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Ezhilarasan D, Mani U. Valproic acid induced liver injury: An insight into molecular toxicological mechanism. ENVIRONMENTAL TOXICOLOGY AND PHARMACOLOGY 2022; 95:103967. [PMID: 36058508 DOI: 10.1016/j.etap.2022.103967] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/02/2022] [Revised: 08/22/2022] [Accepted: 08/29/2022] [Indexed: 06/15/2023]
Abstract
Valproic acid (VPA) is an anti-seizure drug that causes idiosyncratic liver injury. 2-propyl-4-pentenoic acid (Δ4VPA), a metabolite of VPA, has been implicated in VPA-induced hepatotoxicity. This review summarizes the pathogenesis involved in VPA-induced liver injury. The VPA induce liver injury mainly by i) liberation of Δ4VPA metabolites; ii) decrease in glutathione stores and antioxidants, resulting in oxidative stress; iii) inhibition of fatty acid β-oxidation, inducing mitochondrial DNA depletion and hypermethylation; a decrease in proton leak; oxidative phosphorylation impairment and ATP synthesis decrease; iv) induction of fatty liver via inhibition of carnitine palmitoyltransferase I, enhancing nuclear receptor peroxisome proliferator-activated receptor-gamma and acyl-CoA thioesterase 1, and inducing long-chain fatty acid uptake and triglyceride synthesis. VPA administration aggravates liver injury in individuals with metabolic syndromes. Therapeutic drug monitoring, routine serum levels of transaminases, ammonia, and lipid parameters during VPA therapy may thus be beneficial in improving the safety profile or preventing the progression of DILI.
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Affiliation(s)
- Devaraj Ezhilarasan
- Department of Pharmacology, Saveetha Dental College, Saveetha Institute of Medical and Technical Sciences, Chennai, Tamil Nadu 600 077, India.
| | - Uthirappan Mani
- Animal House Division, CSIR-Central Leather Research Institute, Adyar, Chennai 600 020, India
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2
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Movement disorders and neuropathies: overlaps and mimics in clinical practice. J Neurol 2022; 269:4646-4662. [PMID: 35657406 DOI: 10.1007/s00415-022-11200-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2022] [Accepted: 05/16/2022] [Indexed: 10/18/2022]
Abstract
Movement disorders as well as peripheral neuropathies are extremely frequent in the general population; therefore, it is not uncommon to encounter patients with both these conditions. Often, the coexistence is coincidental, due to the high incidence of common causes of peripheral neuropathy, such as diabetes and other age-related disorders, as well as of Parkinson disease (PD), which has a typical late onset. Nonetheless, there is broad evidence that PD patients may commonly develop a sensory and/or autonomic polyneuropathy, triggered by intrinsic and/or extrinsic mechanisms. Similarly, some peripheral neuropathies may develop some movement disorders in the long run, such as tremor, and rarely dystonia and myoclonus, suggesting that central mechanisms may ensue in the pathogenesis of these diseases. Although rare, several acquired or hereditary causes may be responsible for the combination of movement and peripheral nerve disorders as a unique entity, some of which are potentially treatable, including paraneoplastic, autoimmune and nutritional aetiologies. Finally, genetic causes should be pursued in case of positive family history, young onset or multisystemic involvement, and examined for neuroacanthocytosis, spinocerebellar ataxias, mitochondrial disorders and less common causes of adult-onset cerebellar ataxias and spastic paraparesis. Deep phenotyping in terms of neurological and general examination, as well as laboratory tests, neuroimaging, neurophysiology, and next-generation genetic analysis, may guide the clinician toward the correct diagnosis and management.
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Senthilvelan S, Sekar SS, Kesavadas C, Thomas B. Neuromitochondrial Disorders : Genomic Basis and an Algorithmic Approach to Imaging Diagnostics. Clin Neuroradiol 2021; 31:559-574. [PMID: 34106285 DOI: 10.1007/s00062-021-01030-4] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2021] [Accepted: 04/28/2021] [Indexed: 10/21/2022]
Abstract
Mitochondrial disorders have been an enigma for a long time due to the varied clinical presentations. Although a genetic confirmation will be mandatory most of the time, half the number of Leigh syndrome would be negative for genetic mutations. There are a growing number of mutations in clinical practice, which escape detection on routine clinical exome sequencing. Imaging would render help in pointing towards a mitochondrial disorder. There are a few case reports which brief about specific mitochondrial mutations and their specific imaging appearance. This article tries to provide a comprehensive review on the imaging-genomic correlation of mitochondrial disorders with an objective of performing a specific genetic testing to arrive at an accurate diagnosis.
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Affiliation(s)
- Santhakumar Senthilvelan
- Department of IS&IR, Sree Chitra Tirunal Institute for Medical Sciences and Technology, Kerala, Trivandrum, India
| | - Sabarish S Sekar
- Department of IS&IR, Sree Chitra Tirunal Institute for Medical Sciences and Technology, Kerala, Trivandrum, India
| | - Chandrasekharan Kesavadas
- Department of IS&IR, Sree Chitra Tirunal Institute for Medical Sciences and Technology, Kerala, Trivandrum, India
| | - Bejoy Thomas
- Department of IS&IR, Sree Chitra Tirunal Institute for Medical Sciences and Technology, Kerala, Trivandrum, India.
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Darin N, Siibak T, Peter B, Hedberg-Oldfors C, Kollberg G, Kalbin V, Moslemi AR, Macao B, Oldfors A, Falkenberg M. Functional analysis of a novel POLγA mutation associated with a severe perinatal mitochondrial encephalomyopathy. Neuromuscul Disord 2021; 31:348-358. [PMID: 33579567 DOI: 10.1016/j.nmd.2021.01.004] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2020] [Revised: 01/05/2021] [Accepted: 01/06/2021] [Indexed: 12/18/2022]
Abstract
Mutations in the mitochondrial DNA polymerase gamma catalytic subunit (POLγA) compromise the stability of mitochondrial DNA (mtDNA) by leading to mutations, deletions and depletions in mtDNA. Patients with mutations in POLγA often differ remarkably in disease severity and age of onset. In this work we have studied the functional consequence of POLγA mutations in a patient with an uncommon and a very severe disease phenotype characterized by prenatal onset with intrauterine growth restriction, lactic acidosis from birth, encephalopathy, hepatopathy, myopathy, and early death. Muscle biopsy identified scattered COX-deficient muscle fibers, respiratory chain dysfunction and mtDNA depletion. We identified a novel POLγA mutation (p.His1134Tyr) in trans with the previously identified p.Thr251Ile/Pro587Leu double mutant. Biochemical characterization of the purified recombinant POLγA variants showed that the p.His1134Tyr mutation caused severe polymerase dysfunction. The p.Thr251Ile/Pro587Leu mutation caused reduced polymerase function in conditions of low dNTP concentration that mimic postmitotic tissues. Critically, when p.His1134Tyr and p.Thr251Ile/Pro587Leu were combined under these conditions, mtDNA replication was severely diminished and featured prominent stalling. Our data provide a molecular explanation for the patient´s mtDNA depletion and clinical features, particularly in tissues such as brain and muscle that have low dNTP concentration.
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Affiliation(s)
- Niklas Darin
- Department of Pediatrics, Institute of Clinical Sciences, University of Gothenburg, Gothenburg, Sweden.
| | - Triinu Siibak
- Department of Medical Biochemistry and Cell Biology, Institute of Biomedicine, University of Gothenburg, Box 440, 40530 Gothenburg, Sweden
| | - Bradley Peter
- Department of Medical Biochemistry and Cell Biology, Institute of Biomedicine, University of Gothenburg, Box 440, 40530 Gothenburg, Sweden
| | - Carola Hedberg-Oldfors
- Department of Laboratory Medicine, Institute of Biomedicine, University of Gothenburg, Gothenburg, Sweden
| | - Gittan Kollberg
- Department of Laboratory Medicine, Institute of Biomedicine, University of Gothenburg, Gothenburg, Sweden
| | - Vassili Kalbin
- Department of Medical Biochemistry and Cell Biology, Institute of Biomedicine, University of Gothenburg, Box 440, 40530 Gothenburg, Sweden
| | - Ali-Reza Moslemi
- Department of Laboratory Medicine, Institute of Biomedicine, University of Gothenburg, Gothenburg, Sweden
| | - Bertil Macao
- Department of Medical Biochemistry and Cell Biology, Institute of Biomedicine, University of Gothenburg, Box 440, 40530 Gothenburg, Sweden
| | - Anders Oldfors
- Department of Laboratory Medicine, Institute of Biomedicine, University of Gothenburg, Gothenburg, Sweden
| | - Maria Falkenberg
- Department of Medical Biochemistry and Cell Biology, Institute of Biomedicine, University of Gothenburg, Box 440, 40530 Gothenburg, Sweden.
