Mitochondrial cardiomyopathies: how to identify candidate pathogenic mutations by mitochondrial DNA sequencing, MITOMASTER and phylogeny

Pathogenic mitochondrial DNA (mtDNA) mutations leading to mitochondrial dysfunction can cause cardiomyopathy and heart failure. Owing to a high mutation rate, mtDNA defects may occur at any nucleotide in its 16 569 bp sequence. Complete mtDNA sequencing may detect pathogenic mutations, which can be difficult to interpret because of normal ethnic/geographic-associated haplogroup variation. Our goal is to show how to identify candidate mtDNA mutations by sorting out polymorphisms using readily available online tools. The purpose of this approach is to help investigators in prioritizing mtDNA variants for functional analysis to establish pathogenicity. We analyzed complete mtDNA sequences from 29 Italian patients with mitochondrial cardiomyopathy or suspected disease. Using MITOMASTER and PhyloTree, we characterized 593 substitution variants by haplogroup and allele frequencies to identify all novel, non-haplogroup-associated variants. MITOMASTER permitted determination of each variant''s location, amino acid change and evolutionary conservation. We found that 98% of variants were common or rare, haplogroup-associated variants, and thus unlikely to be primary cause in 80% of cases. Six variants were novel, non-haplogroup variants and thus possible contributors to disease etiology. Two with the greatest pathogenic potential were heteroplasmic, nonsynonymous variants: m.15132T>C in MT-CYB for a patient with hypertrophic dilated cardiomyopathy and m.6570G>T in MT-CO1 for a patient with myopathy. In summary, we have used our automated information system, MITOMASTER, to make a preliminary distinction between normal mtDNA variation and pathogenic mutations in patient samples; this fast and easy approach allowed us to select the variants for traditional analysis to establish pathogenicity.     

Analyses of the mitochondrial mutations in the Chinese patients with sporadic Creutzfeldt–Jakob disease

Pathogenic mitochondrial DNA (mtDNA) mutations leading to mitochondrial dysfunction can cause a variety of chronic diseases in central nervous system (CNS). However, the role of mtDNA mutations in sporadic Creutzfeldt–Jakob disease (sCJD) has still been unknown. In this study, we comparatively analyzed complete mtDNA sequences of 31 Chinese sCJD patients and 32 controls. Using MITOMASTER and PhyloTree, we characterized 520 variants in sCJD patients and 507 variants in control by haplogroup and allele frequencies. We classified the mtDNAs into 40 sub-haplogroups of 5 haplogroups, most of them being Asian-specific haplogroups. Haplogroup U, an European-specific haplogroups mtDNA, was found only in sCJD. The analysis to control region (CR) revealed a 31% increase in the frequency of mtDNA CR mutations in sCJD versus controls. In functional elements of the mtDNA CR, six CR mutations were in conserved sequence blocks I (CSBI) in sCJD, while only one in control (P<0.05). More mutants in transfer ribonucleic acid-Leu (tRNA-Leu) were detected in sCJD. The frequencies of two synonymous amino-acid changes, m.11467A>G, p.(=) in NADH dehydrogenase subunit 4 (ND4) and m.12372G>A, p.(=) in NADH dehydrogenase subunit 5 (ND5), in sCJD patients were higher than that of controls. Our study, for the first time, screened the variations of mtDNA of Chinese sCJD patients and identified some potential disease-related mutations for further investigations.     

Comparative analysis of the complete mitochondrial genome between Tibetan and Han population

OBJECTIVE: To construct the haplogroup and perform an analysis of mitochondrial whole-genome sequence in Tibetan and Han Chinese. Variations of nucleotide of mitochondrial DNA (mtDNA) were identified and compared between the Tibetan and Han population. METHODS: The mtDNA whole sequences of 40 Tibetan and 50 Han individuals were sequenced by an Applied Biosystems 3730 DNA automatic sequencer. The sequences were assembled using software phredPhrap16.0, and all assembled sequences were manually verified according to the criterion of rCRS (revised Cambridge Reference Sequence). The haplogroups of mtDNA were constructed using phylogenetic analysis according to the criteria of MITOMAP by Network method. The data were elucidated by integrated methods. RESULTS: Authors' results showed that all the pooled 90 subjects belonged to the Macrohaplogroup M and N, and were classified into 13 haplogroups. No differences were observed among the haplogroups of the two populations except for M9 haplogroup. A total of 21 variants were detected by comparing the mtDNA whole sequences between Tibetan and Han population; of those, 5 variants have not been reported before. In addition, we constructed the haplotypes of 5 variants harboring the D-loop region, and founded prominent difference in both supertype 1 and supertype 2 between Tibetan and Han population. CONCLUSION: The phylogenetic analysis indicates that the Tibetan and Han ethnic groups shared close maternal relationship in origin. The biological implication of the significant variants is worth elucidating; whether they are the results of adaptive selection or neutral selection or pathological variations need to be further studied.     

