Variation In Mitochondrial Genes Research Articles

PSIII-21 Variation in mitochondrial genes involved in oxidative phosphorylation in cattle

Abstract The mitochondrion is a maternally inherited organelle that produces approximately 90% of cellular energy. The mitochondrial genome (mtDNA) consists of 13 genes that are critical components of oxidative phosphorylation. Identifying and understanding variation within this genome could elucidate differences in metabolic and physiological traits, specifically growth efficiency in cattle. Our aim is to identify how variation in the mitochondrial genome influences efficiency in beef cattle. Low-pass sequencing data (average 0.5X coverage of the autosomes) were collected (Neogen) from 49 animals within the UNL herd (composite Simmental, Red Angus, and Gelbvieh). The data were trimmed and mapped (BWA-MEM) to the ARS-UCD1.2 cattle genome. After variant impacts were predicted (Ensembl VEP) haplotype networks were created to visualize variation among samples. Over 60X coverage was achieved across the mitochondrial genome, on average. Excluding the D-loop, 62 variants were identified in the 49 animals: 2 tRNA, 6 rRNA, and 54 coding single nucleotide polymorphisms (SNPs). These 62 variants were encompassed in 23 unique haplotypes. Of the coding variants, 13 were nonsynonymous and found in the following genes encoding components of oxidative phosphorylation: ND1 (n = 3), ND2 (n = 1), ND3 (n = 1), ND4 (n = 1), ND5 (n = 1), ND6 (n = 3), COX3 (n = 2), and CYTB (n = 1). Nine unique haplotypes were present considering only nonsynonymous variants. Nonsynonymous mutations were identified in complex I genes (ND1-6), in the complex IV gene COX3, and in CYTB, which is involved in multiple processes including the electron transport chain. These data, from a closed herd at UNL, support that there is a great deal of mtDNA variation present among beef cattle for which to analyze the impact of mitochondrial genotype on animal efficiency. Performance data demonstrate variation in average daily gain (ADG) and residual feed intake (RFI) in this herd, with a mean ADG of 1.95 kg/d (SD = 0.23 kg/d) and a mean RFI of -0.11 kg (SD = 0.57 kg). Data on individual feed intake, growth rates, and carcass performance values will continue to be collected on all animals sequenced. Based upon these data we hypothesize that variation in the mitochondrial genome will be associated with altered complex I and IV activity. For a more comprehensive understanding of this variation, the sample size will be expanded to over 1,500 animals in the next 2 yr. Overall, from our initial analysis of the mitochondrial genomes from 49 animals, we have identified 62 variants that we anticipate will explain variation in cellular and growth efficiency.

Mitochondrial DNA Haplogroups and Variants Predispose to Chagas Disease Cardiomyopathy

Cardiomyopathies are major causes of heart failure. Chagas disease (CD) is caused by the parasite Trypanosoma cruzi, and it is endemic in Central and South America. Thirty percent of cases evolve into chronic chagas cardiomyopathy (CCC), which has worse prognosis as compared with other cardiomyopathies. In vivo bioenergetic analysis and ex vivo proteomic analysis of myocardial tissues highlighted worse mitochondrial dysfunction in CCC, and previous studies identified nuclear-encoded mitochondrial gene variants segregating with CCC. Here, we assessed the role of the mitochondrial genome through mtDNA copy number variations and mtDNA haplotyping and sequencing from heart or blood tissues of severe, moderate CCC and asymptomatic/indeterminate Chagas disease as well as healthy controls as an attempt to help decipher mitochondrial-intrinsic genetic involvement in Chagas disease development. We have found that the mtDNA copy number was significantly lower in CCC than in heart tissue from healthy individuals, while blood mtDNA content was similar among asymptomatic Chagas disease, moderate, and severe CCC patients. An MtDNA haplogrouping study has indicated that African haplogroups were over represented in the Chagas subject groups in comparison with healthy Brazilian individuals. The European lineage is associated with protection against cardiomyopathy and the macro haplogroup H is associated with increased risk towards CCC. Using mitochondria DNA sequencing, 84 mtDNA-encoded protein sequence pathogenic variants were associated with CCC. Among them, two variants were associated to left ventricular non-compaction and two to hypertrophic cardiomyopathy. The finding that mitochondrial protein-coding SNPs and mitochondrial haplogroups associate with risk of evolving to CCC is consistent with a key role of mitochondrial DNA in the development of chronic chagas disease cardiomyopathy.