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Lujan SA, Longley MJ, Humble MH, Lavender CA, Burkholder A, Blakely EL, Alston CL, Gorman GS, Turnbull DM, McFarland R, Taylor RW, Kunkel TA, Copeland WC. Ultrasensitive deletion detection links mitochondrial DNA replication, disease, and aging. Genome Biol 2020; 21:248. [PMID: 32943091 PMCID: PMC7500033 DOI: 10.1186/s13059-020-02138-5] [Citation(s) in RCA: 36] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2020] [Accepted: 08/07/2020] [Indexed: 12/31/2022] Open
Abstract
BACKGROUND Acquired human mitochondrial genome (mtDNA) deletions are symptoms and drivers of focal mitochondrial respiratory deficiency, a pathological hallmark of aging and late-onset mitochondrial disease. RESULTS To decipher connections between these processes, we create LostArc, an ultrasensitive method for quantifying deletions in circular mtDNA molecules. LostArc reveals 35 million deletions (~ 470,000 unique spans) in skeletal muscle from 22 individuals with and 19 individuals without pathogenic variants in POLG. This nuclear gene encodes the catalytic subunit of replicative mitochondrial DNA polymerase γ. Ablation, the deleted mtDNA fraction, suffices to explain skeletal muscle phenotypes of aging and POLG-derived disease. Unsupervised bioinformatic analyses reveal distinct age- and disease-correlated deletion patterns. CONCLUSIONS These patterns implicate replication by DNA polymerase γ as the deletion driver and suggest little purifying selection against mtDNA deletions by mitophagy in postmitotic muscle fibers. Observed deletion patterns are best modeled as mtDNA deletions initiated by replication fork stalling during strand displacement mtDNA synthesis.
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Affiliation(s)
- Scott A Lujan
- Genome Integrity and Structural Biology Laboratory, DNA Replication Fidelity Group, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, NC, 27709, USA
| | - Matthew J Longley
- Genome Integrity and Structural Biology Laboratory, Mitochondrial DNA Replication Group, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, NC, 27709, USA
| | - Margaret H Humble
- Genome Integrity and Structural Biology Laboratory, Mitochondrial DNA Replication Group, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, NC, 27709, USA
| | - Christopher A Lavender
- Integrative Bioinformatics, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, NC, 27709, USA
| | - Adam Burkholder
- Integrative Bioinformatics, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, NC, 27709, USA
| | - Emma L Blakely
- Wellcome Centre for Mitochondrial Research, Translational and Clinical Research Institute, Faculty of Medical Sciences, Newcastle University, Newcastle upon Tyne, NE2 4HH, UK
- NHS Highly Specialised Mitochondrial Diagnostic Laboratory, Newcastle upon Tyne Hospitals NHS Foundation Trust, Newcastle upon Tyne, NE1 4LP, UK
| | - Charlotte L Alston
- Wellcome Centre for Mitochondrial Research, Translational and Clinical Research Institute, Faculty of Medical Sciences, Newcastle University, Newcastle upon Tyne, NE2 4HH, UK
- NHS Highly Specialised Mitochondrial Diagnostic Laboratory, Newcastle upon Tyne Hospitals NHS Foundation Trust, Newcastle upon Tyne, NE1 4LP, UK
| | - Grainne S Gorman
- Wellcome Centre for Mitochondrial Research, Translational and Clinical Research Institute, Faculty of Medical Sciences, Newcastle University, Newcastle upon Tyne, NE2 4HH, UK
| | - Doug M Turnbull
- Wellcome Centre for Mitochondrial Research, Translational and Clinical Research Institute, Faculty of Medical Sciences, Newcastle University, Newcastle upon Tyne, NE2 4HH, UK
| | - Robert McFarland
- Wellcome Centre for Mitochondrial Research, Translational and Clinical Research Institute, Faculty of Medical Sciences, Newcastle University, Newcastle upon Tyne, NE2 4HH, UK
| | - Robert W Taylor
- Wellcome Centre for Mitochondrial Research, Translational and Clinical Research Institute, Faculty of Medical Sciences, Newcastle University, Newcastle upon Tyne, NE2 4HH, UK
- NHS Highly Specialised Mitochondrial Diagnostic Laboratory, Newcastle upon Tyne Hospitals NHS Foundation Trust, Newcastle upon Tyne, NE1 4LP, UK
| | - Thomas A Kunkel
- Genome Integrity and Structural Biology Laboratory, DNA Replication Fidelity Group, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, NC, 27709, USA
| | - William C Copeland
- Genome Integrity and Structural Biology Laboratory, Mitochondrial DNA Replication Group, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, NC, 27709, USA.
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6
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Piekutowska-Abramczuk D, Kaliszewska M, Sułek A, Jurkowska N, Ołtarzewski M, Jabłońska E, Trubicka J, Głowacka A, Ciara E, Kowalski P, Langiewicz-Wojciechowska K, Tesarova M, Zeman J, Kierdaszuk B, Kuczyński D, Chmielewski D, Szymańska E, Bakuła A, Łusakowska A, Lipowska M, Brodacki B, Pera J, Dorobek M, Rydzanicz M, Płoski R, Chrzanowska KH, Bartnik E, Placha G, Kamińska A, Kostera-Pruszczyk A, Krajewska-Walasek M, Tońska K, Pronicka E. The frequency of mitochondrial polymerase gamma related disorders in a large Polish population cohort. Mitochondrion 2019; 47:179-187. [DOI: 10.1016/j.mito.2018.11.004] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2018] [Revised: 10/02/2018] [Accepted: 11/02/2018] [Indexed: 02/06/2023]
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Zhou Z, Austin GL, Young LEA, Johnson LA, Sun R. Mitochondrial Metabolism in Major Neurological Diseases. Cells 2018; 7:E229. [PMID: 30477120 PMCID: PMC6316877 DOI: 10.3390/cells7120229] [Citation(s) in RCA: 36] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2018] [Revised: 11/19/2018] [Accepted: 11/21/2018] [Indexed: 01/18/2023] Open
Abstract
Mitochondria are bilayer sub-cellular organelles that are an integral part of normal cellular physiology. They are responsible for producing the majority of a cell's ATP, thus supplying energy for a variety of key cellular processes, especially in the brain. Although energy production is a key aspect of mitochondrial metabolism, its role extends far beyond energy production to cell signaling and epigenetic regulation⁻functions that contribute to cellular proliferation, differentiation, apoptosis, migration, and autophagy. Recent research on neurological disorders suggest a major metabolic component in disease pathophysiology, and mitochondria have been shown to be in the center of metabolic dysregulation and possibly disease manifestation. This review will discuss the basic functions of mitochondria and how alterations in mitochondrial activity lead to neurological disease progression.
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Affiliation(s)
- Zhengqiu Zhou
- Molecular & Cellular Biochemistry Department, University of Kentucky, Lexington, KY 40536, USA.
| | - Grant L Austin
- Molecular & Cellular Biochemistry Department, University of Kentucky, Lexington, KY 40536, USA.
| | - Lyndsay E A Young
- Molecular & Cellular Biochemistry Department, University of Kentucky, Lexington, KY 40536, USA.
| | - Lance A Johnson
- Department of Physiology, University of Kentucky, Lexington, KY 40536, USA.
| | - Ramon Sun
- Molecular & Cellular Biochemistry Department, University of Kentucky, Lexington, KY 40536, USA.
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8
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The clinical spectrum and natural history of early-onset diseases due to DNA polymerase gamma mutations. Genet Med 2017; 19:1217-1225. [DOI: 10.1038/gim.2017.35] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2016] [Revised: 02/16/2017] [Accepted: 02/17/2017] [Indexed: 12/26/2022] Open
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Saneto RP. Alpers-Huttenlocher syndrome: the role of a multidisciplinary health care team. J Multidiscip Healthc 2016; 9:323-33. [PMID: 27555780 PMCID: PMC4968991 DOI: 10.2147/jmdh.s84900] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
Alpers–Huttenlocher syndrome (AHS) is a mitochondrial DNA-depletion syndrome. Age of onset is bimodal: early onset at 2–4 years and later adolescent onset at 17–24 years of age. Early development is usually normal, with epilepsy heralding the disorder in ~50% of patients. The onset of seizures is coupled with progressive cognitive decline. Hepatopathy is variable, and when present is a progressive dysfunction leading to liver failure in many cases. These features of seizures, cognitive degeneration, and hepatopathy represent the “classic triad” of AHS. However, most patients develop other system involvement. Therefore, although AHS is ultimately a lethal disorder, medical care is required for sustained quality of life. Frequently, additional organ systems – gastrointestinal, respiratory, nutritional, and psychiatric – abnormalities appear and need treatment. Rarely, cardiovascular dysfunction and even pregnancy complicate medical treatment. Optimal care requires a team of physicians and caretakers to make sure quality of life is optimized. The care team, together with the family and palliative care specialists, need to be in communication as the disease progresses and medical changes occur. Although the unpredictable losses of function challenge medical care, the team approach can foster the individual quality-of-life care needed for the patient and family.
