不育男性精子线粒体DNA突变与线粒体超微结构改变

目的：探讨精子线粒体DNA突变和线粒体超微结构变化与男性不育之间的关系。方法：应用PCR技术,DNA测序技术对不育男性的76例精了动力差的精液标本进行MTCYB、MTATP6片段检测,从中选出5例有线粒体DNA缺失的标本进行透射电镜观察。结果5例病人的标本电镜下大多数精子尾部可见线粒体有体积异常,或为小线粒体,或为大线粒体,排列紊乱,,分布不对称;多层线粒体包绕尾部轴丝。与已育男性的精子标本的形态差别明显。结论：线粒体DNA突变的精子标本可以观察到线粒体结构改变。精子线粒体DNA的突变和线粒体结构的改变均可影响精子受精过程的能量供给,可导致男性不良。     

RT-PCR法检测PD线粒体的缺失突变

目的研究线粒体DNA突变与自发性帕金森病（PD）的关系。方法从帕金森病患者以及正常对照者血液中提取线粒体DNA并运用RT-PCR法进行检测分析。结果在帕金森患者和对照组中都发现了线粒体DNA 4977bp的缺失,但是在帕金森病患者中缺失的量远大于对照组（P〈0.05）。结论线粒体DNA 4977bp的缺失可能是导致帕金森病的机制之一。     

线粒体肌病患者线粒体DNA的突变分析

目的分析线粒体肌病患者线粒体DNA的突变情况，为疾病诊断提供依据。方法用常规HE、酶组化染色和电镜检查等病理形态学方法对3例线粒体肌病疑似患者进行诊断，并用聚合酶链反应-单链构象多态和DNA测序等方法对患者线粒体DNA中全部22个tRNA基因进行突变筛查。结果3例患者均被确诊为线粒体肌病，其中例1tRNA—VaI基因发生A1627G纯合突变，例2tRNA—Val基因发生A1627G／A杂合突变，例3tRNA—Trp基因发生T5554C突变、tRNA—Arg基因发生A10412C／A杂合突变。结论线粒体DNA中的tRNA基因突变是线粒体肌病的重要病因之一。     

线粒体DNA点突变与肥厚型心肌病的关系

肥厚型心肌病 (hypertrophic cardiomyopathy,HCM)是以心肌肥厚、心肌纤维排列紊乱为特征的一种特发性心肌病。已证实 HCM是儿童及青年人猝死最常见原因之一 ,发生率为1%～ 6 % [1 ,2 ]。由于该病临床表现多样 ,部分患者可在无任何症状且心电图、超声心动图未出现异常的情况下因剧烈运动发生猝死 ,因此 ,从分子水平对 HCM进行研究 ,对于阐明该病的发生机理 ,早期诊断、防治具有重要意义。有些学者 [3- 6 ] 研究发现某些 HCM与线粒体 (mt DNA)的缺失和点突变有关。我们应用PCR、PCR- SSCP及 PCR产物直接银染测序技术 ,对 19例HC…     

线粒体转运系统和降解系统的研究进展

线粒体蛋白稳态的维持需要线粒体转运系统和降解系统协同调控,其功能障碍是代谢疾病的病因之一。转运系统障碍使核编码的线粒体蛋白无法进入线粒体,降解系统障碍则使细胞无法及时清除异常蛋白,最终导致线粒体损伤。在糖尿病患者的心肌细胞线粒体中,转运系统和降解系统失调引起的电子传递链(ETC)活性降低、活性氧(ROS)生成增加和产能减少是糖尿病心肌病(DCM)发生发展的主要原因。     

线粒体脑肌病的影像学表现

线粒体病：是由线粒体DNA（mtDNA）和细胞核DNA（nDNA）编码线粒体相关蛋白的基因突变,导致线粒体的结构及功能异常,而引起细胞呼吸链及能量代谢障碍的一种多系统受累疾病（骨骼肌、脑、心、周围神经）,线粒体几乎存在人体所有细胞内,脑和肌肉组织线粒体含量丰富。病变累及骨骼肌称线粒体肌病,如中枢神经系统同时受累称线粒体脑肌病。线粒体mtDNA的突变（位点突变、缺失、重复及丢失）引起不同类型,临床呈现多个症候群。     

