增GJB2、线粒体12S rRNA基因全序列,DNA测序,以验证基因芯片检测结果的准确性。结果:在10名耳聋患者中,基因芯片方法检出1例携带线粒体DNA 12S rRNA C1494T突变;2例GJB2基因235delC纯合突变;2例235delC杂合突变;SLC26A4基因和GJB3基因未检出突变。基因芯片的结果与测序结果完全一致。结论:遗传性耳聋基因芯片技术对中国人常见耳聋相关基因热点突变的检出率高,结果准确、可靠,具有快速、高通量、高准确性、低成本等特点,能够满足临床耳聋基因检测的要求,同时结合产前诊断技术能有效预防耳聋患儿的出生,因而具有广阔的临床应用前景。     

非综合征型耳聋患者耳聋易感基因突变的检测分析

目的:探究非综合征型耳聋患者耳聋易感基因的携带情况及突变类型,为耳聋患者治疗或遗传咨询提供理论依据。方法:收集821例非综合征型耳聋患者的外周静脉血,提取基因组DNA后,进行4个常见耳聋易感基因GJB2、GJB3、SLC26A4和线粒体12S r RNA的9个突变热点筛查。结果:821例非综合征型耳聋患者中耳聋易感基因筛查阳性375例,阳性率为45.7%,不同性别之间阳性率无明差异(P=0.625)。375例存在耳聋易感基因突变的研究对象中,4个易感基因的9突变热点共检测出447例点突变,其中GJB2基因的有241例点突变(53.9%),以235 del C位点突变率最高;SLC26A4基因的有126例点突变(28.2%),以IVS7-2 AG位点突变为主;线粒体12S r RNA基因的有79例点突变(17.7%),绝大部分为1555 AG位点突变;而GJB3基因仅有1例点突变(0.2%)。375例存在耳聋易感基因突变的研究对象中,304例发生1种突变(81.1%),有70例发生2种突变(18.7%),仅有1例发生3种突变(0.3%)。结论:非综合征型耳聋患者中GJB2基因的235 del C位点以及SLC26A4基因的IVS7-2 AG位点突变率较高,常见耳聋易感基因筛查有助于非综合征型耳聋患者的诊断、干预及治疗。     

黑龙江省非综合性耳聋基因位点的研究

目的:分析黑龙江地区新生儿耳聋易感基因的携带情况。方法:选取2014年6月至2015年3月在我院出生、义诊以及门诊筛查的新生儿1036例,采取EDTA抗凝静脉全血,提取基因组DNA进行PCR,利用直接测序法检测非综合性耳聋常见突变基因GJB2、SLC26A4及线粒体12S rRNA。结果:1036例新生儿中,64例筛查阳性,阳性检出率6.18%。其中GJB2 235del C 26例,35del G 3例,109GA 5例,176-191del16 4例,299-300delAT 9例,SLC26A4IVS7-2 14例,SLC2168 3例,12S rRNA突变2例。其中有家族史的新生儿63例,携带耳聋基因的患儿17例,阳性检出率为27.0%。结论:GJB2 235del C和SLC26A4 IVS7-2为本省的高发致病位点,对新生儿进行耳聋基因筛查,亦或对年轻夫妇进行孕前检查,部分耳聋可早期发现,制定相应的干预措施,可预防或降低耳聋的发生。     

湖北汉族人群载脂蛋白A5遗传多态性分析

采用聚合酶链反应-限制性片断长度多态性(polymerase chain reaction restriction-fragment length polymorphism, PCR-RFLP)对257例湖北健康汉族人群APOA5 -1131T>C及56C>G基因多态性进行鉴定。结果发现: 湖北汉族人群中ApoA5 -1131T>C存在TT、TC、CC基因型, 3种基因型的频率分别为50.9%、32.9%及16.2%; 56C>G位点存在CC、CG基因型, 257名研究对象中, G等位基因分布频率小于5%; 各基因型频率和等位基因频率在不同种族和地域间分布存在显著性差异。结论: 湖北汉族人群中ApoA5基因-1131T>C位点存在单核苷酸多态性(single nucleotide polymorphism, SNP), 56C>G在该人群中应视为一个突变位点而不是多态性位点     