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Affiliation(s)
- Russell P Saneto
- Department of Neurology, University of Washington; Division of Pediatric Neurology, Seattle Children's Hospital, Seattle, WA, USA
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10
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Formichi P, Radi E, Branca C, Battisti C, Brunetti J, Da Pozzo P, Giannini F, Dotti MT, Bracci L, Federico A. Oxidative stress-induced apoptosis in peripheral blood lymphocytes from patients with POLG-related disorders. J Neurol Sci 2016; 368:359-68. [PMID: 27538665 DOI: 10.1016/j.jns.2016.07.047] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2016] [Revised: 07/07/2016] [Accepted: 07/19/2016] [Indexed: 12/29/2022]
Abstract
BACKGROUND POLG-related disorders are a group of heterogeneous diseases characterized by an overlapping clinical presentations and associated with mutations in the POLG gene. POLG codes for the catalytic subunit of mitochondrial polymerase gamma (POLG), essential for mitochondrial DNA (mtDNA) replication and repair. Studies on mutator POLG mice showed an increase in oxidative stress and apoptosis. In this regard we analysed the involvement of POLG mutations in the apoptotic regulation, evaluating apoptosis in peripheral blood lymphocytes (PBLs) from patients with POLG-related diseases. METHODS Cells were cultured under basal conditions and with 2-deoxy-d-ribose (dRib), a reducing sugar that induces apoptosis by oxidative stress. Apoptosis rate was assessed by flow cytometry. Phosphatidylserine translocation, mitochondrial membrane depolarization and caspase 3 activation were also analysed. RESULTS Our data showed higher percentages of apoptosis after dRib treatment in patients with POLG mutations than in controls, while under basal culture conditions, apoptosis levels were similar in the two groups. CONCLUSIONS Cells with POLG mutations are more sensitive than control cells to oxidative stress-induced apoptosis, confirming that mtDNA mutations may have a role in mitochondrial apoptosis pathway. We also suggest that redox state homeostasis may play a crucial role in phenotypic expression of POLG-related diseases.
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Affiliation(s)
- Patrizia Formichi
- Department of Medicine, Surgery and Neurosciences, University of Siena, Siena, Italy
| | - Elena Radi
- Department of Medicine, Surgery and Neurosciences, University of Siena, Siena, Italy
| | - Chiara Branca
- Department of Medicine, Surgery and Neurosciences, University of Siena, Siena, Italy
| | - Carla Battisti
- Department of Medicine, Surgery and Neurosciences, University of Siena, Siena, Italy
| | - Jlenia Brunetti
- Department of Medical Biotechnologies, University of Siena, Siena, Italy
| | - Paola Da Pozzo
- Department of Medicine, Surgery and Neurosciences, University of Siena, Siena, Italy
| | - Fabio Giannini
- Department of Medicine, Surgery and Neurosciences, University of Siena, Siena, Italy
| | - Maria Teresa Dotti
- Department of Medicine, Surgery and Neurosciences, University of Siena, Siena, Italy
| | - Luisa Bracci
- Department of Medical Biotechnologies, University of Siena, Siena, Italy
| | - Antonio Federico
- Department of Medicine, Surgery and Neurosciences, University of Siena, Siena, Italy.
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Li S, Guo J, Ying Z, Chen S, Yang L, Chen K, Long Q, Qin D, Pei D, Liu X. Valproic acid-induced hepatotoxicity in Alpers syndrome is associated with mitochondrial permeability transition pore opening-dependent apoptotic sensitivity in an induced pluripotent stem cell model. Hepatology 2015; 61:1730-9. [PMID: 25605636 DOI: 10.1002/hep.27712] [Citation(s) in RCA: 64] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/18/2014] [Accepted: 01/13/2015] [Indexed: 12/29/2022]
Abstract
UNLABELLED Valproic acid (VPA) is widely used to treat epilepsy, migraine, chronic headache, bipolar disorder, and as adjuvant chemotherapy, but potentially causes idiosyncratic liver injury. Alpers-Huttenlocher syndrome (AHS), a neurometabolic disorder caused by mutations in mitochondrial DNA polymerase gamma (POLG), is associated with an increased risk of developing fatal VPA hepatotoxicity. However, the mechanistic link of this clinical mystery remains unknown. Here, fibroblasts from 2 AHS patients were reprogrammed to induced pluripotent stem cells (iPSCs) and then differentiated to hepatocyte-like cells (AHS iPSCs-Hep). Both AHS iPSCs-Hep are more sensitive to VPA-induced mitochondrial-dependent apoptosis than controls, showing more activated caspase-9 and cytochrome c release. Strikingly, levels of both soluble and oligomeric optic atrophy 1, which together keep cristae junctions tight, are reduced in AHS iPSCs-Hep. Furthermore, POLG mutation cells show reduced POLG expression, mitochondrial DNA (mtDNA) amount, mitochondrial adenosine triphosphate production, as well as abnormal mitochondrial ultrastructure after differentiation to hepatocyte-like cells. Superoxide flashes, spontaneous bursts of superoxide generation, caused by opening of the mitochondrial permeability transition pore (mPTP), occur more frequently in AHS iPSCs-Hep. Moreover, the mPTP inhibitor, cyclosporine A, rescues VPA-induced apoptotic sensitivity in AHS iPSCs-Hep. This result suggests that targeting mPTP opening could be an effective method to prevent hepatotoxicity by VPA in AHS patients. In addition, carnitine or N-acetylcysteine, which has been used in the treatment of VPA-induced hepatotoxicity, is able to rescue VPA-induced apoptotic sensitivity in AHS iPSCs-Hep. CONCLUSION AHS iPSCs-Hep are more sensitive to the VPA-induced mitochondrial-dependent apoptotic pathway, and this effect is mediated by mPTP opening. Toxicity models in genetic diseases using iPSCs enable the evaluation of drugs for therapeutic targets.
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Affiliation(s)
- Shengbiao Li
- Key Laboratory of Regenerative Biology, Guangdong Provincial Key Laboratory of Stem Cell and Regenerative Medicine, South China Institute for Stem Cell Biology and Regenerative Medicine, Guangzhou Institutes of Biomedicine and Health, Chinese Academy of Sciences, Guangzhou, China; University of Science and Technology of China, Hefei, Anhui, China
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12
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The in cis T251I and P587L POLG1 base changes: Description of a new family and literature review. Neuromuscul Disord 2015; 25:333-9. [DOI: 10.1016/j.nmd.2015.01.004] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2014] [Revised: 01/07/2015] [Accepted: 01/14/2015] [Indexed: 11/19/2022]
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13
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15
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Sitarz KS, Elliott HR, Karaman BS, Relton C, Chinnery PF, Horvath R. Valproic acid triggers increased mitochondrial biogenesis in POLG-deficient fibroblasts. Mol Genet Metab 2014; 112:57-63. [PMID: 24725338 PMCID: PMC4013927 DOI: 10.1016/j.ymgme.2014.03.006] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/17/2014] [Revised: 03/18/2014] [Accepted: 03/19/2014] [Indexed: 12/25/2022]
Abstract
Valproic acid (VPA) is a widely used antiepileptic drug and also prescribed to treat migraine, chronic headache and bipolar disorder. Although it is usually well tolerated, a severe hepatotoxic reaction has been repeatedly reported after VPA administration. A profound toxic reaction on administration of VPA has been observed in several patients carrying POLG mutations, and heterozygous genetic variation in POLG has been strongly associated with VPA-induced liver toxicity. Here we studied the effect of VPA in fibroblasts of five patients carrying pathogenic mutations in the POLG gene. VPA administration caused a significant increase in the expression of POLG and several regulators of mitochondrial biogenesis. It was further supported by elevated mtDNA copy numbers. The effect of VPA on mitochondrial biogenesis was observed in both control and patient cell lines, but the capacity of mutant POLG to increase the expression of mitochondrial genes and to increase mtDNA copy numbers was less effective. No evidence of substantive differences in DNA methylation across the genome was observed between POLG mutated patients and controls. Given the marked perturbation of gene expression observed in the cell lines studied, we conclude that altered DNA methylation is unlikely to make a major contribution to POLG-mediated VPA toxicity. Our data provide experimental evidence that VPA triggers increased mitochondrial biogenesis by altering the expression of several mitochondrial genes; however, the capacity of POLG-deficient liver cells to address the increased metabolic rate caused by VPA administration is significantly impaired.
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Affiliation(s)
- Kamil S Sitarz
- Institute of Genetic Medicine, Newcastle University, Central Parkway, Newcastle upon Tyne NE1 3BZ UK
| | - Hannah R Elliott
- Institute of Genetic Medicine, Newcastle University, Central Parkway, Newcastle upon Tyne NE1 3BZ UK; MRC Integrative Epidemiology Unit, Oakfield House, University of Bristol, Bristol BS8 2BN, UK
| | - Betül S Karaman
- Institute of Genetic Medicine, Newcastle University, Central Parkway, Newcastle upon Tyne NE1 3BZ UK; Nijmegen Center for Mitochondrial Disorders, Radboud University, Nijmegen Medical Center, Nijmegen, The Netherlands
| | - Caroline Relton
- Institute of Genetic Medicine, Newcastle University, Central Parkway, Newcastle upon Tyne NE1 3BZ UK; MRC Integrative Epidemiology Unit, Oakfield House, University of Bristol, Bristol BS8 2BN, UK
| | - Patrick F Chinnery
- Institute of Genetic Medicine, Newcastle University, Central Parkway, Newcastle upon Tyne NE1 3BZ UK
| | - Rita Horvath
- Institute of Genetic Medicine, Newcastle University, Central Parkway, Newcastle upon Tyne NE1 3BZ UK.