贵州苗族、布依族、侗族人群线粒体DNA 9 bp序列缺失频率分析

目的 调查贵州苗族、布依族、侗族人群线粒体DNA细胞色素氧化酶Ⅱ和t RNALys基因间小非编码Ⅴ区串联重复序列9 bp的缺失频率.方法 采用聚合酶链反应-聚丙烯酰胺凝胶方法及DNA序列分析法对105名苗族、97名布依族、102名侗族的男性个体线粒体DNA的9 bp缺失多态频率进行分析.结果 在304名男性中仅发现标准型和短型(即9 bp缺失)两种多态,缺失频率为23.0％(70/304).其中苗族缺失频率为28.6％(30/105)、布依族为26.8％(26/97)、侗族为13.7％(14/102).三者之间的差异具有统计学意义(P＜0.05).结论 贵州苗族、布依族、侗族人群线粒体DNA 9 bp缺失基因频率均较高,三者之间差异有统计学意义.     

中国人非综合征性耳聋患者线粒体基因组C1494T突变筛查

目的进行非综合征性聋患者的线粒体DNA C1494T突变的分子流行病学调查。方法对中国人群中20例氨基糖甙类药物致聋患者、136例散发的非综合征性聋患者以及50例非综合征性聋家系先证者，以聚合酶链反应结合限制性片段长度多态性分析法检测线粒体DNA C1494T突变的发生情况。结果全部受检者无线粒体DNA C1494T突变的发生。结论中国人群中非综合征性聋患者的线粒体DNA C1494T突变的发生率较低，且明显低于线粒体DNA A1555G的突变发生率。通过聋病分子流行病学调查，提示线粒体DNA C1494T突变不是氨基糖甙类药物致聋的主要病因。     

弱精子症病人精子线粒体DNA4977—bp缺失研究

本文采用聚合酶链反应（ＰＣＲ） 技术对４１ 例标本,其中２０ 例弱精子症病人和２１ 例精子活力正常人进行了精子线粒体ＤＮＡ（ｍｔＤＮＡ）缺失的研究。结果发现２０ 例弱精子症病人中１８ 例有缺失,而２１ 例精子活力正常人中仅有两例有缺失。说明线粒体ＤＮＡ４９７７ｂｐ 缺失在弱精子症的发病中起重要作用。     

成年人肥厚型心肌病表型的临床诊治研究进展

很多遗传代谢性心肌病可表现为肥厚型心肌病表型,但导致心肌肥厚的病因各不同,其治疗策略、预后也不相同。由于部分遗传代谢性心肌病在明确病因后进行病因治疗可以明显改善心功能状态,甚至完全逆转心肌病变。早期诊断、识别和治疗以左心室肥厚为主要表型的遗传代谢性心肌病尤为重要。笔者综述肥厚型心肌病、心脏淀粉样变、AndersonFabry病、线粒体心肌病及Danon病等表现为肥厚型心肌病表型的遗传性代谢性心肌病,分析其发病机制、临床表现,超声心动图特点,总结诊断及治疗方法。对于遗传代谢性心肌肥厚患者的超声心动图,大多无特异性,早期诊断还存在一定难度。因此,在日常工作中需要提高警惕,详细询问病史,结合相关生物化学检查和组织病理改变,甚至基因检查进行明确诊断。     

Is Age a Contributory Factor of Mitochondrial Bioenergetic Decline and DNA Defects in Idiopathic Dilated Cardiomyopathy?

