MITOMAP: a human mitochondrial genome database

New Canary Islands Roman mediated settlement hypothesis deduced from coalescence ages of curated maternal indigenous lineages

Numerous genetic studies have contributed to reconstructing the human history of the Canary Islands population. The recent use of new ancient DNA targeted enrichment and next-generation sequencing techniques on new Canary Islands samples have greatly improved these molecular results. However, the bulk of the available data is still provided by the classic mitochondrial DNA phylogenetic and phylogeographic studies carried out on the indigenous, historical, and extant human populations of the Canary Islands. In the present study, making use of all the accumulated mitochondrial information, the existence of DNA contamination and archaeological sample misidentification in those samples is evidenced. Following a thorough review of these cases, the new phylogeographic analysis revealed the existence of a heterogeneous indigenous Canarian population, asymmetrically distributed across the various islands, which most likely descended from a unique mainland settlement. These new results and new proposed coalescent ages are compatible with a Roman-mediated arrival driven by the exploitation of the purple dye manufacture in the Canary Islands.

The genetic identity of the Vedda: A language isolate of South Asia

Linguistic data from South Asia identified several language isolates in the subcontinent. The Vedda, an indigenous population of Sri Lanka, are the least studied amongst them. Therefore, to understand the initial peopling of Sri Lanka and the genetic affinity of the Vedda with other populations in Eurasia, we extensively studied the high-resolution autosomal and mitogenomes from the Vedda population of Sri Lanka. Our autosomal analyses suggest a close genetic link of Vedda with the tribal populations of India despite no evidence of close linguistic affinity, thus suggesting a deep genetic link of the Vedda with these populations. The mitogenomic analysis supports this association by pointing to an ancient link with Indian populations. We suggest that the Vedda population is a genetically drifted group with limited gene flow from neighbouring Sinhalese and Sri Lankan Tamil populations. Interestingly, the genetic ancestry sharing of Vedda neglects the isolation-by-distance model. Collectively, the demography of Sri Lanka is unique, where Sinhalese and Sri Lankan Tamil populations excessively admixed, whilst Vedda largely preserved their isolation and deep genetic association with India.

D-Loop Mutations as Prognostic Markers in Glioblastoma-A Pilot Study

Glioblastoma, a highly aggressive brain tumor, poses significant treatment challenges. A deeper investigation into its molecular complexity is essential for the identification of novel prognostic biomarkers and therapeutic strategies, potentially improving patient outcomes in terms of survival and quality of life. While nuclear DNA mutations have been extensively studied, the role of mitochondrial DNA (mtDNA) mutations, specifically in the D-loop region, remains poorly understood. This prospective case-control study aimed to assess the prognostic significance of the mtDNA D-loop m.16126T>C variant in glioblastoma patients. Immunohistochemistry and droplet digital PCR (ddPCR) were employed for mutation analysis, complemented by statistical analyses and a literature review. The study cohort comprised 22 glioblastoma patients (mean age 59.36 ± 14.17, 12 (54.55%) females), and 25 controls (59.48 ± 13.22, 12 (80%) females). The D-loop m.16126T>C variant was observed in four (18%) of the glioblastoma samples and was associated with shorter median survival (9.5 vs. 18 months; p = 0.016, log-rank test). This study underscores the importance of investigating mtDNA, especially D-loop variants, in glioblastoma, suggesting its potential as a prognostic biomarker and, therefore, its possible therapeutic targets, warranting further exploration.

Mitochondrial genome editing: strategies, challenges, and applications

Mitochondrial DNA (mtDNA), a multicopy genome found in mitochondria, is crucial for oxidative phosphorylation. Mutations in mtDNA can lead to severe mitochondrial dysfunction in tissues and organs with high energy demand. MtDNA mutations are closely associated with mitochondrial and age-related disease. To better understand the functional role of mtDNA and work toward developing therapeutics, it is essential to advance technology that is capable of manipulating the mitochondrial genome. This review discusses ongoing efforts in mitochondrial genome editing with mtDNA nucleases and base editors, including the tools, delivery strategies, and applications. Future advances in mitochondrial genome editing to address challenges regarding their efficiency and specificity can achieve the promise of therapeutic genome editing. [BMB Reports 2024; 57(1): 19-29].

Nuclear-embedded mitochondrial DNA sequences in 66,083 human genomes

DNA transfer from cytoplasmic organelles to the cell nucleus is a legacy of the endosymbiotic event-the majority of nuclear-mitochondrial segments (NUMTs) are thought to be ancient, preceding human speciation^1-3. Here we analyse whole-genome sequences from 66,083 people-including 12,509 people with cancer-and demonstrate the ongoing transfer of mitochondrial DNA into the nucleus, contributing to a complex NUMT landscape. More than 99% of individuals had at least one of 1,637 different NUMTs, with 1 in 8 individuals having an ultra-rare NUMT that is present in less than 0.1% of the population. More than 90% of the extant NUMTs that we evaluated inserted into the nuclear genome after humans diverged from apes. Once embedded, the sequences were no longer under the evolutionary constraint seen within the mitochondrion, and NUMT-specific mutations had a different mutational signature to mitochondrial DNA. De novo NUMTs were observed in the germline once in every 10⁴ births and once in every 10³ cancers. NUMTs preferentially involved non-coding mitochondrial DNA, linking transcription and replication to their origin, with nuclear insertion involving multiple mechanisms including double-strand break repair associated with PR domain zinc-finger protein 9 (PRDM9) binding. The frequency of tumour-specific NUMTs differed between cancers, including a probably causal insertion in a myxoid liposarcoma. We found evidence of selection against NUMTs on the basis of size and genomic location, shaping a highly heterogenous and dynamic human NUMT landscape.

Targeting Mitochondria as a Therapeutic Approach for Parkinson's Disease

Neurodegeneration is among the most critical challenges that involve modern societies and annually influences millions of patients worldwide. While the pathophysiology of Parkinson's disease (PD) is complicated, the role of mitochondrial is demonstrated. The in vitro and in vivo models and genome-wide association studies in human cases proved that specific genes, including PINK1, Parkin, DJ-1, SNCA, and LRRK2, linked mitochondrial dysfunction with PD. Also, mitochondrial DNA (mtDNA) plays an essential role in the pathophysiology of PD. Targeting mitochondria as a therapeutic approach to inhibit or slow down PD formation and progression seems to be an exciting issue. The current review summarized known mutations associated with both mitochondrial dysfunction and PD. The significance of mtDNA in Parkinson's disease pathogenesis and potential PD therapeutic approaches targeting mitochondrial dysfunction was then discussed.

Left ventricular noncompaction: a disorder with genotypic and phenotypic heterogeneity-a narrative review

Background and Objective

Left ventricular noncompaction (LVNC) is a cardiomyopathy characterized by excessive trabecular formation and deep recesses in the ventricular wall, with a bilaminar structure consisting of an endocardial noncompaction layer and an epicardial compacted layer. Although genetic variants have been reported in patients with LVNC, understanding of LVNC and its pathogenesis has not yet been fully elucidated. We addressed the latest findings on genes reported to be associated with LVNC morphogenesis and possible pathologies to understand the diverse spectrum between genotype and phenotype in LVNC. Also, the latest findings and issues related to the diagnosis of LVNC were summarized.

