Mitochondrial DNA Deletions Research Articles

Long-term hematopoietic dysfunction in patients with large-scale mitochondrial DNA deletion syndromes.

Pearson syndrome (PS) and Kearns-Sayre syndrome (KSS) are single large-scale mitochondrial DNA deletion (SLSMD) syndromes. PS is characterized by severe, transient childhood cytopenia, whereas KSS typically manifests later in life without hematologic abnormalities. Despite distinct clinical presentations, both share a common mitochondrial DNA deletion. Recent observations suggest a potential link between PS progression and myeloid malignancy development, indicating that bone marrow failure (BMF) may be a key aspect of PS pathology and potentially universal across SLSMDs. This study explores longitudinal hematological manifestations of SLSMD syndromes, focusing on bone marrow (BM) dysfunction. Sixteen patients with SLSMDs (13 PS and 3 KSS) were followed, of whom 75% experienced cytopenia, necessitating blood transfusions in 56%. Despite achieving transfusion independence at a median age of 24 months, persistent hematological abnormalities were noted. Comprehensive longitudinal BM studies were conducted in 62% of subjects and consistently revealed signs of marrow dysfunction, even without concurrent cytopenia. Median BM cellularity at a median age of four years and eight months was 50%, with histological signs of dyserythropoiesis, abnormal megakaryocytes, and signs suggesting myelodysplasia. Reduced CD34+ counts and BM colony-forming unit capacity were noted, alongside chromosome 7 aberrations in 16% of patients on cytogenetic studies. Our findings establish BM dysfunction as a persistent hallmark of SLSMD syndromes, posing a risk of clonal evolution and acquisition of chromosome 7 aberrations. This aligns with recent literature, emphasizing enduring BMF in SLSMD syndromes and advocating for tailored hematological monitoring guidelines for this unique patient cohort.

Clinical features and genetic analysis of child with Progressive external ophthalmoplegia with mitochondrial DNA deletions, autosomal dominant 6 due to variant of DNA2 gene

To explore the genetic etiology for a child with Progressive external ophthalmoplegia with mitochondrial DNA deletions, autosomal dominant 6 (PEOA6). A child who had attended the Women and Children's Hospital Affiliated to Ningbo University on 7 August, 2023 was selected as the study subject. Clinical data of the child were analyzed retrospectively. The child and her parents were subjected to whole exome sequencing (WES), and candidate variant was verified by Sanger sequencing and bioinformatic analysis. This study was approved by the Women and Children's Hospital Affiliated to Ningbo University (Ethics No. EC2020-048). The child, a 7-year-old female, had presented with limb muscle pain, amyosthenia, significantly increased creatine kinase, congenital diaphragmatic hernia and recurrent respiratory tract infections. WES revealed that the she has harbored a heterozygous c.1590G>C (p.L530F) variant of the DNA2 gene, which was verified to have a de novo origin by Sanger sequencing. Based on the guidelines from the American College of Medical Genetics and Genomics (ACMG), the c.1590G>C was rated as a likely pathogenic variant (PS2+PM2_Supporting+PP3). The c.1590G>C (p.L530F) variant of the DNA2 gene probably underlay the PEOA6 in this child.

GDF-15 and mtDNA Deletions Are Useful Biomarkers of Mitochondrial Dysfunction in Insulin Resistance and PCOS.

There is no literature available about the growth differentiation factor-15 (GDF-15) biomarker in combination with mitochondrial DNA (mtDNA) deletions in insulin resistance (IR), and polycystic ovary syndrome (PCOS); however, it would be useful to achieve optimal metabolic status and improve pregnancy success. In this study, the role of GDF-15 and mtDNA deletions as biomarkers in the pathogenesis of IR and PCOS was investigated. In our study, 81 female patients who were treated for IR and/or PCOS and 41 healthy controls were included. GDF-15 levels in patients showed a marked increase compared to controls. Elevated GDF-15 levels were found in 12 patients; all of them had a BMI > 25 kg/m2, which is associated with reactive hyperinsulinemia. The presence of mitochondrial dysfunction was mainly observed in the IR-only subgroup. The increase in plasma levels of GDF-15 and the prevalence of mtDNA deletions is directly proportional to body mass index. The more marked metabolic abnormalities required more intensive drug therapy with a parallel increase in plasma GDF-15 levels. Elevated levels of GDF-15 and the presence of mitochondrial DNA deletions may be a consequence of carbohydrate metabolism disorders in patients and thus a predictor of the process of accelerated aging.

