1
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Berardo A, Engelstad K, Hirano M. Advances in Thymidine Kinase 2 Deficiency: Clinical Aspects, Translational Progress, and Emerging Therapies. J Neuromuscul Dis 2022; 9:225-235. [PMID: 35094997 PMCID: PMC9028656 DOI: 10.3233/jnd-210786] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Defects in the replication, maintenance, and repair of mitochondrial DNA (mtDNA) constitute a growing and genetically heterogeneous group of mitochondrial disorders. Multiple genes participate in these processes, including thymidine kinase 2 (TK2) encoding the mitochondrial matrix protein TK2, a critical component of the mitochondrial nucleotide salvage pathway. TK2 deficiency (TK2d) causes mtDNA depletion, multiple deletions, or both, which manifest predominantly as mitochondrial myopathy. A wide clinical spectrum phenotype includes a severe, rapidly progressive, early onset form (median survival: < 2 years); a less severe childhood-onset form; and a late-onset form with a variably slower rate of progression. Clinical presentation typically includes progressive weakness of limb, neck, facial, oropharyngeal, and respiratory muscle, whereas limb myopathy with ptosis, ophthalmoparesis, and respiratory involvement is more common in the late-onset form. Deoxynucleoside monophosphates and deoxynucleosides that can bypass the TK2 enzyme defect have been assessed in a mouse model, as well as under open-label compassionate use (expanded access) in TK2d patients, indicating clinical efficacy with a favorable side-effect profile. This treatment is currently undergoing testing in clinical trials intended to support approval in the US and European Union (EU). In the early expanded access program, growth differentiation factor 15 (GDF-15) appears to be a useful biomarker that correlates with therapeutic response. With the advent of a specific treatment and given the high morbidity and mortality associated with TK2d, clinicians need to know how to recognize and diagnose this disorder. Here, we summarize translational research about this rare condition emphasizing clinical aspects.
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Affiliation(s)
- Andres Berardo
- Department of Neurology, Columbia University Irving Medical Center, New York, NY, USA
| | - Kristin Engelstad
- Department of Neurology, Columbia University Irving Medical Center, New York, NY, USA
| | - Michio Hirano
- Department of Neurology, Columbia University Irving Medical Center, New York, NY, USA
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2
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Schijvens AM, van de Kar NC, Bootsma-Robroeks CM, Cornelissen EA, van den Heuvel LP, Schreuder MF. Mitochondrial Disease and the Kidney With a Special Focus on CoQ 10 Deficiency. Kidney Int Rep 2020; 5:2146-2159. [PMID: 33305107 PMCID: PMC7710892 DOI: 10.1016/j.ekir.2020.09.044] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2020] [Accepted: 09/29/2020] [Indexed: 12/13/2022] Open
Abstract
Mitochondrial cytopathies include a heterogeneous group of diseases that are characterized by impaired oxidative phosphorylation, leading to multi-organ involvement and progressive clinical deterioration. Most mitochondrial cytopathies that cause kidney symptoms are characterized by tubular defects, but glomerular, tubulointerstitial, and cystic diseases have also been described. Mitochondrial cytopathies can result from mitochondrial or nuclear DNA mutations. Early recognition of defects in the coenzyme Q10 (CoQ10) biosynthesis is important, as patients with primary CoQ10 deficiency may be responsive to treatment with oral CoQ10 supplementation, in contrast to most mitochondrial diseases. A literature search was conducted to investigate kidney involvement in genetic mitochondrial cytopathies and to identify mitochondrial and nuclear DNA mutations involved in mitochondrial kidney disease. Furthermore, we identified all reported cases to date with a CoQ10 deficiency with glomerular involvement, including 3 patients with variable renal phenotypes in our clinic. To date, 144 patients from 95 families with a primary CoQ10 deficiency and glomerular involvement have been described based on mutations in PDSS1, PDSS2, COQ2, COQ6, and COQ8B/ADCK4. This review provides an overview of kidney involvement in genetic mitochondrial cytopathies with a special focus on CoQ10 deficiency.
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Affiliation(s)
- Anne M. Schijvens
- Department of Pediatric Nephrology, Radboud University Medical Center, Radboud Institute for Molecular Life Sciences, Amalia Children’s Hospital, Nijmegen, the Netherlands
| | - Nicole C. van de Kar
- Department of Pediatric Nephrology, Radboud University Medical Center, Radboud Institute for Molecular Life Sciences, Amalia Children’s Hospital, Nijmegen, the Netherlands
| | - Charlotte M. Bootsma-Robroeks
- Department of Pediatric Nephrology, Radboud University Medical Center, Radboud Institute for Molecular Life Sciences, Amalia Children’s Hospital, Nijmegen, the Netherlands
| | - Elisabeth A. Cornelissen
- Department of Pediatric Nephrology, Radboud University Medical Center, Radboud Institute for Molecular Life Sciences, Amalia Children’s Hospital, Nijmegen, the Netherlands
| | - Lambertus P. van den Heuvel
- Department of Pediatric Nephrology, Radboud University Medical Center, Radboud Institute for Molecular Life Sciences, Amalia Children’s Hospital, Nijmegen, the Netherlands
- Department of Development and Regeneration,University Hospital Leuven, Leuven, Belgium
| | - Michiel F. Schreuder
- Department of Pediatric Nephrology, Radboud University Medical Center, Radboud Institute for Molecular Life Sciences, Amalia Children’s Hospital, Nijmegen, the Netherlands
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3
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Domínguez-González C, Madruga-Garrido M, Mavillard F, Garone C, Aguirre-Rodríguez FJ, Donati MA, Kleinsteuber K, Martí I, Martín-Hernández E, Morealejo-Aycinena JP, Munell F, Nascimento A, Kalko SG, Sardina MD, Álvarez Del Vayo C, Serrano O, Long Y, Tu Y, Levin B, Thompson JLP, Engelstad K, Uddin J, Torres-Torronteras J, Jimenez-Mallebrera C, Martí R, Paradas C, Hirano M. Deoxynucleoside Therapy for Thymidine Kinase 2-Deficient Myopathy. Ann Neurol 2019; 86:293-303. [PMID: 31125140 DOI: 10.1002/ana.25506] [Citation(s) in RCA: 61] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2018] [Revised: 05/21/2019] [Accepted: 05/22/2019] [Indexed: 12/22/2022]
Abstract
OBJECTIVE Thymidine kinase 2, encoded by the nuclear gene TK2, is required for mitochondrial DNA maintenance. Autosomal recessive TK2 mutations cause depletion and multiple deletions of mtDNA that manifest predominantly as a myopathy usually beginning in childhood and progressing relentlessly. We investigated the safety and efficacy of deoxynucleoside monophosphate and deoxynucleoside therapies. METHODS We administered deoxynucleoside monophosphates and deoxynucleoside to 16 TK2-deficient patients under a compassionate use program. RESULTS In 5 patients with early onset and severe disease, survival and motor functions were better than historically untreated patients. In 11 childhood and adult onset patients, clinical measures stabilized or improved. Three of 8 patients who were nonambulatory at baseline gained the ability to walk on therapy; 4 of 5 patients who required enteric nutrition were able to discontinue feeding tube use; and 1 of 9 patients who required mechanical ventilation became able to breathe independently. In motor functional scales, improvements were observed in the 6-minute walk test performance in 7 of 8 subjects, Egen Klassifikation in 2 of 3, and North Star Ambulatory Assessment in all 5 tested. Baseline elevated serum growth differentiation factor 15 levels decreased with treatment in all 7 patients tested. A side effect observed in 8 of the 16 patients was dose-dependent diarrhea, which did not require withdrawal of treatment. Among 12 other TK2 patients treated with deoxynucleoside, 2 adults developed elevated liver enzymes that normalized following discontinuation of therapy. INTERPRETATION This open-label study indicates favorable side effect profiles and clinical efficacy of deoxynucleoside monophosphate and deoxynucleoside therapies for TK2 deficiency. ANN NEUROL 2019;86:293-303.
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Affiliation(s)
- Cristina Domínguez-González
- Neuromuscular Disorders Unit, Neurology Department, Hospital 12 de Octubre, Madrid, Spain.,Instituto de Investigación i + 12, Hospital 12 de Octubre, Madrid, Spain.,Center for Biomedical Network Research on Rare Diseases (CIBERER), Instituto de Salud Carlos III, Madrid, Spain
| | - Marcos Madruga-Garrido
- Neuromuscular Disorders Unit, Pediatric Neurology Department, Instituto de Biomedicina de Sevilla, Hospital U. Virgen del Rocío, Consejo Superior de Investigaciones Científicas, University of Seville, Seville, Spain
| | - Fabiola Mavillard
- Neuromuscular Disorders Unit, Neurology Department, Instituto de Biomedicina de Sevilla, Hospital U. Virgen del Rocío, Consejo Superior de Investigaciones Científicas, University of Seville, Seville, Spain.,Center for Biomedical Network Research on Neurodegenerative Diseases, Instituto de Salud Carlos III, Madrid, Spain
| | - Caterina Garone
- Medical Research Council Mitochondrial Biology Unit, Cambridge Biomedical Campus, Cambridge, UK
| | | | - M Alice Donati
- Metabolic and Neuromuscular Unit, Meyer Hospital, Florence, Italy
| | - Karin Kleinsteuber
- Pediatric Neurology Department, Faculty of Medicine, University of Chile, Las Condes Clinic, Santiago, Chile
| | - Itxaso Martí
- Pediatric Neurology Department, Donostia University Hospital, San Sebastian, Spain
| | - Elena Martín-Hernández
- Instituto de Investigación i + 12, Hospital 12 de Octubre, Madrid, Spain.,Center for Biomedical Network Research on Rare Diseases (CIBERER), Instituto de Salud Carlos III, Madrid, Spain.,Hereditary Metabolic and Mitochondrial Disorders Unit, Pediatric Department, October 12 Hospital, Madrid, Spain
| | | | - Francina Munell
- Pediatric Department, Vall d'Hebron Hospital, Barcelona, Spain
| | - Andrés Nascimento
- Center for Biomedical Network Research on Rare Diseases (CIBERER), Instituto de Salud Carlos III, Madrid, Spain.,Neuromuscular Unit, Neurology Department, Sant Joan de Déu Research Institute, Sant Joan de Déu Hospital, Barcelona, Spain
| | - Susana G Kalko
- Center for Biomedical Network Research on Rare Diseases (CIBERER), Instituto de Salud Carlos III, Madrid, Spain.,Neuromuscular Unit, Neurology Department, Sant Joan de Déu Research Institute, Sant Joan de Déu Hospital, Barcelona, Spain
| | - M Dolores Sardina
- Pediatric Neurology Department, Badajoz Hospital Complex, Badajoz, Spain
| | - Concepcion Álvarez Del Vayo
- Center for Biomedical Network Research on Neurodegenerative Diseases, Instituto de Salud Carlos III, Madrid, Spain.,Pharmacy Department, Virgin of el Rocío University Hospital, Seville, Spain
| | - Olga Serrano
- Pharmacy Department, October 12 Hospital, Madrid, Spain
| | - Yuelin Long
- Department of Biostatistics, Mailman School of Public Health, Columbia University Medical Center, New York, NY
| | - Yuqi Tu
- Department of Biostatistics, Mailman School of Public Health, Columbia University Medical Center, New York, NY
| | - Bruce Levin
- Department of Biostatistics, Mailman School of Public Health, Columbia University Medical Center, New York, NY
| | - John L P Thompson
- Department of Biostatistics, Mailman School of Public Health, Columbia University Medical Center, New York, NY
| | - Kristen Engelstad
- Neurology Department, H. Houston Merritt Center, Columbia University Medical Center, New York, NY
| | - Jasim Uddin
- Neurology Department, H. Houston Merritt Center, Columbia University Medical Center, New York, NY
| | - Javier Torres-Torronteras
- Center for Biomedical Network Research on Rare Diseases (CIBERER), Instituto de Salud Carlos III, Madrid, Spain.,Research Group on Neuromuscular and Mitochondrial Diseases, Vall d'Hebron Research Institute, Autonomous University of Barcelona, Barcelona, Spain
| | - Cecilia Jimenez-Mallebrera
- Center for Biomedical Network Research on Rare Diseases (CIBERER), Instituto de Salud Carlos III, Madrid, Spain.,Neuromuscular Unit, Neurology Department, Sant Joan de Déu Research Institute, Sant Joan de Déu Hospital, Barcelona, Spain
| | - Ramon Martí
- Center for Biomedical Network Research on Rare Diseases (CIBERER), Instituto de Salud Carlos III, Madrid, Spain.,Research Group on Neuromuscular and Mitochondrial Diseases, Vall d'Hebron Research Institute, Autonomous University of Barcelona, Barcelona, Spain
| | - Carmen Paradas
- Neuromuscular Disorders Unit, Neurology Department, Instituto de Biomedicina de Sevilla, Hospital U. Virgen del Rocío, Consejo Superior de Investigaciones Científicas, University of Seville, Seville, Spain.,Center for Biomedical Network Research on Neurodegenerative Diseases, Instituto de Salud Carlos III, Madrid, Spain
| | - Michio Hirano
- Neurology Department, H. Houston Merritt Center, Columbia University Medical Center, New York, NY
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4
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Quadri MM, Fatima SS, Che RC, Zhang AH. Mitochondria and Renal Fibrosis. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2019; 1165:501-524. [PMID: 31399982 DOI: 10.1007/978-981-13-8871-2_25] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Mitochondria are important organelles in eukaryotic cells and perform a variety of biosynthetic and metabolic functions. Many human diseases are closely related to mitochondrial dysfunction. Kidney is an organ with high-energy requirements, which is distributed with a large number of mitochondria. Mitochondrial dysfunction plays a crucial role in the pathogenesis of kidney disease, and studies have shown that mitochondrial dysfunction is involved in the physiological process of renal fibrosis. This review introduced the biogenesis and pathophysiology of mitochondria, illustrated the involvement of mitochondrial dysfunction in renal fibrosis based on various kinds of cells, and finally summarized the latest mitochondria-targeted therapies.