Abstract 18721: Increased Predisposition to Hypertrophic Cardiomyopathy in Mitochondria Gene CYP2E1 Rare Variant Carriers

Introduction: With a prevalence of up to 1 in 200, hypertrophic cardiomyopathy (HCM) is the most common monogenic hereditary cardiovascular disease. Previous studies have observed that mitochondrial dysfunction and mitochondria-associated metabolic remodeling are major metabolic features in HCM. However, the impact of mitochondrial gene mutations on HCM were poorly understood. Methods and Results: We selected 2272 mitochondrial genes from the Mitocarta database 3.0 and screened rare variants from the whole-exome sequencing data in 985 HCM patients (excluding patients with HCM phenotypes, including mitochondrial myopathy) and 759 non-HCM controls. We found that CYP2E1 rare variants were significantly enriched in HCM patients (OR = 9.56, Bonferroni corrected P = 0.001). Patients with or without CYP2E1 rare variants shared similar demographic and echocardiographic variables at baseline. With a median follow-up time of 5.31 years in 735 HCM patients, we revealed that HCM patients with CYP2E1 rare variants were more likely to experience myocardial infarction (HR 14.1, P < 0.001). Conclusion: We demonstrated that rare variants in the mitochondrial gene CYP2E1 might increase the risk of HCM onset and may be associated with the occurrence of myocardial infarction endpoints in HCM. We hypothesize that the mechanism is related to the extensive and complex mitochondrial metabolic processes in which CYP2E1 is involved. Our findings provided new evidence for the association between mitochondrial gene variants and HCM, and more multi-center evidence is needed to confirm this association in the future.

Mitochondria and telomeres: hand in glove.

Born as an endosymbiont, the bacteria engulfed by the proto-eukaryotic cell more than 1.45billion years ago progressively evolved as an important organelle with multiple interactions with the host cell. In particular, strong connections between mitochondria and the chromosome ends, the telomeres, led to propose a new theory of ageing in which dysfunctional telomeres and mitochondria are the main actors of a vicious circle reducing cell fitness and promoting cellular ageing. We review the evidences that oxidative stress and dysfunctional mitochondria damage telomeres and further discuss the interrelationship between telomere biology and mitochondria through the lens of telomerase which shuttles between the nucleus and mitochondria. Finally, we elaborate on the possible role of the mitochondrial genome on the inheritance of human telomere length through the expression of mitochondrial gene variants.

CHARACTERIZATION OF cox3 AND rnl GENES ENCODED IN MITOCHONDRIA OF Fusarium graminearum Schwabe

In this study, the phylogenetic relationship among Fusarium graminearum Schwabe isolates was established for the first time based on mitochondrial cox3 and rnl gene variations. The genes were amplified from 45 isolates purified from Türkiye and Iran together with 2 Korean strains by polymerase chain reaction. The amplicons were sequenced and nucleotide polymorphisms were detected by alignment. The phylogenetic relationship was constructed by using PAUP 4.0a with the maximum parsimony method. Fragments with 477 bp length, belonging to cox3, were obtained from 46 samples; 1547 bp-amplicons of rnl were produced from 45 samples. Sequence similarities were calculated as 30-100 % and 17-94 % for cox3 and rnl, respectively. Nucleotide variations within the rnl was found higher than within cox3. It was shown that SNPs and in-dels, found in coding regions, cause a codon change and may alter more than one codon by causing frame shift without affect gene functions. Bootstrap values belonging to cox3 and rnl dataset was found ranging from 57 to 84 %, and 54 to 100 %, respectively. Parsimony analysis revealed that Korean isolates were in monophyletic relationship with Turkish and Iranian isolates. It is proposed that the methodology can be applied to other fungal species because the phylogenetic relationships at the intraspecific level are able to establish among Fusarium species based on mitochondrial gene variation.