Human sperm mitochondrial DNA copy numbers and deletion rates: Comparing persons living in two urban industrial agglomerations differing in sources of air pollution

Persons living in industrial environments are exposed to levels of air pollution that can affect their health and fertility. The Czech capital city, Prague, and the Ostrava industrial agglomeration differ in their major sources of air pollution. In Prague, heavy traffic produces high levels of nitrogen oxides throughout the year. In the Ostrava region, an iron industry and local heating are sources of particulate matter (PM) and benzo[a]pyrene (B[a]P), especially in the winter. We evaluated the effects of air pollution on human sperm mitochondrial DNA (mtDNA). Using real-time PCR, we analysed sperm mtDNA copy number and deletion rate in Prague city policemen in two seasons (spring and autumn) and compared the results with those from Ostrava. In Prague, the sperm mtDNA deletion rate was significantly higher in autumn than in spring, which is the opposite of the results from Ostrava. The sperm mtDNA copy number did not show any seasonal differences in either of the cities; it was correlated negatively with sperm concentration, motility, and viability, and with sperm chromatin integrity (assessed with the Sperm Chromatin Structure Assay). The comparison between the two cities showed that the sperm mtDNA deletion rate in spring and the sperm mtDNA copy number in autumn were significantly lower in Prague vs. Ostrava. Our study supports the hypothesis that sperm mtDNA deletion rate is affected by the composition of air pollution. Sperm mtDNA abundance is closely associated with chromatin damage and standard semen characteristics.

β-hydroxybutyrate and mitochondria mediate the association between medium-chain fatty acids, DHA and mild cognitive impairment: a nested case–control study

ABSTRACT Background Medium-chain fatty acids (MCFAs) and docosahexaenoic acid (DHA) could affect the occurrence of mild cognitive impairment (MCI). β-hydroxybutyrate (BHB), mitochondrial DNA copy number (mtDNAcn) and mitochondrial DNA (mtDNA) deletions might be their potential mechanisms. This study aimed to explore the relationship between MCFAs, DHA and MCI, and potential mechanisms. Methods This study used data from Tianjin Elderly Nutrition and Cognition (TENC) cohort study, 120 individuals were identified with new onset MCI during follow-up, 120 individuals without MCI were selected by 1:1 matching sex, age, and education levels as the control group from TENC. Conditional logistic regression analysis and mediation effect analysis were used to explore their relationship. Results Higher serum octanoic acid levels (OR: 0.633, 95% CI: 0.520, 0.769), higher serum DHA levels (OR: 0.962, 95% CI: 0.942, 0.981), and more mtDNAcn (OR: 0.436, 95% CI: 0.240, 0.794) were associated with lower MCI risk, while more mtDNA deletions was associated with higher MCI risk (OR: 8.833, 95% CI: 3.909, 19.960). Mediation analysis suggested that BHB and mtDNAcn, in series, have mediation roles in the association between octanoic acid and MCI risk, and mtDNA deletions have mediation roles in the association between DHA and MCI risk. Conclusion Higher serum octanoic acid and DHA levels were associated with lower MCI risk. Octanoic acid could affect the incidence of MCI through BHB, then mitochondria function, or through mitochondria function, or directly. Serum DHA level could affect the incidence of MCI through mitochondria function, or directly.

Cadmium causes cerebral mitochondrial dysfunction through regulating mitochondrial HSF1

Mitochondria, as the powerhouse of the cell, play a vital role in maintaining cellular energy homeostasis and are known to be a primary target of cadmium (Cd) toxicity. The improper targeting of proteins to mitochondria can compromise the normal functions of the mitochondria. However, the precise mechanism by which protein localization contributes to the development of mitochondrial dysfunction induced by Cd is still not fully understood. For this research, Hy-Line white variety chicks (1-day-old) were used and equally distributed into 4 groups: the Control group (fed with a basic diet), the Cd35 group (basic diet with 35 mg/kg CdCl2), the Cd70 group (basic diet with 70 mg/kg CdCl2) and the Cd140 group (basic diet with 140 mg/kg CdCl2), respectively for 90 days. It was found that Cd caused the accumulation of heat shock factor 1 (HSF1) in the mitochondria, and the overexpression of HSF1 in the mitochondria led to mitochondrial dysfunction and neuronal damage. This process is due to the mitochondrial HSF1 (mtHSF1), causing mitochondrial fission through the upregulation of dynamin-related protein 1 (Drp1) content, while inhibiting oligomer formation of single-stranded DNA-binding protein 1 (SSBP1), resulting in the mitochondrial DNA (mtDNA) deletion. The findings unveil an unforeseen role of HSF1 in triggering mitochondrial dysfunction.

