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Maio N, Rouault TA. Iron-sulfur cluster biogenesis in mammalian cells: New insights into the molecular mechanisms of cluster delivery. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2014; 1853:1493-512. [PMID: 25245479 DOI: 10.1016/j.bbamcr.2014.09.009] [Citation(s) in RCA: 155] [Impact Index Per Article: 15.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/03/2014] [Accepted: 09/07/2014] [Indexed: 01/19/2023]
Abstract
Iron-sulfur (Fe-S) clusters are ancient, ubiquitous cofactors composed of iron and inorganic sulfur. The combination of the chemical reactivity of iron and sulfur, together with many variations of cluster composition, oxidation states and protein environments, enables Fe-S clusters to participate in numerous biological processes. Fe-S clusters are essential to redox catalysis in nitrogen fixation, mitochondrial respiration and photosynthesis, to regulatory sensing in key metabolic pathways (i.e. cellular iron homeostasis and oxidative stress response), and to the replication and maintenance of the nuclear genome. Fe-S cluster biogenesis is a multistep process that involves a complex sequence of catalyzed protein-protein interactions and coupled conformational changes between the components of several dedicated multimeric complexes. Intensive studies of the assembly process have clarified key points in the biogenesis of Fe-S proteins. However several critical questions still remain, such as: what is the role of frataxin? Why do some defects of Fe-S cluster biogenesis cause mitochondrial iron overload? How are specific Fe-S recipient proteins recognized in the process of Fe-S transfer? This review focuses on the basic steps of Fe-S cluster biogenesis, drawing attention to recent advances achieved on the identification of molecular features that guide selection of specific subsets of nascent Fe-S recipients by the cochaperone HSC20. Additionally, it outlines the distinctive phenotypes of human diseases due to mutations in the components of the basic pathway. This article is part of a Special Issue entitled: Fe/S proteins: Analysis, structure, function, biogenesis and diseases.
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Affiliation(s)
- Nunziata Maio
- Molecular Medicine Program, Eunice Kennedy Shriver National Institute of Child Health and Human Development, 9000 Rockville Pike, 20892 Bethesda, MD, USA
| | - Tracey A Rouault
- Molecular Medicine Program, Eunice Kennedy Shriver National Institute of Child Health and Human Development, 9000 Rockville Pike, 20892 Bethesda, MD, USA.
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Ygland E, Taroni F, Gellera C, Caldarazzo S, Duno M, Soller M, Puschmann A. Atypical Friedreich ataxia in patients with FXN p.R165P point mutation or comorbid hemochromatosis. Parkinsonism Relat Disord 2014; 20:919-23. [PMID: 24816001 DOI: 10.1016/j.parkreldis.2014.04.018] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/24/2014] [Revised: 03/28/2014] [Accepted: 04/14/2014] [Indexed: 11/29/2022]
Abstract
BACKGROUND Compound heterozygosity for a trinucleotide repeat expansion and a point mutation in the FXN gene is a rare cause of Friedreich ataxia (FRDA). METHODS We identified three Swedish FRDA patients with an FXN p.R165P missense mutation and compared their clinical features with six homozygote trinucleotide repeat expansion carriers. Patients were assessed clinically. Trinucleotide expansion length was determined and lymphocyte frataxin levels measured. RESULTS p.R165P mutation carriers became wheelchair bound early, but had retained reflexes, better arm function, milder dysarthria, and were more independent in activities of daily living. One p.R165P mutation carrier developed psychosis. Frataxin levels were higher than in homozygous trinucleotide expansion patients. One patient with homozygous trinucleotide repeat expansions and comorbid hemochromatosis had more severe FRDA symptoms than his sibling without hemochromatosis. CONCLUSION p.R165P patients progress to a less disabling disease state than typical FRDA. Comorbid hemochromatosis may worsen FRDA symptoms through additive effects on iron metabolism.
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Affiliation(s)
- Emil Ygland
- Department of Neurology, Skåne University Hospital, Lund, Sweden; Department of Neurology, Clinical Sciences, Lund University, Lund, Sweden
| | - Franco Taroni
- Unit of Genetics of Neurodegenerative and Metabolic Disease, Fondazione IRCCS Istituto Neurologico Carlo Besta, Milan, Italy
| | - Cinzia Gellera
- Unit of Genetics of Neurodegenerative and Metabolic Disease, Fondazione IRCCS Istituto Neurologico Carlo Besta, Milan, Italy
| | - Serena Caldarazzo
- Unit of Genetics of Neurodegenerative and Metabolic Disease, Fondazione IRCCS Istituto Neurologico Carlo Besta, Milan, Italy
| | - Morten Duno
- Department of Clinical Genetics, Rigshospitalet, Copenhagen University Hospital, Copenhagen, Denmark
| | - Maria Soller
- Department of Clinical Genetics, Skåne University Hospital, University and Regional Laboratories, Lund University, Lund, Sweden
| | - Andreas Puschmann
- Department of Neurology, Skåne University Hospital, Lund, Sweden; Department of Neurology, Clinical Sciences, Lund University, Lund, Sweden.