建立一种反向斑点杂交法检测肺炎支原体23S rRNAV区A2063G基因突变的方法

目的建立检测肺炎支原体（Mycoplasma pneumoniae,MP）23S rRNA V区2063基因型的反向斑点杂交方法,并与PCR产物直接测序法的结果进行比较分析。方法19例自临床咽拭子标本分离培养的MP,用自行设计的反向斑点杂交法检测23S rRNA V区2063基因型,同时对相应序列测序分析。抽提标准菌株FH和127份经PCR测定MP阳性的临床标本基因组DNA,用MP阴性的基因组DNA抽提物5份作阴性对照,用反向斑点杂交法检测23S rRNA V区2063基因型。结果19例分离培养的MP,经反向斑点杂交法检测15株有23S rRNA V区基因A2063G位点突变;4株为2063A,与测序结果一致（Kappa一致性检验,P〉0.05）。经反向斑点杂交法检测,127份MP阳性的基因组DNA抽提物中有122份标本为A2063G位点突变,标准菌株FH和2份DNA抽提物的2063位点碱基为A,还有3份抽提物标本的2063位点碱基既有A又有G,5份阴性对照均无显色。结论反向斑点杂交方法能快速、准确检测临床MP 23S rRNA V区2063基因型。     

福建省慢性HBV感染者HBV基因S区、基本核心启动子区和前C区基因变异特征分析

为研究福建省慢性HBV感染者HBV基因多样性及变异规律,了解该人群HBV-DNA的病毒学特征。收集慢性HBV感染者血清标本,通过巢式PCR法扩增其HBV基因序列,比对NCBI数据库中标准基因型序列,分析HBV基因S区,基本核心启动子区(BCP)及前C区的序列变异情况,并对这些变异可能造成的病毒抗原表达,疫苗逃逸,患者病症改变等情况进行探讨。最终成功扩增82例HBV全长基因序列,其中B基因型56例,C基因型26例。基因组特定功能区序列分析发现慢性HBV感染者HBV基因在S区(23.2%)、BCP区(61.0%)和前C区(29.3%)均出现了不同程度的变异。其中主蛋白(HBsAg)主要抗原决定簇a决定簇45.8%位点出现了变异,这些变异位点中包括与肝炎重症化及免疫逃逸密切相关的位点(aa126、aa129、aa145等)。位点G1896A(19.5%),G1764A(11.0%)和A1762T(9.8%)依然是BCP/前C区的主要突变位点。而位点A1752G(25.6%)高突变率的出现在BCP区应引起关注。此外位点G1764A(χ~2=5.742,P=0.030)、A1896G(χ~2=14.392,P=0.000)以及A1762T/G1764A(χ~2=7.289,P=0.012)的突变更容易发生在HBeAg阴性的样品中;而位点A1846T(χ~2=11.882,P=0.003)、A1762T(χ~2=6.561,P=0.038)和A1896G(χ~2=6.958,P=0.030)的突变与HBV-DNA的病毒载量存在一定相关性。总之,福建省慢性HBV感染者在HBV不同基因功能区域均存在不同程度的变异,一些与HBeAg表达情况、HBV-DNA载量、疫苗免疫逃避及肝细胞癌发生具有相关联的变异位点已经出现,BCP区A1752G位点的高频率出现应值得关注,对于这些变异位点的患者应加强监测。     

Mitochondrial 12S rRNA variants in 1642 Han Chinese pediatric subjects with aminoglycoside-induced and nonsyndromic hearing loss

In this report, we investigated the frequency and spectrum of mitochondrial 12S rRNA variants in a large cohort of 1642 Han Chinese pediatric subjects with aminoglycoside-induced and nonsyndromic hearing loss. Mutational analysis of 12S rRNA gene in these subjects identified 68 (54 known and 14 novel) variants. The frequencies of known 1555A>G and 1494C>T mutations were 3.96% and 0.18%, respectively, in this cohort with nonsyndromic and aminoglycoside-induced hearing loss. Prevalence of other putative deafness-associated mutation at positions 1095 and 961 were 0.61% and 1.7% in this cohort, respectively. Furthermore, the 745A>G, 792C>T, 801A>G, 839A>G, 856A>G, 1027A>G, 1192C>T, 1192C>A, 1310C>T, 1331A>G, 1374A>G and 1452T>C variants conferred increased sensitivity to ototoxic drugs or nonsyndromic deafness as they were absent in 449 Chinese controls and localized at highly conserved nucleotides of this rRNA. However, other variants appeared to be polymorphisms. Moreover, 65 Chinese subjects carrying the 1555A>G mutation exhibited bilateral and sensorineural hearing loss. A wide range of severity, age-of-onset and audiometric configuration was observed among these subjects. In particular, the sloping and flat-shaped patterns were the common audiograms in individuals carrying the 1555A>G mutation. The phenotypic variability in subjects carrying these 12S rRNA mutations indicated the involvement of nuclear modifier genes, mitochondrial haplotypes, epigenetic and environmental factors in the phenotypic manifestation of these mutations. Therefore, our data demonstrated that mitochondrial 12S rRNA is the hot spot for mutations associated with aminoglycoside ototoxicity.     

