线粒体病的分子遗传学研究

近两年来,人mtDNA研究方法的改进,使人线粒体病的分子遗传学研究取得重大进展。Holt和Zeviani于1988年先后在线粒体脑肌病患者的肌肉组织中发现mtDNA的缺失,缺失2～7kb左右,且大多位于mtDNA的D-Loop区,此后,Wallace又在Leber氏遗传性视神经网膜病患者中找到了mtDNA编码NADH脱氢酶的某个基因的点突变。mtDNA在人类疾病中的地位愈来愈受到重视,研究mtDNA突变与线粒体病之间的关系,以及mtDNA的选择性复制机制都有助于揭开线粒体病的本质,从而达到对此病的诊断、预防和治疗。     

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。     

人类线粒体一独特的细胞器或机能网络吗?

新近，与人类多种疾病有关的线粒体DNA（mtD-NA）突变已被确定。与这些突又｛大的致加＿｛5、未知，但有一点是清楚的，u线粒体负传学兀。；E个问题需要更g的了晚。问包上一是，南个人体细胞中数千个mtDNA分子是共存于一个大的线粒体网格中，还是它们2～10个分离成上百个独立的线粒体。与rntDNA相关的疾病都具有突变型与野生型mtDNA间不同比例的特征，且两基因组相互作用潜势均取决干线粒体结构。不久前，有两个研究组已着手提出课题，但他们的观点明显矛盾。双方都使用去核细胞胞质杂种融合技术，使古h一种线粒体的细胞与含有另一种…     

伴随线粒体DNA异胞质基因的新线粒体病

30～40%线粒体肌病病例表现为肌肉线粒体DNA(mtDNA)部分缺失,有2例报道白细胞mtDNA中有一群衔接重复。本文乃报道有些与线粒体肌病临床特征相同的母系遗传疾病,受累者有mtDNA异胞质基因,正常mtDNA的混合和在血和肌肉一群含有在8993部位核苷酸变化。索引病例(例1),女,47岁,12岁时发生夜盲,诊断为色素性视网膜炎。24岁时有全身性癫痫发作用苯妥英治疗。30岁时突     

儿童线粒体病的诊断与治疗研究进展

线粒体病（MD）是指原发于线粒体能量合成系统（MEGS）功能异常所引起的一组特定的疾病.目前已知有5种原因可致MEGS功能障碍,包括线粒体呼吸链（MRC）功能障碍、丙酮酸代谢障碍、三羧酸循环障碍、脂肪酸氧化障碍和肌酸代谢障碍,其中由线粒体DNA（mtDNA）和核DNA（nDNA）突变所致呼吸链传递障碍是MD最常见的原因[1].mtDNA的致病突变率至少为1/8 000[2],而Lamont等[3]发现大部分MD患儿为nDNA突变所致,Skladal等[4]报道遗传性MD（包括mtDNA和nDNA突变）的发病率高达1/5 000活产儿,随着诊断水平的提高,MD的发病率逐渐上升[5,6].MD临床表现复杂多样,仅20%的患者具有临床综合征的表现[7],目前缺乏公认的诊断标准和有效的治疗方法,病死率高达46%,其中80%在3岁以下死亡[8].本文对儿童MD的诊断与治疗进展加以综述.     

不同临床表型的线粒体脑病癫癎发作特点

线粒体脑肌病（mitochondrial encephalomyopa-thy，ME）是线粒体脱氧核糖核酸（mtDNA）发生突变导致线粒体结构错乱和功能障碍、三磷腺苷（ATP）合成不足所致以脑和骨骼机症候群为主的多系统受累疾病，多数为母系遗传,以侵犯中枢神经系统为主则称之为线粒体脑病。ME的临床分型众多，目前尚无统一的诊断标准。临床高度怀疑线粒体病的患者，表型上具有明显的症状和体征，例如眼睑下垂，易疲劳或近端肌无力等，详尽的家族史对诊断有帮助，最为重要的是母亲的患病史和生育史、家系中有儿童死亡病史。尽管有或无症候群的线粒体病大多频繁的表现有部分性或全面性的发作，但有关线粒体病癫痼的信息非常缺乏。线粒体病呈现明显的遗传异质性，基因型与临床表型的关系复杂。     