Multi-Allelic Mitochondrial DNA Deletions in an Adult Dog with Chronic Weakness, Exercise Intolerance and Lactic Acidemia.

(1) Background: An adult dog was presented to a board-certified veterinary neurologist for evaluation of chronic weakness, exercise intolerance and lactic acidemia. (2) Methods: A mitochondrial myopathy was diagnosed based on the histological and histochemical phenotype of numerous COX-negative muscle fibers. Whole-genome sequencing established the presence of multiple extended deletions in the mitochondrial DNA (mtDNA), with the highest prevalence between the 1-11 kb positions of the approximately 16 kb mitochondrial chromosome. Such findings are typically suggestive of an underlying nuclear genome variant affecting mitochondrial replication, repair, or metabolism. (3) Results: Numerous variants in the nuclear genome unique to the case were identified in the whole-genome sequence data, and one, the insertion of a DYNLT1 retrogene, whose parent gene is a regulator of the mitochondrial voltage-dependent anion channel (VDAC), was considered a plausible causal variant. (4) Conclusions: Here, we add mitochondrial deletion disorders to the spectrum of myopathies affecting adult dogs.

Cancerous Conditions Accelerate the Aging of Skeletal Muscle via Mitochondrial DNA Damage.

Skeletal muscle aging and sarcopenia result in similar changes in the levels of aging markers. However, few studies have examined cancer sarcopenia from the perspective of aging. Therefore, this study investigated aging in cancer sarcopenia and explored its causes in vitro and in vivo. In mouse aging, in vitro cachexia, and mouse cachexia models, skeletal muscles showed similar changes in aging markers including oxidative stress, fibrosis, reduced muscle differentiation potential, and telomere shortening. Furthermore, examination of mitochondrial DNA from skeletal muscle revealed a 5 kb deletion in the major arc; truncation of complexes I, IV, and V in the electron transport chain; and reduced oxidative phosphorylation (OXPHOS). The mouse cachexia model demonstrated high levels of high-mobility group box-1 (HMGB1) and tumor necrosis factor-α (TNFα) in cancer ascites. Continuous administration of neutralizing antibodies against HMGB1 and TNFα in this model reduced oxidative stress and abrogated mitochondrial DNA deletion. These results suggest that in cancer sarcopenia, mitochondrial oxidative stress caused by inflammatory cytokines leads to mitochondrial DNA damage, which in turn leads to decreased OXPHOS and the promotion of aging.

Mechanisms and pathologies of human mitochondrial DNA replication and deletion formation.

Human mitochondria possess a multi-copy circular genome, mitochondrial DNA (mtDNA), that is essential for cellular energy metabolism. The number of copies of mtDNA per cell, and their integrity, are maintained by nuclear-encoded mtDNA replication and repair machineries. Aberrant mtDNA replication and mtDNA breakage are believed to cause deletions within mtDNA. The genomic location and breakpoint sequences of these deletions show similar patterns across various inherited and acquired diseases, and are also observed during normal ageing, suggesting a common mechanism of deletion formation. However, an ongoing debate over the mechanism by which mtDNA replicates has made it difficult to develop clear and testable models for how mtDNA rearrangements arise and propagate at a molecular and cellular level. These deletions may impair energy metabolism if present in a high proportion of the mtDNA copies within the cell, and can be seen in primary mitochondrial diseases, either in sporadic cases or caused by autosomal variants in nuclear-encoded mtDNA maintenance genes. These mitochondrial diseases have diverse genetic causes and multiple modes of inheritance, and show notoriously broad clinical heterogeneity with complex tissue specificities, which further makes establishing genotype-phenotype relationships challenging. In this review, we aim to cover our current understanding of how the human mitochondrial genome is replicated, the mechanisms by which mtDNA replication and repair can lead to mtDNA instability in the form of large-scale rearrangements, how rearranged mtDNAs subsequently accumulate within cells, and the pathological consequences when this occurs.

A novel mutation of DNA2 regulates neuronal cell membrane potential and epileptogenesis.