藏汉民族线粒体基因组全序列的比较研究

目的 以藏汉民族线粒体基因组全序列为基础,进行Haplogroup构建和系统发生分析,在全序列水平上比较核苷酸的变异,阐释可能的变异机制和蕴含的生物学意义.方法 采用Applied Biosystems 3730DNA自动测序仪分别对40名藏族和50名汉族的标本进行线粒体DNA序列测定,应用phredPhrap 16.0软件进行全序列拼接,并以rCRS(revised Cambridge Reference Sequence)为标准与测定序列进行比对分析;根据MTTO-MAP的标准,通过Network方法进行Haplogroup构建和系统发生的分析,并结合其它方法对产生的数据进行深入解读.结果 数据分析结果显示:在系统发生上,藏汉民族90个线粒体DNA序列归类到13个Haplogroups,除M9以外,其它各Haplogroup出现频率之间比较差异无统计学意义;通过两个民族的线粒体DNA全序列比对,发现21个分布频率有统计学意义的变异位点,其中的5个为新变异位点;另外,对D-Loop区的5个突变位点进行了单倍型构建,90个标本可分为2种Supertype,发现在藏汉民族之间Supertypel和Supertype 2的分布频率均有统计学意义.结论 藏汉民族在种族起源和系统发生上具有较近的母系遗传关系;在全序列有统计学意义的位点究竟是适应性或者中性选择,抑或是一种病理性突变尚需深入的探讨.     

Deciphering exome sequencing data: Bringing mitochondrial DNA variants to light

The expanding use of exome sequencing (ES) in diagnosis generates a huge amount of data, including untargeted mitochondrial DNA (mtDNA) sequences. We developed a strategy to deeply study ES data, focusing on the mtDNA genome on a large unspecific cohort to increase diagnostic yield. A targeted bioinformatics pipeline assembled mitochondrial genome from ES data to detect pathogenic mtDNA variants in parallel with the “in‐house” nuclear exome pipeline. mtDNA data coming from off‐target sequences (indirect sequencing) were extracted from the BAM files in 928 individuals with developmental and/or neurological anomalies. The mtDNA variants were filtered out based on database information, cohort frequencies, haplogroups and protein consequences. Two homoplasmic pathogenic variants (m.9035T>C and m.11778G>A) were identified in 2 out of 928 unrelated individuals (0.2%): the m.9035T>C (MT‐ATP6) variant in a female with ataxia and the m.11778G>A (MT‐ND4) variant in a male with a complex mosaic disorder and a severe ophthalmological phenotype, uncovering undiagnosed Leber's hereditary optic neuropathy (LHON). Seven secondary findings were also found, predisposing to deafness or LHON, in 7 out of 928 individuals (0.75%). This study demonstrates the usefulness of including a targeted strategy in ES pipeline to detect mtDNA variants, improving results in diagnosis and research, without resampling patients and performing targeted mtDNA strategies.     

An integrated approach for classifying mitochondrial DNA variants: one clinical diagnostic laboratory’s experience

PurposeThe mitochondrial genome is highly polymorphic. A unique feature of deleterious mitochondrial DNA (mtDNA) mutations is heteroplasmy. Genetic background and variable penetrance also play roles in the pathogenicity for a mtDNA variant. Clinicians are increasingly interested in requesting mtDNA testing. However, interpretation of uncharacterized mtDNA variants is a great challenge. We suggest a stepwise interpretation procedure for clinical service.MethodsWe describe the algorithms used to interpret novel and rare mtDNA variants. mtDNA databases and in silico predictive algorithms are used to evaluate the pathogenic potential of novel and/or rare mtDNA variants.ResultsmtDNA variants can be classified into three categories: benign variants, unclassified variants, and deleterious mutations based on database search and in silico prediction. Targeted DNA sequence analysis of matrilineal relatives, heteroplasmy quantification, and functional studies are useful to classify mtDNA variants.ConclusionClinical significance of a novel or rare variant is critical in the diagnosis of the disease and counseling of the family. Based on the results from clinical, biochemical, and molecular genetic studies of multiple family members, proper interpretation of mtDNA variants is important for clinical laboratories and for patient care.     