Methods

This article is written as a commentary narrative review and will provide an update on the current literature and available data on common forms of LVNC published in the past 30 years in English through to May 2022 using PubMed.

Key Content and Findings

Familial forms of LVNC are frequent, and autosomal dominant mode of inheritance has been predominantly observed. Several of the candidate causative genes are also mutated in other cardiomyopathies, suggesting a possible shared molecular and/or cellular etiology. The most common gene functions were sarcomere function whereas genes in mice LVNC models were involved in heart development. Echocardiography and cardiac magnetic resonance imaging (CMR) are useful for diagnosis although there are no unified criteria due to overdiagnosis of imaging, poor consistency between techniques, and lack of association between trabecular severity and adverse clinical outcomes.

Conclusions

This review reflects the current lack of clarity regarding the pathogenesis and significance of LVNC and showed the complexity of imaging diagnostic criteria, interpretation of the role of LVNC as a cause, and uncertainty regarding the specific genetic basis of LVNC.

Best practices for the interpretation and reporting of clinical whole genome sequencing

Whole genome sequencing (WGS) shows promise as a first-tier diagnostic test for patients with rare genetic disorders. However, standards addressing the definition and deployment practice of a best-in-class test are lacking. To address these gaps, the Medical Genome Initiative, a consortium of leading health care and research organizations in the US and Canada, was formed to expand access to high quality clinical WGS by convening experts and publishing best practices. Here, we present best practice recommendations for the interpretation and reporting of clinical diagnostic WGS, including discussion of challenges and emerging approaches that will be critical to harness the full potential of this comprehensive test.

Cochlear Implantation in Patients with Mitochondrial Gene Mutation: Decline in Speech Perception in Retrospective Long-Term Follow-Up Study

Clinical evidence of the effectiveness of cochlear implantation for hearing loss with mitochondrial DNA mutation is limited. Most reports have only described short-term postoperative speech perception, which may not reflect the limitations of cochlear implantation caused by progressive retrocochlear dysfunction. The present study aimed to investigate long-term speech perception after cochlear implantation in patients with severe to profound hearing loss associated with mitochondrial DNA mutation. A retrospective chart review was performed on patients with mitochondrial DNA mutation who had undergone cochlear implantation at the Department of Otolaryngology and Head and Neck Surgery at the University of Tokyo Hospital. We extracted data on causative mutations, clinical types, clinical course, perioperative complications, and short-term and long-term postoperative speech perception. Nine patients with mitochondrial DNA mutation underwent cochlear implantation. The mean observation period was 5.5 ± 4.2 years (range, 1–13 years), and seven patients were followed for more than 3 years. Two of the seven patients who initially showed good speech perception exhibited deterioration during long-term follow-up. The absence of an acute progression of cognitive decline in patients, showing a gradual decrease in speech perception, suggests that the deterioration of speech perception was caused by progressive retrocochlear degeneration. Although most patients with mitochondrial DNA mutation maintained good speech perception for more than 3 years after cochlear implantation, retrocochlear degeneration could cause the deterioration of speech perception during long-term follow-up.

Mitochondrial DNA (CA)n dinucleotide repeat variations in Sinhalese and Vedda populations in Sri Lanka

Sinhalese and Vedda people are respectively the major ethnic group and the descendants of the probably earliest inhabitants of Sri Lanka, both believed to have a long history of settlement on the island. However, very little information is available on the origin and possible migration patterns of the two populations. Some studies have focused on (CA) dinucleotide repeat variations located in the mitochondrial hypervariable region 3 (HVS3) (base pairs 514-524) as a useful biomarker to understand migration patterns of different populations. Hence, here we analyze these repeat variations in these two ethnic groups to understand their historical roots and possible patterns of gene flow. Blood samples were collected from healthy, maternally unrelated individuals (N = 109) and mitochondrial D-loop was amplified and sequenced. The (CA)₄ dinucleotide repeat in hypervariable region 3 was detected in the majority of Vedda samples while the remaining samples were defined by a (CA)₅ cluster. In contrast, the (CA)₅ repeat was the most frequent among Sinhalese followed by (CA)₄ and (CA)₇ repeats. Haplogroup diversity of (CA)₄ variation indicated that the majority of Sinhalese individuals grouped into the M30 haplogroup while Vedda clustered into the R5a2b and U7a2 haplogroups. No significant differences in diversity measures were observed among the two populations. However, Multidimensional Scaling indicated a separate clustering for aboriginal Vedda and contemporary Sinhalese populations. Results from this study can be used together with mitochondrial DNA information from hypervariable regions 1 and 2 to perform anthropological and forensic investigations in the two populations studied.

Insight of the mitochondrial genomes of the Orang Asli and Malays: The heterogeneity and the disease-associated variants

Orang Asli are the oldest inhabitants in Peninsular Malaysia that forms as a national minority while the Malays are the majority. The study aimed to screen the mitochondrial genomes of the Orang Asli and the Malays to discover the disease-associated variants. A total of 99 Orang Asli from six tribes (Bateq, Cheq Wong, Orang Kanaq, Kensiu, Lanoh, and Semai) were recruited. Mitochondrial genome sequencing was conducted using a next-generation sequencing platform. Furthermore, we retrieved mitochondrial DNA sequences from the Malays for comparison. The clinical significance, pathogenicity prediction and frequency of variants were determined using online tools. Variants associated with mitochondrial diseases were detected in the 2 populations. A high frequency of variants associated with mitochondrial diseases, breast cancer, prostate cancer, and cervical cancer were detected in the Orang Asli and modern Malays. As medicine evolves to adopt prediction and prevention of diseases, this study highlights the need for intervention to adopt genomics medicine to strategise better healthcare management as a way forward for Precision Health.

Pathogenic Mitochondrial DNA Mutation Load Inversely Correlates with Malignant Features in Familial Oncocytic Parathyroid Tumors Associated with Hyperparathyroidism-Jaw Tumor Syndrome

While somatic disruptive mitochondrial DNA (mtDNA) mutations that severely affect the respiratory chain are counter-selected in most human neoplasms, they are the genetic hallmark of indolent oncocytomas, where they appear to contribute to reduce tumorigenic potential. A correlation between mtDNA mutation type and load, and the clinical outcome of a tumor, corroborated by functional studies, is currently lacking. Recurrent familial oncocytomas are extremely rare entities, and they offer the chance to investigate the determinants of oncocytic transformation and the role of both germline and somatic mtDNA mutations in cancer. We here report the first family with Hyperparathyroidism-Jaw Tumor (HPT-JT) syndrome showing the inherited predisposition of four individuals to develop parathyroid oncocytic tumors. MtDNA sequencing revealed a rare ribosomal RNA mutation in the germline of all HPT-JT affected individuals whose pathogenicity was functionally evaluated via cybridization technique, and which was counter-selected in the most aggressive infiltrating carcinoma, but positively selected in adenomas. In all tumors different somatic mutations accumulated on this genetic background, with an inverse clear-cut correlation between the load of pathogenic mtDNA mutations and the indolent behavior of neoplasms, highlighting the importance of the former both as modifiers of cancer fate and as prognostic markers.

as a Candidate Gene for an Infection-Induced Acute Encephalopathy Characterized by a Cyst and Calcification of the Pons and Cerebellar Atrophy