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Affiliation(s)
| | - Syeda-Safoorah Fatima
- Department of Nephrology, Children's Hospital of Nanjing Medical University, Nanjing, China
| | - Ruo-Chen Che
- Department of Nephrology, Children's Hospital of Nanjing Medical University, Nanjing, China
| | - Ai-Hua Zhang
- Department of Nephrology, Children's Hospital of Nanjing Medical University, Nanjing, China.
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5
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Wang J, Kim E, Dai H, Stefans V, Vogel H, Al Jasmi F, Schrier Vergano SA, Castro D, Bernes S, Bhambhani V, Long C, El-Hattab AW, Wong LJ. Clinical and molecular spectrum of thymidine kinase 2-related mtDNA maintenance defect. Mol Genet Metab 2018; 124:124-130. [PMID: 29735374 DOI: 10.1016/j.ymgme.2018.04.012] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/06/2018] [Revised: 04/25/2018] [Accepted: 04/26/2018] [Indexed: 11/29/2022]
Abstract
Mitochondrial DNA maintenance (mtDNA) defects have a wide range of causes, each with a set of phenotypes that overlap with many other neurological or muscular diseases. Clinicians face the challenge of narrowing down a long list of differential diagnosis when encountered with non-specific neuromuscular symptoms. Biallelic pathogenic variants in the Thymidine Kinase 2 (TK2) gene cause a myopathic form of mitochondrial DNA maintenance defect. Since the first description in 2001, there have been 71 patients reported with 42 unique pathogenic variants. Here we are reporting 11 new cases with 5 novel pathogenic variants. We describe and analyze a total of 82 cases with 47 unique TK2 pathogenic variants in effort to formulate a comprehensive molecular and clinical spectrum of TK2-related mtDNA maintenance disorders.
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Affiliation(s)
- Julia Wang
- Medical Scientist Training Program, Program in Developmental Biology, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, United States.
| | - Emily Kim
- Department of BioSciences, Rice University, 6100 Main Street, Houston, TX 77005, United States
| | - Honzheng Dai
- Department of Human and Molecular Genetics, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, United States
| | - Vikki Stefans
- UAMS College of Medicine, Arkansas Children's Hospital, 1 Children's Way, Little Rock, AR 72202, United States
| | - Hannes Vogel
- Pathology, Stanford University School of Medicine, R241 Edwards Building, 300 Pasteur Drive, Palo Alto, CA 94305, United States
| | - Fatma Al Jasmi
- Division of Clinical Genetics and Metabolic Disorders, Pediatrics Department, Tawam Hospital, Al-Ain, United Arab Emirates
| | - Samantha A Schrier Vergano
- Division of Medical Genetics and Metabolism, Children's Hospital of The King's Daughters, 601 Children's Lane, Norfolk, VA 23507, United States
| | - Diana Castro
- Department of Pediatric, Neurology and Neurotherapeutics, Children's Health Dallas, University of Texas Southwestern, 2350 N Stemmons Freeway, Dallas, TX 75207, United States
| | - Saunder Bernes
- Department of Neurology, Phoenix Children's Hospital, Barrows Neurological Institute, 1919 East Thomas Road, Phoenix, AZ 85016, United States
| | - Vikas Bhambhani
- Genomics Medicine Program, Children's Hospital Minnesota, 2525 Chicago Ave S, Minneapolis, MN 55404, United States
| | - Catherine Long
- Genomics Medicine Program, Children's Hospital Minnesota, 2525 Chicago Ave S, Minneapolis, MN 55404, United States
| | - Ayman W El-Hattab
- Division of Clinical Genetics and Metabolic Disorders, Pediatrics Department, Tawam Hospital, Al-Ain, United Arab Emirates
| | - Lee-Jun Wong
- Department of Human and Molecular Genetics, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, United States.
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6
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Garone C, Taylor RW, Nascimento A, Poulton J, Fratter C, Domínguez-González C, Evans JC, Loos M, Isohanni P, Suomalainen A, Ram D, Hughes MI, McFarland R, Barca E, Lopez Gomez C, Jayawant S, Thomas ND, Manzur AY, Kleinsteuber K, Martin MA, Kerr T, Gorman GS, Sommerville EW, Chinnery PF, Hofer M, Karch C, Ralph J, Cámara Y, Madruga-Garrido M, Domínguez-Carral J, Ortez C, Emperador S, Montoya J, Chakrapani A, Kriger JF, Schoenaker R, Levin B, Thompson JLP, Long Y, Rahman S, Donati MA, DiMauro S, Hirano M. Retrospective natural history of thymidine kinase 2 deficiency. J Med Genet 2018; 55:515-521. [PMID: 29602790 PMCID: PMC6073909 DOI: 10.1136/jmedgenet-2017-105012] [Citation(s) in RCA: 64] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2017] [Revised: 03/02/2018] [Accepted: 03/11/2018] [Indexed: 12/21/2022]
Abstract
Background Thymine kinase 2 (TK2) is a mitochondrial matrix protein encoded in nuclear DNA and phosphorylates the pyrimidine nucleosides: thymidine and deoxycytidine. Autosomal recessive TK2 mutations cause a spectrum of disease from infantile onset to adult onset manifesting primarily as myopathy. Objective To perform a retrospective natural history study of a large cohort of patients with TK2 deficiency. Methods The study was conducted by 42 investigators across 31 academic medical centres. Results We identified 92 patients with genetically confirmed diagnoses of TK2 deficiency: 67 from literature review and 25 unreported cases. Based on clinical and molecular genetics findings, we recognised three phenotypes with divergent survival: (1) infantile-onset myopathy (42.4%) with severe mitochondrial DNA (mtDNA) depletion, frequent neurological involvement and rapid progression to early mortality (median post-onset survival (POS) 1.00, CI 0.58 to 2.33 years); (2) childhood-onset myopathy (40.2%) with mtDNA depletion, moderate-to-severe progression of generalised weakness and median POS at least 13 years; and (3) late-onset myopathy (17.4%) with mild limb weakness at onset and slow progression to respiratory insufficiency with median POS of 23 years. Ophthalmoparesis and facial weakness are frequent in adults. Muscle biopsies show multiple mtDNA deletions often with mtDNA depletion. Conclusions In TK2 deficiency, age at onset, rate of weakness progression and POS are important variables that define three clinical subtypes. Nervous system involvement often complicates the clinical course of the infantile-onset form while extraocular muscle and facial involvement are characteristic of the late-onset form. Our observations provide essential information for planning future clinical trials in this disorder.