Maternal inheritance of mitochondrial DNA polymorphisms in cultured human fibroblasts

We have isolated the total cellular DNA from the cultured diploid fibroblasts of a six-member, three-generation human family. Using a specific radioactive probe for mitochondrial (mt) sequences we have identified new polymorphic variants in this family for the Hhal restriction endonuclease cleavage pattern of the mtDNA. The inheritance of these cleavage patterns verifies the maternal inheritance of mtDNA through all three generations.     

Role of sequence amplification in the generation of nematode mitochondrial DNA polymorphism

Summary Romanomennis culicivorax, an obligate parasitic nematode of mosquitos, possesses an unusually large mitochondrial genome. Individuals are monomorphic for one of several mitochondrial DNA (mtDNA) size variants ranging from 26–32 kb. In this report, we demonstrate that the mitochondrial genome size differential in three isofemale lineages is due to the presence of mtDNA sequences amplified to different copy numbers within each mtDNA molecule. Restriction enzyme analysis and DNA sequencing studies reveal that each mitochondrial genome contains one of two 3.0 kb repeat types that differ by approximately 30 bp. This difference is primarily due to a short (23 bp) imperfect tandem duplication present within the larger of two polymorphic repeating units. The 3.0 kb reiterated DNA sequences are present as direct, tandem repeats and as inverted portions of the same sequence located elsewhere in the genome. Based on mtDNA analysis of an independently reared R. culicivorax culture, we conclude that events resulting in mitochondrial genome rearrangement occurred in natural field populations prior to propagation within the laboratory.     

Characterization of mtDNA variation in a cohort of South African paediatric patients with mitochondrial disease

Mitochondrial disease can be attributed to both mitochondrial and nuclear gene mutations. It has a heterogeneous clinical and biochemical profile, which is compounded by the diversity of the genetic background. Disease-based epidemiological information has expanded significantly in recent decades, but little information is known that clarifies the aetiology in African patients. The aim of this study was to investigate mitochondrial DNA variation and pathogenic mutations in the muscle of diagnosed paediatric patients from South Africa. A cohort of 71 South African paediatric patients was included and a high-throughput nucleotide sequencing approach was used to sequence full-length muscle mtDNA. The average coverage of the mtDNA genome was 81±26 per position. After assigning haplogroups, it was determined that although the nature of non-haplogroup-defining variants was similar in African and non-African haplogroup patients, the number of substitutions were significantly higher in African patients. We describe previously reported disease-associated and novel variants in this cohort. We observed a general lack of commonly reported syndrome-associated mutations, which supports clinical observations and confirms general observations in African patients when using single mutation screening strategies based on (predominantly non-African) mtDNA disease-based information. It is finally concluded that this first extensive report on muscle mtDNA sequences in African paediatric patients highlights the need for a full-length mtDNA sequencing strategy, which applies to all populations where specific mutations is not present. This, in addition to nuclear DNA gene mutation and pathogenicity evaluations, will be required to better unravel the aetiology of these disorders in African patients.     

Thymidine kinase 2 mutations in autosomal recessive progressive external ophthalmoplegia with multiple mitochondrial DNA deletions

Autosomal-inherited progressive external ophthalmoplegia (PEO) is an adult-onset disease characterized by the accumulation of multiple mitochondrial DNA (mtDNA) deletions in post-mitotic tissues. Mutations in six different genes have been described to cause the autosomal dominant form of the disease, but only mutations in the DNA polymerase gamma gene are known to cause autosomal recessive PEO (arPEO), leaving the genetic background of arPEO mostly unknown. Here we used whole-exome sequencing and identified compound heterozygous mutations, leading to two amino acid alterations R225W and a novel T230A in thymidine kinase 2 (TK2) in arPEO patients. TK2 is an enzyme of the mitochondrial nucleotide salvage pathway and its loss-of-function mutations have previously been shown to underlie the early-infantile myopathic form of mtDNA depletion syndrome (MDS). Our TK2 activity measurements of patient fibroblasts and mutant recombinant proteins show that the combination of the identified arPEO variants, R225W and T230A, leads to a significant reduction in TK2 activity, consistent with the late-onset phenotype, whereas homozygosity for R225W, previously associated with MDS, leads to near-total loss of activity. Our finding identifies a new genetic cause of arPEO with multiple mtDNA deletions. Furthermore, MDS and multiple mtDNA deletion disorders are manifestations of the same pathogenic pathways affecting mtDNA replication and repair, indicating that MDS-associated genes should be studied when searching for genetic background of PEO disorders.     