Three siblings born to Turkish parents from the same village had normal brain development until acute neurological deterioration between 12 months and 8 years of age. Consequent loss of all acquired motor, social, and language functions following infections was associated with a pontine cyst, calcification, and cerebellar atrophy. Exome sequencing revealed a homozygous c.1297G&#x3e;A (p.Gly433Ser) alteration in <i>BEND4</i>, which was predicted to be deleterious in in silico analysis tools and segregated in multiple affected individuals in the family. <i>BEND4</i> has not been associated with any existing disease. Immunofluorescence microscopy analysis of wild-type and mutant BEND4 expressing Vero cells showed nuclear and cytoplasmic localization. Wild-type BEND4 displayed a network-like distribution, whereas mutant BEND4 showed a juxtanuclear distribution pattern. Differential proteome analysis of Vero cells expressing BEND4 revealed that mutant BEND4 expression caused selective increase in reticulocalbin-1 and endoplasmic reticulum resident protein-29. Both proteins are associated with the endoplasmic reticulum and are primarily involved in protein processing and folding pathways. Any defect or stress in protein folding creates stress on cells and may cause chronic damage. This is the first study showing that pathogenic <i>BEND4</i> variants may lead to an infection-induced acute necrotizing encephalopathy as demonstrated in characteristic neuroimaging findings.

Targeted elimination of mutated mitochondrial DNA by a multi-functional conjugate capable of sequence-specific adenine alkylation

Mutations in mitochondrial DNA (mtDNA) cause mitochondrial diseases, characterized by abnormal mitochondrial function. Although eliminating mutated mtDNA has potential to cure mitochondrial diseases, no chemical-based drugs in clinical trials are capable of selective modulation of mtDNA mutations. Here, we construct a class of compounds encompassing pyrrole-imidazole polyamides (PIPs), mitochondria-penetrating peptide, and chlorambucil, an adenine-specific DNA-alkylating reagent. The sequence-selective DNA binding of PIPs allows chlorambucil to alkylate mutant adenine more efficiently than other sites in mtDNA. In vitro DNA alkylation assay shows that our compound 8950A-Chb(Cl/OH) targeting a nonpathogenic point mutation in HeLa S3 cells (m.8950G>A) can specifically alkylate the mutant adenine. Furthermore, the compound reduces the mtDNA possessing the target mutation in cultured HeLa S3 cells. The programmability of PIPs to target different sequences could allow this class of compounds to be developed as designer drugs targeting pathogenic mutations associated with mitochondrial diseases in future studies.

Comparative analysis of nuclear and mitochondrial DNA from tissue and liquid biopsies of colorectal cancer patients

The current standard for molecular profiling of colorectal cancer (CRC) is using resected or biopsied tissue specimens. However, they are limited regarding sampling frequency, representation of tumor heterogeneity, and sampling can expose patients to adverse side effects. The analysis of cell-free DNA (cfDNA) from blood plasma, which is part of a liquid biopsy, is minimally invasive and in principle enables detection of all tumor-specific mutations. Here, we analyzed cfDNA originating from nucleus and mitochondria and investigated their characteristics and mutation status in a cohort of 18 CRC patients and 10 healthy controls using targeted next-generation sequencing (NGS) and digital PCR. Longitudinal analyses of nuclear cfDNA level and size during chemotherapy revealed a decreasing cfDNA content and a shift from short to long fragments, indicating an appropriate therapy response, while shortened cfDNAs and increased cfDNA content corresponded with tumor recurrence. Comparative NGS analysis of nuclear tissue and plasma DNA demonstrated a good patient-level concordance and cfDNA revealed additional variants in three of the cases. Analysis of mitochondrial cfDNA surprisingly revealed a higher plasma copy number in healthy subjects than in CRC patients. These results highlight the potential clinical utility of liquid biopsies in routine diagnostics and surveillance of CRC patients as complementation to tissue biopsies or as an attractive alternative in cases where tissue biopsies are risky or the quantity/quality does not allow testing.

The Isolation and Deep Sequencing of Mitochondrial DNA

In recent years, next-generation sequencing (NGS) has become a powerful tool for studying both inherited and somatic heteroplasmic mitochondrial DNA (mtDNA) variation. NGS has proved particularly powerful when combined with single-cell isolation techniques, allowing the investigation of low-level heteroplasmic variants both between cells and within tissues. Nevertheless, there remain significant challenges, especially around the selective enrichment of mtDNA from total cellular DNA and the avoidance of nuclear pseudogenes. This chapter summarizes the techniques needed to enrich, amplify, sequence, and analyse mtDNA using NGS .

An atlas of mitochondrial DNA genotype-phenotype associations in the UK Biobank

Mitochondrial DNA (mtDNA) variation in common diseases has been underexplored, partly due to a lack of genotype calling and quality-control procedures. Developing an at-scale workflow for mtDNA variant analyses, we show correlations between nuclear and mitochondrial genomic structures within subpopulations of Great Britain and establish a UK Biobank reference atlas of mtDNA-phenotype associations. A total of 260 mtDNA-phenotype associations were new (P < 1 × 10-5), including rs2853822 /m.8655 C>T (MT-ATP6) with type 2 diabetes, rs878966690 /m.13117 A>G (MT-ND5) with multiple sclerosis, 6 mtDNA associations with adult height, 24 mtDNA associations with 2 liver biomarkers and 16 mtDNA associations with parameters of renal function. Rare-variant gene-based tests implicated complex I genes modulating mean corpuscular volume and mean corpuscular hemoglobin. Seven traits had both rare and common mtDNA associations, where rare variants tended to have larger effects than common variants. Our work illustrates the value of studying mtDNA variants in common complex diseases and lays foundations for future large-scale mtDNA association studies.

Mitochondrial DNA mutations contribute to high altitude pulmonary edema via increased oxidative stress and metabolic reprogramming during hypobaric hypoxia

High altitude pulmonary edema (HAPE) is experienced by non-acclimatized sea level individuals on exposure to high altitude hypoxic conditions. Available evidence suggests that genetic factors and perturbed mitochondrial redox status may play an important role in HAPE pathophysiology. However, the precise mechanism has not been fully understood. In the present study, sequencing of mitochondrial DNA (mtDNA) from HAPE subjects and acclimatized controls was performed to identify pathogenic mutations and to determine their role in HAPE. Hypobaric hypoxia induced oxidative stress and metabolic alterations were also assessed in HAPE subjects. mtDNA copy number, mitochondrial oxidative phosphorylation (mtOXPHOS) activity, mitochondrial biogenesis were measured to determine mitochondrial functions. The data revealed that the mutations in Complex I genes affects the secondary structure of protein in HAPE subjects. Further, increased oxidative stress during hypobaric hypoxia, reduced mitochondrial biogenesis and mtOXPHOS activity induced metabolic reprogramming appears to contribute to mitochondrial dysfunctions in HAPE individuals. Haplogroup analysis suggests that mtDNA haplogroup H2a2a1 has potential contribution in the pathobiology of HAPE in lowlanders. This study also suggests contribution of altered mitochondrial functions in HAPE susceptibility.