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Affiliation(s)
- Caterina Garone
- Department of Neurology, Columbia University Medical Center, New York City, New York, USA.,MRC Mitochondrial Biology Unit, Cambridge Biomedical Campus, Cambridge, UK
| | - Robert W Taylor
- Wellcome Trust Centre for Mitochondrial Research, Institute of Neuroscience, The Medical School, Newcastle University, Newcastle upon Tyne, UK
| | - Andrés Nascimento
- Neuromuscular Unit, Hospital Universitario 12 de Octubre, Madrid, Spain
| | - Joanna Poulton
- Nuffield Department of Obstetrics and Gynaecology, University of Oxford, Oxford, UK
| | - Carl Fratter
- Oxford Medical Genetics Laboratories, Oxford University Hospitals NHS Foundation Trust, Oxford, UK
| | - Cristina Domínguez-González
- Neuromuscular Unit, Hospital Universitario 12 de Octubre, Madrid, Spain.,Centre for Biomedical Network Research on Rare Diseases (CIBERER), Instituto de Salud Carlos III, Madrid, Spain.,Instituto de Investigación, Hospital Universitario 12 de Octubre, Madrid, Spain
| | - Julie C Evans
- Oxford Medical Genetics Laboratories, Oxford University Hospitals NHS Foundation Trust, Oxford, UK
| | - Mariana Loos
- Neurology Department, Hospital de Pediatría 'Prof. Dr JP Garrahan', Buenos Aires, Argentina
| | - Pirjo Isohanni
- Research Programs Unit, Molecular Neurology, Biomedicum Helsinki, University of Helsinki, Helsinki, Finland.,Department of Child Neurology, Children's Hospital, University of Helsinki, Helsinki University Hospital, Helsinki, Finland
| | - Anu Suomalainen
- Research Programs Unit, Molecular Neurology, Biomedicum Helsinki, University of Helsinki, Helsinki, Finland.,Neuroscience Center, University of Helsinki, Helsinki, Finland.,Department of Neurology, Helsinki University Hospital, Helsinki, Finland
| | - Dipak Ram
- Department of Paediatric Neurology, Royal Manchester Children's Hospital, Manchester, UK
| | - M Imelda Hughes
- Department of Paediatric Neurology, Royal Manchester Children's Hospital, Manchester, UK
| | - Robert McFarland
- Wellcome Trust Centre for Mitochondrial Research, Institute of Neuroscience, The Medical School, Newcastle University, Newcastle upon Tyne, UK
| | - Emanuele Barca
- Department of Neurology, Columbia University Medical Center, New York City, New York, USA.,UOC Neurology and Neuromuscular Diseases, Department of Clinical and Experimental Medicine, University of Messina, Messina, Italy
| | - Carlos Lopez Gomez
- Department of Neurology, Columbia University Medical Center, New York City, New York, USA
| | - Sandeep Jayawant
- Paediatric Neurology, Oxford University Hospitals NHS Foundation Trust, Oxford, UK
| | - Neil D Thomas
- Paediatric Neurology, University Hospital Southampton NHS Foundation Trust, Southampton, UK
| | - Adnan Y Manzur
- Dubowitz Neuromuscular Centre, Great Ormond Street Hospital for Children NHS Foundation Trust, London, UK
| | - Karin Kleinsteuber
- Pediatric Neurology, Faculty of Medicine, Universidad de Chile, Clínica Las Condes, Santiago, Chile
| | - Miguel A Martin
- Centre for Biomedical Network Research on Rare Diseases (CIBERER), Instituto de Salud Carlos III, Madrid, Spain.,Instituto de Investigación, Hospital Universitario 12 de Octubre, Madrid, Spain
| | - Timothy Kerr
- Paediatric Neurology, St George's University Hospitals NHS Foundation Trust, London, UK
| | - Grainne S Gorman
- Wellcome Trust Centre for Mitochondrial Research, Institute of Neuroscience, The Medical School, Newcastle University, Newcastle upon Tyne, UK
| | - Ewen W Sommerville
- Wellcome Trust Centre for Mitochondrial Research, Institute of Neuroscience, The Medical School, Newcastle University, Newcastle upon Tyne, UK
| | - Patrick F Chinnery
- MRC Mitochondrial Biology Unit, Cambridge Biomedical Campus, Cambridge, UK.,Wellcome Trust Centre for Mitochondrial Research, Institute of Genetic Medicine, Newcastle University, Newcastle upon Tyne, UK
| | - Monika Hofer
- Department of Neuropathology, Oxford University Hospitals NHS Foundation Trust, Oxford, UK
| | - Christoph Karch
- Department of Neurology, University of California San Francisco, San Francisco, California, USA
| | - Jeffrey Ralph
- Department of Neurology, University of California San Francisco, San Francisco, California, USA
| | - Yolanda Cámara
- Research Group on Neuromuscular and Mitochondrial Disorders, Vall d'Hebron Institut de Recerca, Barcelona, Spain.,Centre for Biomedical Network Research on Rare Diseases (CIBERER), Instituto de Salud Carlos III, Barcelona, Spain
| | - Marcos Madruga-Garrido
- Sección de Neuropediatría, Hospital Universitario Virgen del Rocío, Instituto de Biomedicina de Sevilla, Seville, Spain
| | - Jana Domínguez-Carral
- Neuromuscular Unit, Department of Neurology, Hospital Sant Joan de Déu, CIBERER, ISCIII, Universitat de Barcelona, Barcelona, Spain
| | - Carlos Ortez
- Neuromuscular Unit, Hospital Universitario 12 de Octubre, Madrid, Spain
| | - Sonia Emperador
- Department of Biochemistry and Molecular Biology, University of Zaragoza-CIBERER-Instituto de investigaciones Sanitarias de Aragón, Zaragoza, Spain
| | - Julio Montoya
- Department of Biochemistry and Molecular Biology, University of Zaragoza-CIBERER-Instituto de investigaciones Sanitarias de Aragón, Zaragoza, Spain
| | - Anupam Chakrapani
- Metabolic Unit, Great Ormond Street Hospital NHS Foundation Trust, London, UK
| | - Joshua F Kriger
- Department of Biostatistics, Mailman School of Public Health, Columbia University Medical Center, New York City, New York, USA
| | - Robert Schoenaker
- Department of Neurology, Columbia University Medical Center, New York City, New York, USA
| | - Bruce Levin
- Department of Biostatistics, Mailman School of Public Health, Columbia University Medical Center, New York City, New York, USA
| | - John L P Thompson
- Department of Biostatistics, Mailman School of Public Health, Columbia University Medical Center, New York City, New York, USA
| | - Yuelin Long
- Department of Biostatistics, Mailman School of Public Health, Columbia University Medical Center, New York City, New York, USA
| | - Shamima Rahman
- Metabolic Unit, Great Ormond Street Hospital NHS Foundation Trust, London, UK.,Mitochondrial Research Group, Genetics and Genomic Medicine, UCL Great Ormond Street Institute of Child Health, London, UK
| | | | - Salvatore DiMauro
- Department of Neurology, Columbia University Medical Center, New York City, New York, USA
| | - Michio Hirano
- Department of Neurology, Columbia University Medical Center, New York City, New York, USA
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7
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Sun R, Wang L. Thymidine Kinase 2 Enzyme Kinetics Elucidate the Mechanism of Thymidine-Induced Mitochondrial DNA Depletion. Biochemistry 2014; 53:6142-50. [DOI: 10.1021/bi5006877] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Affiliation(s)
- Ren Sun
- Department
of Anatomy, Physiology
and Biochemistry, Swedish University of Agricultural Sciences, Box 7011, SE-750 07 Uppsala, Sweden
| | - Liya Wang
- Department
of Anatomy, Physiology
and Biochemistry, Swedish University of Agricultural Sciences, Box 7011, SE-750 07 Uppsala, Sweden
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8
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Roos S, Lindgren U, Ehrstedt C, Moslemi A, Oldfors A. Mitochondrial DNA depletion in single fibers in a patient with novel TK2 mutations. Neuromuscul Disord 2014; 24:713-20. [DOI: 10.1016/j.nmd.2014.05.009] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2014] [Revised: 05/09/2014] [Accepted: 05/20/2014] [Indexed: 11/30/2022]
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9
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Che R, Yuan Y, Huang S, Zhang A. Mitochondrial dysfunction in the pathophysiology of renal diseases. Am J Physiol Renal Physiol 2014; 306:F367-78. [PMID: 24305473 DOI: 10.1152/ajprenal.00571.2013] [Citation(s) in RCA: 286] [Impact Index Per Article: 28.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Mitochondrial dysfunction has gained recognition as a contributing factor in many diseases. The kidney is a kind of organ with high energy demand, rich in mitochondria. As such, mitochondrial dysfunction in the kidney plays a critical role in the pathogenesis of kidney diseases. Despite the recognized importance mitochondria play in the pathogenesis of the diseases, there is limited understanding of various aspects of mitochondrial biology. This review examines the physiology and pathophysiology of mitochondria. It begins by discussing mitochondrial structure, mitochondrial DNA, mitochondrial reactive oxygen species production, mitochondrial dynamics, and mitophagy, before turning to inherited mitochondrial cytopathies in kidneys (inherited or sporadic mitochondrial DNA or nuclear DNA mutations in genes that affect mitochondrial function). Glomerular diseases, tubular defects, and other renal diseases are then discussed. Next, acquired mitochondrial dysfunction in kidney diseases is discussed, emphasizing the role of mitochondrial dysfunction in the pathogenesis of chronic kidney disease and acute kidney injury, as their prevalence is increasing. Finally, it summarizes the possible beneficial effects of mitochondrial-targeted therapeutic agents for treatment of mitochondrial dysfunction-mediated kidney injury-genetic therapies, antioxidants, thiazolidinediones, sirtuins, and resveratrol-as mitochondrial-based drugs may offer potential treatments for renal diseases.
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Affiliation(s)
- Ruochen Che
- Department of Nephrology, Nanjing Children's Hospital, Affiliated with Nanjing Medical University, Nanjing, China
- Institute of Pediatrics, Nanjing Medical University, Nanjing, China; and
| | - Yanggang Yuan
- Department of Nephrology, First Affiliated Hospital of Nanjing Medical University, Nanjing, China
| | - Songming Huang
- Department of Nephrology, Nanjing Children's Hospital, Affiliated with Nanjing Medical University, Nanjing, China
- Institute of Pediatrics, Nanjing Medical University, Nanjing, China; and
| | - Aihua Zhang
- Department of Nephrology, Nanjing Children's Hospital, Affiliated with Nanjing Medical University, Nanjing, China
- Institute of Pediatrics, Nanjing Medical University, Nanjing, China; and
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10
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Chanprasert S, Wang J, Weng SW, Enns GM, Boué DR, Wong BL, Mendell JR, Perry DA, Sahenk Z, Craigen WJ, Alcala FJC, Pascual JM, Melancon S, Zhang VW, Scaglia F, Wong LJC. Molecular and clinical characterization of the myopathic form of mitochondrial DNA depletion syndrome caused by mutations in the thymidine kinase (TK2) gene. Mol Genet Metab 2013; 110:153-61. [PMID: 23932787 DOI: 10.1016/j.ymgme.2013.07.009] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/03/2013] [Revised: 07/10/2013] [Accepted: 07/10/2013] [Indexed: 11/26/2022]
Abstract
Mitochondrial DNA (mtDNA) depletion syndromes (MDSs) are a clinically and molecularly heterogeneous group of mitochondrial cytopathies characterized by severe mtDNA copy number reduction in affected tissues. Clinically, MDSs are mainly categorized as myopathic, encephalomyopathic, hepatocerebral, or multi-systemic forms. To date, the myopathic form of MDS is mainly caused by mutations in the TK2 gene, which encodes thymidine kinase 2, the first and rate limiting step enzyme in the phosphorylation of pyrimidine nucleosides. We analyzed 9 unrelated families with 11 affected subjects exhibiting the myopathic form of MDS, by sequencing the TK2 gene. Twelve mutations including 4 novel mutations were detected in 9 families. Skeletal muscle specimens were available from 7 out of 11 subjects. Respiratory chain enzymatic activities in skeletal muscle were measured in 6 subjects, and enzymatic activities were reduced in 3 subjects. Quantitative analysis of mtDNA content in skeletal muscle was performed in 5 subjects, and marked mtDNA content reduction was observed in each. In addition, we outline the molecular and clinical characteristics of this syndrome in a total of 52 patients including those previously reported, and a total of 36 TK2 mutations are summarized. Clinically, hypotonia and proximal muscle weakness are the major phenotypes present in all subjects. In summary, our study expands the molecular and clinical spectrum associated with TK2 deficiency.
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Affiliation(s)
- Sirisak Chanprasert
- Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA
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11
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Zhou X, Kannisto K, Curbo S, von Döbeln U, Hultenby K, Isetun S, Gåfvels M, Karlsson A. Thymidine kinase 2 deficiency-induced mtDNA depletion in mouse liver leads to defect β-oxidation. PLoS One 2013; 8:e58843. [PMID: 23505564 PMCID: PMC3591375 DOI: 10.1371/journal.pone.0058843] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2012] [Accepted: 02/07/2013] [Indexed: 02/06/2023] Open
Abstract
Thymidine kinase 2 (TK2) deficiency in humans causes mitochondrial DNA (mtDNA) depletion syndrome. To study the molecular mechanisms underlying the disease and search for treatment options, we previously generated and described a TK2 deficient mouse strain (TK2−/−) that progressively loses its mtDNA. The TK2−/− mouse model displays symptoms similar to humans harboring TK2 deficient infantile fatal encephalomyopathy. Here, we have studied the TK2−/− mouse model to clarify the pathological role of progressive mtDNA depletion in liver for the severe outcome of TK2 deficiency. We observed that a gradual depletion of mtDNA in the liver of the TK2−/− mice was accompanied by increasingly hypertrophic mitochondria and accumulation of fat vesicles in the liver cells. The levels of cholesterol and nonesterified fatty acids were elevated and there was accumulation of long chain acylcarnitines in plasma of the TK2−/− mice. In mice with hepatic mtDNA levels below 20%, the blood sugar and the ketone levels dropped. These mice also exhibited reduced mitochondrial β-oxidation due to decreased transport of long chain acylcarnitines into the mitochondria. The gradual loss of mtDNA in the liver of the TK2−/− mice causes impaired mitochondrial function that leads to defect β-oxidation and, as a result, insufficient production of ketone bodies and glucose. This study provides insight into the mechanism of encephalomyopathy caused by TK2 deficiency-induced mtDNA depletion that may be used to explore novel therapeutic strategies.