Mutational analysis of the mitochondrial 12S rRNA gene in Chinese pediatric subjects with aminoglycoside-induced and non-syndromic hearing loss

Mutations in mitochondrial DNA (mtDNA) have been found to be associated with sensorineural hearing loss. We report here a systematic mutational screening of the mitochondrial 12S rRNA gene in 128 Chinese pediatric subjects with sporadic aminoglycoside-induced and non-syndromic hearing loss. We show that aminoglycoside ototoxicity accounts for 48% of cases of hearing loss in this Chinese pediatric population. Of the known deafness-associated mutations in this gene, the incidence of the A1555G mutation is ~13% and ~2.9% in this Chinese pediatric population with aminoglycoside-induced and non-syndromic hearing loss, respectively. Furthermore, mutations at position 961 in the 12S rRNA gene account for ~1.7% and 4.4% of cases of aminoglycoside-induced and non-syndromic hearing loss in this Chinese clinical population, respectively. The T1095C mutation has been identified in one maternally inherited family with aminoglycoside-induced and non-syndromic hearing loss. However, the C1494T mutation was not detected in this clinical population. In addition, three variants, A827G, T1005C and A1116G, in the 12S rRNA gene, localized at highly conserved sites, may play a role in the pathogenesis of aminoglycoside ototoxicity. These data strongly suggest that the mitochondrial 12S rRNA is a hot-spot for deafness-associated mutations in the Chinese population.Z. Li and R. Li contributed equally to this work.     

Mitochondrial 12S rRNA mutations associated with aminoglycoside ototoxicity

The mitochondrial 12S rRNA is a hot spot for mutations associated with both aminoglycoside-induced and nonsyndromic hearing loss. Of those, the homoplasmic 1555A>G and 1494C>T mutations at the highly conserved decoding region of the 12S rRNA have been associated with hearing loss worldwide. In particular, these two mutations account for a significant number of cases of aminoglycoside ototoxicity. The 1555A>G or 1494C>T mutation is expected to form a novel 1494C-G1555 or 1494U-A1555 base-pair at the highly conserved A-site of 12S rRNA. These transitions make the human mitochondrial ribosomes more bacteria-like and alter binding sites for aminoglycosides. As a result, the exposure to aminoglycosides can induce or worsen hearing loss in individuals carrying one of these mutations. Biochemical characterization demonstrated an impairment of mitochondrial protein synthesis and subsequent defects in respiration in cells carrying the A1555G or 1494C>T mutation. Furthermore, a wide range of severity, age-at-onset and penetrance of hearing loss was observed within and among families carrying these mutations. Nuclear modifier genes, mitochondrial haplotypes and aminoglycosides should modulate the phenotypic manifestation of the 12S rRNA 1555A>G and 1494C>T mutations. Therefore, these data provide valuable information and technology: (1) to predict which individuals are at risk for ototoxicity; (2) to improve the safety of aminoglycoside antibiotic therapy; and (3) eventually to decrease the incidence of hearing loss.     

Mitochondrial haplotypes may modulate the phenotypic manifestation of the deafness-associated 12S rRNA 1555A>G mutation