Genetic findings in over 600 individuals with inherited retinal disorders in Finland

AbstractPurpose: To report genetic findings in patients with suspected inherited retinal disorders (IRD) in a large Finnish cohort.Methods: The study was conducted retrospectively on IRD‐patients treated at the Department of Ophthalmology, Helsinki University Hospital between January 1, 2012, and December 31, 2020. Eligibility criteria were met by 786 patients. Clinical diagnosis, genetic testing method and result, relevant family history, and mode of inheritance were drawn from the electronic health registries.Results: Of the 638 patients who underwent genetic testing, 79% received a genetic diagnosis. The genetic findings corresponded to autosomal recessive (AR) inheritance in 242 patients, X‐linked in 158, and autosomal dominant (AD) in 94, whereas pathogenic variants in mitochondrial genes were found in 22 patients. The most common genetic diagnosis was a pathogenic variant in RS1 causing X‐linked retinoschisis (n = 86, 17% of all patients with a positive genetic finding). Of retinitis pigmentosa ‐associated genes, causative variants were most commonly found in CERKL (n = 43, 8.5%), RPGR (n = 31, 6.1%), and EYS (n = 25, 5.0%). CERKL variant c.375C > G, p.(Cys125Trp) and EYS variant c.1155 T > A, p.(Cys385Ter), both with known founder effects in the Finnish population, were frequently discovered (n = 69 and 53, respectively). Variants in the ABCA4 gene explained IRD in 24 patients. Pathogenic variants were also found in CHM (n = 26), OPA1 (n = 16), and CLRN1 (n = 16).Conclusions: The genetic causes of IRDs in Finland differ from other countries because of its isolated population history. Compared to similar studies in other countries, the percentage of patients with a positive genetic finding was higher (79%), which can partly be explained by the enriched founder mutations in the population. About 20% of the patients still lack a genetic diagnosis. These patients might have causative variants that are difficult to detect with current testing methods (such as complex structural variants) or the variants are in genes not yet associated with IRD.

Contribution of mitochondrial gene variants in diabetes and diabetic kidney disease.

ObjectivesMitochondrial DNA (mtDNA) plays an important role in the pathogenesis of diabetes. Variants in mtDNA have been reported in diabetes, but studies on the whole mtDNA variants were limited. Our study aims to explore the association of whole mtDNA variants with diabetes and diabetic kidney disease (DKD).MethodsThe whole mitochondrial genome was screened by next-generation sequencing in cohort 1 consisting of 50 early-onset diabetes (EOD) patients with a maternally inherited diabetes (MID) family history. A total of 42 variants possibly associated with mitochondrial diseases were identified according to the filtering strategy. These variants were sequenced in cohort 2 consisting of 90 EOD patients with MID. The association between the clinical phenotype and these variants was analyzed. Then, these variants were genotyped in cohort 3 consisting of 1,571 type 2 diabetes mellitus patients and 496 subjects with normal glucose tolerance (NGT) to analyze the association between variants with diabetes and DKD.ResultsPatients with variants in the non-coding region had a higher percentage of obesity and levels of fasting insulin (62.1% vs. 24.6%, P = 0.001; 80.0% vs. 26.5% P < 0.001). The patients with the variants in rRNA had a higher prevalence of obesity (71.4% vs. 30.3%, P = 0.007), and the patients with the variants in mitochondrial complex I had a higher percentage of the upper tertile of FINS (64.3% vs. 34.3%, P = 0.049). Among 20 homogeneous variants successfully captured, two known variants (m.A3943G, m.A10005G) associated with other mitochondrial diseases were only in the diabetic group, but not in the NGT group, which perhaps indicated its possible association with diabetes. The prevalence of DKD was significantly higher in the group with the 20 variants than those without these variants (18.7% vs. 14.6%, P = 0.049) in the participants with diabetes of cohort 3.ConclusionMtDNA variants are associated with MID and DKD, and our findings advance our understanding of mtDNA in diabetes and DKD. It will have important implications for the individual therapy of mitochondrial diabetes.