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Affiliation(s)
- Xiaoshan Zhou
- Division of Clinical Microbiology F-68, Karolinska Institutet, Department of Laboratory Medicine, Karolinska University Hospital, Huddinge, Sweden
| | - Kristina Kannisto
- Division of Clinical Chemistry, C1-72, Karolinska Institutet, Department of Laboratory Medicine, Karolinska University Hospital, Huddinge, Sweden
| | - Sophie Curbo
- Division of Clinical Microbiology F-68, Karolinska Institutet, Department of Laboratory Medicine, Karolinska University Hospital, Huddinge, Sweden
- * E-mail:
| | - Ulrika von Döbeln
- Division of Metabolic Diseases, Karolinska Institutet, Department of Laboratory Medicine, Karolinska University Hospital, Huddinge, Sweden
| | - Kjell Hultenby
- Division of Clinical Research Center, Karolinska Institutet, Department of Laboratory Medicine, Karolinska University Hospital, Huddinge, Sweden
| | - Sindra Isetun
- Division of Metabolic Diseases, Karolinska Institutet, Department of Laboratory Medicine, Karolinska University Hospital, Huddinge, Sweden
| | - Mats Gåfvels
- Division of Clinical Chemistry, C1-72, Karolinska Institutet, Department of Laboratory Medicine, Karolinska University Hospital, Huddinge, Sweden
- Division of Clinical Chemistry, Department of Laboratory Medicine, Lund University, Lund, Sweden
| | - Anna Karlsson
- Division of Clinical Microbiology F-68, Karolinska Institutet, Department of Laboratory Medicine, Karolinska University Hospital, Huddinge, Sweden
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12
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Abstract
Mitochondrial disorders are genetic defects of oxidative phosphorylation. Oxidative phosphorylation takes place in the mitochondrial inner membrane and consists of the oxidation of fuel molecules by oxygen and the concomitant energy transduction into ATP. The mitochondrial respiratory chain is a complex metabolic pathway. It is made of approximately 100 polypeptides, most of which are encoded in the nucleus whereas 13 are encoded in the mitochondria. Mitochondrial DNA is maternally inherited and its mutations are transmitted by the mother. During cell division, mitochondria are randomly partitioned in daughter cells. Therefore, in case normal and mutant DNA are present in the mother's cells, some lineage may have only mutant mitochondrial DNA or normal mitochondrial DNA while others may have both mutant and normal DNA, a condition named heteroplasmy. Renal involvement in mitochondrial cytopathies is rare. Patients most often present with a more or less complete de Toni-Debré-Fanconi syndrome. A few patients present with a nephrotic syndrome or with chronic tubulointerstitial nephritis. The investigation of patients with mitochondrial disorders include metabolic screening for abnormal oxidoreduction status in plasma, investigation of the mitochondrial respiratory chain, including polarographic and spectrophotometric studies, histopathologic studies and genetic studies.
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Affiliation(s)
- Patrick Niaudet
- Service de néphrologie pédiatrique, université Paris Descartes, hôpital Necker-Enfants-Malades, 149, rue de Sèvres, 75743 Paris cedex 15, France.
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13
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Selim L, Mehaney D, Hassan F, Sabry R, Zeyada R, Hassan S, Eldin IG, Bertini E. Mitochondrial DNA depletion syndrome presenting with ataxia and external ophthalmoplegia: Case report. EGYPTIAN JOURNAL OF MEDICAL HUMAN GENETICS 2012. [DOI: 10.1016/j.ejmhg.2012.05.003] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
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14
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Abstract
Mitochondrial DNA (mtDNA) is replicated by the DNA polymerase g in concert with accessory proteins such as the mtDNA helicase, single stranded DNA binding protein, topoisomerase, and initiating factors. Nucleotide precursors for mtDNA replication arise from the mitochondrial salvage pathway originating from transport of nucleosides, or alternatively from cytoplasmic reduction of ribonucleotides. Defects in mtDNA replication or nucleotide metabolism can cause mitochondrial genetic diseases due to mtDNA deletions, point mutations, or depletion which ultimately cause loss of oxidative phosphorylation. These genetic diseases include mtDNA depletion syndromes such as Alpers or early infantile hepatocerebral syndromes, and mtDNA deletion disorders, such as progressive external ophthalmoplegia (PEO), ataxia-neuropathy, or mitochondrial neurogastrointestinal encephalomyopathy (MNGIE). This review focuses on our current knowledge of genetic defects of mtDNA replication (POLG, POLG2, C10orf2) and nucleotide metabolism (TYMP, TK2, DGOUK, and RRM2B) that cause instability of mtDNA and mitochondrial disease.
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Affiliation(s)
- William C Copeland
- Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences, Durham, North Carolina 27709, USA.
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15
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Martí R, Nascimento A, Colomer J, Lara MC, López-Gallardo E, Ruiz-Pesini E, Montoya J, Andreu AL, Briones P, Pineda M. Hearing loss in a patient with the myopathic form of mitochondrial DNA depletion syndrome and a novel mutation in the TK2 gene. Pediatr Res 2010; 68:151-4. [PMID: 20421844 DOI: 10.1203/pdr.0b013e3181e33bbe] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Mitochondrial DNA (mtDNA) depletion syndrome (MDS) is a devastating disorder of infancy caused by a significant reduction of the number of copies of mitochondrial DNA in one or more tissues. We report a Spanish patient with the myopathic form of MDS, harboring two mutations in the thymidine kinase 2 gene (TK2): a previously reported deletion (p.K244del) and a novel nucleotide duplication in the exon 2, generating a frameshift and premature stop codon. Sensorineural hearing loss was a predominant symptom in the patient and a novel feature of MDS due to TK2 mutations. The patient survived up to the age of 8.5 y, which confirms that survival above the age of 5 y is not infrequent in patients with MDS due to TK2 deficiency.
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Affiliation(s)
- Ramon Martí
- Laboratory of Mitochondrial Disorders, Institut de Recerca Hospital Universitari Vall d'Hebron, 08035 Barcelona, Spain
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16
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Collated mutations in mitochondrial DNA (mtDNA) depletion syndrome (excluding the mitochondrial gamma polymerase, POLG1). Biochim Biophys Acta Mol Basis Dis 2009; 1792:1109-12. [DOI: 10.1016/j.bbadis.2009.08.016] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2009] [Accepted: 08/27/2009] [Indexed: 01/09/2023]
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17
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Tarnopolsky MA. MITOCHONDRIAL CYTOPATHIES IN CHILDREN AND ADULTS. Continuum (Minneap Minn) 2009. [DOI: 10.1212/01.con.0000348880.16694.08] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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18
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Al-Dosary M, Whittaker RG, Haughton J, McFarland R, Goodship J, Turnbull DM, Taylor RW. Neuromuscular disease presentation with three genetic defects involving two genomes. Neuromuscul Disord 2009; 19:841-4. [DOI: 10.1016/j.nmd.2009.10.001] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2009] [Revised: 09/16/2009] [Accepted: 10/02/2009] [Indexed: 11/25/2022]
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19
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Progressive myofiber loss with extensive fibro-fatty replacement in a child with mitochondrial DNA depletion syndrome and novel thymidine kinase 2 gene mutations. Neuromuscul Disord 2009; 19:784-7. [PMID: 19736010 DOI: 10.1016/j.nmd.2009.08.002] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2009] [Revised: 07/17/2009] [Accepted: 08/04/2009] [Indexed: 11/21/2022]
Abstract
The mitochondrial DNA depletion syndromes (MDS) are autosomal recessive disorders with a decreased mitochondrial DNA copy number. Mutations in thymidine kinase 2 (TK2) have been responsible for the myopathic form of MDS. We describe a child with congenital muscle weakness who had a progressive mitochondrial myopathy associated with extensive fibro-fatty replacement of myofibers resembling muscular dystrophy. MDS was suspected based upon findings in the initial muscle biopsy. Sequence analysis of the TK2 gene revealed two novel heterozygous mutations: the frame shift mutation, c.255_c.258delAGAA, and the heterozygous missense mutation, c.515G>A, (p.R172Q). This report extends the phenotype and genotype of TK2 defects.
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20
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Rötig A, Poulton J. Genetic causes of mitochondrial DNA depletion in humans. Biochim Biophys Acta Mol Basis Dis 2009; 1792:1103-8. [PMID: 19596444 DOI: 10.1016/j.bbadis.2009.06.009] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2009] [Revised: 06/19/2009] [Accepted: 06/24/2009] [Indexed: 11/16/2022]
Abstract
Mitochondrial DNA (mtDNA) depletion is characterized by a profound reduction of mtDNA copy number. The maintenance of mtDNA copy number requires several nuclear-encoded factors involved in replication and in dNTP supply. In the past decade mutations in several of these factors have been reported in a growing number of syndromes. This article reviews the current knowledge of genes causing mitochondrial DNA depletion syndromes.
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Affiliation(s)
- Agnès Rötig
- INSERM U781, Hôpital Necker-Enfants Malades, Université René Descartes Paris V, 149 rue de Sèvres, 75015 Paris, France.
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21
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Walter JH. Genes, patients, families, doctors-mutation analysis in clinical practice. J Inherit Metab Dis 2009; 32:441-6. [PMID: 19306072 DOI: 10.1007/s10545-009-1085-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/27/2008] [Revised: 02/04/2009] [Accepted: 02/13/2009] [Indexed: 10/21/2022]
Abstract
Developments in mutation analysis have led to significant benefits for patients with inherited metabolic disorders and their families. This is particularly the case where new methodologies have prevented the need for invasive tissue biopsies or have allowed carrier detection or first trimester prenatal testing to be undertaken. Whereas in the past it may have only been possible to identify specific 'common' mutations, the availability of techniques, such as automated sequencing, and novel technologies including mutation scanning techniques, multiplex ligation dependent probe amplification, and array technologies, have vastly improved the diagnostic efficiency of molecular testing.