While mitochondrial abnormalities are increasingly recognized in cardiac diseases including hypertrophic cardiomyopathy, their presence in idiopathic dilated cardiomyopathy and the role that age plays in their incidence and severity have yet not been assessed. Levels of cardiac respiratory enzyme activities and mitochondrial DNA (mtDNA) were examined in 55 subjects with idiopathic dilated cardiomyopathy divided into 3 age groups. Respiratory enzyme activity levels were significantly lower in 37 patients (67%) compared to age-matched controls and increased activity levels were noted in 9 (16%). Decreased activities were found in complex I (n = 11), III (n = 16), IV (n = 12) and V (n = 13), but not in II, the only respiratory complex entirely nuclear-encoded. No age-specific differences were found in the overall frequency of enzymatic abnormalities. However, older patients had significantly increased multiple enzyme activity defects as well as increases in abundance and frequency of the 7.4 kb deletion. In addition, 3 patients were noted with marked reduction in mtDNA levels. None of the pathogenic mtDNA mutations previously associated with hypertrophic cardiomyopathy were found, nor was there any relationship that could be established between levels of specific mtDNA deletions and enzyme activities. In summary, specific mitochondrial abnormalities are heterogenous and frequent in both adults and children with idiopathic dilated cardiomyopathy. Older patients are more likely to have mtDNA deletions and multiple enzyme activity defects. The molecular basis for these abnormalities remains undefined.     

Is 8860 variation a rare polymorphism or associated as a secondary effect in HCM disease?

Introduction

mtDNA defects, both deletions and point mutations, have been associated with hypertrophic cardiomyopathies. The aim of this study was to establish a spectrum for mtDNA mutations in Iranian hypertrophic cardiomyopathy (HCM) patients.

Material and methods

The control group was chosen among the special medical centre visitors who did not have hypertrophic cardiomyopathy or any related heart disease. Hypertrophic cardiomyopathy (HCM) is widely accepted as a pluricausal or multifactorial disease. Because of the linkage between energy metabolism in the mitochondria and cardiac muscle contraction, it is reasonable to assume that mitochondrial abnormalities may be responsible for some forms of HCM. Point mutations and deletions in the two hot spot regions of mtDNA were investigated by PCR and sequencing methods.

Results

Some unreported point mutations have been found in this study but no deletion was detected. Meanwhile some of these point mutations have been investigated among HCM patients for the first time.

Conclusions

A8860G transition was detected in a high proportion, raising the question whether this rare polymorphism is associated as a secondary effect in HCM disease.     

Double-strand breaks of mouse muscle mtDNA promote large deletions similar to multiple mtDNA deletions in humans

Mitochondrial DNA (mtDNA) deletions are a common cause of mitochondrial disorders and have been found to accumulate during normal aging. Despite the fact that hundreds of deletions have been characterized at the molecular level, their mechanisms of genesis are unknown. We tested the effect of double-strand breaks of muscle mtDNA by developing a mouse model in which a mitochondrially targeted restriction endonuclease (PstI) was expressed in skeletal muscle of mice. Because mouse mtDNA harbors two PstI sites, transgenic founders developed a mitochondrial myopathy associated with mtDNA depletion. The founders showed a chimeric pattern of transgene expression and their residual level of wild-type mtDNA in muscle was approximately 40% of controls. We were able to identify the formation of large mtDNA deletions in muscle of transgenic mice. A family of mtDNA deletions was identified, and most of these rearrangements involved one of the PstI sites and the 3' end of the D-loop region. The deletions had no or small direct repeats at the breakpoint region. These features are essentially identical to the ones observed in humans with multiple mtDNA deletions in muscle, suggesting that double-strand DNA breaks mediate the formation of large mtDNA deletions.     