Whole-exome sequencing identifies genetic variants of hearing loss in 113 Chinese families

BackgroundHearing loss is a group of diseases with high genetic heterogeneity. About 160 genes have been reported to be associated with hereditary hearing loss. Methods113 families with hearing loss were collected, and WES was used to detect SNV, InDel, CNV and mitochondrial gene variants. For some probands with negative WES test results, the copy number of STRC and OTOA were determined by using real-time fluorescence quantitative PCR. ResultsPathogenic or likely pathogenic variants were found in 54 probands, of which 98% (53/54) were SNVs or InDels and 2% (1/54) were CNVs, a positive rate of 48%. 16 families (14%) were detected with candidate variants of uncertain significance. 19 novel pathogenic or likely pathogenic variants and 22 candidate variants of uncertain significance were identified in this study. The most common hearing loss gene in the families was GJB2, accounting for 28% (15/53), followed by SLC26A4 and MYO15A, accounting for 21% (11/53) and 11% (6/53), respectively. Heterozygous gene deletion was detected in 3 probands, including 2 with STRC and 1 with OTOA in 43 families with WES negative test. ConclusionGenetic etiology was clarified in 54 families. All of these findings broadened the mutation spectrum of hearing loss genes, thus providing new variant information for the future diagnosis of patients with hearing loss.

Understanding the nomenclature of mitochondrial DNA mutations through examples of two specific disease entities: Mitochondrial encephalopathy with lactic acidosis and stroke-like episodes and Leber hereditary optic neuropathy.

Mitochondrial diseases are genetic disorders that can arise either from maternally inherited mitochondrial DNA (mtDNA) or from mutations in nuclear DNA. This article is the second in a series of papers reviewing mitochondrial genetics and several of the disorders associated with mitochondrial gene variants. With a prevalence of 1:∼4,300 persons, mitochondrial disorders are diagnostic entities with which nurse practitioners should be familiar. In describing genetic mutations, numbering nucleotides (nuclear or mtDNA) is critical for communicating exactly where a variation has occurred in a stretch of nucleotides. This article discusses the nomenclature associated with mtDNA mutations, using the examples of mutations causing mitochondrial encephalopathy with lactic acidosis and stroke-like episodes and Leber hereditary optic neuropathy. Pathophysiology, symptoms, and treatment options for these disease entities are discussed.

Mitochondrial 1555 G>A variant as a potential risk factor for childhood glioblastoma.

BackgroundChildhood glioblastoma multiforme (GBM) is a highly aggressive disease with low survival, and its etiology, especially concerning germline genetic risk, is poorly understood. Mitochondria play a key role in putative tumorigenic processes relating to cellular oxidative metabolism, and mitochondrial DNA variants were not previously assessed for association with pediatric brain tumor risk.MethodsWe conducted an analysis of 675 mitochondrial DNA variants in 90 childhood GBM cases and 2789 controls to identify enrichment of mitochondrial variant associated with GBM risk. We also performed this analysis for other glioma subtypes including pilocytic astrocytoma. Nuclear-encoded mitochondrial gene variants were also analyzed.ResultsWe identified m1555 A>G was significantly associated with GBM risk (adjusted OR 29.30, 95% CI 5.25–163.4, P-value 9.5 X 10–4). No association was detected for other subtypes. Haplotype analysis further supported the independent risk contributed by m1555 G>A, instead of a haplogroup joint effect. Nuclear-encoded mitochondrial gene variants identified significant associations in European (rs62036057 in WWOX, adjusted OR = 2.99, 95% CI 1.88–4.75, P-value = 3.42 X 10–6) and Hispanic (rs111709726 in EFHD1, adjusted OR = 3.57, 95% CI 1.99–6.40, P-value = 1.41 X 10–6) populations in ethnicity-stratified analyses.ConclusionWe report for the first time a potential role played by a functional mitochondrial ribosomal RNA variant in childhood GBM risk, and a potential role for both mitochondrial and nuclear-mitochondrial DNA polymorphisms in GBM tumorigenesis. These data implicate cellular oxidative metabolic capacity as a contributor to the etiology of pediatric glioblastoma.

Gaining Insight into Mitochondrial Genetic Variation and Downstream Pathophysiology: What Can i(PSCs) Do?