Mesial temporal lobe epilepsy (MTLE) is one of the most intractable epilepsies. Previously, we reported that mitochondrial DNA deletions were associated with epileptogenesis. While the underlying mechanism of mitochondrial DNA deletions during epileptogenesis remain unknown. In this study, a novel somatic mutation of DNA2 gene was identified in the hippocampal tissue of two MTLE patients carrying mitochondrial DNA deletions, and this mutation decreased the full-length expression of DNA2 protein significantly, aborting its normal functions. Then, we knocked down the DNA2 protein in zebrafish, and we demonstrated that zebrafish with DNA2 deficiency showed decreased expression of mitochondrial complex II-IV, and exhibited hallmarks of epileptic seizures, including abnormal development of the zebrafish and epileptiform discharge signals in brain, compared to the Cas9-control group. Moreover, our cell-based assays showed that DNA2 deletion resulted in accumulated mitochondrial DNA damage, abnormal oxidative phosphorylation and decreased ATP production in cells. Inadequate ATP generation in cells lead to declined Na+, K+-ATPase activity and change of cell membrane potential. Together, these disorders caused by DNA2 depletion increased cell apoptosis and inhibited the differentiation of SH-SY5Y into branched neuronal phenotype. In conclusion, DNA2 deficiency regulated the cell membrane potential via affecting ATP production by mitochondria and Na+, K+-ATPase activity, and also affected neuronal cell growth and differentiation. These disorders caused by DNA2 dysfunction are important causes of epilepsy. In summary, we are the first to report the pathogenic somatic mutation of DNA2 gene in the patients with MTLE disease, and we uncovered the mechanism of DNA2 regulating the epilepsy. This study provides new insight into the pathogenesis of epilepsy and underscore the value of DNA2 in epilepsy.

Mitochondrial defects in sporadic inclusion body myositis-causes and consequences.

Sporadic inclusion body myositis (sIBM) is a distinct subcategory of Idiopathic Inflammatory Myopathies (IIM), characterized by unique pathological features such as muscle inflammation, rimmed vacuoles, and protein aggregation within the myofibers. Although hyperactivation of the immune system is widely believed as the primary cause of IIM, it is debated whether non-immune tissue dysfunction might contribute to the disease's onset as patients with sIBM are refractory to conventional immunosuppressant treatment. Moreover, the findings that mitochondrial dysfunction can elicit non-apoptotic programmed cell death and the subsequent immune response further support this hypothesis. Notably, abnormal mitochondrial structure and activities are more prominent in the muscle of sIBM than in other types of IIM, suggesting the presence of defective mitochondria might represent an overlooked contributor to the disease onset. The large-scale mitochondrial DNA deletion, aberrant protein aggregation, and slowed organelle turnover have provided mechanistic insights into the genesis of impaired mitochondria in sIBM. This article reviews the disease hallmarks of sIBM, the plausible contributors of mitochondrial damage in the sIBM muscle, and the immunological responses associated with mitochondrial perturbations. Additionally, the potential application of mitochondrial-targeted chemicals as a new treatment strategy to sIBM is explored and discussed.

Exploring the evidence for mitochondrial dysfunction and genetic abnormalities in the etiopathogenesis of tropical ataxic neuropathy

Tropical ataxic neuropathy (TAN) is characterised by ataxic polyneuropathy, degeneration of the posterior columns and pyramidal tracts, optic atrophy, and sensorineural hearing loss. It has been attributed to nutritional/toxic etiologies, but evidence for the same has been equivocal. TAN shares common clinical features with inherited neuropathies and mitochondrial disorders, it may be hypothesised that genetic abnormalities may underlie the pathophysiology of TAN. This study aimed to establish evidence for mitochondrial dysfunction by adopting an integrated biochemical and multipronged genetic analysis. Patients (n = 65) with chronic progressive ataxic neuropathy with involvement of visual and/or auditory pathways underwent deep phenotyping, genetic studies including mitochondrial DNA (mtDNA) deletion analysis, mtDNA and clinical exome sequencing (CES), and respiratory chain complex (RCC) assay. The phenotypic characteristics included dysfunction of visual (n = 14), auditory (n = 12) and visual + auditory pathways (n = 29). Reduced RCC activity was present in 13 patients. Mitochondrial DNA deletions were noted in five patients. Sequencing of mtDNA (n = 45) identified a homoplasmic variant (MT-ND6) and a heteroplasmic variant (MT-COI) in one patient each. CES (n = 45) revealed 55 variants in nuclear genes that are associated with neuropathy (n = 27), deafness (n = 7), ataxia (n = 4), and mitochondrial phenotypes (n = 5) in 36 patients. This study provides preliminary evidence that TAN is associated with a spectrum of genetic abnormalities, including those associated with mitochondrial dysfunction, which is in contradistinction from the prevailing hypothesis that TAN is related to dietary toxins. Analysing the functional relevance of these genetic variants may improve the understanding of the pathogenesis of TAN.