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Greeley NR, Regner S, Willi S, Lynch DR. Cross-sectional analysis of glucose metabolism in Friedreich ataxia. J Neurol Sci 2014; 342:29-35. [PMID: 24819921 DOI: 10.1016/j.jns.2014.04.015] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2013] [Revised: 04/08/2014] [Accepted: 04/12/2014] [Indexed: 12/13/2022]
Abstract
OBJECTIVES To evaluate the relationship between disease features in Friedreich ataxia and aberrant glucose metabolism. METHODS Fasting glucose, fasting insulin and random HbA1C were obtained in 158 patients with Friedreich ataxia. Regression analysis evaluated glucose, insulin, and homeostatic model assessment (HOMA) of insulin resistance (IR) and beta-cell function (ß) in relation to age, BMI, sex, and genetic severity. Categorical glucose values were analyzed in relation to other FRDA-associated disease characteristics. RESULTS In the FRDA cohort, age and GAA repeat length predicted fasting glucose and HbA1c levels (accounting for sex and BMI), while insulin and HOMA-IR were not predicted by these parameters. Within the cohort, average BMI was consistently lower than the national average by age and was marginally associated with insulin levels and HOMA-IR. Within juvenile subjects, insulin and HOMA-IR were predicted by age. Controlling for age and genetic severity, diabetes-related measures were not independent predictors of any quantitative measure of disease severity in FRDA. Glucose handling properties were also predicted by the presence of a point mutation, with 40% of individuals heterozygous for point mutations having diabetes, compared to 4.3% of subjects who carried two expanded GAA repeats. INTERPRETATION In FRDA, aberrant glucose metabolism is linked to increasing age, longer GAA repeat length on the shorter allele, frataxin point mutations, and increasing BMI. The effect of age to some degree may be mediated through changes in BMI, with increasing age associated with increases in BMI, and with HOMA-IR and insulin increases in children.
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Affiliation(s)
- Nathaniel R Greeley
- Division of Neurology, Children's Hospital of Philadelphia, Philadelphia, PA, United States.
| | - Sean Regner
- Division of Neurology, Children's Hospital of Philadelphia, Philadelphia, PA, United States.
| | - Steve Willi
- Division of Endocrinology and Pediatrics, Children's Hospital of Philadelphia, Philadelphia, PA, United States.
| | - David R Lynch
- Division of Neurology, Children's Hospital of Philadelphia, Philadelphia, PA, United States; Department of Neurology, University of Pennsylvania Medical School, Philadelphia, PA, United States; Department of Pediatrics, University of Pennsylvania Medical School, Philadelphia, PA, United States.
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104
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Sanz-Gallego I, Torres-Aleman I, Arpa J. IGF-1 in Friedreich's Ataxia - proof-of-concept trial. CEREBELLUM & ATAXIAS 2014; 1:10. [PMID: 26331034 PMCID: PMC4552279 DOI: 10.1186/2053-8871-1-10] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/19/2014] [Accepted: 02/25/2014] [Indexed: 12/31/2022]
Abstract
BACKGROUND Friedreich's ataxia is an autosomal recessive, severely incapacitating disorder. There is little objective evidence regarding FRDA management. Abnormalities in the insulin/insulin-like growth factor 1 (IGF-1) system (IIS) signalling pathway were thought to play a role in the physiopathological processes of various neurodegenerative disorders, including spinocerebellar ataxias. The objective of the study was to test the safety, tolerability, and efficacy of therapy with IGF-1 in Friedreich's ataxia (FRDA) patients in a clinical pilot study. RESULTS A total of 4 females and 1 male were included in the study; 23 to 36 years of age (average 26.6 ± 5.4), diagnosed with FRDA with normal ventricular function. Patients were treated with IGF-1 therapy with 50 μg/kg twice a day subcutaneously for 12 months. The efficacy of this therapy was assessed by changes from baseline on the scale for the assessment and rating of ataxia, (SARA) and by changes from baseline in echocardiogram parameters. The annual worsening rate (AWR) was estimated in this series as a SARA score of -0.4 ± 0.83 (CI 95%: -1.28 to 0.48) SARA score, whereas the AWR for our FRDA cohort was estimated as a SARA score of 2.05 ± 1.23 (CI 95%: 1.58 to 2.52). Echocardiographic parameters remained normal and stable. CONCLUSION Our results seem to indicate a benefit of this IGF-1 therapy to neurological functions in FRDA.