Chip-based mtDNA mutation screening enables fast and reliable genetic diagnosis of OXPHOS patients.

PURPOSE: Oxidative phosphorylation is under dual genetic control of the nuclear and the mitochondrial DNA (mtDNA). Oxidative phosphorylation disorders are clinically and genetically heterogeneous, which makes it difficult to determine the genetic defect, and symptom-based protocols which link clinical symptoms directly to a specific gene or mtDNA mutation are falling short. Moreover, approximately 25% of the pediatric patients with oxidative phosphorylation disorders is estimated to have mutations in the mtDNA and a standard screening approach for common mutations and deletions will only explain part of these cases. Therefore, we tested a new CHIP-based screening method for the mtDNA. METHODS: MitoChip (Affymetrix) resequencing was performed on three test samples and on 28 patient samples. RESULTS: Call rates were 94% on average and heteroplasmy detection levels varied from 5-50%. A genetic diagnosis can be made in almost one-quarter of the patients at a potential output of 8 complete mtDNA sequences every 4 days. Moreover, a number of potentially pathogenic unclassified variants (UV) were detected. CONCLUSIONS: The availability of long-range PCR protocols and the predominance of single nucleotide substitutions in the mtDNA make the resequencing CHIP a very fast and reliable method to screen the complete mtDNA for mutations.     

Updating the East Asian mtDNA phylogeny: a prerequisite for the identification of pathogenic mutations

Knowledge about the world phylogeny of human mitochondrial DNA (mtDNA) is essential not only for evaluating the pathogenic role of specific mtDNA mutations but also for performing reliable association studies between mtDNA haplogroups and complex disorders. In the past few years, the main features of the East Asian portion of the mtDNA phylogeny have been determined on the basis of complete sequencing efforts, but representatives of several basal lineages were still lacking. Moreover, some recently published complete mtDNA sequences did apparently not fit into the known phylogenetic tree and conflicted with the established nomenclature. To refine the East Asian mtDNA tree and resolve data conflicts, we first completely sequenced 20 carefully selected mtDNAs--likely representatives of novel sub-haplogroups--and then, in order to distinguish diagnostic mutations of novel haplogroups from private variants, we applied a 'motif-search' procedure to a large sample collection. The novel information was incorporated into an updated East Asian mtDNA tree encompassing more than 1000 (near-) complete mtDNA sequences. A reassessment of the mtDNA data from a series of disease studies testified to the usefulness of such a refined mtDNA tree in evaluating the pathogenicity of mtDNA mutations. In particular, the claimed pathogenic role of mutations G3316A, T3394C, A4833G and G15497A appears to be most questionable as those initial claims were derived from anecdotal findings rather than e.g. appropriate association studies. Following a guideline based on the phylogenetic knowledge as proposed here could help avoiding similar problems in the future.     

Quantitative allele-specific PCR: Demonstration of age-associated accumulation in human tissues of the A→G mutation at nucleotide 3243 in mitochondrial DNA

We have developed an improved allele-specific polymerase chain reaction (AS-PCR) procedure that can selectively amplify mutant DNA sequences (which differ from the normal sequences by a single base pair) in the presence of large excess of normal sequences. We applied this procedure to quantification of mutant molecules of human mitochondrial DNA (mtDNA). Conditions for AS-PCR have been systematically varied, encompassing DNA template input, annealing temperature, and PCR cycle number. Adjustment of these three reaction parameters to optimal conditions, using plasmids containing cloned segments of mutant and normal mtDNA, enabled the reliable detection of as little as 0.01% of mutant mtDNA. By standardising the DNA input for AS-PCR, the percentage of mutant molecules can be accurately quantified. This improved procedure was used here to detect and quantify the base substitution at nucleotide position 3243 (A→G) in mtDNA from total cellular DNA isolated from various tissues of both infants and adults. We observed a 5- to 10-fold higher mutant mtDNA (3243 A→G) frequency in adult tissues than in infant tissues. The results are consistent with the hypothesis that the accumulation of mtDNA mutations is an important feature of the human aging process. The quantitative and sensitive allele-specific amplification system described here is applicable to the quantification of low levels of somatic mutations in oncogenes and tumour suppressor genes in the context of human mutation, and could be extended to any biological situation in which only a small proportion of a DNA molecular population is subjected to a particular base substitution. Hum Mutat 9: 265–271, 1997. © 1997 Wiley-Liss, Inc.     