A stagewise response to mitochondrial dysfunction in mitochondrial DNA maintenance disorders

Mitochondrial DNA (mtDNA) deletions which clonally expand in skeletal muscle of patients with mtDNA maintenance disorders, impair mitochondrial oxidative phosphorylation dysfunction. Previously we have shown that these mtDNA deletions arise and accumulate in perinuclear mitochondria causing localised mitochondrial dysfunction before spreading through the muscle fibre. We believe that mito-nuclear signalling is a key contributor in the accumulation and spread of mtDNA deletions, and that knowledge of how muscle fibres respond to mitochondrial dysfunction is key to our understanding of disease mechanisms.To understand the contribution of mito-nuclear signalling to the spread of mitochondrial dysfunction, we use imaging mass cytometry. We characterise the levels of mitochondrial Oxidative Phosphorylation proteins alongside a mitochondrial mass marker, in a cohort of patients with mtDNA maintenance disorders. Our expanded panel included protein markers of key signalling pathways, allowing us to investigate cellular responses to different combinations of oxidative phosphorylation dysfunction and ragged red fibres.We find combined Complex I and IV deficiency to be most common. Interestingly, in fibres deficient for one or more complexes, the remaining complexes are often upregulated beyond the increase of mitochondrial mass typically observed in ragged red fibres. We further find that oxidative phosphorylation deficient fibres exhibit an increase in the abundance of proteins involved in proteostasis, e.g. HSP60 and LONP1, and regulation of mitochondrial metabolism (including oxidative phosphorylation and proteolysis, e.g. PHB1). Our analysis suggests that the cellular response to mitochondrial dysfunction changes depending on the combination of deficient oxidative phosphorylation complexes in each fibre.

Mitochondrial DNA deletions in the cerebrospinal fluid of patients with idiopathic REM sleep behaviour disorder

Idiopathic rapid eye movement (REM) sleep behaviour disorder (IRBD) represents the prodromal stage of Lewy body disorders (Parkinson's disease (PD) and dementia with Lewy bodies (DLB)) which are linked to variations in circulating cell-free mitochondrial DNA (cf-mtDNA). Here, we assessed whether altered cf-mtDNA release and integrity are already present in IRBD. We used multiplex digital PCR (dPCR) to quantify cf-mtDNA copies and deletion ratio in cerebrospinal fluid (CSF) and serum in a cohort of 71 participants, including 1) 17 patients with IRBD who remained disease-free (non-converters), 2) 34 patients initially diagnosed with IRBD who later developed either PD or DLB (converters), and 3) 20 age-matched controls without IRBD or Parkinsonism. In addition, we investigated whether CD9-positive extracellular vesicles (CD9-EVs) from CSF and serum samples contained cf-mtDNA. Patients with IRBD, both converters and non-converters, exhibited more cf-mtDNA with deletions in the CSF than controls. This finding was confirmed in CD9-EVs. The high levels of deleted cf-mtDNA in CSF corresponded to a significant decrease in cf-mtDNA copies in CD9-EVs in both IRBD non-converters and converters. Conversely, a significant increase in cf-mtDNA copies was found in serum and CD9-EVs from the serum of patients with IRBD who later converted to a Lewy body disorder. Alterations in cf-mtDNA copy number and deletion ratio known to occur in Lewy body disorders are already present in IRBD and are not a consequence of Lewy body disease conversion. This suggests that mtDNA dysfunction is a primary molecular mechanism of the pathophysiological cascade that precedes the full clinical motor and cognitive manifestation of Lewy body disorders. Funded by Michael J. Fox Foundation research grant MJFF-001111. Funded by MICIU/AEI/10.13039/501100011033 "ERDF A way of making Europe", grants PID2020-115091RB-I00 (RT) and PID2022-143279OB-I00 (ACo). Funded by Instituto de Salud Carlos III and European Union NextGenerationEU/PRTR, grant PMP22/00100 (RT and ACo). Funded by AGAUR/Generalitat de Catalunya, grant SGR00490 (RT and ACo). MP has an FPI fellowship, PRE2018-083297, funded by MICIU/AEI/10.13039/501100011033 "ESF Investing in your future".