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Affiliation(s)
- Irene Sanz-Gallego
- Reference Unit of Hereditary Ataxias and Paraplegias, Department of Neurology, IdiPAZ, Hospital Universitario La Paz, 28046 Madrid, Spain
| | - Ignacio Torres-Aleman
- Neuroendocrinology Laboratory, Functional and Systems Neurobiology Department, Cajal Institute, CSIC, and CIBERNED, Avda Dr. Arce, 37, 28002 Madrid, Spain
| | - Javier Arpa
- Reference Unit of Hereditary Ataxias and Paraplegias, Department of Neurology, IdiPAZ, Hospital Universitario La Paz, 28046 Madrid, Spain
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Evans-Galea MV, Pébay A, Dottori M, Corben LA, Ong SH, Lockhart PJ, Delatycki MB. Cell and gene therapy for Friedreich ataxia: progress to date. Hum Gene Ther 2014; 25:684-93. [PMID: 24749505 DOI: 10.1089/hum.2013.180] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Neurodegenerative disorders such as Friedreich ataxia (FRDA) present significant challenges in developing effective therapeutic intervention. Current treatments aim to manage symptoms and thus improve quality of life, but none can cure, nor are proven to slow, the neurodegeneration inherent to this disease. The primary clinical features of FRDA include progressive ataxia and shortened life span, with complications of cardiomyopathy being the major cause of death. FRDA is most commonly caused by an expanded GAA trinucleotide repeat in the first intron of FXN that leads to reduced levels of frataxin, a mitochondrial protein important for iron metabolism. The GAA expansion in FRDA does not alter the coding sequence of FXN. It results in reduced production of structurally normal frataxin, and hence any increase in protein level is expected to be therapeutically beneficial. Recently, there has been increased interest in developing novel therapeutic applications like cell and/or gene therapies, and these cutting-edge applications could provide effective treatment options for FRDA. Importantly, since individuals with FRDA produce frataxin at low levels, increased expression should not elicit an immune response. Here we review the advances to date and highlight the future potential for cell and gene therapy to treat this debilitating disease.
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Affiliation(s)
- Marguerite V Evans-Galea
- 1 Bruce Lefroy Centre for Genetic Health Research, Murdoch Children's Research Institute , Parkville Victoria 3052, Australia
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Martelli A, Puccio H. Dysregulation of cellular iron metabolism in Friedreich ataxia: from primary iron-sulfur cluster deficit to mitochondrial iron accumulation. Front Pharmacol 2014; 5:130. [PMID: 24917819 PMCID: PMC4042101 DOI: 10.3389/fphar.2014.00130] [Citation(s) in RCA: 108] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2014] [Accepted: 05/14/2014] [Indexed: 01/25/2023] Open
Abstract
Friedreich ataxia (FRDA) is the most common recessive ataxia in the Caucasian population and is characterized by a mixed spinocerebellar and sensory ataxia frequently associating cardiomyopathy. The disease results from decreased expression of the FXN gene coding for the mitochondrial protein frataxin. Early histological and biochemical study of the pathophysiology in patient's samples revealed that dysregulation of iron metabolism is a key feature of the disease, mainly characterized by mitochondrial iron accumulation and by decreased activity of iron-sulfur cluster enzymes. In the recent past years, considerable progress in understanding the function of frataxin has been provided through cellular and biochemical approaches, pointing to the primary role of frataxin in iron-sulfur cluster biogenesis. However, why and how the impact of frataxin deficiency on this essential biosynthetic pathway leads to mitochondrial iron accumulation is still poorly understood. Herein, we review data on both the primary function of frataxin and the nature of the iron metabolism dysregulation in FRDA. To date, the pathophysiological implication of the mitochondrial iron overload in FRDA remains to be clarified.
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Affiliation(s)
- Alain Martelli
- Department of Translational Medecine and Neurogenetics, Institut de Génétique et de Biologie Moléculaire et Cellulaire Illkirch, France ; INSERM, U596 Illkirch, France ; CNRS, UMR7104 Illkirch, France ; Université de Strasbourg Strasbourg, France ; Chaire de Génétique Humaine, Collège de France Illkirch, France
| | - Hélène Puccio
- Department of Translational Medecine and Neurogenetics, Institut de Génétique et de Biologie Moléculaire et Cellulaire Illkirch, France ; INSERM, U596 Illkirch, France ; CNRS, UMR7104 Illkirch, France ; Université de Strasbourg Strasbourg, France ; Chaire de Génétique Humaine, Collège de France Illkirch, France
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Boesch S, Nachbauer W, Mariotti C, Sacca F, Filla A, Klockgether T, Klopstock T, Schöls L, Jacobi H, Büchner B, vom Hagen JM, Nanetti L, Manicom K. Safety and tolerability of carbamylated erythropoietin in Friedreich's ataxia. Mov Disord 2014; 29:935-9. [PMID: 24515352 DOI: 10.1002/mds.25836] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2013] [Revised: 11/12/2013] [Accepted: 12/09/2013] [Indexed: 01/06/2023] Open
Abstract
BACKGROUND Erythropoietin (EPO) derivatives have been found to increase frataxin levels in Friedreich's ataxia (FRDA) in vitro. This multicenter, double-blind, placebo-controlled, phase II clinical trial aimed to evaluate the safety and tolerability of Lu AA24493 (carbamylated EPO; CEPO). METHODS Thirty-six ambulatory FRDA patients harboring >400 GAA repeats were 2:1 randomly assigned to either CEPO in a fixed dose (325 µg thrice-weekly) or placebo. Safety and tolerability were assessed up to 103 days after baseline. Secondary outcome measures of efficacy (exploration of biomarkers and ataxia ratings) were performed up to 43 days after baseline. RESULTS All patients received six doses of study medication. Adverse events were equally distributed between CEPO and placebo. There was no evidence for immunogenicity of CEPO after multiple dosing. Biomarkers, such as frataxin, or measures for oxidative stress and ataxia ratings did not differ between CEPO and placebo. CONCLUSION CEPO was safe and well tolerated in a 2-week treatment phase. Secondary outcome measures remained without apparent difference between CEPO and placebo.