Mitochondrial Dysfunction in Parkinson's Disease: Focus on Mitochondrial DNA

Mitochondria, the energy stations of the cell, are the only extranuclear organelles, containing their own (mitochondrial) DNA (mtDNA) and the protein synthesizing machinery. The location of mtDNA in close proximity to the oxidative phosphorylation system of the inner mitochondrial membrane, the main source of reactive oxygen species (ROS), is an important factor responsible for its much higher mutation rate than nuclear DNA. Being more vulnerable to damage than nuclear DNA, mtDNA accumulates mutations, crucial for the development of mitochondrial dysfunction playing a key role in the pathogenesis of various diseases. Good evidence exists that some mtDNA mutations are associated with increased risk of Parkinson’s disease (PD), the movement disorder resulted from the degenerative loss of dopaminergic neurons of substantia nigra. Although their direct impact on mitochondrial function/dysfunction needs further investigation, results of various studies performed using cells isolated from PD patients or their mitochondria (cybrids) suggest their functional importance. Studies involving mtDNA mutator mice also demonstrated the importance of mtDNA deletions, which could also originate from abnormalities induced by mutations in nuclear encoded proteins needed for mtDNA replication (e.g., polymerase γ). However, proteomic studies revealed only a few mitochondrial proteins encoded by mtDNA which were downregulated in various PD models. This suggests nuclear suppression of the mitochondrial defects, which obviously involve cross-talk between nuclear and mitochondrial genomes for maintenance of mitochondrial functioning.

Developmental Validation of a MPS Workflow with a PCR-Based Short Amplicon Whole Mitochondrial Genome Panel

For the adoption of massively parallel sequencing (MPS) systems by forensic laboratories, validation studies on specific workflows are needed to support the feasibility of implementation and the reliability of the data they produce. As such, the whole mitochondrial genome sequencing methodology—Precision ID mtDNA Whole Genome Panel, Ion Chef, Ion S5, and Converge—has been subjected to a variety of developmental validation studies. These validation studies were completed in accordance with the Scientific Working Group on DNA Analysis Methods (SWGDAM) validation guidelines and assessed reproducibility, repeatability, accuracy, sensitivity, specificity to human DNA, and ability to analyze challenging (e.g., mixed, degraded, or low quantity) samples. Intra- and inter-run replicates produced an average maximum pairwise difference in variant frequency of 1.2%. Concordance with data generated with traditional Sanger sequencing and an orthogonal MPS platform methodology was used to assess accuracy, and generation of complete and concordant haplotypes at DNA input levels as low as 37.5 pg of nuclear DNA or 187.5 mitochondrial genome copies illustrated the sensitivity of the system. Overall, data presented herein demonstrate that highly accurate and reproducible results were generated for a variety of sample qualities and quantities, supporting the reliability of this specific whole genome mitochondrial DNA MPS system for analysis of forensic biological evidence.

A new method for long-read sequencing of animal mitochondrial genomes: application to the identification of equine mitochondrial DNA variants

BACKGROUND

Mitochondrial DNA is remarkably polymorphic. This is why animal geneticists survey mitochondrial genomes variations for fundamental and applied purposes. We present here an approach to sequence whole mitochondrial genomes using nanopore long-read sequencing. Our method relies on the selective elimination of nuclear DNA using an exonuclease treatment and on the amplification of circular mitochondrial DNA using a multiple displacement amplification step.

RESULTS

We optimized each preparative step to obtain a 100 million-fold enrichment of horse mitochondrial DNA relative to nuclear DNA. We sequenced these amplified mitochondrial DNA using nanopore sequencing technology and obtained mitochondrial DNA reads that represented up to half of the sequencing output. The sequence reads were 2.3 kb of mean length and provided an even coverage of the mitochondrial genome. Long-reads spanning half or more of the whole mtDNA provided a coverage that varied between 118X and 488X. We evaluated SNPs identified using these long-reads by Sanger sequencing as ground truth and found a precision of 100.0%; a recall of 93.1% and a F1-score of 0.964 using the Twilight horse mtDNA reference. The choice of the mtDNA reference impacted variant calling efficiency with F1-scores varying between 0.947 and 0.964.

CONCLUSIONS

Our method to amplify mtDNA and to sequence it using the nanopore technology is usable for mitochondrial DNA variant analysis. With minor modifications, this approach could easily be applied to other large circular DNA molecules.

Specifications of the ACMG/AMP standards and guidelines for mitochondrial DNA variant interpretation

Mitochondrial DNA (mtDNA) variant pathogenicity interpretation has special considerations given unique features of the mtDNA genome, including maternal inheritance, variant heteroplasmy, threshold effect, absence of splicing, and contextual effects of haplogroups. Currently, there are insufficient standardized criteria for mtDNA variant assessment, which leads to inconsistencies in clinical variant pathogenicity reporting. An international working group of mtDNA experts was assembled within the Mitochondrial Disease Sequence Data Resource Consortium and obtained Expert Panel status from ClinGen. This group reviewed the 2015 American College of Medical Genetics and Association of Molecular Pathology standards and guidelines that are widely used for clinical interpretation of DNA sequence variants and provided further specifications for additional and specific guidance related to mtDNA variant classification. These Expert Panel consensus specifications allow for consistent consideration of the unique aspects of the mtDNA genome that directly influence variant assessment, including addressing mtDNA genome composition and structure, haplogroups and phylogeny, maternal inheritance, heteroplasmy, and functional analyses unique to mtDNA, as well as specifications for utilization of mtDNA genomic databases and computational algorithms.

Multi-Omics Approaches to Improve Mitochondrial Disease Diagnosis: Challenges, Advances, and Perspectives

Mitochondrial diseases (MD) are rare disorders caused by deficiency of the mitochondrial respiratory chain, which provides energy in each cell. They are characterized by a high clinical and genetic heterogeneity and in most patients, the responsible gene is unknown. Diagnosis is based on the identification of the causative gene that allows genetic counseling, prenatal diagnosis, understanding of pathological mechanisms, and personalized therapeutic approaches. Despite the emergence of Next Generation Sequencing (NGS), to date, more than one out of two patients has no diagnosis in the absence of identification of the responsible gene. Technologies currently used for detecting causal variants (genetic alterations) is far from complete, leading many variants of unknown significance (VUS) and mainly based on the use of whole exome sequencing thus neglecting the identification of non-coding variants. The complexity of human genome and its regulation at multiple levels has led biologists to develop several assays to interrogate the different aspects of biological processes. While one-dimension single omics investigation offers a peek of this complex system, the combination of different omics data allows the discovery of coherent signatures. The community of computational biologists and bioinformaticians, in order to integrate data from different omics, has developed several approaches and tools. However, it is difficult to understand which suits the best to predict diverse phenotypic outcome. First attempts to use multi-omics approaches showed an improvement of the diagnostic power. However, we are far from a complete understanding of MD and their diagnosis. After reviewing multi-omics algorithms developed in the latest years, we are proposing here a novel data-driven classification and we will discuss how multi-omics will change and improve the diagnosis of MD. Due to the growing use of multi-omics approaches in MD, we foresee that this work will contribute to set up good practices to perform multi-omics data integration to improve the prediction of phenotypic outcomes and the diagnostic power of MD.