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Affiliation(s)
- J H Walter
- Inherited Metabolic Disease, Willink Biochemical Genetics Unit, Royal Manchester Children's Hospital, Manchester M27 4HA, UK
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22
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Rizza T, Vazquez-Memije ME, Meschini MC, Bianchi M, Tozzi G, Nesti C, Piemonte F, Bertini E, Santorelli FM, Carrozzo R. Assaying ATP synthesis in cultured cells: a valuable tool for the diagnosis of patients with mitochondrial disorders. Biochem Biophys Res Commun 2009; 383:58-62. [PMID: 19332025 DOI: 10.1016/j.bbrc.2009.03.121] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2009] [Accepted: 03/24/2009] [Indexed: 11/26/2022]
Abstract
Mitochondrial ATP synthase plays a central role in cell function by synthesising most of the ATP in human tissues. In different cells, active regulation of mitochondrial ATP synthase in response to cellular energy demand has been demonstrated, as well as its alteration under several pathological conditions affecting oxidative phosphorylation (OXPHOS). Traditionally, detection of OXPHOS defects is based on the spectrophotometric measurement of respiratory chain complex activities in muscle biopsies. Considering the broad clinical spectrum of mitochondrial disorders, and the difficulty in arriving at a single diagnostic method, in this study we propose measurement of ATP synthesis in mitochondria from skin fibroblasts as an effective screening tool. In the light of our results this assessment emerges as a useful marker of impaired energy production in primary OXPHOS disorders of childhood and as a tool with the potential to drive further molecular genetic studies.
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23
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Pérez-Pérez MJ, Priego EM, Hernández AI, Familiar O, Camarasa MJ, Negri A, Gago F, Balzarini J. Structure, physiological role, and specific inhibitors of human thymidine kinase 2 (TK2): present and future. Med Res Rev 2008; 28:797-820. [PMID: 18459168 PMCID: PMC7168489 DOI: 10.1002/med.20124] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/05/2022]
Abstract
Human mitochondrial thymidine kinase (TK2) is a pyrimidine deoxynucleoside kinase (dNK) that catalyzes the phosphorylation of pyrimidine deoxynucleosides to their corresponding deoxynucleoside 5′‐monophosphates by γ‐phosphoryl transfer from ATP. In resting cells, TK2 is suggested to play a key role in the mitochondrial salvage pathway to provide pyrimidine nucleotides for mitochondrial DNA (mtDNA) synthesis and maintenance. However, recently the physiological role of TK2turned out to have direct clinical relevance as well. Point mutations in the gene encoding TK2 have been correlated to mtDNA disorders in a heterogeneous group of patients suffering from the so‐called mtDNA depletion syndrome (MDS). TK2 activity could also be involved in mitochondrial toxicity associated to prolonged treatment with antiviral nucleoside analogues like AZT and FIAU. Therefore, TK2 inhibitors can be considered as valuable tools to unravel the role of TK2 in the maintenance and homeostasis of mitochondrial nucleotide pools and mtDNA, and to clarify the contribution of TK2 activity to mitochondrial toxicity of certain antivirals. Highly selective TK‐2 inhibitors having an acyclic nucleoside structure and efficiently discriminating between TK‐2 and the closely related TK‐1 have already been reported. It is actually unclear whether these agents efficiently reach the inner mitochondrial compartment. In the present review article,structural features of TK2, MDS‐related mutations observed in TK2 and their role in MDS will be discussed. Also, an update on novel and selective TK2 inhibitors will be provided. © 2008 Wiley Periodicals, Inc. Med Res Rev, 28, No. 5, 797–820, 2008
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24
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Götz A, Isohanni P, Pihko H, Paetau A, Herva R, Saarenpää-Heikkilä O, Valanne L, Marjavaara S, Suomalainen A. Thymidine kinase 2 defects can cause multi-tissue mtDNA depletion syndrome. Brain 2008; 131:2841-50. [PMID: 18819985 DOI: 10.1093/brain/awn236] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Mitochondrial DNA depletion syndrome (MDS) is a severe recessively inherited disease of childhood. It manifests most often in infancy, is rapidly progressive and leads to early death. MDS is caused by an increasing number of nuclear genes leading to multisystemic or tissue-specific decrease in mitochondrial DNA (mtDNA) copy number. Thymidine kinase 2 (TK2) has been reported to cause a myopathic form of MDS. We report here the clinical, autopsy and molecular genetic findings of rapidly progressive fatal infantile mitochondrial syndrome. All of our seven patients had rapidly progressive myopathy/encephalomyopathy, leading to respiratory failure within the first 3 years of life, with high creatine kinase values and dystrophic changes in the muscle with cytochrome c oxidase-negative fibres. In addition, two patients also had terminal-phase seizures, one had epilepsia partialis continua and one had cortical laminar necrosis. We identified two different homozygous or compound heterozygous mutations in the TK2 gene in all the patients: c.739 C s -> T and c.898 C -> T, leading to p.R172W and p.R225W changes at conserved protein sites. R172W mutation led to myopathy or encephalomyopathy with the onset during the first months of life, and was associated with severe mtDNA depletion in the muscle, brain and liver. Homozygosity for R225W mutation manifested during the second year of life as a myopathy, and showed muscle-specific mtDNA depletion. Both mutations originated from single ancient founders, with Finnish origin and enrichment for the new R172W mutation, and possibly Scandinavian ancestral origin for the R225W. We conclude that TK2 mutations may manifest as infantile-onset fatal myopathy with dystrophic features, but should be considered also in infantile progressive encephalomyopathy with wide-spread mtDNA depletion.
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Affiliation(s)
- Alexandra Götz
- Research Programme of Molecular Neurology, Biomedicum-Helsinki, University of Helsinki, Helsinki, Finland
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25
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Leshinsky-Silver E, Michelson M, Cohen S, Ginsberg M, Sadeh M, Barash V, Lerman-Sagie T, Lev D. A defect in the thymidine kinase 2 gene causing isolated mitochondrial myopathy without mtDNA depletion. Eur J Paediatr Neurol 2008; 12:309-13. [PMID: 17951082 DOI: 10.1016/j.ejpn.2007.09.005] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/23/2007] [Revised: 08/28/2007] [Accepted: 09/02/2007] [Indexed: 11/24/2022]
Abstract
Isolated mitochondrial myopathies (IMM) are either due to primary defects in mtDNA, in nuclear genes that control mtDNA abundance and structure such as thymidine kinase 2 (TK2), or due to CoQ deficiency. Defects in the TK2 gene have been found to be associated with mtDNA depletion attributed to a depleted mitochondrial dNTP pool in non-dividing cells. We report an unusual case of IMM, homozygous for the H90N mutation in the TK2 gene but unlike other cases with the same mutation, does not demonstrate mtDNA depletion. The patient's clinical course is relatively mild and a muscle biopsy showed ragged red muscle fibers with a mild decrease in complexes I and an increase in complexes IV and II activities. This report extends the phenotypic expression of TK2 defects and suggests that all patients who present with an IMM even with normal quantities of mtDNA should be screened for TK2 mutations.
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26
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Abstract
Mitochondrial genetic diseases can result from defects in mitochondrial DNA (mtDNA) in the form of deletions, point mutations, or depletion, which ultimately cause loss of oxidative phosphorylation. These mutations may be spontaneous, maternally inherited, or a result of inherited nuclear defects in genes that maintain mtDNA. This review focuses on our current understanding of nuclear gene mutations that produce mtDNA alterations and cause mitochondrial depletion syndrome (MDS), progressive external ophthalmoplegia (PEO), ataxia-neuropathy, or mitochondrial neurogastrointestinal encephalomyopathy (MNGIE). To date, all of these etiologic nuclear genes fall into one of two categories: genes whose products function directly at the mtDNA replication fork, such as POLG, POLG2, and TWINKLE, or genes whose products supply the mitochondria with deoxynucleotide triphosphate pools needed for DNA replication, such as TK2, DGUOK, TP, SUCLA2, ANT1, and possibly the newly identified MPV17.
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Affiliation(s)
- William C Copeland
- Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709, USA.
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27
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Martínez-Azorín F, Calleja M, Hernández-Sierra R, Farr CL, Kaguni LS, Garesse R. Over-expression of the catalytic core of mitochondrial DNA (mtDNA) polymerase in the nervous system of Drosophila melanogaster reduces median life span by inducing mtDNA depletion. J Neurochem 2007; 105:165-76. [PMID: 17999718 DOI: 10.1111/j.1471-4159.2007.05122.x] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
DNA polymerase gamma (pol gamma) is the sole DNA polymerase devoted to mitochondrial DNA (mtDNA) replication. We have characterized the molecular and physiological effects of over-expression of the catalytic subunit of pol gamma, pol gamma-alpha, in the nervous system of Drosophila melanogaster using the upstream activation sequence (UAS)/yeast transcriptional activator by binding to UAS (GAL4) system. Tissue-specific over-expression of pol gamma-alpha was confirmed by immunoblot analysis, whereas the very low levels of endogenous protein are undetectable in UAS or GAL4 control lines. The transgenic flies over-expressing pol gamma-alpha in the nervous system showed a moderate increase in pupal lethality, and a significant decrease in the median life span of adult flies. Moreover, these flies displayed a decrease in the rate of synthesis of mtDNA, which is accompanied by a significant mtDNA depletion, and a corresponding decrease in the levels of mitochondrial transcription factor A (mtTFA). Biochemical analysis showed an oxidative phosphorylation (OXPHOS) defect in transgenic flies, which were more susceptible to oxidative stress. Although we did not detect apoptosis in the nervous system of adult transgenic flies, brains of larvae over-expressing pol gamma-alpha showed evidence of increased cell death that correlates with the observed phenotypes. Our data establish an animal model that mimics some of the features of human mtDNA depletion syndromes.
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Affiliation(s)
- Francisco Martínez-Azorín
- Departamento de Bioquímica, Instituto de Investigaciones Biomédicas Alberto Sols CSIC-UAM, Facultad de Medicina CIBERER ISCIII, Universidad Autónoma de Madrid, Madrid, Spain.
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28
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deBruyn JC, Chan AK, Bhargava R, Idikio H, Huynh HQ. Liver failure in mitochondrial DNA depletion syndrome: the importance of serial neuroimaging in liver transplantation evaluation. J Pediatr Gastroenterol Nutr 2007; 45:252-6. [PMID: 17667724 DOI: 10.1097/mpg.0b013e318048838f] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/10/2022]
Affiliation(s)
- Jennifer C deBruyn
- Division of Pediatric Gastroenterology and Nutrition, Department of Pediatrics, University of Alberta, Edmonton, Alberta, Canada
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29
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Moslemi AR, Darin N. Molecular genetic and clinical aspects of mitochondrial disorders in childhood. Mitochondrion 2007; 7:241-52. [PMID: 17376748 DOI: 10.1016/j.mito.2007.02.002] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2006] [Revised: 01/17/2007] [Accepted: 02/02/2007] [Indexed: 12/21/2022]
Abstract
Mitochondrial OXPHOS disorders are caused by mutations in mitochondrial or nuclear genes, which directly or indirectly affect mitochondrial oxidative phosphorylation (OXPHOS). Primary mtDNA abnormalities in children are due to rearrangements (deletions or duplications) and point mutations or insertions. Mutations in the nuclear-encoded polypeptide subunits of OXPHOS result in complex I and II deficiency, whereas mutations in the nuclear proteins involved in the assembly of OXPHOS subunits cause defects in complexes I, III, IV, and V. Here, we review recent progress in the identification of mitochondrial and nuclear gene defects and the associated clinical manifestations of these disorders in childhood.
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Affiliation(s)
- Ali-Reza Moslemi
- Department of Pathology, Göteborg University, Sahlgrenska University Hospital, SE-413 45 Göteborg, Sweden.