线粒体病与癫癎的研究进展

1概述
　　线粒体病是由于线粒体功能障碍导致ATP（三磷酸腺苷）合成障碍、能量来源不足的一组异质性疾病。ATP主要在线粒体呼吸链中生产，呼吸链由5个大型多亚基复合物组成，包含80多种蛋白质，这些蛋白质由核DNA和mtDNA（线粒体DNA）共同编码，使得线粒体疾病不仅表现出母系遗传的特点，也同时遵循孟德尔经典遗传定律。人体生长发育中，由于不同组织对能量的需求量不同，线粒体的分布也不尽相同。所以线粒体功能障碍在诸如中枢神经系统、心脏、肌肉、肝脏、肾脏等高代谢器官中更容易体现。线粒体病单纯引起神经肌肉的症状，称之线粒体肌病，若累及到脑部，称线粒体脑肌病。线粒体病还可以引起糖尿病、贫血、耳聋、胃功能紊乱等。     

线粒体遗传与人类系统性高血压

线粒体DNA(mitochondrial DNA,mtDNA)具有母系遗传的特点,由mtDNA突变引起的家族性线粒体疾病常累及心、脑、骨骼肌等高能耗器官.近年来,研究者发现部分原发性高血压患者具有典型的母系遗传特点,从而证实并丰富了mtDNA突变在母系遗传性高血压中的作用.然而,一些根本的共性问题仍然有待于进一步的研究与探讨.本文就线粒体基因组的进化、mtDNA的遗传方式、mtDNA突变在母系遗传性高血压中的分子机理进行综述,并对今后的研究方向提出设想.     

Leber氏遗传性视神经病的分子遗传学

Leber氏遗传性视神经病是由于线粒体DNA(mtDNA)损伤所致遗传病。与核DNA不同,mtDNA为闭合,环状双链分子,且以多拷贝存在于细胞中。这些特点决定了mtDNA损伤所致遗传病具有不同于一般核DNA遗传病的特殊之处。本文对Leber氏遗传性视神经病在mtDNA中的突变位点,mtDNA杂合型,组织间差异性以及mtDNA和核DNA互作等方面都作了较为详细的综述,最后还介绍了Leber氏遗传性视神经病基因诊断的研究进展。     

线粒体DNA D-Loop区突变与肿瘤

线粒体DNA(mitochondrialDNA, mtDNA)是独立于细胞核DNA外的遗传物质.过去十多年的研究表明线粒体功能异常以及线粒体DNA(mitochondrial DNA,mtDNA)突变和人类肿瘤形成与发展之间密切相关.本文将目前对线粒体DNA D-Loop区突变与肿瘤之间的研究加以简单的介绍,以利于人们了解线粒体,便于日后对其进行更深层次的研究.     

Approaches to mitochondrial gene therapy

Since their discovery during the end of the 80's the number of diseases found to be associated with defects in the mitochondrial genome has grown significantly. Organs affected by mutations in mitochondrial DNA (mtDNA) include in decreasing order of vulnerability the brain, skeletal muscle, heart, kidney and liver. Hence neuromuscular and neurodegenerative diseases represent the two largest groups of mtDNA diseases. Despite major advances in understanding mtDNA defects at the genetic and biochemical level, there is however no satisfactory treatment available to the vast majority of patients. This is largely due to the fact that most of these patients have respiratory chain defects, i.e. defects that involve the final common pathway of oxidative metabolism, making it impossible to bypass the defect by administering alternative metabolic carriers of energy. Conventional biochemical treatment having reached an impasse, the exploration of gene therapeutic approaches for patients with mtDNA defects is warranted. For now mitochondrial gene therapy appears to be only theoretical and speculative. Any possibility for gene replacement is dependent on the development of an efficient mitochondrial transfection vector. In this review we describe the current state of the development of mitochondria-specific DNA delivery systems. We summarize our own efforts in exploring the properties of dequalinium and other similar cationic bolaamphiphiles with delocalized charge centers, for the design of a vector suited for the transport of DNA to mitochondria in living cells. Further, we outline some unique hurdles that need to be overcome if the development of such delivery systems is to progress.     