Mitochondrial DNA alterations as ageing-associated molecular events

Mitochondrial DNA (mtDNA) is a naked double-stranded circular extrachromosomal genetic element continuously exposed to the matrix that contains great amounts of reactive oxygen species and free radicals. The age-dependent decline in the capability and capacity of mitochondria to dispose these oxy-radicals will render mtDNA more vulnerable to mutations during the ageing process. During the past 3 years, more than 10 different types of deletions have been identified in the mtDNA of various tissues of old humans. Some of them were found only in a certain tissue but some others appeared in more than one organ or tissue. The 4977-bp deletion is the most prevalent and abundant one among these deletions. Skeletal muscle is the target tissue of most ageing-associated mtDNA deletions and has often been found to carry multiple deletions. The onset age of the various deletions in mtDNA varies greatly with individual and type of the deletion. The 4977-bp deletion has been independently demonstrated to occur in the mtDNA of various tissues of the human in the early third decade of life. However, the 7436-bp deletion was only detected in the heart mtDNA of human subjects in their late thirties. The others appeared only in older humans over 40 years old. No apparent sex difference was found in the onset age of these ageing-associated mtDNA deletions. The various ageing-associated deletions could be classified into two groups. Most of the deletions belong to the first group, in which the 5′- and 3′-end breakpoints of the deletion are flanked by 4-bp or longer direct repeats. The deletion in the second group occurs less frequently and shows no distinct repeat sequences flanking the deletion sites. These two groups of mtDNA deletions may occur by different mechanisms. The first group is most probably caused by internal recombination or slippage mispairing during replication mtDNA by the D-loop mechanism. The deleted mtDNA and the deleted DNA fragment may be further degraded or escape from the mitochondria and get translocated into the nucleus. The latter route has been substantiated by many observations of inserted mtDNA sequences in the nuclear DNA. Thus, the fragments of migrating mtDNA may change the information content and expression level of certain nuclear genes and thereby promote the ageing process or cause cancer. Similar ageing-associated alterations of mtDNA have also been observed in aged animals and plants. I suggest that mtDNA deletions and other mutations to be discovered are molecular events generally associated with the ageing process.     

Genetic counseling for DAPK1 mutation in a chronic lymphocytic leukemia family

Many published studies have indicated that various mechanisms could be involved in the genesis of variant chronic myelogeneous leukemia (CML) translocations. These are mainly one-step or two-step mechanisms, associated or not with deletions adjacent to the translocation junction on der(9) or der(22) chromosomes (or both). Based on the mechanism of genesis, it has been suggested that the complexity may affect the occurrence of ABL1 and BCR deletions (either or both), or may be associated with the CML disease course, and thus could determine the response to imatinib therapy. Through a retrospective molecular cytogenetic study of 41 CML patients with variant Philadelphia chromosome (Ph), we explored the genesis of these variant rearrangements and analyzed the correlation with deletion status and imatinib efficiency. Our results confirmed that the one-step mechanism is the most frequent, evidenced in 30 of 41 patients (73%); 3 patients demonstrated other more complex multistep events and 8 patients (19.5%) harbored ABL1 or BCR deletions that are not significantly associated with the complexity of translocation genesis. We also found no association between one-step, two-step, or multistep mechanisms and the response to imatinib therapy.     

Importance of searching for associated mitochondrial DNA alterations in patients with multiple deletions

Multiple mitochondrial DNA (mtDNA) deletions have been reported in patients with autosomal dominant and recessive disorders. We studied several affected and one non-affected individuals belonging to a pedigree in which the inheritance of the pathological trait was compatible with an autosomique dominant transmission. Affected members had late-onset multisystem disorders with multiple mtDNA deletions in skeletal muscle. But this family presented a striking difference from previously described cases, because none of the patients had progressive external ophthalmoplegia (PEO). We also studied one young boy with a no contributary family history. He had a cerebellar ataxia with PEO and multiple mtDNA deletions in muscle. Molecular analysis revealed that in the first family, repeated sequences were present at the breakpoint junctions, whereas such motifs were not found in the young patient's case. In the first family, we evidenced mtDNA point mutations in clones containing breakpoint junctions and a 9-bp motif triplication in the intergenic COII/tRNA(Lys) region, whereas this sequence is repeated twice in the wild type mtDNA. Our results suggest that multiple deletions observed in the two pedigrees result from different molecular mechanisms and point out the role of repeated sequences in the first pedigree. No mtDNA repair system has been described in mammals so far, but the molecular abnormalities found in the first family suggest that a defect in an mtDNA repair system, homologous to the E. coli MutHLS pathway, could be responsible for such a phenotype.     