Mitochondria are specialized organelles involved in energy production that have retained their own genome throughout evolutionary history. The mitochondrial genome (mtDNA) is maternally inherited and requires coordinated regulation with nuclear genes to produce functional enzyme complexes that drive energy production. Each mitochondrion contains 5–10 copies of mtDNA and consequently, each cell has several hundreds to thousands of mtDNAs. Due to the presence of multiple copies of mtDNA in a mitochondrion, mtDNAs with different variants may co-exist, a condition called heteroplasmy. Heteroplasmic variants can be clonally expanded, even in post-mitotic cells, as replication of mtDNA is not tied to the cell-division cycle. Heteroplasmic variants can also segregate during germ cell formation, underlying the inheritance of some mitochondrial mutations. Moreover, the uneven segregation of heteroplasmic variants is thought to underlie the heterogeneity of mitochondrial variation across adult tissues and resultant differences in the clinical presentation of mitochondrial disease. Until recently, however, the mechanisms mediating the relation between mitochondrial genetic variation and disease remained a mystery, largely due to difficulties in modeling human mitochondrial genetic variation and diseases. The advent of induced pluripotent stem cells (iPSCs) and targeted gene editing of the nuclear, and more recently mitochondrial, genomes now provides the ability to dissect how genetic variation in mitochondrial genes alter cellular function across a variety of human tissue types. This review will examine the origins of mitochondrial heteroplasmic variation and propagation, and the tools used to model mitochondrial genetic diseases. Additionally, we discuss how iPSC technologies represent an opportunity to advance our understanding of human mitochondrial genetics in disease.

Targeted Sequencing of Mitochondrial Genes Reveals Signatures of Molecular Adaptation in a Nearly Panmictic Small Pelagic Fish Species.

Ongoing climatic changes, with predictable impacts on marine environmental conditions, are expected to trigger organismal responses. Recent evidence shows that, in some marine species, variation in mitochondrial genes involved in the aerobic conversion of oxygen into ATP at the cellular level correlate with gradients of sea surface temperature and gradients of dissolved oxygen. Here, we investigated the adaptive potential of the European sardine Sardina pilchardus populations offshore the Iberian Peninsula. We performed a seascape genetics approach that consisted of the high throughput sequencing of mitochondria’s ATP6, COI, CYTB and ND5 and five microsatellite loci on 96 individuals coupled with environmental information on sea surface temperature and dissolved oxygen across five sampling locations. Results show that, despite sardines forming a nearly panmictic population around Iberian Peninsula, haplotype frequency distribution can be explained by gradients of minimum sea surface temperature and dissolved oxygen. We further identified that the frequencies of the most common CYTB and ATP6 haplotypes negatively correlate with minimum sea surface temperature across the sampled area, suggestive of a signature of selection. With signatures of selection superimposed on highly connected populations, sardines may be able to follow environmental optima and shift their distribution northwards as a response to the increasing sea surface temperatures.

Mitochondrial G12630A variation is associated with statin-induced myalgia in Chinese patients with coronary artery disease

To identify mitochondrial gene variants associated with statin-induced myalgia in Chinese patients with coronary artery disease (CHD). This study was conducted in a cohort of 403 patients with CHD receiving rosuvastatin therapy, among whom 341 patients had complete follow-up data concerning myalgia and 389 patients had documented measurements of plasma creatine kinase (CK) level. All these patients underwent genetic analysis using GSA chip for detecting mitochondria gene variants associated with myalgia. A logistic regression model was used to assess the association between 69 mitochondrial single-nucleotide polymorphisms (SNPs) and myopathy in 341 patients. The impact of these mutation sites on CK levels in 389 patients was evaluated by linear regression analysis. G12630A variant was identified to correlate with an increased risk of myalgia in CHD patients (OR: 8.689, 95% CI: 1.586-47.6; P=0.01273), but CK levels did not differ significantly between patients with different genotypes of G12630A (P > 0.05). SNPs at T12285C and A13105G were found to significantly correlate with CK levels in these patients (P < 0.05). Mitochondrial G12630A variation is associated with statin-induced myalgia in patients with CHD, indicating the necessity of different treatment strategies for patients who carry this risk allele.