Mitochondrial DNA Haplotypes as Genetic Modifiers of Cancer

Mitochondria play an essential role in cellular metabolism, generation of reactive oxygen species (ROS), and the initiation of apoptosis. These properties enable mitochondria to be crucial integrators in the pathways of tumorigenesis. An open question is to what extent variation in the mitochondrial genome (mtDNA) contributes to the biological heterogeneity observed in human tumors. In this review, we summarize our current understanding of the role of mtDNA genetics in relation to human cancers.

Distinguishing mitochondrial DNA and NUMT sequences amplified with the precision ID mtDNA whole genome panel

Nuclear mitochondrial DNA segments (NUMTs) are generated via transfer of portions of the mitochondrial genome into the nuclear genome. Given their common origin, there is the possibility that both the mitochondrial and NUMT segments may co-amplify using the same set of primers. Thus, analysis of the variation of the mitochondrial genome must take into account this co-amplification of mitochondrial and NUMT sequences. The study herein builds on data from the study by Strobl et al. (Strobl et al., 2019), in which multiple point heteroplasmies were called with an "N" to prevent labeling NUMT sequences mimicking mitochondrial heteroplasmy and being interpreted as true mitochondrial in origin sequence variants. Each of these point heteroplasmies was studied in greater detail, both molecularly and bioinformatically, to determine whether NUMT or true mitochondrial DNA variation was present. The bioinformatic and molecular tools available to help distinguish between NUMT and mitochondrial DNA and the effect of NUMT sequences on interpretation were discussed.

Maternally inherited mitochondrial respiratory disorders: from pathogenetic principles to therapeutic implications

Maternally inherited mitochondrial respiratory disorders are rare, progressive, and multi-systemic diseases that remain intractable, with no effective therapeutic interventions. Patients share a defective oxidative phosphorylation pathway responsible for mitochondrial ATP synthesis, in most cases due to pathogenic mitochondrial variants transmitted from mother to child or to a rare de novo mutation or large-scale deletion of the mitochondrial genome. The clinical diagnosis of these mitochondrial diseases is difficult due to exceptionally high clinical variability, while their genetic diagnosis has improved with the advent of next-generation sequencing. The mechanisms regulating the penetrance of the mitochondrial variants remain unresolved with the patient's nuclear background, epigenomic regulation, heteroplasmy, mitochondrial haplogroups, and environmental factors thought to act as rheostats. The lack of animal models mimicking the phenotypic manifestations of these disorders has hampered efforts toward curative therapies. Patient-derived cellular paradigms provide alternative models for elucidating the pathogenic mechanisms and screening pharmacological small molecules to enhance mitochondrial function. Recent progress has been made in designing promising approaches to curtail the negative impact of dysfunctional mitochondria and alleviate clinical symptoms: 1) boosting mitochondrial biogenesis; 2) shifting heteroplasmy; 3) reprogramming metabolism; and 4) administering hypoxia-based treatment. Here, we discuss their varying efficacies and limitations and provide an outlook on their therapeutic potential and clinical application.

Placental mitochondrial DNA mutations and copy numbers in intrauterine growth restricted (IUGR) pregnancy

Intrauterine Growth Restriction (IUGR) is a common and significant complication that arises during pregnancy wherein the fetus fails to attain its full growth potential. Mitochondria being one of the primary sources of energy, plays an important role in placentation and fetal development. In IUGR pregnancy, increased oxidative stress due to inadequate oxygen and nutrient supply could possibly alter mitochondrial functions and homeostasis. In this study, we evaluated the biochemical and molecular changes in mitochondria as biosignature for early and better characterization of IUGR pregnancies. We identified significant increase in mtDNA copy number in both IUGR (p = 0.0001) and Small for Gestational Age (SGA) but healthy (p = 0.0005) placental samples when compared to control. Whole mitochondrial genome sequencing identified novel mutations in both coding and non-coding regions of mtDNA in multiple IUGR placental samples. Sirtuin-3 (Sirt3) protein expression was significantly downregulated (p = 0.027) in IUGR placenta but there was no significant difference in Nrf1 expression in IUGR when compared to control group. Our study provides an evidence for altered mitochondrial homeostasis and paves a way towards interrogating mitochondrial abnormalities in IUGR pregnancies.

Evaluating heteroplasmic variations of the mitochondrial genome from whole genome sequencing data

BACKGROUND

Detecting heteroplasmic variations in the mitochondrial genome can help identify potential pathogenic possibilities, which is significant for disease prevention. The development of next-generation sequencing changed the quantification of mitochondrial DNA (mtDNA) heteroplasmy from scanning limited recorded points to the entire mitochondrial genome. However, due to the presence of nuclear mtDNA homologous sequences (nuMTs), maximally retaining real variations while excluding falsest heteroplasmic variations from nuMTs and sequencing errors presents a dilemma.

RESULTS

Herein, we used an improved method for detecting low-frequency mtDNA heteroplasmic variations from whole genome sequencing data, including point variations and short-fragment length alterations, and evaluated the effect of this method. A two-step alignment was designed and performed to accelerate data processing, to obtain and retain the true mtDNA reads and to eliminate most nuMTs reads. After analyzing whole genome sequencing data of K562 and GM12878 cells, ~90% of heteroplasmic point variations were identified in MitoMap. The results were consistent with the results of an amplification refractory mutation system qPCR. Many linkages of the detected heteroplasmy variations were also discovered.

CONCLUSIONS

Our improved method is a simple, efficient and accurate way to mine mitochondrial low-frequency heteroplasmic variations from whole genome sequencing data. By evaluating the highest misalignment possibility caused by the remaining nuMTs-like reads and sequencing errors, our procedure can detect mtDNA heteroplasmic variations whose heteroplasmy frequencies are as low as 0.2%.

MtBrowse: An integrative genomics browser for human mitochondrial DNA

The human mitochondrion is a unique semi-autonomous organelle with a genome of its own and also requires nuclear encoded components to carry out its functions. In addition to being the powerhouse of the cell, mitochondria plays a central role in several metabolic pathways. It is therefore challenging to delineate the cause-effect relationship in context of mitochondrial dysfunction. Several studies implicate mutations in mitochondrial DNA (mtDNA) in various complex diseases. The human mitochondrial DNA (mtDNA) encodes a set of 37 genes, 13 protein coding, 22 tRNAs and two ribosomal RNAs, which are essential structural and functional components of the electron transport chain. As mentioned above, variations in these genes have been implicated in a broad spectrum of diseases and are extensively reported in literature and various databases. A large number of databases and prediction methods have been published to elucidate the role of human mitochondrial DNA in various disease phenotypes. However, there is no centralized resource to visualize this genotype-phenotype data. Towards this, we have developed MtBrowse: an integrative genomics browser for human mtDNA. As of now, MtBrowse has four categories - Gene, Disease, Reported variation and Variation prediction. These categories have 105 tracks and house data on mitochondrial reference genes, around 600 variants reported in literature with respect to various disease phenotypes and predictions for potential pathogenic variations in protein-coding genes. MtBrowse also hosts genomic variation data from over 5000 individuals on 22 disease phenotypes. MtBrowse may be accessed at http://ab-openlab.csir.res.in/cgi-bin/gb2/gbrowse.