Mitochondrial DNA Mutations and Mitochondrial Abnormalities in Dilated Cardiomyopathy

Mitochondrial (mt)DNA defects, both deletions and tRNA point mutations, have been associated with cardiomyopathies. The aim of the study was to determine the prevalence of pathological mtDNA mutations and to assess associated defects of mitochondrial enzyme activity in dilated cardiomyopathy (DCM) patients with ultrastructural abnormalities of cardiac mitochondria. In a large cohort of 601 DCM patients we performed conventional light and electron microscopy on endomyocardial biopsy samples. Cases with giant organelles, angulated, tubular, and concentric cristae, and crystalloid or osmiophilic inclusion bodies were selected for mtDNA analysis. Mutation screening techniques, automated DNA sequencing, restriction enzyme digestion, and densitometric assays were performed to identify mtDNA mutations, assess heteroplasmy, and quantify the amount of mutant in myocardial and blood DNA. Of 601 patients (16 to 63 years; mean, 43.5 ± 12.7 years), 85 had ultrastructural evidence of giant organelles, with abnormal cristae and inclusion bodies; 19 of 85 (22.35%) had heteroplasmic mtDNA mutations (9 tRNA, 5 rRNA, and 4 missense, one in two patients) that were not found in 111 normal controls and in 32 DCM patients without the above ultrastructural mitochondrial abnormalities. In all cases, the amount of mutant was higher in heart than in blood. In hearts of patients that later underwent transplantation, cytochrome c oxidase (Cox) activity was significantly lower in cases with mutations than in those without or controls (P = 0.0008). NADH dehydrogenase activity was only slightly reduced in cases with mutations (P = 0.0388), whereas succinic dehydrogenase activity did not significantly differ between DCM patients with mtDNA mutations and those without or controls. The present study represents the first attempt to detect a morphological, easily identifiable marker to guide mtDNA mutation screening. Pathological mtDNA mutations are associated with ultrastructurally abnormal mitochondria, and reduced Cox activity in a small subgroup of non-otherwise-defined, idiopathic DCMs, in which mtDNA defects may constitute the basis for, or contribute to, the development of congestive heart failure.     

慢性进行性眼外肌瘫痪和Kearns-Sayre综合征的线粒体DNA突变分析

目的 探讨慢性进行性眼外肌瘫痪(chronic progressive external ophthalmoplegia，CPEO)和Kearns-Sayre综合征(Kearns—Sayre syndrome，KSS)的线粒体DINA(mitochondrial DNA，mtDNA)突变特点。方法 用Southern印迹方法检测7例CPEO和4例KSS患者的肌肉组织mtDNA，并进一步用聚合酶链反应产物直接测序来明确缺失的具体范围；用聚合酶链反应-限制性内切酶分析法检测有无mtDNA A3243G点突变。结果 发现5例患者(2例CPEO和3例KSS)存在mtDNA的大片段缺失；1例KSS患者存在A3243G点突变。5例大片段缺失的大小及缺失范围各不相同，从3．0～8．0kb不等，缺失型mtDNA占总mtDNA的比例为37．6％～87．0％。聚合酶链反应产物测序表明这5例缺失类型均未见文献报道。结论 与CPEO和KSS患者相关的最常见的mtDNA突变为大片段缺失，A3243G点突变也可在少数患者中检测到。     

Disorders Associated with Multiple Deletions of Mitochondrial DNA

Multiple deletions of mitochondrial DNA (mtDNA) have recently been described in a number of patients with neurological disorders. Most cases have been clinically characterized by autosomal dominant inheritance, adult onset, and a slowly progressive course with external ophthalmoplegia and muscle weakness. Some patients have had evidence of central or peripheral nervous system involvement or episodes of myoglobinuria. Muscle biopsy findings include ragged-red fibres (RRF), muscle fibres with absent COX-activity and abundant abnormal mitochondria with paracrystalline inclusions. Biochemically, a generalized reduction in the activities of mtDNA-encoded enzymes is observed in skeletal muscle. Southern blotting or PCR analysis reveal multiple populations of deleted mtDNA. The deletions occur at multiple sites between the replication initiation sites, involving a large portion of mtDNA, and most deletions seem to be flanked by direct sequence repeats, shown to be "hot spots" in the case of single large deletions. Apparently, a defect in a nuclear gene results in multiple deletions of mtDNA. Both clinical, genetic and molecular genetic observations indicate heterogeneity of this new disease category, apparently based on a disturbance in the "cross-talk" between the nuclear and the mitochondrial genomes.