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16
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Nogueira C, Almeida LS, Nesti C, Pezzini I, Videira A, Vilarinho L, Santorelli FM. Syndromes associated with mitochondrial DNA depletion. Ital J Pediatr 2014; 40:34. [PMID: 24708634 PMCID: PMC3985578 DOI: 10.1186/1824-7288-40-34] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/19/2013] [Accepted: 03/28/2014] [Indexed: 01/21/2023] Open
Abstract
Mitochondrial dysfunction accounts for a large group of inherited metabolic disorders most of which are due to a dysfunctional mitochondrial respiratory chain (MRC) and, consequently, deficient energy production. MRC function depends on the coordinated expression of both nuclear (nDNA) and mitochondrial (mtDNA) genomes. Thus, mitochondrial diseases can be caused by genetic defects in either the mitochondrial or the nuclear genome, or in the cross-talk between the two. This impaired cross-talk gives rise to so-called nuclear-mitochondrial intergenomic communication disorders, which result in loss or instability of the mitochondrial genome and, in turn, impaired maintenance of qualitative and quantitative mtDNA integrity. In children, most MRC disorders are associated with nuclear gene defects rather than alterations in the mtDNA itself. The mitochondrial DNA depletion syndromes (MDSs) are a clinically heterogeneous group of disorders with an autosomal recessive pattern of transmission that have onset in infancy or early childhood and are characterized by a reduced number of copies of mtDNA in affected tissues and organs. The MDSs can be divided into least four clinical presentations: hepatocerebral, myopathic, encephalomyopathic and neurogastrointestinal. The focus of this review is to offer an overview of these syndromes, listing the clinical phenotypes, together with their relative frequency, mutational spectrum, and possible insights for improving diagnostic strategies.
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Affiliation(s)
| | | | | | | | | | - Laura Vilarinho
- National Institute of Health, Genetics Department, Research and Development Unit, Porto, Portugal.
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Siciliano G, Pasquali L, Mancuso M, Murri L. Molecular diagnostics and mitochondrial dysfunction: a future perspective. Expert Rev Mol Diagn 2014; 8:531-49. [DOI: 10.1586/14737159.8.4.531] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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18
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Severe toxicity and polymerase-γ gene abnormalities in Malawian adults on stavudine-based antiretroviral therapy. Pharmacogenet Genomics 2013; 23:624-6. [DOI: 10.1097/fpc.0b013e3283655053] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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19
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Woodbridge P, Liang C, Davis RL, Vandebona H, Sue CM. POLG mutations in Australian patients with mitochondrial disease. Intern Med J 2013; 43:150-6. [PMID: 22647225 DOI: 10.1111/j.1445-5994.2012.02847.x] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2012] [Accepted: 05/05/2012] [Indexed: 11/29/2022]
Abstract
BACKGROUND/AIM The nuclear POLG gene encodes the catalytic subunit of DNA polymerase gamma (polγ), the only polymerase involved in the replication and proofreading of mitochondrial DNA. As a consequence, POLG mutations can cause disease through impaired replication of mitochondrial DNA. To date, over 150 different mutations have been identified, with a growing number of associated phenotypes described. The aim of this study was to determine the prevalence of POLG mutations in an adult population of Australian patients with mitochondrial disease, displaying symptoms commonly associated with POLG-related diseases. METHODS The clinical presentations of 322 patients from a specialist adult mitochondrial disease clinic were reviewed. Nineteen exhibited a cluster of three or more predefined clinical manifestations suggestive of POLG-related disease: progressive external ophthalmoplegia, seizures and/or an abnormal electroencephalogram, neuropathy, ataxia, liver function abnormalities, migraine or dysphagia/dysarthria. Patients were screened for mutations by direct nucleotide sequencing of the coding and exon-flanking intronic regions of POLG. RESULTS Five of the 19 patients (26%) displaying a phenotype suggestive of POLG-related disease were found to have informative POLG coding mutations (p.T851A, p.N468D, p.Y831C, p.G517V and novel p.P163S variant). Literature and analysis of these mutations revealed that two of these patients had pathogenic mutations known to cause POLG-related disease (patient #1: p.T851A and p.P163S; patient #2: p.T851A and p.N468D). CONCLUSIONS We conclude that the prevalence of pathogenic POLG mutations in our selected adult Australian cohort with suggestive clinical manifestations was 10%. A further 16% of patients had POLG variants but are unlikely to be responsible for causing their disease.
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Affiliation(s)
- P Woodbridge
- Department of Neurogenetics, Kolling Institute of Medical Research and University of Sydney, Sydney, Australia
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20
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McInnes J. Mitochondrial-associated metabolic disorders: foundations, pathologies and recent progress. Nutr Metab (Lond) 2013; 10:63. [PMID: 24499129 PMCID: PMC3853754 DOI: 10.1186/1743-7075-10-63] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2013] [Accepted: 10/08/2013] [Indexed: 01/06/2023] Open
Abstract
Research in the last decade has revolutionized the way in which we view mitochondria. Mitochondria are no longer viewed solely as cellular powerhouses; rather, mitochondria are now understood to be vibrant, mobile structures, constantly undergoing fusion and fission, and engaging in intimate interactions with other cellular compartments and structures. Findings have implicated mitochondria in a wide variety of cellular processes and molecular interactions, such as calcium buffering, lipid flux, and intracellular signaling. As such, it does not come as a surprise that an increasing number of human pathologies have been associated with functional defects in mitochondria. The difficulty in understanding and treating human pathologies caused by mitochondrial dysfunction arises from the complex relationships between mitochondria and other cellular processes, as well as the genetic background of such diseases. This review attempts to provide a summary of the background knowledge and recent developments in mitochondrial processes relating to mitochondrial-associated metabolic diseases arising from defects or deficiencies in mitochondrial function, as well as insights into current and future avenues for investigation.
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Affiliation(s)
- Joseph McInnes
- School of Engineering and Science, Research Center MOLIFE - Molecular Life Science, Jacobs University Bremen, Campus Ring 1, Research II, Room 120, Bremen D-28759, Germany.
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21
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Stumpf JD, Saneto RP, Copeland WC. Clinical and molecular features of POLG-related mitochondrial disease. Cold Spring Harb Perspect Biol 2013; 5:a011395. [PMID: 23545419 DOI: 10.1101/cshperspect.a011395] [Citation(s) in RCA: 95] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
The inability to replicate mitochondrial genomes (mtDNA) by the mitochondrial DNA polymerase (pol γ) leads to a subset of mitochondrial diseases. Many mutations in POLG, the gene that encodes pol γ, have been associated with mitochondrial diseases such as myocerebrohepatopathy spectrum (MCHS) disorders, Alpers-Huttenlocher syndrome, myoclonic epilepsy myopathy sensory ataxia (MEMSA), ataxia neuropathy spectrum (ANS), and progressive external ophthalmoplegia (PEO). This chapter explores five important topics in POLG-related disease: (1) clinical symptoms that identify and distinguish POLG-related diseases, (2) molecular characterization of defects in polymerase activity by POLG disease variants, (3) the importance of holoenzyme formation in disease presentation, (4) the role of pol γ exonuclease activity and mutagenesis in disease and aging, and (5) novel approaches to therapy and avoidance of toxicity based on primary research in pol γ replication.
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Affiliation(s)
- Jeffrey D Stumpf
- Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, NC 27709, USA
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22
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Abstract
Alpers-Huttenlocher syndrome is an uncommon mitochondrial disease most often associated with mutations in the mitochondrial DNA replicase, polymerase-γ. Alterations in enzyme activity result in reduced levels or deletions in mitochondrial DNA. Phenotypic manifestations occur when the functional content of mitochondrial DNA reaches a critical nadir. The tempo of disease progression and onset varies among patients, even in identical genotypes. The classic clinical triad of seizures, liver degeneration, and progressive developmental regression helps define the disorder, but a wide range of clinical expression occurs. The majority of patients are healthy before disease onset, and seizures herald the disorder in most patients. Seizures can rapidly progress to medical intractability, with frequent episodes of epilepsia partialis continua or status epilepticus. Liver involvement may precede or occur after seizure onset. Regardless, eventual liver failure is common. Both the tempo of disease progression and range of organ involvement vary from patient to patient, and are only partly explained by pathogenic effects of genetic mutations. Diagnosis involves the constellation of organ involvement, not the sequence of signs. This disorder is relentlessly progressive and ultimately fatal.