Mitochondrial 12S rRNA 1555A>G mutation is one of the important causes of aminoglycoside-induced and nonsyndromic deafness. Our previous investigations showed that the A1555G mutation was a primary factor underlying the development of deafness but was insufficient to produce deafness phenotype. However, it has been proposed that mitochondrial haplotypes modulate the phenotypic manifestation of the 1555A>G mutation. Here, we performed systematic and extended mutational screening of 12S rRNA gene in a cohort of 1742 hearing-impaired Han Chinese pediatric subjects from Zhejiang Province, China. Among these, 69 subjects with aminoglycoside-induced and nonsyndromic deafness harbored the homoplasmic 1555A>G mutation. These translated to a frequency of ～3.96% for the 1555A>G mutation in this hearing–impaired population. Clinical and genetic characterizations of 69 Chinese families carrying the 1555A>G mutation exhibited a wide range of penetrance and expressivity of hearing impairment. The average penetrances of deafness were 29.5% and 17.6%, respectively, when aminoglycoside-induced hearing loss was included or excluded. Furthermore, the average age-of-onset for deafness without aminoglycoside exposure ranged from 5 and 30 years old, with the average of 14.5 years. Their mitochondrial genomes exhibited distinct sets of polymorphisms belonging to ten Eastern Asian haplogroups A, B, C, D, F, G, M, N, R and Y, respectively. These indicated that the 1555A>G mutation occurred through recurrent origins and founder events. The haplogroup D accounted for 40.6% of the patient’s mtDNA samples but only 25.8% of the Chinese control mtDNA samples. Strikingly, these Chinese families carrying mitochondrial haplogroup B exhibited higher penetrance and expressivity of hearing loss. In addition, the mitochondrial haplogroup specific variants: 15927G>A of haplogroup B5b, 12338T>C of haplogroup F2, 7444G>A of haplogroup B4, 5802T>C, 10454T>C, 12224C>T and 11696G>A of D4 haplogroup, 5821G>A of haplogroup C, 14693A>G of haplogroups Y2 and F, and 15908T>C of Y2 may enhance the penetrace of hearing loss in these Chinese families. Moreover, the absence of mutation in nuclear modifier gene TRMU suggested that TRMU may not be a modifier for the phenotypic expression of the 1555A>G mutation in these Chinese families. These observations suggested that mitochondrial haplotypes modulate the variable penetrance and expressivity of deafness among these Chinese families.     

The Role of Mitochondrial DNA Mutations in Hearing Loss

Mutations in mitochondrial DNA (mtDNA) are one of the most important causes of hearing loss. Of these, the homoplasmic A1555G and C1494T mutations at the highly conserved decoding site of the 12S rRNA gene are well documented as being associated with either aminoglycoside-induced or nonsyndromic hearing loss in many families worldwide. Moreover, five mutations associated with nonsyndromic hearing loss have been identified in the tRNA^Ser(UCN) gene: A7445G, 7472insC, T7505C, T7510C, and T7511C. Other mtDNA mutations associated with deafness are mainly located in tRNA and protein-coding genes. Failures in mitochondrial tRNA metabolism or protein synthesis were observed from cybrid cells harboring these primary mutations, thereby causing the mitochondrial dysfunctions responsible for deafness. This review article provides a detailed summary of mtDNA mutations that have been reported in deafness and further discusses the molecular mechanisms of these mtDNA mutations in deafness expression.     

The A1555G Mutation in the 12S rRNA Gene of Human mtDNA: Recurrent Origins and Founder Events in Families Affected by Sensorineural Deafness

The mtDNA variation of 50 Spanish and 4 Cuban families affected by nonsyndromic sensorineural deafness due to the A1555G mutation in the 12S rRNA gene was studied by high-resolution RFLP analysis and sequencing of the control region. Phylogenetic analyses of haplotypes and detailed survey of population controls revealed that the A1555G mutation can be attributed to >/=30 independent mutational events among the 50 Spanish families and that it occurs on mtDNA haplogroups that are common in all European populations. This indicates that the relatively high detection rate of this mutation in Spain is not due to sampling biases or to a single major founder event. Moreover, the distribution of these mutational events on different haplogroups is compatible with a random occurrence of the A1555G mutation and tends to support the conclusion that mtDNA backgrounds do not play a significant role in the expression of the mutation. Overall, these findings appear to indicate that the rare detection of this mutation in other populations is most likely due to inadequacy in patient ascertainment and molecular screening. This probable lack of identification of the A1555G mutation in subjects affected by sensorineural hearing loss implies that their maternally related relatives are not benefiting from presymptomatic detection and information concerning their increased risk of ototoxicity due to aminoglycoside treatments.     

Maternally inherited aminoglycoside-induced and nonsyndromic deafness is associated with the novel C1494T mutation in the mitochondrial 12S rRNA gene in a large Chinese family