Genetic and phenotypic variation of Phytophthora crassamura isolates from California nurseries and restoration sites

Phenotypic and sequence data were used to characterize 28 isolates resembling Phytophthora megasperma from 14 host species in 2 plant production facilities and 10 restoration sites across the San Francisco Bay Area (California; USA). Size of the oogonia and DNA sequences (nuclear internal transcribed spacer (ITS) and mitochondrial cytochrome c oxidase subunit 1 (COX 1)) were compared, and sensitivity to mefenoxam and pathogenicity were measured. Based on ITS 61 % of isolates matched ex-type sequences of Phytophthora crassamura from Italy, and the remainder matched or were close to the P. megasperma ex-type. However, all California P. crassamura genotypes belonged to four unique COX 1 haplotype lineages isolated from both nurseries and restoration sites. Although lineages were sensitive to mefenoxam, a significant difference in sensitivity was identified, and all continued growth in-vitro. These results suggested previous mefenoxam exposure in plant production facilities resulting in tolerance. In conclusion, all evidence pointed to a nursery origin of novel P. crassamura lineages found in California restoration sites. In this study, COX 1 sequences and oogonia size provided information relevant to identify geographic and evolutionary intraspecific variation within P. crassamura, and was additionally used to track the spread of this species from nurseries into wildlands.

Bioinformatics Tools and Databases to Assess the Pathogenicity of Mitochondrial DNA Variants in the Field of Next Generation Sequencing

The development of next generation sequencing (NGS) has greatly enhanced the diagnosis of mitochondrial disorders, with a systematic analysis of the whole mitochondrial DNA (mtDNA) sequence and better detection sensitivity. However, the exponential growth of sequencing data renders complex the interpretation of the identified variants, thereby posing new challenges for the molecular diagnosis of mitochondrial diseases. Indeed, mtDNA sequencing by NGS requires specific bioinformatics tools and the adaptation of those developed for nuclear DNA, for the detection and quantification of mtDNA variants from sequence alignment to the calling steps, in order to manage the specific features of the mitochondrial genome including heteroplasmy, i.e., coexistence of mutant and wildtype mtDNA copies. The prioritization of mtDNA variants remains difficult, relying on a limited number of specific resources: population and clinical databases, and in silico tools providing a prediction of the variant pathogenicity. An evaluation of the most prominent bioinformatics tools showed that their ability to predict the pathogenicity was highly variable indicating that special efforts should be directed at developing new bioinformatics tools dedicated to the mitochondrial genome. In addition, massive parallel sequencing raised several issues related to the interpretation of very low mtDNA mutational loads, discovery of variants of unknown significance, and mutations unrelated to patient phenotype or the co-occurrence of mtDNA variants. This review provides an overview of the current strategies and bioinformatics tools for accurate annotation, prioritization and reporting of mtDNA variations from NGS data, in order to carry out accurate genetic counseling in individuals with primary mitochondrial diseases.

Big data analysis of human mitochondrial DNA substitution models: a regression approach

BACKGROUND

We study Phylotree, a comprehensive representation of the phylogeny of global human mitochondrial DNA (mtDNA) variations, to better understand the mtDNA substitution mechanism and its most influential factors. We consider a substitution model, where a set of genetic features may predict the rate at which mtDNA substitutions occur. To find an appropriate model, an exhaustive analysis on the effect of multiple factors on the substitution rate is performed through Negative Binomial and Poisson regressions. We examine three different inclusion options for each categorical factor: omission, inclusion as an explanatory variable, and by-value partitioning. The examined factors include genes, codon position, a CpG indicator, directionality, nucleotide, amino acid, codon, and context (neighboring nucleotides), in addition to other site based factors. Partitioning a model by a factor's value results in several sub-models (one for each value), where the likelihoods of the sub-models can be combined to form a score for the entire model. Eventually, the leading models are considered as viable candidates for explaining mtDNA substitution rates.

RESULTS

Initially, we introduce a novel clustering technique on genes, based on three similarity tests between pairs of genes, supporting previous results regarding gene functionalities in the mtDNA. These clusters are then used as a factor in our models. We present leading models for the protein coding genes, rRNA and tRNA genes and the control region, showing it is disadvantageous to separate the models of transitions/transversions, or synonymous/non-synonymous substitutions. We identify a context effect that cannot be attributed solely to protein level constraints or CpG pairs. For protein-coding genes, we show that the substitution model should be partitioned into sub-models according to the codon position and input codon; additionally we confirm that gene identity and cluster have no significant effect once the above factors are accounted for.

CONCLUSIONS

We leverage the large, high-confidence Phylotree mtDNA phylogeny to develop a new statistical approach. We model the substitution rates using regressions, allowing consideration of many factors simultaneously. This admits the use of model selection tools helping to identify the set of factors best explaining the mutational dynamics when considered in tandem.

A Monochrome Multiplex Real-Time Quantitative PCR Assay for the Measurement of Mitochondrial DNA Content

Mitochondrial DNA copies per cell (mtDNA content) can fluctuate with cellular aging, oxidative stress, and mitochondrial dysfunction, and has been investigated in cancer, diabetes, HIV, and metabolic disease. mtDNA content testing in both clinical and basic settings is expected to increase as research uncovers its biological relevance. Herein, we present a novel mtDNA content assay developed on monochrome multiplex real-time quantitative PCR (MMqPCR) principles. This assay offers a greater than twofold improvement on time effectiveness and cost-effectiveness over conventional (monoplex) qPCR, as well as improved reproducibility given the reduced effects of human pipetting errors. The new MMqPCR method was compared with the gold standard monoplex qPCR assay on DNA from a variety of sources, including human whole blood, skeletal muscle, and commercial cell lines. The MMqPCR assay is reproducible (n = 98, r = 0.99, P < 0.0001) and highly correlated to the monoplex qPCR assay (n = 160, r > 0.98, P < 0.0001). Intra-assay and interassay variabilities, as established independently by multiple operators, range between 4.3% and 7.9% and between 2.9% and 9.2%, respectively. This robust assay can quantify >82 pg of template DNA per reaction, with a minimum mtDNA/nuclear DNA ratio of 20, and is especially suitable for studies that require high throughput.

Mitochondrial Genomics: A complex field now coming of age

Purpose of review

The groundwork for mitochondrial medicine was laid 30 years ago with identification of the first disease-causing mitochondrial DNA (mtDNA) mutations in 1988. Three decades later, mutations in nearly 300 genes involving every possible mode of inheritance within both nuclear and mitochondrial genomes are now recognized to collectively comprise the largest class of inherited metabolic disease affecting at least 1 in 4,300 individuals across all ages. Significant progress has been made in recent years to improve understanding of mitochondrial biology and disease pathophysiology.

Recent findings

Markedly improved understanding of the highly diverse molecular etiologies of multi-systemic phenotypes in primary mitochondrial disease has resulted from massively parallel genomic sequencing technologies and improved bioinformatic resources that enable identification in individual patients of their disease's precise genetic etiology. Key informatics resources of particular utility to the mitochondrial disease genomics community have been developed, including: (1) Mitocarta 2.0 repository of 1200+ verified mitochondria-localized proteins, (2) MITOMAP Web resource of curated mtDNA genome variants, and (3) Mitochondrial Disease Sequence Data Resource (MSeqDR) that centralizes Web curation and annotation of mitochondrial disease genes and variants in both genomes, ontology-defined phenotypes, and access to many analytic tools to support genomic data mining and interpretation. Gene and mutation-based disease categorization has proven particularly useful to identify the full clinical spectrum of disease that may affect a given individual.