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Affiliation(s)
- Sylvia Boesch
- Department of Neurology, Medical University Innsbruck, Innsbruck, Austria
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108
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Dhamija R, Kirmani S. A 7-year-old girl with hypertrophic cardiomyopathy and progressive scoliosis. Semin Pediatr Neurol 2014; 21:67-71. [PMID: 25149925 DOI: 10.1016/j.spen.2014.04.003] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
We report a 7 year old girl who was evaluated for progressive thoracolumbar scoliosis and hypertrophic cardiomyopathy. Neurological examination was found to be abnormal and significant for absent reflexes and weakness distally in lower extremities and positive Romberg sign. Electromyogram showed length-dependent, axonal, sensorimotor polyneuropathy. Frataxin levels were low at 3ng/mL. Molecular testing for Friedreich ataxia showed significantly expanded GAA repeats at 799 (abnormal >67 GAA repeats) on one allele and a heterozygous disease causing mutation, c.317T>C (p.Leu106Ser) on the other allele, confirming the diagnosis. A review of Friedreich ataxia is provided in the case report.
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Affiliation(s)
| | - Salman Kirmani
- Department of Medical Genetics, Mayo Clinic, Rochester, MN
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109
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Puccio H, Anheim M, Tranchant C. Pathophysiogical and therapeutic progress in Friedreich ataxia. Rev Neurol (Paris) 2014; 170:355-65. [PMID: 24792433 DOI: 10.1016/j.neurol.2014.03.008] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2013] [Revised: 03/25/2014] [Accepted: 03/26/2014] [Indexed: 01/10/2023]
Abstract
Friedreich ataxia (FRDA) is the most common hereditary autosomal recessive ataxia, but is also a multisystemic condition with frequent presence of cardiomyopathy or diabetes. It has been linked to expansion of a GAA-triplet repeat in the first intron of the FXN gene, leading to a reduced level of frataxin, a mitochondrial protein which, by controlling both iron entry and/or sulfide production, is essential to properly assemble and protect the Fe-S cluster during the initial stage of biogenesis. Several data emphasize the role of oxidative damage in FRDA, but better understanding of pathophysiological consequences of FXN mutations has led to develop animal models. Conditional knockout models recapitulate important features of the human disease but lack the genetic context, GAA repeat expansion-based knock-in and transgenic models carry a GAA repeat expansion but they only show a very mild phenotype. Cells derived from FRDA patients constitute the most relevant frataxin-deficient cell model as they carry the complete frataxin locus together with GAA repeat expansions and regulatory sequences. Induced pluripotent stem cell (iPSC)-derived neurons present a maturation delay and lower mitochondrial membrane potential, while cardiomyocytes exhibit progressive mitochondrial degeneration, with frequent dark mitochondria and proliferation/accumulation of normal mitochondria. Efforts in developing therapeutic strategies can be divided into three categories: iron chelators, antioxidants and/or stimulants of mitochondrial biogenesis, and frataxin level modifiers. A promising therapeutic strategy that is currently the subject of intense research is to directly target the heterochromatin state of the GAA repeat expansion with histone deacytelase inhibitors (HDACi) to restore frataxin levels.
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Affiliation(s)
- H Puccio
- Translational medicine and neurogenetics, institut de génétique et de biologie moléculaire et cellulaire (IGBMC), 1, rue Laurent-Fries, BP 10142, 67404 Illkirch cedex, France; Inserm, U596, 1, rue Laurent-Fries, 67400 Illkirch Graffenstaden, France; CNRS, UMR7104, 1, rue Laurent-Fries, 67400 Illkirch Graffenstaden, France; Université de Strasbourg, 4, rue Blaise-Pascal, 67400 Strasbourg, France; Collège de France, chaire de génétique humaine, 1, rue Laurent-Fries, 67400 Illkirch Graffenstaden, France
| | - M Anheim
- Translational medicine and neurogenetics, institut de génétique et de biologie moléculaire et cellulaire (IGBMC), 1, rue Laurent-Fries, BP 10142, 67404 Illkirch cedex, France; Inserm, U596, 1, rue Laurent-Fries, 67400 Illkirch Graffenstaden, France; CNRS, UMR7104, 1, rue Laurent-Fries, 67400 Illkirch Graffenstaden, France; Université de Strasbourg, 4, rue Blaise-Pascal, 67400 Strasbourg, France; Service de neurologie, unité des pathologies du mouvement, hôpital de Hautepierre, hôpital universitaire, 1, place de l'Hôpital, 67000 Strasbourg, France
| | - C Tranchant
- Translational medicine and neurogenetics, institut de génétique et de biologie moléculaire et cellulaire (IGBMC), 1, rue Laurent-Fries, BP 10142, 67404 Illkirch cedex, France; Inserm, U596, 1, rue Laurent-Fries, 67400 Illkirch Graffenstaden, France; CNRS, UMR7104, 1, rue Laurent-Fries, 67400 Illkirch Graffenstaden, France; Université de Strasbourg, 4, rue Blaise-Pascal, 67400 Strasbourg, France; Service de neurologie, unité des pathologies du mouvement, hôpital de Hautepierre, hôpital universitaire, 1, place de l'Hôpital, 67000 Strasbourg, France.