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30
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Carrozzo R, Dionisi-Vici C, Steuerwald U, Lucioli S, Deodato F, Di Giandomenico S, Bertini E, Franke B, Kluijtmans LAJ, Meschini MC, Rizzo C, Piemonte F, Rodenburg R, Santer R, Santorelli FM, van Rooij A, Vermunt-de Koning D, Morava E, Wevers RA. SUCLA2 mutations are associated with mild methylmalonic aciduria, Leigh-like encephalomyopathy, dystonia and deafness. Brain 2007; 130:862-74. [PMID: 17301081 DOI: 10.1093/brain/awl389] [Citation(s) in RCA: 133] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
One pedigree with four patients has been recently described with mitochondrial DNA depletion and mutation in SUCLA2 gene leading to succinyl-CoA synthase deficiency. Patients had a Leigh-like encephalomyopathy and deafness but besides the presence of lactic acidosis, the profile of urine organic acid was not reported. We have studied 14 patients with mild 'unlabelled' methylmalonic aciduria (MMA) from 11 families. Eight of the families are from the Faroe Islands, having a common ancestor, and three are from southern Italy. Since the reaction catalysed by succinyl-CoA synthase in the tricarboxylic acid (TCA) cycle represents a distal step of the methylmalonic acid pathway, we investigated the SUCLA2 gene as a candidate gene in our patients. Genetic analysis of the gene in the 14 patients confirmed the defect in all patients and led to the identification of three novel mutations (p.Gly118Arg; p.Arg284Cys; c.534 + 1G --> A). The defect could be convincingly shown at the protein level and our data also confirm the previously described mitochondrial DNA depletion. Defects in SUCLA2 can be found at the metabolite level and are defined by mildly elevated methylmalonic acid and C4-dicarboxylic carnitine concentrations in body fluids in association with variable lactic acidosis. Clinically the diagnosis should be considered in patients with early/neonatal onset encephalomyopathy, dystonia, deafness and Leigh-like MRI abnormalities mainly affecting the putamen and the caudate nuclei. The frequency of the mutated allele in the Faroese population amounted to 2%, corresponding with an estimated homozygote frequency of 1 : 2500. Our data extend knowledge on the genetic defects causing MMA. Our patients present with an early infantile Leigh-like encephalomyopathy with deafness, and later on a progressive dystonia. Mild MMA, lactic acidosis and specific abnormalities in the carnitine ester profile are the biochemical hallmarks of the disease. In view of the frequency of the mutated allele on the Faroe Islands, measures become feasible to prevent the occurrence of the disease on the islands. We confirm and extend the findings on this inborn error of metabolism in the TCA cycle that must be carefully investigated by accurate metabolite analyses.
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Affiliation(s)
- Rosalba Carrozzo
- Unit of Molecular Medicine, Bambino Gesù Children's Hospital, Rome, Italy
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31
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Oldfors A, Tulinius M. Mitochondrial encephalomyopathies. HANDBOOK OF CLINICAL NEUROLOGY 2007; 86:125-165. [PMID: 18808998 DOI: 10.1016/s0072-9752(07)86006-4] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
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32
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Alberio S, Mineri R, Tiranti V, Zeviani M. Depletion of mtDNA: syndromes and genes. Mitochondrion 2006; 7:6-12. [PMID: 17280874 DOI: 10.1016/j.mito.2006.11.010] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2006] [Accepted: 10/06/2006] [Indexed: 11/23/2022]
Abstract
Maintenance of mitochondrial DNA (mtDNA) requires the concerted activity of several nuclear-encoded factors that participate in its replication, being part of the mitochondrial replisome or ensuring the balanced supply of dNTPs to mitochondria. In the past decade, a growing number of syndromes associated with dysfunction due to tissue-specific depletion of mtDNA (MDS) have been reported. This article reviews the current knowledge of the genes responsible for these disorders, the impact of different mutations in the epidemiology of MDS and their role in the pathogenic mechanisms underlying the different clinical presentations.
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Affiliation(s)
- Simona Alberio
- Unit of Molecular Neurogenetics-Pierfranco and Luisa Mariani Center for the Study of Children's Mitochondrial Disorders, C. Besta Neurological Institute Foundation, IRCCS, Italy
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33
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Reichenbach J, Schubert R, Horvàth R, Petersen J, Fütterer N, Malle E, Stumpf A, Gebhardt BR, Koehl U, Schraven B, Zielen S. Fatal neonatal-onset mitochondrial respiratory chain disease with T cell immunodeficiency. Pediatr Res 2006; 60:321-6. [PMID: 16857757 DOI: 10.1203/01.pdr.0000233252.60457.cf] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
We present the clinical and laboratory features of a boy with a new syndrome of mitochondrial depletion syndrome and T cell immunodeficiency. The child suffered from severe recurrent infectious diseases, anemia, and thrombocytopenia. Clinically, he presented with severe psychomotor retardation, axial hypotonia, and a disturbed pain perception leading to debilitating biting of the thumb, lower lip, and tongue. Brain imaging showed hypoplasia of corpus callosum and an impaired myelinization of the temporo-occipital region with consecutive supratentorial hydrocephalus. Histologic examination of a skeletal muscle biopsy was normal. Biochemical investigation showed combined deficiency of respiratory chain complexes II+III and IV. MtDNA depletion was found by real-time PCR. No pathogenic mutations were identified in the TK2, SUCLA2, DGUOK, and ECGF1 genes. A heterozygous missense mutation was found in POLG1. The pathogenic relevance of this mutation is unclear. Interestingly, a lack of CD8(+) T lymphocytes as well as NK cells was also observed. The percentage of CD45RO-expressing cells was decreased in activated CD8(+) T lymphocytes. Activation of T lymphocytes via IL-2 was diminished. The occurrence of the immunologic deficiency in our patient with mtDNA depletion is a rare finding, implying that cells of the immune system might also be affected by mitochondrial disease.
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Affiliation(s)
- Janine Reichenbach
- Department of General Paediatrics, JW Goethe University Frankfurt, 60590 Frankfurt, Germany.
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34
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Wittig I, Carrozzo R, Santorelli FM, Schägger H. Supercomplexes and subcomplexes of mitochondrial oxidative phosphorylation. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2006; 1757:1066-72. [PMID: 16782043 DOI: 10.1016/j.bbabio.2006.05.006] [Citation(s) in RCA: 171] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/27/2006] [Revised: 04/07/2006] [Accepted: 05/03/2006] [Indexed: 10/24/2022]
Abstract
Dimerization or oligomerization of ATP synthase has been proposed to play an important role for mitochondrial cristae formation and to be involved in regulating ATP synthase activity. We found comparable oligomycin-sensitive ATPase activity for monomeric and oligomeric ATP synthase suggesting that oligomerization/monomerization dynamics are not directly involved in regulating ATP synthase activity. Binding of the natural IF1 inhibitor protein has been shown to induce dimerization of F1-subcomplexes. This suggested that binding of IF1 might also dimerize holo ATP synthase, and possibly link dimerization and inhibition. Analyzing mitochondria of human rho zero cells that contain mitochondria but lack mitochondrial DNA, we identified three subcomplexes of ATP synthase: (i) F1 catalytic domain, (ii) F1-domain with bound IF1, and (iii) F1-c subcomplex with bound IF1 and a ring of subunits c. Since both IF1 containing subcomplexes were present in monomeric state and exhibited considerably reduced ATPase activity as compared to the third subcomplex lacking IF1, we postulate that inhibition and induction of dimerization of F1-subcomplexes by IF1 are independent events. F1-subcomplexes were also found in mitochondria of patients with specific mitochondrial disorders, and turned out to be useful for the clinical differentiation between various types of mitochondrial biosynthesis disorders. Supramolecular associations of respiratory complexes, the "respirasomes", seem not to be the largest assemblies in the structural organization of the respiratory chain, as suggested by differential solubilization of mitochondria and electron microscopic analyses of whole mitochondria. We present a model for a higher supramolecular association of respirasomes into a "respiratory string".
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Affiliation(s)
- Ilka Wittig
- Molekulare Bioenergetik, Zentrum der Biologischen Chemie, Universitätsklinikum Frankfurt, Theodor-Stern-Kai 7, Haus 26, D-60590 Frankfurt, Germany.
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35
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Lewis W, Kohler JJ, Hosseini SH, Haase CP, Copeland WC, Bienstock RJ, Ludaway T, McNaught J, Russ R, Stuart T, Santoianni R. Antiretroviral nucleosides, deoxynucleotide carrier and mitochondrial DNA: evidence supporting the DNA pol gamma hypothesis. AIDS 2006; 20:675-84. [PMID: 16514297 PMCID: PMC1779943 DOI: 10.1097/01.aids.0000216367.23325.58] [Citation(s) in RCA: 84] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
DESIGN Nucleoside reverse transcriptase inhibitors (NRTIs) exhibit mitochondrial toxicity. The mitochondrial deoxynucleotide carrier (DNC) transports nucleotide precursors (or phosphorylated NRTIs) into mitochondria for mitochondrial (mt)DNA replication or inhibition of mtDNA replication by NRTIs. Transgenic mice (TG) expressing human DNC targeted to murine myocardium served to define mitochondrial events from NRTIs in vivo and findings were corroborated by biochemical events in vitro. METHODS Zidovudine (3'-azido-2',3'-deoxythymidine; ZDV), stavudine (2', 3'-didehydro-2', 3'-deoxythymidine; d4T), or lamivudine ((-)-2'-deoxy-3'-thiacytidine; 3TC) were administered individually to TGs and wild-type (WT) littermates (35 days) at human doses with drug-free vehicle as control. Left ventricle (LV) mass was defined echocardiographically, mitochondrial ultrastructural defects were identified by electron microscopy, the abundance of cardiac mtDNA was quantified by real time polymerase chain reaction, and mtDNA-encoded polypeptides were quantified. RESULTS Untreated TGs exhibited normal LV mass with minor mitochondrial damage. NRTI monotherapy (either d4T or ZDV) increased LV mass in TGs and caused significant mitochondrial destruction. Cardiac mtDNA was depleted in ZDV and d4T-treated TG hearts and mtDNA-encoded polypeptides decreased. Changes were absent in 3TC-treated cohorts. In supportive structural observations from molecular modeling, ZDV demonstrated close contacts with K947 and Y951 in the DNA pol gamma active site that were absent in the HIV reverse transcriptase active site. CONCLUSIONS NRTIs deplete mtDNA and polypeptides, cause mitochondrial structural and functional defects in vivo, follow inhibition kinetics with DNA pol gamma in vitro, and are corroborated by molecular models. Disrupted pools of nucleotide precursors and inhibition of DNA pol gamma by specific NRTIs are mechanistically important in mitochondrial toxicity.
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Affiliation(s)
- William Lewis
- Department of Pathology, Emory University, Atlanta, Georgia 30322, USA.