Summary

Extensive genomic advances, both in technologic platforms and bioinformatics resources, have facilitated dramatic improvement in the accurate recognition and understanding of primary mitochondrial disease.

Mitochondrial Regulatory Pathways in the Pathogenesis of Alzheimer's Disease

Alzheimer's disease (AD) is an age-associated neurodegenerative brain disorder with progressive cognitive decline that leads to terminal dementia and death. For decades, amyloid-beta (Aβ) and neurofibrillary tangle (NFT) aggregation hypotheses have dominated studies on the pathogenesis and identification of potential therapeutic targets in AD. Little attention has been paid to the mitochondrial molecular/biochemical pathways leading to AD. Mitochondria play a critical role in cell viability and death including neurons and neuroglia, not only because they regulate energy and oxygen metabolism but also because they regulate cell death pathways. Mitochondrial impairment and oxidative stress are implicated in the pathogenesis of AD. Interestingly, current therapeutics provide symptomatic benefits to AD patients resulting in the use of preventive trials on presymptomatic subjects. This review article elucidates the pathophysiology of AD and emphasizes the need to explore the mitochondrial pathways to provide solutions to unanswered questions in the prevention and treatment of AD.

Mutational load of the mitochondrial genome predicts pathological features and biochemical recurrence in prostate cancer

Prostate cancer management is complicated by extreme disease heterogeneity, which is further limited by availability of prognostic biomarkers. Recognition of prostate cancer as a genetic disease has prompted a focus on the nuclear genome for biomarker discovery, with little attention given to the mitochondrial genome. While it is evident that mitochondrial DNA (mtDNA) mutations are acquired during prostate tumorigenesis, no study has evaluated the prognostic value of mtDNA variation. Here we used next-generation sequencing to interrogate the mitochondrial genomes from prostate tissue biopsies and matched blood of 115 men having undergone a radical prostatectomy for which there was a mean of 107 months clinical follow-up. We identified 74 unique prostate cancer specific somatic mtDNA variants in 50 patients, providing significant expansion to the growing catalog of prostate cancer mtDNA mutations. While no single variant or variant cluster showed recurrence across multiple patients, we observe a significant positive correlation between the total burden of acquired mtDNA variation and elevated Gleason Score at diagnosis and biochemical relapse. We add to accumulating evidence that total acquired genomic burden, rather than specific mtDNA mutations, has diagnostic value. This is the first study to demonstrate the prognostic potential of mtDNA mutational burden in prostate cancer.

High-confidence assessment of functional impact of human mitochondrial non-synonymous genome variations by APOGEE

24,189 are all the possible non-synonymous amino acid changes potentially affecting the human mitochondrial DNA. Only a tiny subset was functionally evaluated with certainty so far, while the pathogenicity of the vast majority was only assessed in-silico by software predictors. Since these tools proved to be rather incongruent, we have designed and implemented APOGEE, a machine-learning algorithm that outperforms all existing prediction methods in estimating the harmfulness of mitochondrial non-synonymous genome variations. We provide a detailed description of the underlying algorithm, of the selected and manually curated training and test sets of variants, as well as of its classification ability.

MitoSuite: a graphical tool for human mitochondrial genome profiling in massive parallel sequencing

Recent rapid advances in high-throughput, next-generation sequencing (NGS) technologies have promoted mitochondrial genome studies in the fields of human evolution, medical genetics, and forensic casework. However, scientists unfamiliar with computer programming often find it difficult to handle the massive volumes of data that are generated by NGS. To address this limitation, we developed MitoSuite, a user-friendly graphical tool for analysis of data from high-throughput sequencing of the human mitochondrial genome. MitoSuite generates a visual report on NGS data with simple mouse operations. Moreover, it analyzes high-coverage sequencing data but runs on a stand-alone computer, without the need for file upload. Therefore, MitoSuite offers outstanding usability for handling massive NGS data, and is ideal for evolutionary, clinical, and forensic studies on the human mitochondrial genome variations. It is freely available for download from the website https://mitosuite.com.

mit-o-matic: a comprehensive computational pipeline for clinical evaluation of mitochondrial variations from next-generation sequencing datasets

The human mitochondrial genome has been reported to have a very high mutation rate as compared with the nuclear genome. A large number of mitochondrial mutations show significant phenotypic association and are involved in a broad spectrum of diseases. In recent years, there has been a remarkable progress in the understanding of mitochondrial genetics. The availability of next-generation sequencing (NGS) technologies have not only reduced sequencing cost by orders of magnitude but has also provided us good quality mitochondrial genome sequences with high coverage, thereby enabling decoding of a number of human mitochondrial diseases. In this study, we report a computational and experimental pipeline to decipher the human mitochondrial DNA variations and examine them for their clinical correlation. As a proof of principle, we also present a clinical study of a patient with Leigh disease and confirmed maternal inheritance of the causative allele. The pipeline is made available as a user-friendly online tool to annotate variants and find haplogroup, disease association, and heteroplasmic sites. The "mit-o-matic" computational pipeline represents a comprehensive cloud-based tool for clinical evaluation of mitochondrial genomic variations from NGS datasets. The tool is freely available at http://genome.igib.res.in/mitomatic/.

MitoCarta2.0: an updated inventory of mammalian mitochondrial proteins

Mitochondria are complex organelles that house essential pathways involved in energy metabolism, ion homeostasis, signalling and apoptosis. To understand mitochondrial pathways in health and disease, it is crucial to have an accurate inventory of the organelle's protein components. In 2008, we made substantial progress toward this goal by performing in-depth mass spectrometry of mitochondria from 14 organs, epitope tagging/microscopy and Bayesian integration to assemble MitoCarta (www.broadinstitute.org/pubs/MitoCarta): an inventory of genes encoding mitochondrial-localized proteins and their expression across 14 mouse tissues. Using the same strategy we have now reconstructed this inventory separately for human and for mouse based on (i) improved gene transcript models, (ii) updated literature curation, including results from proteomic analyses of mitochondrial sub-compartments, (iii) improved homology mapping and (iv) updated versions of all seven original data sets. The updated human MitoCarta2.0 consists of 1158 human genes, including 918 genes in the original inventory as well as 240 additional genes. The updated mouse MitoCarta2.0 consists of 1158 genes, including 967 genes in the original inventory plus 191 additional genes. The improved MitoCarta 2.0 inventory provides a molecular framework for system-level analysis of mammalian mitochondria.