Mitochondrial DNA Polymerase γ Mutations and Their Implications in mtDNA Alterations in Colorectal Cancer

Mitochondrial DNA was found to be highly mutated in colorectal cancer cells. One of the key molecules involved in the maintenance of the mitochondrial genome is the nuclear‐encoded polymerase gamma. The aim of our study was to determine if there is a link between polymorphisms within the polymerase gamma gene (POLG) and somatic mutations within the mitochondrial genome in cancer cells. We investigated POLG sequence variability in 50 colorectal cancer patients whose complete mitochondrial genome sequences were determined. Relative mtDNA copy number was also determined. We identified 251 sequence variants in the POLG gene. Most of them were germline‐specific (～92%). Twenty‐one somatic changes in POLG were found in 10 colorectal cancer patients. We have found no association between the occurrence of mtDNA somatic mutations and the somatically occurring variants in POLG. MtDNA content was reduced in patients carrying somatic variants in POLG or germline nucleotide variants located in the region encoding the POLG polymerase domain, but the difference did not reach statistical significance. Our findings suggest that somatic mtDNA mutations occurring in colorectal cancer are not a consequence of somatic mutations in POLG. Nevertheless, POLG nucleotide variants may lead to a decrease in mtDNA content, and consequently result in mitochondrial dysfunction.     

Single‐fiber studies for assigning pathogenicity of eight mitochondrial DNA variants associated with mitochondrial diseases

Whole mitochondrial DNA (mtDNA) sequencing is now systematically used in clinical laboratories to screen patients with a phenotype suggestive of mitochondrial disease. Next Generation Sequencing (NGS) has significantly increased the number of identified pathogenic mtDNA variants. Simultaneously, the number of variants of unknown significance (VUS) has increased even more, thus challenging their interpretation. Correct classification of the variants' pathogenicity is essential for optimal patient management, including treatment and genetic counseling. Here, we used single muscle fiber studies to characterize eight heteroplasmic mtDNA variants, among which were three novel variants. By applying the pathogenicity scoring system, we classified four variants as “definitely pathogenic” (m.590A>G, m.9166T>C, m.12293G>A, and m.15958A>T). Two variants remain “possibly pathogenic” (m.4327T>C and m.5672T>C) but should these be reported in a different family, they would be reclassified as “definitely pathogenic.” We also illustrate the contribution of single‐fiber studies to the diagnostic approach in patients harboring pathogenic variants with low level heteroplasmy.     

A compendium of human mitochondrial DNA control region: development of an international standard forensic database

A compendium of human mitochondrial DNA (mtDNA) control region types has been constructed. This updated compilation indexes over 10,000 population-specific mtDNA nucleotide sequences in a standardized format. The sequences represent mtDNA types from the Scientific Working Group on DNA Analysis Methods (SWGDAM) mtDNA database and from the public literature. The SWGDAM data are considered to be of higher quality than the public data, particularly for counting the number of times a particular haplotype has been observed.     

Mitochondrial DNA somatic mutations (point mutations and large deletions) and mitochondrial DNA variants in human thyroid pathology: a study with emphasis on Hürthle cell tumors

In an attempt to progress in the understanding of the relationship of mitochondrial DNA (mtDNA) alterations and thyroid tumorigenesis, we studied the mtDNA in 79 benign and malignant tumors (43 Hürthle and 36 non-Hürthle cell neoplasms) and respective normal parenchyma. The mtDNA common deletion (CD) was evaluated by semiquantitative polymerase chain reaction. Somatic point mutations and sequence variants of mtDNA were searched for in 66 tumors (59 patients) and adjacent parenchyma by direct sequencing of 70% of the mitochondrial genome (including all of the 13 OXPHOS system genes). We detected 57 somatic mutations, mostly transitions, in 34 tumors and 253 sequence variants in 59 patients. Follicular and papillary carcinomas carried a significantly higher prevalence of non-silent point mutations of complex I genes than adenomas. We also detected a significantly higher prevalence of complex I and complex IV sequence variants in the normal parenchyma adjacent to the malignant tumors. Every Hürthle cell tumor displayed a relatively high percentage (up to 16%) of mtDNA CD independently of the lesion's histotype. The percentage of deleted mtDNA molecules was significantly higher in tumors with D-loop mutations than in mtDNA stable tumors. Sequence variants of the ATPase 6 gene, one of the complex V genes thought to play a role in mtDNA maintenance and integrity in yeast, were significantly more prevalent in patients with Hürthle cell tumors than in patients with non-Hürthle cell neoplasms. We conclude that mtDNA variants and mtDNA somatic mutations of complex I and complex IV genes seem to be involved in thyroid tumorigenesis. Germline polymorphisms of the ATPase 6 gene are associated with the occurrence of mtDNA CD, the hallmark of Hürthle cell tumors.     