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36
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Galbiati S, Bordoni A, Papadimitriou D, Toscano A, Rodolico C, Katsarou E, Sciacco M, Garufi A, Prelle A, Aguennouz M', Bonsignore M, Crimi M, Martinuzzi A, Bresolin N, Papadimitriou A, Comi GP. New mutations in TK2 gene associated with mitochondrial DNA depletion. Pediatr Neurol 2006; 34:177-85. [PMID: 16504786 DOI: 10.1016/j.pediatrneurol.2005.07.013] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/12/2005] [Revised: 06/14/2005] [Accepted: 07/11/2005] [Indexed: 11/17/2022]
Abstract
Mitochondrial deoxyribonucleic acid depletion syndromes are autosomal recessive disorders characterized by a reduction of the amount of mitochondrial deoxyribonucleic acid, which impairs the synthesis of respiratory chain complexes. Mutations in the deoxyguanosine kinase and polymerase gamma genes have been identified in hepatocerebral forms, whereas thymidine kinase 2 gene mutations have been found in patients with isolated myopathy, encephalomyopathy, or spinal muscular atrophy. Mutations in the gene encoding the beta subunit of the adenosine diphosphate-forming succinyl-coenzyme A synthetase have also been reported in a family. In this report, the clinical, molecular, morphologic, and biochemical features of five children from two independent families with an infantile encephalomyopathy are characterized. The affected children manifested muscle mitochondrial deoxyribonucleic acid depletion and three novel thymidine kinase 2 gene mutations. They consist of a homozygous substitution resulting in Ala to Val change at the highly conserved position 181 of thymidine kinase in the first family, and two heterozygous substitutions in the second family: a Cys to Trp change at residue 108 and a Leu to Pro change at residue 257 of the enzyme. Common clinical features associated with these TK2 mutations are a normal early developmental phase followed by psychomotor regression, encephalopathy often with epileptic seizures, and myopathy with features of a progressive dystrophic process.
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Affiliation(s)
- Sara Galbiati
- Centro Dino Ferrari, Department of Neurological Sciences, University of Milan, I.R.C.C.S. Ospedale Maggiore Policlinico, Milano, Italy.
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37
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Curbo S, Lagier-Tourenne C, Carrozzo R, Palenzuela L, Lucioli S, Hirano M, Santorelli F, Arenas J, Karlsson A, Johansson M. Human mitochondrial pyrophosphatase: cDNA cloning and analysis of the gene in patients with mtDNA depletion syndromes. Genomics 2006; 87:410-6. [PMID: 16300924 DOI: 10.1016/j.ygeno.2005.09.017] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2005] [Revised: 08/29/2005] [Accepted: 09/27/2005] [Indexed: 11/20/2022]
Abstract
Pyrophosphatases (PPases) catalyze the hydrolysis of inorganic pyrophosphate generated in several cellular enzymatic reactions. A novel human pyrophosphatase cDNA encoding a 334-amino-acid protein approximately 60% identical to the previously identified human cytosolic PPase was cloned and characterized. The novel enzyme, named PPase-2, was enzymatically active and catalyzed hydrolysis of pyrophosphate at a rate similar to that of the previously identified PPase-1. A functional mitochondrial import signal sequence was identified in the N-terminus of PPase-2, which targeted the enzyme to the mitochondrial matrix. The human pyrophosphatase 2 gene (PPase-2) was mapped to chromosome 4q25 and the 1.4-kb mRNA was ubiquitously expressed in human tissues, with highest levels in muscle, liver, and kidney. The yeast homologue of the mitochondrial PPase-2 is required for mitochondrial DNA maintenance and yeast cells lacking the enzyme exhibit mitochondrial DNA depletion. We sequenced the PPA2 gene in 13 patients with mitochondrial DNA depletion syndromes (MDS) of unknown cause to determine if mutations in the PPA2 gene of these patients were associated with this disease. No pathogenic mutations were identified in the PPA2 gene of these patients and we found no evidence that PPA2 gene mutations are a common cause of MDS in humans.
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MESH Headings
- Amino Acid Sequence
- Blotting, Northern
- Calcium Chloride/pharmacology
- Cell Line, Tumor
- Chromosome Mapping
- Chromosomes, Human, Pair 4/genetics
- Cloning, Molecular
- DNA, Complementary/chemistry
- DNA, Complementary/genetics
- Diphosphates/metabolism
- Female
- Gene Expression Regulation, Enzymologic
- Green Fluorescent Proteins/genetics
- Green Fluorescent Proteins/metabolism
- HeLa Cells
- Humans
- Hydrolysis/drug effects
- Inorganic Pyrophosphatase/genetics
- Inorganic Pyrophosphatase/metabolism
- Isoenzymes/genetics
- Isoenzymes/metabolism
- Mitochondrial Myopathies/enzymology
- Mitochondrial Myopathies/genetics
- Mitochondrial Myopathies/pathology
- Mitochondrial Proteins/genetics
- Mitochondrial Proteins/metabolism
- Molecular Sequence Data
- Protein Sorting Signals/genetics
- Pyrophosphatases/antagonists & inhibitors
- Pyrophosphatases/genetics
- Pyrophosphatases/metabolism
- RNA, Messenger/genetics
- RNA, Messenger/metabolism
- RNA, Small Interfering/genetics
- Recombinant Fusion Proteins/genetics
- Recombinant Fusion Proteins/metabolism
- Sequence Alignment
- Sequence Analysis, DNA
- Sequence Homology, Amino Acid
- Syndrome
- Transfection
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Affiliation(s)
- Sophie Curbo
- Division of Metabolic Disorders, Karolinska Institute, Stockholm, Sweden
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38
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Carrozzo R, Wittig I, Santorelli FM, Bertini E, Hofmann S, Brandt U, Schägger H. Subcomplexes of human ATP synthase mark mitochondrial biosynthesis disorders. Ann Neurol 2005; 59:265-75. [PMID: 16365880 DOI: 10.1002/ana.20729] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
OBJECTIVE METHODS We describe biochemically and clinically relevant aspects of mitochondrial ATP synthase, the enzyme that supplies most ATP for the cells energy demand. RESULTS Analyzing human Rho zero cells we could identify three subcomplexes of ATP synthase: F1 catalytic domain, F1 domain with bound natural IF1 inhibitor protein, and F1-c subcomplex, an assembly of F1 domain and a ring of F(O)-subunits c. Large amounts of F1 subcomplexes accumulated also in mitochondria of patients with specific mitochondrial disorders. By quantifying the F1 subcomplexes and other oxidative phosphorylation complexes in parallel, we were able to discriminate three classes of defects in mitochondrial biosynthesis, namely, mitochondrial DNA depletion, mitochondrial transfer RNA (tRNA) mutations, and mutations in the mitochondrial ATP6 gene. INTERPRETATION The relatively simple electrophoretic assay used here is a straightforward approach to differentiate between various types of genetic alterations affecting the biosynthesis of oxidative phosphorylation complexes and will be useful to guide molecular genetic diagnostics in the field of mitochondrial neuromuscular disorders.
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Affiliation(s)
- Rosalba Carrozzo
- Unit of Molecular Medicine, Bambino Gesù Hospital and Research Institute, Rome, Italy
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39
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Slama A, Giurgea I, Debrey D, Bridoux D, de Lonlay P, Levy P, Chretien D, Brivet M, Legrand A, Rustin P, Munnich A, Rötig A. Deoxyguanosine kinase mutations and combined deficiencies of the mitochondrial respiratory chain in patients with hepatic involvement. Mol Genet Metab 2005; 86:462-5. [PMID: 16263314 DOI: 10.1016/j.ymgme.2005.09.006] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/14/2005] [Revised: 09/13/2005] [Accepted: 09/13/2005] [Indexed: 10/25/2022]
Abstract
The activity of deoxyguanosine kinase (DGUOK), a mitochondrial enzyme involved in the anabolism of mitochondrial (mt) deoxyribonucleotides, governs the maintenance of the mtDNA. Deleterious mutations of the DGUOK gene are thus associated with mtDNA depletion and result in combined deficiencies of mtDNA-encoded respiratory chain enzymes. With the aim to estimate the prevalence of DGUOK mutations in a cohort of 30 patients with hepatocerebral disease and combined respiratory chain deficiencies, we studied the DGUOK gene and identified previously unreported mutations in five families. Two patients and their affected sibs, born to non-consanguineous parents, were homozygous for a missense mutation (M1T, and L250S, respectively). One patient presented a homozygous 4 pb insertion (796 insTGAT) and two other patients, and their affected sibs, were compound heterozygous (E165V/L266R and E211G/L266R, respectively). These findings allowed us to propose prenatal diagnosis in two families. In conclusion, we observed a high prevalence of DGUOK mutations (17%) in patients with hepatic involvement and combined respiratory chain deficiencies with hepatic involvement.
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Affiliation(s)
- A Slama
- Laboratoire de Biochimie 1, APHP, hôpital de Bicêtre, Le Kremlin-Bicêtre, France.
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40
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García-Cazorla A, De Lonlay P, Nassogne MC, Rustin P, Touati G, Saudubray JM. Long-term follow-up of neonatal mitochondrial cytopathies: a study of 57 patients. Pediatrics 2005; 116:1170-7. [PMID: 16264005 DOI: 10.1542/peds.2004-2407] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
OBJECTIVES We sought to determine the long-term clinical and biochemical outcome of newborns with mitochondrial cytopathies (MCs) and to identify possible prognostic factors that may modify the course of these diseases. MATERIAL AND METHODS Fifty-seven newborns with MCs were identified in a retrospective review (1983-2002). We defined 2 different outcome categories: clinical (neurologic, hepatic, myopathic, and multiorganic) and biochemical (lactate level normalization or initially normal remaining unchanged, decreased but not normalized, and persistently high). We used 2 different statistical approaches: (1) survival studies depending on the initial symptoms and lactate and enzymatic deficiencies using the Kaplan-Meier method; and (2) the same variables compared with different survival age groups and clinical and biochemical outcome categories using the chi2 test. RESULTS Thirty-three patients died (57.8%), 12 remain alive (21%), and 12 were lost in the follow-up; 6 of them are currently older than 4 years. Most of the patients manifested multiorganic disease (64.8%) and high lactate level (77.1%) over time. Children surviving to 2.5 to 3 years of age were more likely to survive for a long period of time. Initial neurologic and hepatic presentation increased the risk to develop neurologic disease and severe persistent hyperlactacidemia, respectively. Initial severe hyperlactacidemia and combined enzyme deficiencies were significant risk factors for higher mortality and multiorganic disorders. Two patients with exclusively myopathic outcome are alive and cognitively normal at 12 years of life. CONCLUSIONS Children with neonatal-onset MCs have very high mortality and poor prospects. However, some with life-threatening presentations may gradually improve, giving rise to less severe diseases. Those with exclusively myopathic symptoms have a better prognosis.
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Affiliation(s)
- A García-Cazorla
- Department of Pediatrics, Centre Hospitalier Universitaire Necker Enfants-Malades, Paris, France.
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41
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Labarthe F, Dobbelaere D, Devisme L, De Muret A, Jardel C, Taanman JW, Gottrand F, Lombès A. Clinical, biochemical and morphological features of hepatocerebral syndrome with mitochondrial DNA depletion due to deoxyguanosine kinase deficiency. J Hepatol 2005; 43:333-41. [PMID: 15964659 DOI: 10.1016/j.jhep.2005.03.023] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/28/2005] [Revised: 03/10/2005] [Accepted: 03/14/2005] [Indexed: 12/04/2022]
Abstract
BACKGROUND/AIMS The aim of this study was to delineate the specific clinical, biological and liver morphological alterations of the hepatocerebral syndrome due to alterations in the deoxyguanosine kinase gene, a rare and severe form of mitochondrial DNA depletion syndrome. METHODS We report seven cases from three unrelated families with the same mutation in the deoxyguanosine kinase gene. RESULTS All the patients presented in the first weeks of life with hepatomegaly and progressive liver failure that led to death few months later. Major psychomotor delay and multidirectional nystagmus were reported shortly after onset of the disease. Severe hyperlactacidaemia was constant. Histological examination of the liver disclosed a multifocal injury of hepatocytes with irregular foamy steatosis, cholestasis, and fibrosis, associated with different degrees of hepatosiderosis and glycogen depletion. Liver respiratory chain activities were abnormal in all analysed patients and the amount of liver mitochondrial DNA was severely decreased. An identical homozygous 4bp GATT duplication was identified in the deoxyguanosine kinase gene of all the cases. CONCLUSIONS These patients, together with patients reported in the literature, permit to delineate the specific features of the hepatocerebral form of mitochondrial DNA depletion syndrome and to differentiate them from other causes of neonatal liver failure.