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23
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Neeve VCM, Samuels DC, Bindoff LA, van den Bosch B, Van Goethem G, Smeets H, Lombès A, Jardel C, Hirano M, Dimauro S, De Vries M, Smeitink J, Smits BW, de Coo IFM, Saft C, Klopstock T, Keiling BC, Czermin B, Abicht A, Lochmüller H, Hudson G, Gorman GG, Turnbull DM, Taylor RW, Holinski-Feder E, Chinnery PF, Horvath R. What is influencing the phenotype of the common homozygous polymerase-γ mutation p.Ala467Thr? ACTA ACUST UNITED AC 2013; 135:3614-26. [PMID: 23250882 PMCID: PMC3525059 DOI: 10.1093/brain/aws298] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Polymerase-γ (POLG) is a major human disease gene and may account for up to 25% of all mitochondrial diseases in the UK and in Italy. To date, >150 different pathogenic mutations have been described in POLG. Some mutations behave as both dominant and recessive alleles, but an autosomal recessive inheritance pattern is much more common. The most frequently detected pathogenic POLG mutation in the Caucasian population is c.1399G>A leading to a p.Ala467Thr missense mutation in the linker domain of the protein. Although many patients are homozygous for this mutation, clinical presentation is highly variable, ranging from childhood-onset Alpers-Huttenlocher syndrome to adult-onset sensory ataxic neuropathy dysarthria and ophthalmoparesis. The reasons for this are not clear, but familial clustering of phenotypes suggests that modifying factors may influence the clinical manifestation. In this study, we collected clinical, histological and biochemical data from 68 patients carrying the homozygous p.Ala467Thr mutation from eight diagnostic centres in Europe and the USA. We performed DNA analysis in 44 of these patients to search for a genetic modifier within POLG and flanking regions potentially involved in the regulation of gene expression, and extended our analysis to other genes affecting mitochondrial DNA maintenance (POLG2, PEO1 and ANT1). The clinical presentation included almost the entire phenotypic spectrum of all known POLG mutations. Interestingly, the clinical presentation was similar in siblings, implying a genetic basis for the phenotypic variability amongst homozygotes. However, the p.Ala467Thr allele was present on a shared haplotype in each affected individual, and there was no correlation between the clinical presentation and genetic variants in any of the analysed nuclear genes. Patients with mitochondrial DNA haplogroup U developed epilepsy significantly less frequently than patients with any other mitochondrial DNA haplotype. Epilepsy was reported significantly more frequently in females than in males, and also showed an association with one of the chromosomal markers defining the POLG haplotype. In conclusion, our clinical results show that the homozygous p.Ala467Thr POLG mutation does not cause discrete phenotypes, as previously suggested, but rather there is a continuum of clinical symptoms. Our results suggest that the mitochondrial DNA background plays an important role in modifying the disease phenotype but nuclear modifiers, epigenetic and environmental factors may also influence the severity of disease.
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Affiliation(s)
- Vivienne C M Neeve
- Institute of Genetic Medicine, Newcastle University, Central Parkway, Newcastle upon Tyne NE1 3BZ, UK
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24
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Bulst S, Holinski-Feder E, Payne B, Abicht A, Krause S, Lochmüller H, Chinnery PF, Walter MC, Horvath R. In vitro supplementation with deoxynucleoside monophosphates rescues mitochondrial DNA depletion. Mol Genet Metab 2012; 107:95-103. [PMID: 22608879 PMCID: PMC4038513 DOI: 10.1016/j.ymgme.2012.04.022] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/26/2012] [Accepted: 04/26/2012] [Indexed: 01/10/2023]
Abstract
Mitochondrial DNA depletion syndromes are a genetically heterogeneous group of often severe diseases, characterized by reduced cellular mitochondrial DNA content. Investigation of potential therapeutic strategies for mitochondrial DNA depletion syndromes will be dependent on good model systems. We have previously suggested that myotubes may be the optimal model system for such studies. Here we firstly validate this technique in a diverse range of cells of patients with mitochondrial DNA depletion syndromes, showing contrasting effects in cell lines from genetically and phenotypically differing patients. Secondly, we developed a putative therapeutic approach using variable combinations of deoxynucleoside monophosphates in different types of mitochondrial DNA depletion syndromes, showing near normalization of mitochondrial DNA content in many cases. Furthermore, we used nucleoside reverse transcriptase inhibitors to precisely titrate mtDNA depletion in vitro. In this manner we can unmask a physiological defect in mitochondrial depletion syndrome cell lines which is also ameliorated by deoxynucleoside monophosphate supplementation. Finally, we have extended this model to study fibroblasts after myogenic transdifferentiation by MyoD transfection, which similar to primary myotubes also showed deoxynucleoside monophosphate responsive mitochondrial DNA depletion in vitro, thus providing a more convenient method for deriving future models of mitochondrial DNA depletion. Our results suggest that using different combinations of deoxynucleoside monophosphates depending on the primary gene defect and molecular mechanism may be a possible therapeutic approach for many patients with mitochondrial DNA depletion syndromes and is worthy of further clinical investigation.
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Affiliation(s)
- Stefanie Bulst
- Medical Genetic Center, Munich, Germany
- Friedrich-Baur-Institute, Department of Neurology, Ludwig-Maximilians-University of Munich, Germany
| | | | - Brendan Payne
- Institute of Genetic Medicine, Newcastle University, UK
| | - Angela Abicht
- Medical Genetic Center, Munich, Germany
- Friedrich-Baur-Institute, Department of Neurology, Ludwig-Maximilians-University of Munich, Germany
| | - Sabine Krause
- Friedrich-Baur-Institute, Department of Neurology, Ludwig-Maximilians-University of Munich, Germany
| | | | | | - Maggie C. Walter
- Friedrich-Baur-Institute, Department of Neurology, Ludwig-Maximilians-University of Munich, Germany
| | - Rita Horvath
- Medical Genetic Center, Munich, Germany
- Institute of Genetic Medicine, Newcastle University, UK
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25
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Fratter C, Raman P, Alston CL, Blakely EL, Craig K, Smith C, Evans J, Seller A, Czermin B, Hanna MG, Poulton J, Brierley C, Staunton TG, Turnpenny PD, Schaefer AM, Chinnery PF, Horvath R, Turnbull DM, Gorman GS, Taylor RW. RRM2B mutations are frequent in familial PEO with multiple mtDNA deletions. Neurology 2011; 76:2032-4. [PMID: 21646632 DOI: 10.1212/wnl.0b013e31821e558b] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Affiliation(s)
- C Fratter
- Oxford Medical Genetics Laboratories, Churchill Hospital, Oxford, UK
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26
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Ferreira M, Evangelista T, Almeida LS, Martins J, Macario MC, Martins E, Moleirinho A, Azevedo L, Vilarinho L, Santorelli FM. Relative frequency of known causes of multiple mtDNA deletions: two novel POLG mutations. Neuromuscul Disord 2011; 21:483-8. [PMID: 21550804 DOI: 10.1016/j.nmd.2011.03.011] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2010] [Revised: 03/23/2011] [Accepted: 03/29/2011] [Indexed: 11/26/2022]
Abstract
Diseases affecting mtDNA stability, termed nuclear-mitochondrial intergenomic communication disorders, are caused by a primary nuclear gene defect resulting in multiple mtDNA deletions. The aim of this study was to estimate the frequency of known etiologies and the spectrum of mutations in a cohort of 21 patients harboring multiple mtDNA deletions in skeletal muscle. We showed that 10 cases (48%) display mutations in POLG, including eight previously reported variants and two novel mutations (namely, p.Trp585X and p.Arg1081Gln). The novel mutations affect evolutionary conserved residues and were absent in a large set of control chromosomes. These findings expand the array of mutations associated with multiple rearranged mtDNA attributed to mutations in POLG. The relatively high diagnostic yield (about one in two cases) supports the notion that it is recommended to test POLG routinely in diagnostic laboratories whenever multiple mtDNA deletions are present, regardless of the age of onset of patients and their clinical phenotype.
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Affiliation(s)
- Mariana Ferreira
- Centro de Genética Médica Jacinto de Magalhães, Instituto Nacional Saúde Ricardo Jorge, Porto, Portugal
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27
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Yu-Wai-Man P, Griffiths PG, Chinnery PF. Mitochondrial optic neuropathies - disease mechanisms and therapeutic strategies. Prog Retin Eye Res 2011; 30:81-114. [PMID: 21112411 PMCID: PMC3081075 DOI: 10.1016/j.preteyeres.2010.11.002] [Citation(s) in RCA: 431] [Impact Index Per Article: 33.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Leber hereditary optic neuropathy (LHON) and autosomal-dominant optic atrophy (DOA) are the two most common inherited optic neuropathies in the general population. Both disorders share striking pathological similarities, marked by the selective loss of retinal ganglion cells (RGCs) and the early involvement of the papillomacular bundle. Three mitochondrial DNA (mtDNA) point mutations; m.3460G>A, m.11778G>A, and m.14484T>C account for over 90% of LHON cases, and in DOA, the majority of affected families harbour mutations in the OPA1 gene, which codes for a mitochondrial inner membrane protein. Optic nerve degeneration in LHON and DOA is therefore due to disturbed mitochondrial function and a predominantly complex I respiratory chain defect has been identified using both in vitro and in vivo biochemical assays. However, the trigger for RGC loss is much more complex than a simple bioenergetic crisis and other important disease mechanisms have emerged relating to mitochondrial network dynamics, mtDNA maintenance, axonal transport, and the involvement of the cytoskeleton in maintaining a differential mitochondrial gradient at sites such as the lamina cribosa. The downstream consequences of these mitochondrial disturbances are likely to be influenced by the local cellular milieu. The vulnerability of RGCs in LHON and DOA could derive not only from tissue-specific, genetically-determined biological factors, but also from an increased susceptibility to exogenous influences such as light exposure, smoking, and pharmacological agents with putative mitochondrial toxic effects. Our concept of inherited mitochondrial optic neuropathies has evolved over the past decade, with the observation that patients with LHON and DOA can manifest a much broader phenotypic spectrum than pure optic nerve involvement. Interestingly, these phenotypes are sometimes clinically indistinguishable from other neurodegenerative disorders such as Charcot-Marie-Tooth disease, hereditary spastic paraplegia, and multiple sclerosis, where mitochondrial dysfunction is also thought to be an important pathophysiological player. A number of vertebrate and invertebrate disease models has recently been established to circumvent the lack of human tissues, and these have already provided considerable insight by allowing direct RGC experimentation. The ultimate goal is to translate these research advances into clinical practice and new treatment strategies are currently being investigated to improve the visual prognosis for patients with mitochondrial optic neuropathies.