The pathophysiology of mitochondrial disease as modeled in the mouse

It is now clear that mitochondrial defects are associated with a plethora of clinical phenotypes in man and mouse. This is the result of the mitochondria''s central role in energy production, reactive oxygen species (ROS) biology, and apoptosis, and because the mitochondrial genome consists of roughly 1500 genes distributed across the maternal mitochondrial DNA (mtDNA) and the Mendelian nuclear DNA (nDNA). While numerous pathogenic mutations in both mtDNA and nDNA mitochondrial genes have been identified in the past 21 years, the causal role of mitochondrial dysfunction in the common metabolic and degenerative diseases, cancer, and aging is still debated. However, the development of mice harboring mitochondrial gene mutations is permitting demonstration of the direct cause-and-effect relationship between mitochondrial dysfunction and disease. Mutations in nDNA-encoded mitochondrial genes involved in energy metabolism, antioxidant defenses, apoptosis via the mitochondrial permeability transition pore (mtPTP), mitochondrial fusion, and mtDNA biogenesis have already demonstrated the phenotypic importance of mitochondrial defects. These studies are being expanded by the recent development of procedures for introducing mtDNA mutations into the mouse. These studies are providing direct proof that mtDNA mutations are sufficient by themselves to generate major clinical phenotypes. As more different mtDNA types and mtDNA gene mutations are introduced into various mouse nDNA backgrounds, the potential functional role of mtDNA variation in permitting humans and mammals to adapt to different environments and in determining their predisposition to a wide array of diseases should be definitively demonstrated.     

The novel mitochondrial tRNAAsn gene mutation m.5709T>C produces ophthalmoparesis and respiratory impairment

Although mutations in mitochondrial tRNAs constitute the most common mtDNA defect, the presence of pathological variants in mitochondrial tRNA(Asn) is extremely rare. We were able to identify a novel mtDNA tRNA(Asn) gene pathogenic mutation associated with a myopathic phenotype and a previously unreported respiratory impairment. Our proband is an adult woman with ophthalmoparesis and respiratory impairment. Her muscle biopsy presented several cytochrome c oxidase-negative (COX-) fibres and signs of mitochondrial proliferation (ragged red fibres). Sequence analysis of the muscle-derived mtDNA revealed an m.5709T>C substitution, affecting mitochondrial tRNA(Asn) gene. Restriction-fragment length polymorphism analysis of the mutation in isolated muscle fibres showed that a threshold of at least 91.9% mutated mtDNA results in the COX deficiency phenotype. The new phenotype further increases the clinical spectrum of mitochondrial diseases caused by mutations in the tRNA(Asn) gene.     

Delivery of bioactive molecules to the mitochondrial genome using a membrane-fusing, liposome-based carrier, DF-MITO-Porter

Mitochondrial dysfunction has been implicated in a variety of human diseases. It is now well accepted that mutations and defects in the mitochondrial genome form the basis of these diseases. Therefore, mitochondrial gene therapy and diagnosis would be expected to have great medical benefits. To achieve such a strategy, it will be necessary to deliver therapeutic agents into mitochondria in living cells. We report here on an approach to accomplish this via the use of a Dual Function (DF)-MITO-Porter, aimed at the mitochondrial genome, so-called mitochondrial DNA (mtDNA). The DF-MITO-Porter, a nano carrier for mitochondrial delivery, has the ability to penetrate the endosomal and mitochondrial membranes via step-wise membrane fusion. We first constructed a DF-MITO-Porter encapsulating DNase I protein as a bioactive cargo. It was expected that mtDNA would be digested, when the DNase I was delivered to the mitochondria. We observed the intracellular trafficking of the carriers, and then measured mitochondrial activity and mtDNA-levels after the delivery of DNase I by the DF-MITO-Porter. The findings confirm that the DF-MITO-Porter effectively delivered the DNase I into the mitochondria, and provides a demonstration of its potential use in therapies that are selective for the mitochondrial genome.     

Diseases caused by nuclear genes affecting mtDNA stability

Diseases caused by nuclear genes that affect mitochondrial DNA (mtDNA) stability are an interesting group of mitochondrial disorders, involving both cellular genomes. In these disorders, a primary nuclear gene defect causes secondary mtDNA loss or deletion formation, which leads to tissue dysfunction. Therefore, the diseases clinically resemble those caused by mtDNA mutations, but follow a Mendelian inheritance pattern. Several clinical entities associated with multiple mtDNA deletions have been characterized, the most frequently described being autosomal dominant progressive external ophthalmoplegia (adPEO). MtDNA depletion syndrome (MDS) is a severe disease of childhood, in which tissue-specific loss of mtDNA is seen. Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) patients may have multiple mtDNA deletions and/or mtDNA depletion. Recent reports of thymidine phosphorylase mutations in MNGIE and adenine nucleotide translocator mutations in adPEO have given new insights into the mechanisms of mtDNA maintenance in mammals. The common mechanism underlying both of these gene defects could be disturbed mitochondrial nucleoside pools, the building blocks of mtDNA. Future studies on MNGIE and adPEO pathogenesis, and identification of additional gene defects in adPEO and MDS will provide further understanding about the mammalian mtDNA maintenance and the crosstalk between the nuclear and mitochondrial genomes.     

False positive results of mitochondrial DNA depletion/deletion due to single nucleotide substitutions causing appearance of additional PvuII restriction sites.