Mitochondria and the thermal limits of ectotherms.

Temperature is a critical abiotic factor shaping the distribution and abundance of species, but the mechanisms that underpin organismal thermal limits remain poorly understood. One possible mechanism underlying these limits is the failure of mitochondrial processes, as mitochondria play a crucial role in animals as the primary site of ATP production. Conventional measures of mitochondrial performance suggest that these organelles can function at temperatures much higher than those that limit whole-organism function, suggesting that they are unlikely to set organismal thermal limits. However, this conclusion is challenged by recent data connecting sequence variation in mitochondrial genes to whole-organism thermal tolerance. Here, we review the current state of knowledge of mitochondrial responses to thermal extremes and ask whether they are consistent with a role for mitochondrial function in shaping whole-organism thermal limits. The available data are fragmentary, but it is possible to draw some conclusions. There is little evidence that failure of maximal mitochondrial oxidative capacity as assessed in vitro sets thermal limits, but there is some evidence to suggest that temperature effects on ATP synthetic capacity may be important. Several studies suggest that loss of mitochondrial coupling is associated with the thermal limits for organismal growth, although this needs to be rigorously tested. Most studies have utilized isolated mitochondrial preparations to assess the effects of temperature on these organelles, and there remain many untapped opportunities to address these questions using preparations that retain more of their biological context to better connect these subcellular processes with whole-organism thermal limits.

Intraspecific mitochondrial gene variation can be as low as that of nuclear rRNA

Background: Mitochondrial DNA (mtDNA) has long been used to date historical demographic events. The idea that it is useful for molecular dating rests on the premise that its evolution is neutral. Even though this idea has long been challenged, the evidence against clock-like evolution of mtDNA is often ignored. Here, we present a particularly clear and simple example to illustrate the implications of violations of the assumption of selective neutrality. Methods: DNA sequences were generated for the mtDNA COI gene and the nuclear 28S rRNA of two closely related rocky shore snails, and species-level variation was compared. Nuclear rRNA is not usually used to study intraspecific variation in species that are not spatially structured, presumably because this marker is assumed to evolve so slowly that it is more suitable for phylogenetics. Results: Even though high inter-specific divergence reflected the faster evolutionary rate of COI, intraspecific genetic variation was similar for both markers. As a result, estimates of population expansion times based on mismatch distributions differed between the two markers by millions of years. Conclusions: Assuming that 28S evolution is more clock-like, these findings can be explained by variation-reducing purifying selection in mtDNA at the species level, and an elevated divergence rate caused by diversifying selection between the two species. Although these two selective forces together make mtDNA suitable as a marker for species identifications by means of DNA barcoding because they create a ‘barcoding gap’, estimates of demographic change based on this marker can be expected to be highly unreliable. Our study contributes to the growing evidence that the utility of mtDNA sequence data beyond DNA barcoding is limited.

Increased Burden of Ion Channel Gene Variants Is Related to Distinct Phenotypes in Pediatric Patients With Left Ventricular Noncompaction.

Left ventricular noncompaction (LVNC) is a hereditary type of cardiomyopathy. Although it is associated with high morbidity and mortality, the related ion channel gene variants in children have not been fully investigated. This study aimed to elucidate the ion channel genetic landscape of LVNC and identify genotype-phenotype correlations in a large Japanese cohort. We enrolled 206 children with LVNC from 2002 to 2017 in Japan. LVNC was classified as follows: LVNC with congenital heart defects, arrhythmia, dilated phenotype, or normal function. In the enrolled patients, 182 genes associated with cardiomyopathy were screened using next-generation sequencing. We identified 99 pathogenic variants in 40 genes in 87 patients. Of the pathogenic variants, 8.8% were in genes associated with channelopathies, 27% were in sarcomere genes, and 11.5% were in mitochondrial genes. Ion channel gene variants were mostly associated with the arrhythmia classification, whereas sarcomere and mitochondrial gene variants were associated with the dilated phenotype. Echocardiography revealed that the group with ion channel gene variants had almost normal LV ejection fraction and LV diastolic diameter Z scores. Fragmented QRS, old age, and an arrhythmia phenotype were the most significant risk factors for ventricular tachycardia (P=0.165, 0.0428, and 0.0074, respectively). Moreover, the group with ion channel variants exhibited a greater risk of a higher prevalence of arrhythmias such as ventricular tachycardia, rather than congestive heart failure. This is the first study that focused on genotype-phenotype correlations in a large pediatric LVNC patient cohort with ion channel gene variants that were determined using next-generation sequencing. Ion channel gene variants were strongly correlated with arrhythmia phenotypes. Genetic testing and phenotype specification allow for appropriate medical management of specific LVNC targets.