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Gene expression profiling of mitochondrial oxidative phosphorylation (OXPHOS) complex I in Friedreich ataxia (FRDA) patients. PLoS One 2014; 9:e94069. [PMID: 24705504 PMCID: PMC3976380 DOI: 10.1371/journal.pone.0094069] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2013] [Accepted: 03/11/2014] [Indexed: 11/19/2022] Open
Abstract
Friedreich ataxia (FRDA) is the most frequent progressive autosomal recessive disorder associated with unstable expansion of GAA trinucleotide repeats in the first intron of the FXN gene, which encodes for the mitochondrial frataxin protein. The number of repeats correlates with disease severity, where impaired transcription of the FXN gene results in reduced expression of the frataxin protein. Gene expression studies provide insights into disease pathogenicity and identify potential biomarkers, an important goal of translational research in neurodegenerative diseases. Here, using real-time PCR (RT-PCR), the expression profiles of mitochondrial (mtDNA) and nuclear DNA (nDNA) genes that encode for the mitochondrial subunits of respiratory oxidative phosphorylation (OXPHOS) complex I in the blood panels of 21 FRDA patients and 24 healthy controls were investigated. Here, the expression pattern of mtDNA-encoded complex I subunits was distinctly different from the expression pattern of nDNA-encoded complex I subunits, where significant (p<0.05) down-regulation of the mitochondrial ND2, ND4L, and ND6 complex I genes, compared to controls, were observed. In addition, the expression pattern of one nDNA-encoded gene, NDUFA1, was significantly (p<0.05) down-regulated compared to control. These findings suggest, for the first time, that the regulation of complex I subunit expression in FRDA is complex, rather than merely being a reflection of global co-regulation, and may provide important clues toward novel therapeutic strategies for FRDA and mitochondrial complex I deficiency.
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111
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Sandi C, Sandi M, Jassal H, Ezzatizadeh V, Anjomani-Virmouni S, Al-Mahdawi S, Pook MA. Generation and characterisation of Friedreich ataxia YG8R mouse fibroblast and neural stem cell models. PLoS One 2014; 9:e89488. [PMID: 24586819 PMCID: PMC3931792 DOI: 10.1371/journal.pone.0089488] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2013] [Accepted: 01/20/2014] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND Friedreich ataxia (FRDA) is an autosomal recessive neurodegenerative disease caused by GAA repeat expansion in the first intron of the FXN gene, which encodes frataxin, an essential mitochondrial protein. To further characterise the molecular abnormalities associated with FRDA pathogenesis and to hasten drug screening, the development and use of animal and cellular models is considered essential. Studies of lower organisms have already contributed to understanding FRDA disease pathology, but mammalian cells are more related to FRDA patient cells in physiological terms. METHODOLOGY/PRINCIPAL FINDINGS We have generated fibroblast cells and neural stem cells (NSCs) from control Y47R mice (9 GAA repeats) and GAA repeat expansion YG8R mice (190+120 GAA repeats). We then differentiated the NSCs in to neurons, oligodendrocytes and astrocytes as confirmed by immunocytochemical analysis of cell specific markers. The three YG8R mouse cell types (fibroblasts, NSCs and differentiated NSCs) exhibit GAA repeat stability, together with reduced expression of frataxin and reduced aconitase activity compared to control Y47R cells. Furthermore, YG8R cells also show increased sensitivity to oxidative stress and downregulation of Pgc-1α and antioxidant gene expression levels, especially Sod2. We also analysed various DNA mismatch repair (MMR) gene expression levels and found that YG8R cells displayed significant reduction in expression of several MMR genes, which may contribute to the GAA repeat stability. CONCLUSIONS/SIGNIFICANCE We describe the first fibroblast and NSC models from YG8R FRDA mice and we confirm that the NSCs can be differentiated into neurons and glia. These novel FRDA mouse cell models, which exhibit a FRDA-like cellular and molecular phenotype, will be valuable resources to further study FRDA molecular pathogenesis. They will also provide very useful tools for preclinical testing of frataxin-increasing compounds for FRDA drug therapy, for gene therapy, and as a source of cells for cell therapy testing in FRDA mice.