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MESH Headings
- Animals
- DNA, Mitochondrial/genetics
- Disease Models, Animal
- Humans
- Optic Atrophy, Autosomal Dominant/pathology
- Optic Atrophy, Autosomal Dominant/physiopathology
- Optic Atrophy, Autosomal Dominant/therapy
- Optic Atrophy, Hereditary, Leber/pathology
- Optic Atrophy, Hereditary, Leber/physiopathology
- Optic Atrophy, Hereditary, Leber/therapy
- Optic Nerve/pathology
- Phenotype
- Point Mutation
- Retinal Ganglion Cells/pathology
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Affiliation(s)
- Patrick Yu-Wai-Man
- Mitochondrial Research Group, Institute for Ageing and Health, The Medical School, Newcastle University, UK.
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28
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Moustris A, Edwards MJ, Bhatia KP. Movement disorders and mitochondrial disease. HANDBOOK OF CLINICAL NEUROLOGY 2011; 100:173-92. [PMID: 21496577 DOI: 10.1016/b978-0-444-52014-2.00010-0] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Affiliation(s)
- Andreas Moustris
- Sobell Department of Motor Neuroscience and Movement Disorders, UCL Institute of Neurology, London, UK
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29
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Stewart JD, Horvath R, Baruffini E, Ferrero I, Bulst S, Watkins PB, Fontana RJ, Day CP, Chinnery PF. Polymerase γ gene POLG determines the risk of sodium valproate-induced liver toxicity. Hepatology 2010; 52:1791-6. [PMID: 21038416 PMCID: PMC3841971 DOI: 10.1002/hep.23891] [Citation(s) in RCA: 151] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
UNLABELLED Sodium valproate (VPA) is widely used throughout the world to treat epilepsy, migraine, chronic headache, bipolar disorder, and as adjuvant chemotherapy. VPA toxicity is an uncommon but potentially fatal cause of idiosyncratic liver injury. Rare mutations in POLG, which codes for the mitochondrial DNA polymerase γ (polγ), cause Alpers-Huttenlocher syndrome (AHS). AHS is a neurometabolic disorder associated with an increased risk of developing fatal VPA hepatotoxicity. We therefore set out to determine whether common genetic variants in POLG explain why some otherwise healthy individuals develop VPA hepatotoxicity. We carried out a prospective study of subjects enrolled in the Drug Induced Liver Injury Network (DILIN) from 2004 to 2008 through five US centers. POLG was sequenced and the functional consequences of VPA and novel POLG variants were evaluated in primary human cell lines and the yeast model system Saccharomyces cerevisiae. Heterozygous genetic variation in POLG was strongly associated with VPA-induced liver toxicity (odds ratio = 23.6, 95% confidence interval [CI] = 8.4-65.8, P = 5.1 × 10⁻⁷). This was principally due to the p.Q1236H substitution which compromised polγ function in yeast. Therapeutic doses of VPA inhibited human cellular proliferation and high doses caused nonapoptotic cell death, which was not mediated through mitochondrial DNA depletion, mutation, or a defect of fatty acid metabolism. CONCLUSION These findings implicate impaired liver regeneration in VPA toxicity and show that prospective genetic testing of POLG will identify individuals at high risk of this potentially fatal consequence of treatment.
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Affiliation(s)
- Joanna D Stewart
- Mitochondrial Research Group, Institute of Human Genetics, Newcastle University, UK
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30
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Martikainen MH, Hinttala R, Majamaa K. Novel POLG1 mutations in a patient with adult-onset progressive external ophthalmoplegia and encephalopathy. BMJ Case Rep 2010; 2010:2010/sep23_1/bcr0120102604. [PMID: 22778364 DOI: 10.1136/bcr.01.2010.2604] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022] Open
Abstract
Mutations in POLG1 are an important cause of human mitochondrial disease. We describe a woman who presented with bilateral ptosis and external ophthalmoplegia at 64 years of age. Neurological examination revealed symptoms of diffuse encephalopathy. The symptoms were progressive and at 67 years she was severely cognitively impaired, had severe bilateral ptosis and complete external ophthalmoplegia. Frequent cytochrome c oxidase-negative fibres were detected in muscle. Electrophysiological examination revealed myopathic changes and axonal neuropathy. Standard laboratory tests were normal. Brain CT showed general, moderate cortical atrophy. Molecular analysis of muscle DNA revealed multiple mitochondrial DNA deletions. Sequencing of the entire POLG1 gene revealed two changes c.2993C>T (p.998S>L) and c.3550G>C (p.1184D>H). Both mutations are previously unreported and confirmed to be compound heterozygous. Late-onset progressive external ophthalmoplegia with severe encephalopathy is an unusual combination in patients with POLG1 mutations. POLG-associated disease should be considered in any patient with unexplained or unusual neurological features.
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31
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Saneto RP, Naviaux RK. Polymerase gamma disease through the ages. ACTA ACUST UNITED AC 2010; 16:163-74. [DOI: 10.1002/ddrr.105] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
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32
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Lee YS, Johnson KA, Molineux IJ, Yin YW. A single mutation in human mitochondrial DNA polymerase Pol gammaA affects both polymerization and proofreading activities of only the holoenzyme. J Biol Chem 2010; 285:28105-16. [PMID: 20513922 DOI: 10.1074/jbc.m110.122283] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Common causes of human mitochondrial diseases are mutations affecting DNA polymerase (Pol) gamma, the sole polymerase responsible for DNA synthesis in mitochondria. Although the polymerase and exonuclease active sites are located on the catalytic subunit Pol gammaA, in holoenzyme both activities are regulated by the accessory subunit Pol gammaB. Several patients with severe neurological and muscular disorders were reported to carry the Pol gammaA substitutions R232G or R232H, which lie outside of either active site. We report that Arg(232) substitutions have no effect on independent Pol gammaA activities but show major defects in the Pol gammaA-Pol gammaB holoenzyme, including decreased polymerase and increased exonuclease activities, the latter with decreased selectivity for mismatches. We show that Pol gammaB facilitates distinguishing mismatched from base-paired primer termini and that Pol gammaA Arg(232) is essential for mediating this regulatory function of the accessory subunit. This study provides a molecular basis for the disease symptoms exhibited by patients carrying those substitutions.
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Affiliation(s)
- Young-Sam Lee
- Institute for Cellular and Molecular Biology, University of Texas at Austin, Austin, Texas 78712, USA
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33
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Yu-Wai-Man P, Sitarz KS, Samuels DC, Griffiths PG, Reeve AK, Bindoff LA, Horvath R, Chinnery PF. OPA1 mutations cause cytochrome c oxidase deficiency due to loss of wild-type mtDNA molecules. Hum Mol Genet 2010; 19:3043-52. [PMID: 20484224 PMCID: PMC2901142 DOI: 10.1093/hmg/ddq209] [Citation(s) in RCA: 84] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Pathogenic OPA1 mutations cause autosomal dominant optic atrophy (DOA), a condition characterized by the preferential loss of retinal ganglion cells and progressive optic nerve degeneration. Approximately 20% of affected patients will also develop more severe neuromuscular complications, an important disease subgroup known as DOA+. Cytochrome c oxidase (COX)-negative fibres and multiple mitochondrial DNA (mtDNA) deletions have been identified in skeletal muscle biopsies from patients manifesting both the pure and syndromal variants, raising the possibility that the accumulation of somatic mtDNA defects contribute to the disease process. In this study, we investigated the mtDNA changes induced by OPA1 mutations in skeletal muscle biopsies from 15 patients with both pure DOA and DOA+ phenotypes. We observed a 2- to 4-fold increase in mtDNA copy number at the single-fibre level, and patients with DOA+ features had significantly greater mtDNA proliferation in their COX-negative skeletal muscle fibres compared with patients with isolated optic neuropathy. Low levels of wild-type mtDNA molecules were present in COX-deficient muscle fibres from both pure DOA and DOA+ patients, implicating haplo-insufficiency as the mechanism responsible for the biochemical defect. Our findings are consistent with the ‘maintenance of wild-type’ hypothesis, the secondary mtDNA deletions induced by OPA1 mutations triggering a compensatory mitochondrial proliferative response in order to maintain an optimal level of wild-type mtDNA genomes. However, when deletion levels reach a critical level, further mitochondrial proliferation leads to replication of the mutant species at the expense of wild-type mtDNA, resulting in the loss of respiratory chain COX activity.