Intraspecific mitochondrial gene variation can be as low as that of nuclear rRNA.

Background: Mitochondrial DNA (mtDNA) has long been used to date historical demographic events. The idea that it is useful for molecular dating rests on the premise that its evolution is neutral. Even though this idea has long been challenged, the evidence against clock-like evolution of mtDNA is often ignored. Here, we present a particularly clear and simple example to illustrate the implications of violations of the assumption of selective neutrality. Methods: DNA sequences were generated for the mtDNA COI gene and the nuclear 28S rRNA of two closely related rocky shore snails, and species-level variation was compared. To our knowledge, this is the first study to use nuclear rRNA at this taxonomic level, presumably because this marker is assumed to evolve so slowly that it is only suitable for phylogenetics. Results: Even though high inter-specific divergence reflected the faster evolutionary rate of COI, intraspecific genetic variation was similar for both markers. As a result, estimates of population expansion times based on mismatch distributions differed between the two markers by millions of years. Conclusions: Assuming that 28S evolves effectively clock-like, these findingscan be explained by variation-reducing purifying selection in mtDNA at the species level, and an elevated divergence rate caused by diversifying selection between the two species. Although these two selective forces together make mtDNA suitable as a marker for species identifications by means of DNA barcoding because they create a 'barcoding gap', estimates of demographic changebased on this marker can be expected to be highly unreliable. Our study contributes to the growing evidence that the utility of mtDNA sequence data beyond DNA barcoding is limited.

Association between mitochondrial genetic variation and breast cancer risk: The Multiethnic Cohort.

BackgroundThe mitochondrial genome encodes for thirty-seven proteins, among them thirteen are essential for the oxidative phosphorylation (OXPHOS) system. Inherited variation in mitochondrial genes may influence cancer development through changes in mitochondrial proteins, altering the OXPHOS process and promoting the production of reactive oxidative species.MethodsTo investigate the association between mitochondrial genetic variation and breast cancer risk, we tested 314 mitochondrial SNPs (mtSNPs), capturing four complexes of the mitochondrial OXPHOS pathway and mtSNP groupings for rRNA and tRNA, in 2,723 breast cancer cases and 3,260 controls from the Multiethnic Cohort Study.ResultsWe examined the collective set of 314 mtSNPs as well as subsets of mtSNPs grouped by mitochondrial OXPHOS pathway, complexes, and genes, using the sequence kernel association test and adjusting for age, sex, and principal components of global ancestry. We also tested haplogroup associations using unconditional logistic regression and adjusting for the same covariates. Stratified analyses were conducted by self-reported maternal race/ethnicity. No significant mitochondrial OXPHOS pathway, gene, and haplogroup associations were observed in African Americans, Asian Americans, Latinos, and Native Hawaiians. In European Americans, a global test of all genetic variants of the mitochondrial genome identified an association with breast cancer risk (P = 0.017, q = 0.102). In mtSNP-subset analysis, the gene MT-CO2 (P = 0.001, q = 0.09) in Complex IV (cytochrome c oxidase) and MT-ND2 (P = 0.004, q = 0.19) in Complex I (NADH dehydrogenase (ubiquinone)) were significantly associated with breast cancer risk.ConclusionsIn summary, our findings suggest that collective mitochondrial genetic variation and particularly in the MT-CO2 and MT-ND2 may play a role in breast cancer risk among European Americans. Further replication is warranted in larger populations and future studies should evaluate the contribution of mitochondrial proteins encoded by both the nuclear and mitochondrial genomes to breast cancer risk.