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Affiliation(s)
- François Labarthe
- Groupement de Médecine Pédiatrique, Hôpital Clocheville, CHU Tours, France
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42
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Tulinius M, Moslemi AR, Darin N, Holme E, Oldfors A. Novel mutations in the thymidine kinase 2 gene (TK2) associated with fatal mitochondrial myopathy and mitochondrial DNA depletion. Neuromuscul Disord 2005; 15:412-5. [PMID: 15907288 DOI: 10.1016/j.nmd.2005.03.010] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2004] [Revised: 02/25/2005] [Accepted: 03/06/2005] [Indexed: 11/21/2022]
Abstract
We describe the clinical, morphological and genetic findings in two siblings with the myopathic form of mitochondrial DNA depletion syndrome (MIM 251880). Sequencing of the thymidine kinase-2 gene revealed two heterozygous missense mutations, a C-->T mutation at nucleotide 191 resulting in a change of threonine to methionine at residue 64 in exon 3, and a C-->T mutation at nucleotide 547 resulting in an arginine to tryptophan amino acid change at residue 183 in exon 8. Both mutations changed highly conserved residues in the gene and neither one has been described previously. This report extends the phenotypic expression of mutations in the thymidine kinase-2 gene.
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Affiliation(s)
- Már Tulinius
- The Queen Silvia Children's Hospital, S-416 85 Göteborg, Sweden.
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43
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Abstract
Mitochondrial DNA (mtDNA) depends on numerous nuclear encoded factors and a constant supply of deoxyribonucleoside triphosphates (dNTP), for its maintenance and replication. The function of proteins involved in nucleotide metabolism is perturbed in a heterogeneous group of disorders associated with depletion, multiple deletions, and mutations of the mitochondrial genome. Disturbed homeostasis of the mitochondrial dNTP pools are likely the underlying cause. Understanding of the biochemical and molecular basis of these disorders will promote the development of new therapeutic approaches. This article reviews the current knowledge of deoxyribonucleotide metabolism in relation to disorders affecting mtDNA integrity.
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Affiliation(s)
- Ann Saada
- Metabolic Disease Unit, Shaare Zedek Medical Center, Jerusalem, Israel.
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44
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Saada-Reisch A. Deoxyribonucleoside kinases in mitochondrial DNA depletion. NUCLEOSIDES NUCLEOTIDES & NUCLEIC ACIDS 2005; 23:1205-15. [PMID: 15571232 DOI: 10.1081/ncn-200027480] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
Mitochondrial DNA (mtDNA) depletion syndromes (MDS) are a heterogeneous group of mitochondrial disorders, manifested by a decreased mtDNA copy number and respiratory chain dysfunction. Primary MDS are inherited autosomally and may affect a single organ or multiple tissues. Mutated mitochondrial deoxyribonucleoside kinases; deoxyguanosine kinase (dGK) and thymidine kinase 2 (TK2), were associated with the hepatocerebral and myopathic forms of MDS respectively. dGK and TK2 are key enzymes in the mitochondrial nucleotide salvage pathway, providing the mitochondria with deoxyribonucleotides (dNP) essential for mtDNA synthesis. Although the mitochondrial dNP pool is physically separated from the cytosolic one, dNP's may still be imported through specific transport. Non-replicating tissues, where cytosolic dNP supply is down regulated, are thus particularly vulnerable to dGK and TK2 deficiency. The overlapping substrate specificity of deoxycytidine kinase (dCK) may explain the relative sparing of muscle in dGK deficiency, while low basal TK2 activity render this tissue susceptible to TK2 deficiency. The precise pathophysiological mechanisms of mtDNA depletion due to dGK and TK2 deficiencies remain to be determined, though recent findings confirm that it is attributed to imbalanced dNTP pools.
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Affiliation(s)
- Ann Saada-Reisch
- Metabolic Disease Unit, Shaare Zedek Medical Center, Jerusalem, Israel
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45
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Janes MS, Hanson BJ, Hill DM, Buller GM, Agnew JY, Sherwood SW, Cox WG, Yamagata K, Capaldi RA. Rapid analysis of mitochondrial DNA depletion by fluorescence in situ hybridization and immunocytochemistry: potential strategies for HIV therapeutic monitoring. J Histochem Cytochem 2004; 52:1011-8. [PMID: 15258176 DOI: 10.1369/jhc.3a6209.2004] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Nucleoside reverse transcriptase inhibitors (NRTIs) have been a mainstay in the treatment of human immunodeficiency virus since the introduction of azidothymidine (AZT) in 1987. However, none of the current therapies can completely eradicate the virus, necessitating long-term use of anti-retroviral drugs to prevent viral re-growth. One of the side effects associated with long-term use of NRTIs is mitochondrial toxicity stemming from inhibition of the mitochondrial DNA (mtDNA) polymerase gamma, which leads to mtDNA depletion and consequently to mitochondrial dysfunction. Here we report the use of fluorescence in situ hybridization (FISH) and immunocytochemistry (ICC) to monitor mtDNA depletion in cultured fibroblasts treated with the NRTI 2',3'-dideoxycytidine (ddC). These techniques are amenable to both microscopy and flow cytometry, allowing analysis of populations of cells on a single-cell basis. We show that, as mtDNA depletion progresses, a mosaic population develops, with some cells being depleted of and others retaining mtDNA. These techniques could be useful as potential therapeutic monitors to indicate when NRTI therapy should be interrupted to prevent mitochondrial toxicity and could aid in the development of less toxic NRTIs by providing an assay suitable for pharmacodynamic evaluation of candidate molecules.
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Affiliation(s)
- Michael S Janes
- Molecular Probes, Inc., 29851 Willow Creek Road, Eugene, Oregon 97402, USA.
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Wang L, Eriksson S. Mitochondrial deoxyguanosine kinase mutations and mitochondrial DNA depletion syndrome. FEBS Lett 2003; 554:319-22. [PMID: 14623087 DOI: 10.1016/s0014-5793(03)01181-5] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Mitochondrial deoxyguanosine kinase (dGK) catalyzes the initial phosphorylation of purine deoxynucleosides. Mutations in the dGK gene leading to deficiency in dGK activity is one of the causes of severe mitochondrial DNA depletion diseases. We used site-directed mutagenesis to introduce the clinically observed genetic alterations in the dGK gene and characterized the recombinant enzymes. The R142K enzyme had very low activity with deoxyguanosine and no activity with deoxyadenosine. The E227K mutant enzyme had unchanged K(m) values for all its substrates but very low V(max) values. C-terminal truncated dGK proteins were inactive. These results may help to define the role of dGK in mitochondrial DNA (mtDNA) precursor synthesis.
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Affiliation(s)
- Liya Wang
- Department of Molecular Biosciences, Section of Veterinary Medical Biochemistry, SLU, The Biomedical Centre, P.O. Box 575, SE-751 23 Uppsala, Sweden.
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Saada A, Ben-Shalom E, Zyslin R, Miller C, Mandel H, Elpeleg O. Mitochondrial deoxyribonucleoside triphosphate pools in thymidine kinase 2 deficiency. Biochem Biophys Res Commun 2003; 310:963-6. [PMID: 14550298 DOI: 10.1016/j.bbrc.2003.09.104] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Deficiency of mitochondrial thymidine kinase (TK2) is associated with mitochondrial DNA (mtDNA) depletion and manifests by severe skeletal myopathy in infancy. In order to elucidate the pathophysiology of this condition, mitochondrial deoxyribonucleoside triphosphate (dNTP) pools were determined in patients' fibroblasts. Despite normal mtDNA content and cytochrome c oxidase (COX) activity, mitochondrial dNTP pools were imbalanced. Specifically, deoxythymidine triphosphate (dTTP) content was markedly decreased, resulting in reduced dTTP:deoxycytidine triphosphate ratio. These findings underline the importance of balanced mitochondrial dNTP pools for mtDNA synthesis and may serve as the basis for future therapeutic interventions.
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Affiliation(s)
- Ann Saada
- Metabolic Disease Unit, Shaare-Zedek Medical Center, Jerusalem, Israel.
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Lewis W, Day BJ, Copeland WC. Mitochondrial toxicity of NRTI antiviral drugs: an integrated cellular perspective. Nat Rev Drug Discov 2003; 2:812-22. [PMID: 14526384 DOI: 10.1038/nrd1201] [Citation(s) in RCA: 349] [Impact Index Per Article: 16.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Highly active antiretroviral therapy (HAART) regimes based on nucleoside reverse transcriptase inhibitors (NRTIs) have revolutionized the treatment of AIDS in recent years. Although HAART can successfully suppress viral replication in the long term, it is not without significant toxicity, which can seriously compromise treatment effectiveness. A major toxicity that has been recognized for more than a decade is NRTI-related mitochondrial toxicity, which manifests as serious side effects such as hepatic failure and lactic acidosis. However, a lack of understanding of the mechanisms underlying mitochondrial toxicity has hampered efforts to develop novel drugs with better side-effect profiles. This review characterizes the pharmacological mechanisms and pathways that are involved in mitochondrial dysfunction caused by NRTIs, and suggests opportunities for future pharmacological research.
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Affiliation(s)
- William Lewis
- Emory University, Department of Pathology, 1639 Pierce Drive, Room 7117, Atlanta, Georgia 30322, USA
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Taanman JW, Muddle JR, Muntau AC. Mitochondrial DNA depletion can be prevented by dGMP and dAMP supplementation in a resting culture of deoxyguanosine kinase-deficient fibroblasts. Hum Mol Genet 2003; 12:1839-45. [PMID: 12874104 DOI: 10.1093/hmg/ddg192] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Deoxyguanosine kinase is a constitutively expressed, mitochondrial enzyme of the deoxyribonucleoside salvage pathway. Deficiency of deoxyguanosine kinase causes early-onset, hepatocerebral mitochondrial DNA (mtDNA) depletion syndrome. To clarify the molecular mechanism of the disease, a skin fibroblast culture was studied from a patient carrying a homozygous nonsense mutation in the gene for deoxyguanosine kinase. In situ examination of DNA synthesis demonstrated that, although mtDNA synthesis is cell cycle independent in control fibroblasts, mtDNA synthesis occurs mainly during the S-phase in deoxyguanosine kinase-deficient cells. Consistent with this observation, it was found that the mtDNA content of exponentially growing, deoxyguanosine kinase-deficient cells is only mildly affected. When cycling is inhibited by serum-deprivation and cells are in a resting state, however, the mtDNA content drops considerably in deoxyguanosine kinase-deficient cells, yet remains stable in control fibroblasts. The decline in mtDNA content in resting, deoxyguanosine kinase-deficient cells can be prevented by dGMP and dAMP supplementation, providing conclusive evidence that substrate limitation triggers mtDNA depletion in deoxyguanosine kinase-deficient cells.
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Affiliation(s)
- Jan-Willem Taanman
- University Department of Clinical Neurosciences, Royal Free and University College Medical School, University College London, Rowland Hill Street, London NW3 2PF, UK.
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