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Affiliation(s)
- Patrick Yu-Wai-Man
- Mitochondrial Research Group, Institute for Ageing and Health, The Medical School, Newcastle University, Newcastle upon Tyne NE2 4HH, UK
- Department of Ophthalmology, Royal Victoria Infirmary, Newcastle upon Tyne, UK
| | - Kamil S. Sitarz
- Mitochondrial Research Group, Institute for Ageing and Health, The Medical School, Newcastle University, Newcastle upon Tyne NE2 4HH, UK
| | - David C. Samuels
- Department of Molecular Physiology and Biophysics, Center for Human Genetics Research, Vanderbilt University Medical Center, Nashville, TN, USA
| | - Philip G. Griffiths
- Mitochondrial Research Group, Institute for Ageing and Health, The Medical School, Newcastle University, Newcastle upon Tyne NE2 4HH, UK
- Department of Ophthalmology, Royal Victoria Infirmary, Newcastle upon Tyne, UK
| | - Amy K. Reeve
- Mitochondrial Research Group, Institute for Ageing and Health, The Medical School, Newcastle University, Newcastle upon Tyne NE2 4HH, UK
| | - Laurence A. Bindoff
- Department of Clinical Medicine, University of Bergen, Bergen, Norway
- Department of Neurology, Haukeland University Hospital, Bergen, Norway and
| | - Rita Horvath
- Mitochondrial Research Group, Institute for Ageing and Health, The Medical School, Newcastle University, Newcastle upon Tyne NE2 4HH, UK
| | - Patrick F. Chinnery
- Mitochondrial Research Group, Institute for Ageing and Health, The Medical School, Newcastle University, Newcastle upon Tyne NE2 4HH, UK
- Institute of Human Genetics, Newcastle University, Newcastle upon Tyne, UK
- To whom correspondence should be addressed. Tel: +44 1912824375; Fax: +44 1912824373;
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34
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Suomalainen A, Isohanni P. Mitochondrial DNA depletion syndromes--many genes, common mechanisms. Neuromuscul Disord 2010; 20:429-37. [PMID: 20444604 DOI: 10.1016/j.nmd.2010.03.017] [Citation(s) in RCA: 154] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2010] [Revised: 03/25/2010] [Accepted: 03/29/2010] [Indexed: 02/07/2023]
Abstract
Mitochondrial DNA depletion syndrome has become an important cause of inherited metabolic disorders, especially in children, but also in adults. The manifestations vary from tissue-specific mtDNA depletion to wide-spread multisystemic disorders. Nine genes are known to underlie this group of disorders, and many disease genes are still unidentified. However, the disease mechanisms seem to be intimately associated with mtDNA replication and nucleotide pool regulation. We review here the current knowledge on the clinical and molecular genetic features of mitochondrial DNA depletion syndrome.
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Affiliation(s)
- Anu Suomalainen
- Research Program of Molecular Neurology, Biomedicum-Helsinki, University of Helsinki, Helsinki, Finland.
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35
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Yu-Wai-Man P, Griffiths PG, Gorman GS, Lourenco CM, Wright AF, Auer-Grumbach M, Toscano A, Musumeci O, Valentino ML, Caporali L, Lamperti C, Tallaksen CM, Duffey P, Miller J, Whittaker RG, Baker MR, Jackson MJ, Clarke MP, Dhillon B, Czermin B, Stewart JD, Hudson G, Reynier P, Bonneau D, Marques W, Lenaers G, McFarland R, Taylor RW, Turnbull DM, Votruba M, Zeviani M, Carelli V, Bindoff LA, Horvath R, Amati-Bonneau P, Chinnery PF. Multi-system neurological disease is common in patients with OPA1 mutations. ACTA ACUST UNITED AC 2010; 133:771-86. [PMID: 20157015 PMCID: PMC2842512 DOI: 10.1093/brain/awq007] [Citation(s) in RCA: 318] [Impact Index Per Article: 22.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Additional neurological features have recently been described in seven families transmitting pathogenic mutations in OPA1, the most common cause of autosomal dominant optic atrophy. However, the frequency of these syndromal 'dominant optic atrophy plus' variants and the extent of neurological involvement have not been established. In this large multi-centre study of 104 patients from 45 independent families, including 60 new cases, we show that extra-ocular neurological complications are common in OPA1 disease, and affect up to 20% of all mutational carriers. Bilateral sensorineural deafness beginning in late childhood and early adulthood was a prominent manifestation, followed by a combination of ataxia, myopathy, peripheral neuropathy and progressive external ophthalmoplegia from the third decade of life onwards. We also identified novel clinical presentations with spastic paraparesis mimicking hereditary spastic paraplegia, and a multiple sclerosis-like illness. In contrast to initial reports, multi-system neurological disease was associated with all mutational subtypes, although there was an increased risk with missense mutations [odds ratio = 3.06, 95% confidence interval = 1.44-6.49; P = 0.0027], and mutations located within the guanosine triphosphate-ase region (odds ratio = 2.29, 95% confidence interval = 1.08-4.82; P = 0.0271). Histochemical and molecular characterization of skeletal muscle biopsies revealed the presence of cytochrome c oxidase-deficient fibres and multiple mitochondrial DNA deletions in the majority of patients harbouring OPA1 mutations, even in those with isolated optic nerve involvement. However, the cytochrome c oxidase-deficient load was over four times higher in the dominant optic atrophy + group compared to the pure optic neuropathy group, implicating a causal role for these secondary mitochondrial DNA defects in disease pathophysiology. Individuals with dominant optic atrophy plus phenotypes also had significantly worse visual outcomes, and careful surveillance is therefore mandatory to optimize the detection and management of neurological disability in a group of patients who already have significant visual impairment.
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Affiliation(s)
- P Yu-Wai-Man
- Mitochondrial Research Group, The Medical School, Newcastle University, Newcastle upon Tyne, NE2 4HH, UK
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Saneto RP, Lee IC, Koenig MK, Bao X, Weng SW, Naviaux RK, Wong LJC. POLG DNA testing as an emerging standard of care before instituting valproic acid therapy for pediatric seizure disorders. Seizure 2010; 19:140-6. [PMID: 20138553 DOI: 10.1016/j.seizure.2010.01.002] [Citation(s) in RCA: 93] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2009] [Revised: 12/31/2009] [Accepted: 01/07/2010] [Indexed: 11/17/2022] Open
Abstract
PURPOSE To review our clinical experience and determine if there are appropriate signs and symptoms to consider POLG sequencing prior to valproic acid (VPA) dosing in patients with seizures. METHODS Four patients who developed VPA-induced hepatotoxicity were examined for POLG sequence variations. A subsequent chart review was used to describe clinical course prior to and after VPA dosing. RESULTS Four patients of multiple different ethnicities, age 3-18 years, developed VPA-induced hepatotoxicity. All were given VPA due to intractable partial seizures. Three of the patients had developed epilepsia partialis continua. The time from VPA exposure to liver failure was between 2 and 3 months. Liver failure was reversible in one patient. Molecular studies revealed homozygous p.R597W or p.A467T mutations in two patients. The other two patients showed compound heterozygous mutations, p.A467T/p.Q68X and p.L83P/p.G888S. Clinical findings and POLG mutations were diagnostic of Alpers-Huttenlocher syndrome. CONCLUSION Our cases underscore several important findings: POLG mutations have been observed in every ethnic group studied to date; early predominance of epileptiform discharges over the occipital region is common in POLG-induced epilepsy; the EEG and MRI findings varying between patients and stages of the disease; and VPA dosing at any stage of Alpers-Huttenlocher syndrome can precipitate liver failure. Our data support an emerging proposal that POLG gene testing should be considered in any child or adolescent who presents or develops intractable seizures with or without status epilepticus or epilepsia partialis continua, particularly when there is a history of psychomotor regression.
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Affiliation(s)
- Russell P Saneto
- Division of Pediatric Neurology, Seattle Children's Hospital/University of Washington, Seattle, WA 98105, USA
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Structural insight into processive human mitochondrial DNA synthesis and disease-related polymerase mutations. Cell 2009; 139:312-24. [PMID: 19837034 PMCID: PMC3018533 DOI: 10.1016/j.cell.2009.07.050] [Citation(s) in RCA: 158] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2008] [Revised: 05/18/2009] [Accepted: 07/21/2009] [Indexed: 01/07/2023]
Abstract
Human mitochondrial DNA polymerase (Pol gamma) is the sole replicase in mitochondria. Pol gamma is vulnerable to nonselective antiretroviral drugs and is increasingly associated with mutations found in patients with mitochondriopathies. We determined crystal structures of the human heterotrimeric Pol gamma holoenzyme and, separately, a variant of its processivity factor, Pol gammaB. The holoenzyme structure reveals an unexpected assembly of the mitochondrial DNA replicase where the catalytic subunit Pol gammaA interacts with its processivity factor primarily via a domain that is absent in all other DNA polymerases. This domain provides a structural module for supporting both the intrinsic processivity of the catalytic subunit alone and the enhanced processivity of holoenzyme. The Pol gamma structure also provides a context for interpreting the phenotypes of disease-related mutations in the polymerase and establishes a foundation for understanding the molecular basis of toxicity of anti-retroviral drugs targeting HIV reverse transcriptase.