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Affiliation(s)
- Chiranjeevi Sandi
- Ataxia Research Group, Division of Biosciences, School of Health Sciences and Social Care, Brunel University, Uxbridge, United Kingdom
| | - Madhavi Sandi
- Ataxia Research Group, Division of Biosciences, School of Health Sciences and Social Care, Brunel University, Uxbridge, United Kingdom
| | - Harvinder Jassal
- Ataxia Research Group, Division of Biosciences, School of Health Sciences and Social Care, Brunel University, Uxbridge, United Kingdom
| | - Vahid Ezzatizadeh
- Ataxia Research Group, Division of Biosciences, School of Health Sciences and Social Care, Brunel University, Uxbridge, United Kingdom
| | - Sara Anjomani-Virmouni
- Ataxia Research Group, Division of Biosciences, School of Health Sciences and Social Care, Brunel University, Uxbridge, United Kingdom
| | - Sahar Al-Mahdawi
- Ataxia Research Group, Division of Biosciences, School of Health Sciences and Social Care, Brunel University, Uxbridge, United Kingdom
| | - Mark A. Pook
- Ataxia Research Group, Division of Biosciences, School of Health Sciences and Social Care, Brunel University, Uxbridge, United Kingdom
- * E-mail:
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Maalej M, Mkaouar-Rebai E, Mnif M, Mezghani N, Ben Ayed I, Chamkha I, Abid M, Fakhfakh F. A mitochondrial implication in a Tunisian patient with Friedreich's ataxia-like. PATHOLOGIE-BIOLOGIE 2014; 62:41-8. [PMID: 24011957 DOI: 10.1016/j.patbio.2013.07.013] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/13/2013] [Accepted: 07/05/2013] [Indexed: 06/02/2023]
Abstract
Genes encoding the DNA helicase TWINKLE (C10orf2) or the two subunits of mtDNA polymerase γ (POLγ) (POLG1 and POLG2) have a direct effect on the mitochondrial DNA replication machinery and were reported in many mitochondrial disorders. Friedreich's ataxia (FRDA) is the common cause of ataxia often associated with the expansion of a GAA repeat in intron 1 of the frataxin gene (FXN). Mitochondrial DNA could be considered as a candidate modifier factor for FRDA disease, since mitochondrial oxidative stress is thought to be involved in the pathogenesis of this disease. We screened the FXN, POLG1 and C10orf2 genes in a Tunisian patient with clinical features of Friedreich's ataxia-like. The results showed the absence of the expansion of a GAA triplet repeat in intron 1 of the FXN gene. Besides, the sequencing of all the exons and their flanking regions of the FXN, POLG1 and C10orf2 genes revealed the presence of intronic polymorphisms. In addition, screening of the mtDNA revealed the presence of several mitochondrial known variations and the absence of mitochondrial deletions in this patient. The detected m.16187C>T and the m.16189T>C change the order of the homopolymeric tract of cytosines between 16184 and 16193 in the mitochondrial D-loop and could lead to a mitochondrial dysfunction by inhibiting replication and affecting protein involved in the replication process of the mtDNA which could be responsible for the clinical features of Friedreich ataxia observed in the studied patient.
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Affiliation(s)
- M Maalej
- Laboratoire de génétique moléculaire humaine, faculté de médecine de Sfax, avenue Magida Boulila, 3029 Sfax, Tunisia
| | - E Mkaouar-Rebai
- Laboratoire de génétique moléculaire humaine, faculté de médecine de Sfax, avenue Magida Boulila, 3029 Sfax, Tunisia.
| | - M Mnif
- Service d'endocrinologie, CHU Hédi Chaker de Sfax, avenue Magida Boulila, 3029 Sfax, Tunisia
| | - N Mezghani
- Laboratoire de génétique moléculaire humaine, faculté de médecine de Sfax, avenue Magida Boulila, 3029 Sfax, Tunisia
| | - I Ben Ayed
- Laboratoire de génétique moléculaire humaine, faculté de médecine de Sfax, avenue Magida Boulila, 3029 Sfax, Tunisia
| | - I Chamkha
- Laboratoire de génétique moléculaire humaine, faculté de médecine de Sfax, avenue Magida Boulila, 3029 Sfax, Tunisia
| | - M Abid
- Service d'endocrinologie, CHU Hédi Chaker de Sfax, avenue Magida Boulila, 3029 Sfax, Tunisia
| | - F Fakhfakh
- Laboratoire de génétique moléculaire humaine, faculté de médecine de Sfax, avenue Magida Boulila, 3029 Sfax, Tunisia
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113
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Beilschmidt LK, Puccio HM. Mammalian Fe-S cluster biogenesis and its implication in disease. Biochimie 2014; 100:48-60. [PMID: 24440636 DOI: 10.1016/j.biochi.2014.01.009] [Citation(s) in RCA: 65] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2013] [Accepted: 01/07/2014] [Indexed: 10/25/2022]
Abstract
Iron-sulfur (Fe-S) clusters are inorganic cofactors that are ubiquitous and essential. Due to their chemical versatility, Fe-S clusters are implicated in a wide range of protein functions including mitochondrial respiration and DNA repair. Composed of iron and sulfur, they are sensible to oxygen and their biogenesis requires a highly conserved protein machinery that facilitates assembly of the cluster as well as its insertion into apoproteins. Mitochondria are the central cellular compartment for Fe-S cluster biogenesis in eukaryotic cells and the importance of proper function of this biogenesis for life is highlighted by a constantly increasing number of human genetic diseases that are associated with dysfunction of this Fe-S cluster biogenesis pathway. Although these disorders are rare and appear dissimilar, common aspects are found among them. This review will give an overview on what is known on mammalian Fe-S cluster biogenesis today, by putting it into the context of what is known from studies from lower model organisms, and focuses on the associated diseases, by drawing attention to the respective mutations. Finally, it outlines the importance of adequate cellular and murine models to uncover not only each protein function, but to resolve their role and requirement throughout the mammalian organism.
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Affiliation(s)
- Lena K Beilschmidt
- Translational Medicine and Neurogenetics, IGBMC (Institut de Génétique et de Biologie Moléculaire et Cellulaire), Illkirch, France; Inserm, U596, Illkirch, France; CNRS, UMR7104, Illkirch, France; Université de Strasbourg, Strasbourg, France; Collège de France, Chaire de génétique humaine, Illkirch, France
| | - Hélène M Puccio
- Translational Medicine and Neurogenetics, IGBMC (Institut de Génétique et de Biologie Moléculaire et Cellulaire), Illkirch, France; Inserm, U596, Illkirch, France; CNRS, UMR7104, Illkirch, France; Université de Strasbourg, Strasbourg, France; Collège de France, Chaire de génétique humaine, Illkirch, France.