Evidence for adaptive selection acting on the tRNA and rRNA genes of human mitochondrial DNA

In order to identify putative adaptive human mitochondrial DNA (mtDNA), transfer RNA (tRNA), and ribosomal RNA (rRNA) variants, we assembled a sequential mutational tree from 2,460 human mtDNA coding sequences, thus providing the relative age of all mtDNA sequence variants. Deleterious mutations affect evolutionarily conserved nucleotides and have been eliminated from the older internal branches of the tree by purifying selection, while beneficial mutations also alter conserved nucleotides but have been enriched in the internal branches of the tree by adaptive selection. Neutral polymorphisms alter poorly conserved nucleotides and are distributed throughout the tree. Stem nucleotides are more constrained than loop nucleotides. The functional importance of both types of nucleotide variants was assessed by comparison to the average evolutionary conservation index (CI) of all known pathogenic tRNA mutations, thus permitting discrimination between internal branch neutral and adaptive tRNA variants. This revealed that 19% of the stem and 13% of the loop internal branch tRNA variants were potentially adaptive. Since few pathogenic rRNA mutations are known, evidence for adaptive rRNA variation was revealed by higher stem to loop variant ratios and elevated CIs in the internal branches vs. external branches. Moreover, variants among stem noncanonical apposition bases predominantly created new Watson-Crick (WC) base pairs, thus also suggesting adaptive selection. Among the putative adaptive tRNA and rRNA polymorphisms, a number were found to occur at the base of the branches of the tree, to have recurred multiple times, and to be associated with altered human phenotypes. Therefore, a significant portion of ancient tRNA and rRNA polymorphisms appear to have been adaptive, and these are affecting human health today.     

Use of stereotypical mutational motifs to define resolution limits for the ultra-deep resequencing of mitochondrial DNA

Massively parallel resequencing of mitochondrial DNA (mtDNA) has led to significant advances in the study of heteroplasmic mtDNA variants in health and disease, but confident resolution of very low-level variants (<2% heteroplasmy) remains challenging due to the difficulty in distinguishing signal from noise at this depth. However, it is likely that such variants are precisely those of greatest interest in the study of somatic (acquired) mtDNA mutations. Previous approaches to this issue have included the use of controls such as phage DNA and mtDNA clones, both of which may not accurately recapitulate natural mtDNA. We have therefore explored a novel approach, taking advantage of mtDNA with a known stereotyped mutational motif (nAT>C, from patient with MNGIE, mitochondrial neurogastrointestinal encephalomyopathy) and comparing mutational pattern distribution with healthy mtDNA by ligation-mediated deep resequencing (Applied Biosystems SOLiD). We empirically derived mtDNA-mutant heteroplasmy detection limits, demonstrating that the presence of stereotypical mutational motif could be statistically validated for heteroplasmy thresholds ≥0.22% (P=0.034). We therefore provide empirical evidence from biological samples that very low-level mtDNA mutants can be meaningfully resolved by massively parallel resequencing, confirming the utility of the approach for studying somatic mtDNA mutation in health and disease. Our approach could also usefully be employed in other settings to derive platform-specific deep resequencing resolution limits.     

Maternal inheritance and mitochondrial DNA variants in familial Parkinson's disease

Background  

Mitochondrial function is impaired in Parkinson's disease (PD) and may contribute to the pathogenesis of PD, but the causes of mitochondrial impairment in PD are unknown. Mitochondrial dysfunction is recapitulated in cell lines expressing mitochondrial DNA (mtDNA) from PD patients, implicating mtDNA variants or mutations, though the role of mtDNA variants or mutations in PD risk remains unclear. We investigated the potential contribution of mtDNA variants or mutations to the risk of PD.