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Mitochondrial DNA mutations and human disease. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2009; 1797:113-28. [PMID: 19761752 DOI: 10.1016/j.bbabio.2009.09.005] [Citation(s) in RCA: 417] [Impact Index Per Article: 27.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/19/2009] [Revised: 09/04/2009] [Accepted: 09/09/2009] [Indexed: 01/07/2023]
Abstract
Mitochondrial disorders are a group of clinically heterogeneous diseases, commonly defined by a lack of cellular energy due to oxidative phosphorylation (OXPHOS) defects. Since the identification of the first human pathological mitochondrial DNA (mtDNA) mutations in 1988, significant efforts have been spent in cataloguing the vast array of causative genetic defects of these disorders. Currently, more than 250 pathogenic mtDNA mutations have been identified. An ever-increasing number of nuclear DNA mutations are also being reported as the majority of proteins involved in mitochondrial metabolism and maintenance are nuclear-encoded. Understanding the phenotypic diversity and elucidating the molecular mechanisms at the basis of these diseases has however proved challenging. Progress has been hampered by the peculiar features of mitochondrial genetics, an inability to manipulate the mitochondrial genome, and difficulties in obtaining suitable models of disease. In this review, we will first outline the unique features of mitochondrial genetics before detailing the diseases and their genetic causes, focusing specifically on primary mtDNA genetic defects. The functional consequences of mtDNA mutations that have been characterised to date will also be discussed, along with current and potential future diagnostic and therapeutic advances.
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Bortot B, Barbi E, Biffi S, Lunazzi G, Bussani R, Burlina A, Norbedo S, Ventura A, Carrozzi M, Severini GM. Two novel POLG mutations causing hepatic mitochondrial DNA depletion with recurrent hypoketotic hypoglycaemia and fatal liver dysfunction. Dig Liver Dis 2009; 41:494-9. [PMID: 19195941 DOI: 10.1016/j.dld.2008.11.013] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/01/2008] [Revised: 10/29/2008] [Accepted: 11/13/2008] [Indexed: 12/11/2022]
Abstract
BACKGROUND Inherited mtDNA depletion syndromes (MDS) are a group of severe mitochondrial disorders resulting from defects in nucleus-encoded factors and often associated with severe or fatal liver failure. PATIENT In this article, we describe the case of an 18-month-old patient with recurrent hypoketotic hypoglycaemia and fatal hepatic dysfunction with liver mtDNA depletion. METHODS The assessment of mtDNA copy number was performed on leucocytes, liver and muscle biopsy by Quantitative Real Time PCR and total RNA from liver biopsy was used as a template to amplify the cDNA of the POLG1 gene. RESULTS Sequence analysis identified two previously undescribed mutations (1868T>G and 2263A>G) located in the gene coding the catalytic subunit of mitochondrial DNA polymerase gamma (POLG), predicting an L623W and K755E amino acid change, respectively. Both mutations were located in the highly conserved linker region of the protein and were absent in more than 200 healthy unrelated control subjects. The identification of these two mutations allowed us to perform genetic counselling and prenatal diagnosis. CONCLUSION Our data further expand the spectrum of POLG1 gene mutations and the unique phenotype reported (late onset isolated liver disease without lactic acidosis) increase the variability of clinical presentations associated with mutations in this gene.
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Affiliation(s)
- B Bortot
- Children's Neurology and Psychiatry Unit, Institute of Child Health IRCCS, Burlo Garofolo, Via dell'Istria, Trieste, Italy
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Wolf NI, Rahman S, Schmitt B, Taanman JW, Duncan AJ, Harting I, Wohlrab G, Ebinger F, Rating D, Bast T. Status epilepticus in children with Alpers’ disease caused byPOLG1mutations: EEG and MRI features. Epilepsia 2009; 50:1596-607. [DOI: 10.1111/j.1528-1167.2008.01877.x] [Citation(s) in RCA: 112] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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163rd ENMC International Workshop: nucleoid and nucleotide biology in syndromes of mitochondrial DNA depletion myopathy 12-14 December 2008, Naarden, The Netherlands. Neuromuscul Disord 2009; 19:439-43. [PMID: 19464176 DOI: 10.1016/j.nmd.2009.04.009] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2009] [Indexed: 11/23/2022]
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Multisystem manifestations of mitochondrial disorders. J Neurol 2009; 256:693-710. [DOI: 10.1007/s00415-009-5028-3] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2008] [Accepted: 11/11/2008] [Indexed: 01/13/2023]
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Goffart S, Cooper HM, Tyynismaa H, Wanrooij S, Suomalainen A, Spelbrink JN. Twinkle mutations associated with autosomal dominant progressive external ophthalmoplegia lead to impaired helicase function and in vivo mtDNA replication stalling. Hum Mol Genet 2008; 18:328-40. [PMID: 18971204 PMCID: PMC2638771 DOI: 10.1093/hmg/ddn359] [Citation(s) in RCA: 109] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Mutations in the mitochondrial helicase Twinkle underlie autosomal dominant progressive external ophthalmoplegia (PEO), as well as recessively inherited infantile-onset spinocerebellar ataxia and rare forms of mitochondrial DNA (mtDNA) depletion syndrome. Familial PEO is typically associated with the occurrence of multiple mtDNA deletions, but the mechanism by which Twinkle dysfunction induces deletion formation has been under debate. Here we looked at the effects of Twinkle adPEO mutations in human cell culture and studied the mtDNA replication in the Deletor mouse model, which expresses a dominant PEO mutation in Twinkle and accumulates multiple mtDNA deletions during life. We show that expression of dominant Twinkle mutations results in the accumulation of mtDNA replication intermediates in cell culture. This indicated severe replication pausing or stalling and caused mtDNA depletion. A strongly enhanced accumulation of replication intermediates was evident also in six-week-old Deletor mice compared with wild-type littermates, even though mtDNA deletions accumulate in a late-onset fashion in this model. In addition, our results in cell culture pointed to a problem of transcription that preceded the mtDNA depletion phenotype and might be of relevance in adPEO pathophysiology. Finally, in vitro assays showed functional defects in the various Twinkle mutants and broadly agreed with the cell culture phenotypes such as the level of mtDNA depletion and the level of accumulation of replication intermediates. On the basis of our results we suggest that mtDNA replication pausing or stalling is the common consequence of Twinkle PEO mutations that predisposes to multiple deletion formation.
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Affiliation(s)
- Steffi Goffart
- Institute of Medical Technology and Tampere University Hospital, Biokatu 6, 33014, Tampere, Finland
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Ashley N, O'Rourke A, Smith C, Adams S, Gowda V, Zeviani M, Brown GK, Fratter C, Poulton J. Depletion of mitochondrial DNA in fibroblast cultures from patients with POLG1 mutations is a consequence of catalytic mutations. Hum Mol Genet 2008; 17:2496-506. [PMID: 18487244 PMCID: PMC2486441 DOI: 10.1093/hmg/ddn150] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We investigated clinical and cellular phenotypes of 24 children with mutations in the catalytic (alpha) subunit of the mitochondrial DNA (mtDNA) gamma polymerase (POLG1). Twenty-one had Alpers syndrome, the commonest severe POLG1 autosomal recessive phenotype, comprising hepatoencephalopathy and often mtDNA depletion. The cellular mtDNA content reflected the genotype more closely than did clinical features. Patients with tissue depletion of mtDNA all had at least one allele with either a missense mutation in a catalytic domain or a nonsense mutation. Four out of 12 patients exhibited a progressive, mosaic pattern of mtDNA depletion in cultured fibroblasts. All these patients had mutations in a catalytic domain in both POLG1 alleles, in either the polymerase or exonuclease domain or both. The tissue mtDNA content of patients who had two linker mutations was normal, and their phenotypes the mildest. Epilepsy and/or movement disorder were major features in all 21. Previous studies have implicated replication stalling as a mechanism for mtDNA depletion. The mosaic cellular depletion that we have demonstrated in cell cultures may be a manifestation of severe replication stalling. One patient with a severe cellular and clinical phenotype was a compound heterozygote with POLG1 mutations in the polymerase and exonuclease domain intrans. This suggests that POLG1 requires both polymerase and 3'-5' exonuclease activity in the same molecule. This is consistent with current functional models for eukaryotic DNA polymerases, which alternate between polymerizing and editing modes, as determined by competition between these two active sites for the 3' end of the DNA.
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Affiliation(s)
- Neil Ashley
- Nuffield Department of Obstetrics and Gynaecology, University of Oxford, The Women's Centre, John Radcliffe Hospital, Oxford OX3 9DU, UK
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