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114
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Lynch DR, Regner SR, Schadt KA, Friedman LS, Lin KY, Sutton MGSJ. Management and therapy for cardiomyopathy in Friedreich’s ataxia. Expert Rev Cardiovasc Ther 2014; 10:767-77. [DOI: 10.1586/erc.12.57] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
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115
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Tan EC, Lai PS. Molecular diagnosis of neurogenetic disorders involving trinucleotide repeat expansions. Expert Rev Mol Diagn 2014; 5:101-9. [PMID: 15723596 DOI: 10.1586/14737159.5.1.101] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
There are more than 15 known neurogenetic disorders involving trinucleotide repeat expansion. Expanded repeats range from small expansions of 20-100 copies to larger expansions of up to several thousand units. These dynamic expansions result in variability in age of onset, degree of severity and clinical presentation. Individuals carrying alleles in the intermediate range, known as premutation alleles, are often asymptomatic, but can potentially transmit a further expanded allele to his/her offspring. For autosomal dominant adult-onset disorders, carriers are asymptomatic prior to disease onset. With current molecular tools, it is now possible to determine the presence and number of expanded repeats for accurate diagnosis, presymptomatic testing and carrier status screening. This review examines some of the current approaches for molecular diagnosis and discusses the issues unique to triplet repeat diseases.
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Affiliation(s)
- Ene-Choo Tan
- DSO National Laboratories, Population Genetics Programme, Defence Medical and Environmental Research Institute, 27 Medical Drive, 117510 Singapore.
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116
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Arpa J, Sanz-Gallego I, Rodríguez-de-Rivera FJ, Domínguez-Melcón FJ, Prefasi D, Oliva-Navarro J, Moreno-Yangüela M. Triple therapy with deferiprone, idebenone and riboflavin in Friedreich's ataxia - open-label trial. Acta Neurol Scand 2014; 129:32-40. [PMID: 23668357 DOI: 10.1111/ane.12141] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/09/2013] [Indexed: 12/12/2022]
Abstract
OBJECTIVES The objective of the study was to test the efficacy, safety and tolerability of triple therapy with deferiprone, idebenone and riboflavin in Friedreich's ataxia (FRDA) patients in a clinical pilot study. PATIENTS AND METHODS Patients included in this study were 10 males and three females, 14-61 years of age (average 30.2 ± 12.1), diagnosed with FRDA with normal ventricular function. Patients were treated with triple therapy with deferiprone at 5-25 mg/kg/day, idebenone at 10-20 mg/kg/day and riboflavin at 10-15 mg/kg/day for 15-45 months. The efficacy of this triple therapy was assessed by change from baseline on the scale for the assessment and rating of ataxia (SARA) and by the change from baseline in echocardiogram parameters. RESULTS Four patients discontinued due to adverse events (AEs) related with deferiprone. The annual worsening rate (AWR) was estimated in this series as 0.96 (CI 95%: 0.462-1.608) SARA score, whereas AWR for our FRDA cohort was estimated as 2.05 ± 1.23 SARA score. LVMI only decreased by 6.5 g/m(2) (6.2%) at the end of the first year of therapy. LVEF remained stable, except in case of three patients. CONCLUSION Our results seem to indicate some uncertain benefit on the neurological and heart functions of this triple therapy in FRDA.
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Affiliation(s)
- J. Arpa
- Reference Unit of Hereditary Ataxias and Paraplegias; Departments of Neurology; IdiPAZ; Hospital Universitario La Paz; Madrid Spain
| | - I. Sanz-Gallego
- Reference Unit of Hereditary Ataxias and Paraplegias; Departments of Neurology; IdiPAZ; Hospital Universitario La Paz; Madrid Spain
| | - F. J. Rodríguez-de-Rivera
- Reference Unit of Hereditary Ataxias and Paraplegias; Departments of Neurology; IdiPAZ; Hospital Universitario La Paz; Madrid Spain
| | | | - D. Prefasi
- Reference Unit of Hereditary Ataxias and Paraplegias; Departments of Neurology; IdiPAZ; Hospital Universitario La Paz; Madrid Spain
| | - J. Oliva-Navarro
- Reference Unit of Hereditary Ataxias and Paraplegias; Departments of Neurology; IdiPAZ; Hospital Universitario La Paz; Madrid Spain
| | - M. Moreno-Yangüela
- Departments of Cardiology; IdiPAZ; Hospital Universitario La Paz; Madrid Spain
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117
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Lufino MM, Silva AM, Németh AH, Alegre-Abarrategui J, Russell AJ, Wade-Martins R. A GAA repeat expansion reporter model of Friedreich's ataxia recapitulates the genomic context and allows rapid screening of therapeutic compounds. Hum Mol Genet 2013; 22:5173-87. [PMID: 23943791 PMCID: PMC3842177 DOI: 10.1093/hmg/ddt370] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2013] [Revised: 07/15/2013] [Accepted: 07/26/2013] [Indexed: 01/19/2023] Open
Abstract
Friedreich's ataxia (FRDA) is caused by large GAA expansions in intron 1 of the frataxin gene (FXN), which lead to reduced FXN expression through a mechanism not fully understood. Understanding such mechanism is essential for the identification of novel therapies for FRDA and this can be accelerated by the development of cell models which recapitulate the genomic context of the FXN locus and allow direct comparison of normal and expanded FXN loci with rapid detection of frataxin levels. Here we describe the development of the first GAA-expanded FXN genomic DNA reporter model of FRDA. We modified BAC vectors carrying the whole FXN genomic DNA locus by inserting the luciferase gene in exon 5a of the FXN gene (pBAC-FXN-Luc) and replacing the six GAA repeats present in the vector with an ∼310 GAA repeat expansion (pBAC-FXN-GAA-Luc). We generated human clonal cell lines carrying the two vectors using site-specific integration to allow direct comparison of normal and expanded FXN loci. We demonstrate that the presence of expanded GAA repeats recapitulates the epigenetic modifications and repression of gene expression seen in FRDA. We applied the GAA-expanded reporter model to the screening of a library of novel small molecules and identified one molecule which up-regulates FXN expression in FRDA patient primary cells and restores normal histone acetylation around the GAA repeats. These results suggest the potential use of genomic reporter cell models for the study of FRDA and the identification of novel therapies, combining physiologically relevant expression with the advantages of quantitative reporter gene expression.