We report here the characterization of a large Chinese family with maternally transmitted aminoglycoside-induced and nonsyndromic deafness. In the absence of aminoglycosides, some matrilineal relatives in this family exhibited late-onset/progressive deafness, with a wide range of severity and age at onset. Notably, the average age at onset of deafness has changed from 55 years (generation II) to 10 years (generation IV). Clinical data reveal that the administration of aminoglycosides can induce or worsen deafness in matrilineal relatives. The age at the time of drug administration appears to be correlated with the severity of hearing loss experienced by affected individuals. Sequence analysis of mitochondrial DNA in this pedigree identified a homoplasmic C-to-T transition at position 1494 (C1494T) in the 12S rRNA gene. The C1494T mutation is expected to form a novel U1494-1555A base pair, which is in the same position as the C1494-1555G pair created by the deafness-associated A1555G mutation, at the highly conserved A site of 12S rRNA. Exposure to a high concentration of paromomycin or neomycin caused a variable but significant average increase in doubling time in lymphoblastoid cell lines derived from four symptomatic and two asymptomatic individuals in this family carrying the C1494T mutation when compared to four control cell lines. Furthermore, a significant decrease in the rate of total oxygen consumption was observed in the mutant cell lines. Thus, our data strongly support the idea that the A site of mitochondrial 12S rRNA is the primary target for aminoglycoside-induced deafness. These results also strongly suggest that the nuclear background plays a role in the aminoglycoside ototoxicity and in the development of the deafness phenotype associated with the C1494T mutation in the mitochondrial 12S rRNA gene.     

Very low penetrance of hearing loss in seven Han Chinese pedigrees carrying the deafness-associated 12S rRNA A1555G mutation

Mutations in mitochondrial DNA (mtDNA) have been found to be associated with sensorineural hearing loss. We report here the clinical, genetic and molecular characterizations of seven Han Chinese pedigrees with aminoglycoside-induced and nonsyndromic bilateral hearing loss. Clinical evaluation revealed the variable phenotype of hearing impairment including severity, age-at-onset and audiometric configuration in these subjects. The penetrance of hearing loss in these pedigrees ranged from 3% to 29%, with an average of 13.6%, when aminoglycoside-induced deafness was included. When the effect of aminoglycosides was excluded, the penetrances of hearing loss in these seven pedigrees varied from 0% to 17%, with an average of 5.3%. Sequence analysis of the complete mitochondrial genomes in these pedigrees showed the presence of the deafness-associated 12S rRNA A1555G mutation, in addition to distinct sets of mtDNA polymorphism belonging to East Asian haplogroups B4, D4, D5 and F1, respectively. This suggested that the A1555G mutation occurred sporadically and multiplied through evolution of the mtDNA in China. Despite the presence of several evolutionary conservative variants in protein-encoding genes, there was the absence of functionally significant mutations in tRNA and rRNAs or secondary LHON mutations in these seven Chinese families. These suggest that these mtDNA haplogroup-specific variants may not play an important role in the phenotypic expression of the A1555G mutation in those Chinese families with very low penetrance of hearing loss. However, aminoglycosides appear to be a major modifier factor for the phenotypic manifestation of the A1555G mutation in these Chinese families.     

Coexistence of mitochondrial 12S rRNA C1494T and CO1/tRNA(Ser(UCN)) G7444A mutations in two Han Chinese pedigrees with aminoglycoside-induced and non-syndromic hearing loss

Mutations in mitochondrial DNA are one of the important causes of hearing loss. We report here the clinical, genetic, and molecular characterization of two Han Chinese pedigrees with maternally transmitted aminoglycoside-induced and nonsyndromic bilateral hearing loss. Clinical evaluation revealed the wide range of severity, age-at-onset, and audiometric configuration of hearing impairment in matrilineal relatives in these families. The penetrances of hearing loss in these pedigrees were 20% and 18%, when aminoglycoside-induced deafness was included. When the effect of aminoglycosides was excluded, the penetrances of hearing loss in these seven pedigrees were 10% and 15%. Sequence analysis of the complete mitochondrial genomes in these pedigrees showed the presence of the deafness-associated 12S rRNA C1494T and CO1/tRNA(Ser(UCN)) G7444A mutations. Their distinct sets of mtDNA polymorphism belonged to Eastern Asian haplogroup C4a1, while other previously identified six Chinese mitochondrial genomes harboring the C1494T mutation belong to haplogroups D5a2, D, R, and F1, respectively. This suggested that the C1494T or G7444A mutation occurred sporadically and multiplied through evolution of the mitochondrial DNA (mtDNA). The absence of functionally significant mutations in tRNA and rRNAs or secondary LHON mutations in their mtDNA suggest that these mtDNA haplogroup-specific variants may not play an important role in the phenotypic expression of the 12S rRNA C1494T and CO1/tRNA(Ser(UCN)) G7444A mutations in those Chinese families. However, aminoglycosides and other nuclear modifier genes play a modifying role in the phenotypic manifestation of the C1494T mutation in these Chinese families.