An omics-based strategy using coenzyme Q10 in patients with Parkinson\u2019s disease: concept evaluation in a double-blind randomized placebo-controlled parallel group trial

BackgroundThis study focuses on genetically stratified subgroups of Parkinson’s disease patients (PD) with an enrichment of risk variants in mitochondrial genes,who might benefit from treatment with the “mitochondrial enhancer” coenzyme Q10 (156 mg coenzyme Q10/d [QuinoMit Q10® Fluid] over six months). The study will be performed in a double-blind, randomized, and placebo-controlled parallel group manner.MethodsPD patients will be specifically identified and assigned to treatment groups stratified by their genetic “mitochondrial risk burden” and consequently expected mitochondrial dysfunction and treatment response to coenzyme Q10 (homozygous or compound heterozygous Parkin/PINK1 mutation carriers [P++], heterozygous Parkin/PINK1 mutation carriers [P+], “omics” positive [omics+], and “omics” negative PD patients [omics-]). The primary endpoint is the change in motor symptoms over six months (as measured by the change in the motor subscore of the MDS-UPDRS). Secondary clinical endpoints include motor fluctuations, non-motor symptoms, results of magnetic resonance imaging of brain energy metabolism (31P-magnetic resonance spectroscopy imaging), and changes in structural and functional brain anatomy (MRI).PerspectiveThis study may be a first step towards a successful prediction of treatment response based on the genetic status of PD patients and translate progress in molecular genetics into personalized patient care. Further, magnetic resonance spectroscopy imaging may help quantify increased energy supply objectively and within a brief time after the start of treatment. Therefore, the potential of MRSI also for other studies addressing brain energy metabolism may will be assessed.Trial registrationThis study was registered at the German Clinical Trial Registry (DRKS, DRKS00015880) on November 15th, 2018.

Whole Exome Sequencing Is the Preferred Strategy to Identify the Genetic Defect in Patients With a Probable or Possible Mitochondrial Cause.

Mitochondrial disorders, characterized by clinical symptoms and/or OXPHOS deficiencies, are caused by pathogenic variants in mitochondrial genes. However, pathogenic variants in some of these genes can lead to clinical manifestations which overlap with other neuromuscular diseases, which can be caused by pathogenic variants in non-mitochondrial genes as well. Mitochondrial pathogenic variants can be found in the mitochondrial DNA (mtDNA) or in any of the 1,500 nuclear genes with a mitochondrial function. We have performed a two-step next-generation sequencing approach in a cohort of 117 patients, mostly children, in whom a mitochondrial disease-cause could likely or possibly explain the phenotype. A total of 86 patients had a mitochondrial disorder, according to established clinical and biochemical criteria. The other 31 patients had neuromuscular symptoms, where in a minority a mitochondrial genetic cause is present, but a non-mitochondrial genetic cause is more likely. All patients were screened for pathogenic variants in the mtDNA and, if excluded, analyzed by whole exome sequencing (WES). Variants were filtered for being pathogenic and compatible with an autosomal or X-linked recessive mode of inheritance in families with multiple affected siblings and/or consanguineous parents. Non-consanguineous families with a single patient were additionally screened for autosomal and X-linked dominant mutations in a predefined gene-set. We identified causative pathogenic variants in the mtDNA in 20% of the patient-cohort, and in nuclear genes in 49%, implying an overall yield of 68%. We identified pathogenic variants in mitochondrial and non-mitochondrial genes in both groups with, obviously, a higher number of mitochondrial genes affected in mitochondrial disease patients. Furthermore, we show that 31% of the disease-causing genes in the mitochondrial patient group were not included in the MitoCarta database, and therefore would have been missed with MitoCarta based gene-panels. We conclude that WES is preferable to panel-based approaches for both groups of patients, as the mitochondrial gene-list is not complete and mitochondrial symptoms can be secondary. Also, clinically and genetically heterogeneous disorders would require sequential use of multiple different gene panels. We conclude that WES is a comprehensive and unbiased approach to establish a genetic diagnosis in these patients, able to resolve multi-genic disease-causes.