Consequences of zygote injection and germline transfer of mutant human mitochondrial DNA in mice

Considerable evidence supports mutations in mitochondrial genes as the cause of maternally inherited diseases affecting tissues that rely primarily on oxidative energy metabolism, usually the nervous system, the heart, and skeletal muscles. Mitochondrial diseases are diverse, and animal models currently are limited. Here we introduced a mutant human mitochondrial gene responsible for Leber hereditary optic neuropathy (LHON) into the mouse germ line using fluorescence imaging for tissue-specific enrichment in the target retinal ganglion cells. A mitochondria-targeted adeno-associated virus (MTS-AAV) containing the mutant human NADH ubiquinone oxidoreductase subunit 4 (ND4) gene followed by mitochondrial-encoded mCherry was microinjected into zygotes. Female founders with mCherry fluorescence on ophthalmoscopy were backcrossed with normal males for eight generations. Mutant human ND4 DNA was 20% of mouse ND4 and did not integrate into the host genome. Translated human ND4 protein assembled into host respiratory complexes, decreasing respiratory chain function and increasing oxidative stress. Swelling of the optic nerve head was followed by progressive demise of ganglion cells and their axons, the hallmarks of human LHON. Early visual loss that began at 3 mo and progressed to blindness 8 mo after birth was reversed by intraocular injection of MTS-AAV expressing wild-type human ND4. The technology of introducing human mitochondrial genes into the mouse germ line has never been described, to our knowledge, and has implications not only for creating animal models recapitulating the counterpart human disorder but more importantly for reversing the adverse effects of the mutant gene using gene therapy to deliver the wild-type allele.

FMiR: A Curated Resource of Mitochondrial DNA Information for Fish

Mitochondrial genome sequences have been widely used for evolutionary and phylogenetic studies. Among vertebrates, fish are an important, diverse group, and their mitogenome sequences are growing rapidly in public repositories. To facilitate mitochondrial genome analysis and to explore the valuable genetic information, we developed the Fish Mitogenome Resource (FMiR) database to provide a workbench for mitogenome annotation, species identification and microsatellite marker mining. The microsatellites are also known as simple sequence repeats (SSRs) and used as molecular markers in studies on population genetics, gene duplication and marker assisted selection. Here, easy-to-use tools have been implemented for mining SSRs and for designing primers to identify species/habitat specific markers. In addition, FMiR can analyze complete or partial mitochondrial genome sequence to identify species and to deduce relational distances among sequences across species. The database presently contains curated mitochondrial genomes from 1302 fish species belonging to 297 families and 47 orders reported from saltwater and freshwater ecosystems. In addition, the database covers information on fish species such as conservation status, ecosystem, family, distribution and occurrence downloaded from the FishBase and IUCN Red List databases. Those fish information have been used to browse mitogenome information for the species belonging to a particular category. The database is scalable in terms of content and inclusion of other analytical modules. The FMiR is running under Linux operating platform on high performance server accessible at URL http://mail.nbfgr.res.in/fmir.

Resources, challenges and way forward in rare mitochondrial diseases research

Over 300 million people are affected by about 7000 rare diseases globally. There are tremendous resource limitations and challenges in driving research and drug development for rare diseases. Hence, innovative approaches are needed to identify potential solutions. This review focuses on the resources developed over the past years for analysis of genome data towards understanding disease biology especially in the context of mitochondrial diseases, given that mitochondria are central to major cellular pathways and their dysfunction leads to a broad spectrum of diseases. Platforms for collaboration of research groups, clinicians and patients and the advantages of community collaborative efforts in addressing rare diseases are also discussed. The review also describes crowdsourcing and crowdfunding efforts in rare diseases research and how the upcoming initiatives for understanding disease biology including analyses of large number of genomes are also applicable to rare diseases.

Resources, challenges and way forward in rare mitochondrial diseases research

Over 300 million people are affected by about 7000 rare diseases globally. There are tremendous resource limitations and challenges in driving research and drug development for rare diseases. Hence, innovative approaches are needed to identify potential solutions. This review focuses on the resources developed over the past years for analysis of genome data towards understanding disease biology especially in the context of mitochondrial diseases, given that mitochondria are central to major cellular pathways and their dysfunction leads to a broad spectrum of diseases. Platforms for collaboration of research groups, clinicians and patients and the advantages of community collaborative efforts in addressing rare diseases are also discussed. The review also describes crowdsourcing and crowdfunding efforts in rare diseases research and how the upcoming initiatives for understanding disease biology including analyses of large number of genomes are also applicable to rare diseases.

MitImpact: an exhaustive collection of pre-computed pathogenicity predictions of human mitochondrial non-synonymous variants

Mitochondrial DNA carries a tiny, but fundamental portion of the eukaryotic genetic code. As its nuclear counterpart, it is susceptible to point mutations. Their level of pathogenicity has been assessed for the newly discovered mutations only, leaving some degree of uncertainty on the potential impact of the unknown mutations. Here we present Mitochondrial mutation Impact (MitImpact), a queryable lightweight web interface to a reasoned collection of structurally and evolutionary annotated pathogenicity predictions, obtained by assembling pre-computed with on-the-fly-computed sets of pathogenicity estimations, for all the possible mitochondrial missense variants. It presents itself as a resource for fast and reliable evaluation of gene-specific susceptibility of unknown and verified amino acid changes. MitImpact is freely available at http://bioinformatics.css-mendel.it/ (tools section). ©2014 Wiley Periodicals, Inc.

Polymorphism in mtDNA control region of Mizo-Mongloid Breast Cancer samples as revealed by PCR-RFLP analysis

Mutations in mitochondrial D-loop region of DNA (mtDNA) may serve as a potential sensor for cellular DNA damage and marker for cancer development. We investigated the restriction fragment length polymorphism (RFLP) pattern of the D-loop region in the blood samples of breast cancer patients among Mizoram population. Significant differences were observed among breast cancer and healthy blood samples in the RFLP pattern using AluI, HaeIII and RsaI enzymes. Polymorphic information content (PIC - 0.258), band informativeness (∑Ib - 3.283) and marker index (MI - 0.006) were highest in the case of RsaI enzyme. Our data suggest that the RsaI polymorphic site in the mitochondrial control region is an informative marker for breast cancer development in Mizo population.

Novel mitochondrial tRNA(Ile) m.4282A>G gene mutation leads to chronic progressive external ophthalmoplegia plus phenotype

BACKGROUND/AIM

To investigate the underlying pathomechanism in a 33-year-old female Caucasian patient presenting with chronic progressive external ophthalmoplegia (CPEO) plus symptoms.

METHODS

Histochemical analysis of skeletal muscle and biochemical measurements of individual oxidative phosphorylation (OXPHOS) complexes. Genetic analysis of mitochondrial DNA in various tissues with subsequent investigation of single muscle fibres for correlation of mutational load.

RESULTS

The patient's skeletal muscle showed 20% of cytochrome c oxidase-negative fibres and 8% ragged-red fibres. Genetic analysis of the mitochondrial DNA revealed a novel point mutation in the mitochondrial tRNA(Ile) (MTTI) gene at position m.4282G>A. The heteroplasmy was determined in blood, buccal cells and muscle by restriction fragment length polymorphism (RFLP) combined with a last fluorescent cycle. The total mutational load was 38% in skeletal muscle, but was not detectable in blood or buccal cells of the patient. The phenotype segregated with the mutational load as determined by analysis of single cytochrome c oxidase-negative/positive fibres by laser capture microdissection and subsequent LFC-RFLP.

CONCLUSIONS

We describe a novel MTTI transition mutation at nucleotide position m.4282G>A associated with a CPEO plus phenotype. The novel variant at position m.4282G>A disrupts the middle bond of the D-stem of the tRNA(Ile) and is highly conserved. The conservation and phenotype-genotype segregation strongly suggest pathogenicity and is in good agreement with the MTTI gene being frequently associated with CPEO. This novel variant broadens the spectrum of MTTI mutations causing CPEO.