Human mitochondrial diseases are usually caused by dysfunction of mitochondrial DNA (mtDNA), particularly by point mutations, deletions, or depletions. In commonly used procedures for molecular diagnostics of mitochondrial dysfunction, one of the first steps is linearization of circular mitochondrial genomes with either BamHI or PvuII restriction endonulease, which cuts human mtDNA at a unique site. Here, we describe a case of false positive results, which suggested mtDNA depletion or a large deletion in a patient's tissue sample. More detailed analysis (mtDNA sequencing) revealed that these false positive results were caused by the presence of the 12753A>G substitution in the gene coding for NADH dehydrogenase subunit 5 (ND5). This substitution results in no change in amino acid sequence of the gene product but creates an additional PvuII site. Investigating a population of 200 patients not affected by mitochondrial diseases, we found an additional case of 12753A>G, and also another substitution, 12804T>C, which also results in no change in amino acid sequence of ND5 but creates an additional PvuII site. A few cases of 12753A>G and 12804T>C substitutions were found previously in Asian, American, African, and European populations (though they were not reported to date in the MITOMAP), but those samples were used in population studies and not tested for mtDNA deletion or depletion. Therefore, we present a cautionary report indicating that these mtDNA polymorphisms exist in various human populations (and thus, they are panethnic) and may cause false positive results of standard molecular analyses, including molecular diagnostics, of human mtDNA.     

Improving upon nature’s somatic mitochondrial DNA therapies

Mitochondrial DNA (mtDNA) directs key metabolic functions in eukaryotic cells. While a number of mtDNA mutations are known causes of human diseases and age-related dysfunctions, some mtDNA haplotypes are associated with extreme longevity. Despite the mutagenic mitochondrial environment naturally enhancing somatic mtDNA mutation rates, mtDNA remains grossly stable along generations of plant and animal species including man. This relative stability can be accounted for by the purging of deleterious mutations by natural selection operating on growing cells, tissues, organisms and populations, as observed in gametogenesis, embryogenesis, oncogenesis and cladogenesis. In the adult multicellular organism, however, mtDNA mutations accumulate in slowly dividing cells, and, to a much higher degree, in postmitotic cells and tissues. Dynamic mitochondrial fusion and fission, by redistributing polymorphic mtDNA molecules; mitophagy, by clearing defective mitochondria and mutated mtDNA; compensatory mutations and mtDNA repair can compensate for the accumulation of mtDNA mutations only to a certain extent, thereby creating a dysfunctional threshold. Here we hypothesize that this threshold is naturally up-regulated by both vertical and horizontal transfers of mtDNA from stem cells or cell types which retain the capacity of purging deleterious mtDNA through cell division and natural selection in the adult organism. When these natural cell and tissue mtDNA reserves are exhausted, artificial mtDNA therapy may provide for additional threshold up-regulation. Replacement of mtDNA has been already successfully accomplished in early stage embryos and stem cells in a number of species including primates. It is thus simply a matter of refinement of technique that somatic mtDNA therapy, i.e., therapy of pathological conditions based on the transfer of mtDNA to somatic eukaryotic cells and tissues, becomes a medical reality.     

The transmission of OXPHOS disease and methods to prevent this

Diseases owing to defects of oxidative phosphorylation (OXPHOS) affect approximately 1 in 8,000 individuals. Clinical manifestations can be extremely variable and range from single-affected tissues to multisystemic syndromes. In general, tissues with a high energy demand, like brain, heart and muscle, are affected. The OXPHOS system is under dual genetic control, and mutations in both nuclear and mitochondrial genes can cause OXPHOS diseases. The expression and segregation of mitochondrial DNA (mtDNA) mutations is different from nuclear gene defects. The mtDNA mutations can be either homoplasmic or heteroplasmic and in the latter case disease becomes manifest when the mutation exceeds a tissue-specific threshold. This mutation load can vary between tissues and often an exact correlation between mutation load and phenotypic expression is lacking. The transmission of mtDNA mutations is exclusively maternal, but the mutation load between embryos can vary tremendously because of a segregational bottleneck. Diseases by nuclear gene mutations show a normal Mendelian inheritance pattern and often have a more constant clinical manifestation. Given the prevalence and severity of OXPHOS disorders and the lack of adequate therapy, existing and new methods for the prevention of transmission of OXPHOS disorders, like prenatal diagnosis (PND), preimplantation genetic diagnosis (PGD), cytoplasmic transfer (CT) and nuclear transfer (NT), are technically and ethically evaluated.