Dermatologic Manifestations of Mitochondrial Dysfunction: A Review of the Literature.

Mitochondria are eukaryotic cellular organelles that function in energy metabolism, ROS production, and programmed cell death. Cutaneous epithelial and hair follicle dermal papilla cells are energy-rich cells that thereby may be affected by mitochondrial dysfunction and DNA mutation accumulation. In this review, we aimed to summarize the medical literature assessing dermatologic conditions and outcomes associated with mitochondrial dysfunction. A search of PubMed and Embase was performed with subsequent handsearching to retrieve additional relevant articles. Mitochondrial DNA (mtDNA) deletions, mutation accumulation, and damage are associated with phenotypic signs of cutaneous aging, hair loss, and impaired wound healing. In addition, several dermatologic conditions are associated with aberrant mitochondrial activity, such as systemic lupus erythematosus, psoriasis, vitiligo, and atopic dermatitis. Mouse model studies have better established causality between mitochondrial damage and dermatologic outcomes, with some depicting reversibility upon restoration of mitochondrial function. Mitochondrial function mediates a variety of dermatologic conditions, and mitochondrial components may be a promising target for therapeutic strategies.

Management of Ptosis in Kearns-Sayre Syndrome: A Case Report and Literature Review.

Kearns-Sayre syndrome (KSS) is a rare mitochondrial disease that affects young adults, due to a deletion of mitochondrial DNA and characterized by the triad: age of onset lower than 20 years, chronic progressive external ophthalmoplegia, and an atypical pigmentary retinopathy. It is also characterized by other endocrine, neurological, and especially cardiac impairment with a very high risk of cardiac complications during surgical procedures under all types of anesthesia. We report a case of KSS revealed by severe bilateral ptosis and confirmed by a muscle biopsy with "ragged red fibers." The ptosis was surgically managed by cautious Frontal suspension under local anesthesia "Frontal nerve block." Through this case, we discuss challenges in the management of KSS patients.

Common mitochondrial deletions in RNA-Seq: evaluation of bulk, single-cell, and spatial transcriptomic datasets

Common mitochondrial DNA (mtDNA) deletions are large structural variants in the mitochondrial genome that accumulate in metabolically active tissues with age and have been investigated in various diseases. We applied the Splice-Break2 pipeline (designed for high-throughput quantification of mtDNA deletions) to human RNA-Seq datasets and describe the methodological considerations for evaluating common deletions in bulk, single-cell, and spatial transcriptomics datasets. A robust evaluation of 1570 samples from 14 RNA-Seq studies showed: (i) the abundance of some common deletions detected in PCR-amplified mtDNA correlates with levels observed in RNA-Seq data; (ii) RNA-Seq library preparation method has a strong effect on deletion detection; (iii) deletions had a significant, positive correlation with age in brain and muscle; (iv) deletions were enriched in cortical grey matter, specifically in layers 3 and 5; and (v) brain regions with dopaminergic neurons (i.e., substantia nigra, ventral tegmental area, and caudate nucleus) had remarkable enrichment of common mtDNA deletions.

Mitochondrial myopathies diagnosed in adulthood: clinico-genetic spectrum and long-term outcomes.

Mitochondrial myopathies are frequently recognized in childhood as part of a broader multisystem disorder and often overlooked in adulthood. Herein, we describe the phenotypic and genotypic spectrum and long-term outcomes of mitochondrial myopathies diagnosed in adulthood, focusing on neuromuscular features, electrodiagnostic and myopathological findings and survival. We performed a retrospective chart review of adult patients diagnosed with mitochondrial myopathy at Mayo Clinic (2005-21). We identified 94 patients. Median time from symptom onset to diagnosis was 11 years (interquartile range 4-21 years). Median age at diagnosis was 48 years (32-63 years). Primary genetic defects were identified in mitochondrial DNA in 48 patients (10 with single large deletion, 38 with point mutations) and nuclear DNA in 29. Five patients had multiple mitochondrial DNA deletions or depletion without nuclear DNA variants. Twelve patients had histopathological features of mitochondrial myopathy without molecular diagnosis. The most common phenotypes included multisystem disorder (n = 30); mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes (14); limb myopathy (13); chronic progressive external ophthalmoplegia (12); and chronic progressive external ophthalmoplegia-plus (12). Isolated skeletal muscle manifestations occurred in 27%. Sixty-nine per cent had CNS and 21% had cardiac involvement. Mutations most frequently involved MT-TL1 (27) and POLG (17); however, a wide spectrum of established and novel molecular defects, with overlapping phenotypes, was identified. Electrodiagnostic studies identified myopathy (77%), fibrillation potentials (27%) and axonal peripheral neuropathy (42%, most common with nuclear DNA variants). Among 42 muscle biopsies available, median percentage counts were highest for cytochrome C oxidase negative fibres (5.1%) then ragged blue (1.4%) and ragged red fibres (0.5%). Skeletal muscle weakness was mild and slowly progressive (decline in strength summated score of 0.01/year). Median time to gait assistance was 5.5 years from diagnosis and 17 years from symptom onset. Thirty patients died, with median survival of 33.4 years from symptom onset and 10.9 years from diagnosis. Median age at death was 55 years. Cardiac involvement was associated with increased mortality [hazard ratio 2.36 (1.05, 5.29)]. There was no difference in survival based on genotype or phenotype. Despite the wide phenotypic and genotypic spectrum, mitochondrial myopathies in adults share similar features with slowly progressive limb weakness, contrasting with common multiorgan involvement and high mortality.

Kearns–Sayre Syndrome with Bilateral Ptosis and External Ophthalmoplegia: A Rare Case Report

Abstract
 Introduction : Kearns-Sayre syndrome (KSS) is a rare genetic disorder caused by a deletion of mitochondrial DNA (mtDNA) segment, typically characterized by a triad of symptoms includes external ophthalmoplegia, pigmentary retinopathy and appeared before the age of 20. The prevalence rate is about 1–3 per 100.000 individuals. It was diagnosed based on clinical features and supported by biochemical, radiological, histologic, and molecular genetic tests.
 Case Illustration : 26-year-old male with bilateral ptosis, chronic progressive external ophthalmoplegia, pigmentary retinopathy was shown from ophthalmology examination and associated with hearing loss. Physical examination showed short stature, wasting, and weakness of limb muscles. MRI examination revealed focal brain atrophy on bilateral parietal regions.
 Discussion : Mitochondrial DNA defect led to dysfunction of the central nervous system, endocrine system, extraocular muscle, myocardium, skeletal muscle, and other multiple systems. The clinical findings in this patient are appropriate for classical signs and symptoms of KSS. Central nervous involvementis shown by the neuroimaging result. There is no cardiac involvement suggested by normal cardiology examination. Although muscle pathology and molecular genetic analysis can play a great role to diagnose KSS, the classical triad of clinical signs plus one of the other symptoms could establish KSS diagnosis.
 Conclusion : KSS is a rare genetic disorder and challenging to diagnose. However, if a patient presents with the classic triad of symptoms, clinicians should have a high level of suspicion for the disorder. Additionally, It is important to perform a thorough evaluation to rule out other conditions that can cause similar symptoms.

An Integrated Undergraduate Laboratory Exercise to Demonstrate Microbial Evolution

Understanding that evolution progresses through generation of DNA variants followed by selection is a key learning outcome for biology students. We designed an integrated and innovative undergraduate laboratory exercise using Saccharomyces cerevisiae to demonstrate these principles. Students perform in vitro experimental evolution by repeatedly propagating large or small yeast colonies on a weekly basis. Small-colony variants known as petites arise by mutations that disrupt aerobic respiration. To demonstrate the effects of increased mutation rates, half of the selection lines are exposed to ultraviolet irradiation. To understand how the petite phenotype arises, polymerase chain reaction (PCR) is performed to examine mitochondrial DNA, while biochemical assays are used to assess the ability of petites to undergo aerobic respiration. This exercise demonstrates evolution by artificial selection over a suitably short timeframe and links the results to a critical biochemical process: the role of mitochondria in aerobic respiration and ATP production. By implementing these experiments, we successfully demonstrated that the frequencies of petite mutants in evolved populations varied according to the selection pressure we applied, and that petite mutants carried deletions in mitochondrial DNA as anticipated. Through an integrated learning context, this practical exercise promotes fundamental understanding of evolutionary processes and fosters critical thinking skills.