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Affiliation(s)
- Michele M.P. Lufino
- Department of Physiology, Anatomy and Genetics, University of Oxford, Le Gros Clark Building, South Parks Road, OxfordOX1 3QX, UK
| | - Ana M. Silva
- Department of Physiology, Anatomy and Genetics, University of Oxford, Le Gros Clark Building, South Parks Road, OxfordOX1 3QX, UK
- Faculdade de Medicina, Universidade de Lisboa, Lisboa1649-028, Portugal
| | - Andrea H. Németh
- Nuffield Department of Clinical Neurosciences, University of Oxford, OxfordOX3 9DU, UK
- Department of Clinical Genetics, Churchill Hospital, Oxford University Hospitals NHS Trust, OxfordOX3 7LE, UK
| | - Javier Alegre-Abarrategui
- Department of Physiology, Anatomy and Genetics, University of Oxford, Le Gros Clark Building, South Parks Road, OxfordOX1 3QX, UK
- Oxford Parkinson's Disease Centre, University of Oxford, Le Gros Clark Building, South Parks Road, Oxford OX1 3QX, UK
| | - Angela J. Russell
- Department of Chemistry, Chemistry Research Laboratory and
- Department of Pharmacology, University of Oxford, Mansfield Road, OxfordOX1 3QT, UK
| | - Richard Wade-Martins
- Department of Physiology, Anatomy and Genetics, University of Oxford, Le Gros Clark Building, South Parks Road, OxfordOX1 3QX, UK
- Oxford Parkinson's Disease Centre, University of Oxford, Le Gros Clark Building, South Parks Road, Oxford OX1 3QX, UK
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Abstract
Friedreich ataxia is the most common autosomal recessive ataxia. It is a progressive neurodegenerative disorder, typically with onset before 20 years of age. Signs and symptoms include progressive ataxia, ascending weakness and ascending loss of vibration and joint position senses, pes cavus, scoliosis, cardiomyopathy, and arrhythmias. There are no disease-modifying medications to either slow or halt the progression of the disease, but research investigating therapies to increase endogenous frataxin production and decrease the downstream consequences of disrupted iron homeostasis is ongoing. Clinical trials of promising medications are underway, and the treatment era of Friedreich ataxia is beginning.
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Affiliation(s)
- Abigail Collins
- Pediatrics and Neurology, Children's Hospital Colorado, University of Colorado, Denver, School of Medicine, 13123 East 16th Avenue, B155, Aurora, CO 80045, USA.
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119
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Evans-Galea MV, Hannan AJ, Carrodus N, Delatycki MB, Saffery R. Epigenetic modifications in trinucleotide repeat diseases. Trends Mol Med 2013; 19:655-63. [DOI: 10.1016/j.molmed.2013.07.007] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2013] [Revised: 07/12/2013] [Accepted: 07/22/2013] [Indexed: 12/18/2022]
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121
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Neuhann T, Rautenstrauss B. Genetic and phenotypic variability of optic neuropathies. Expert Rev Neurother 2013; 13:357-67. [PMID: 23545052 DOI: 10.1586/ern.13.19] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Hereditary optic neuropathies comprise a group of clinically and genetically heterogeneous disorders. Two subgroups can be formed: isolated hereditary optic atrophies and optic neuropathy as part of complex disorders. In group 1 of hereditary optic neuropathies, optic nerve dysfunction is typically the only manifestation of the disease. This group comprises autosomal dominant, autosomal recessive and X-linked recessive optic atrophy and the maternally inherited Leber's hereditary optic neuropathy. Among the autosomal-dominant forms of optic atrophy, Kjer's disease is most frequently observed. In the second group of complex disorders, various neurologic and other systemic abnormalities are regularly observed. Most frequent in this group are mtDNA mutations, inherited peripheral neuropathies, Charcot-Marie-Tooth disorders (CMT2A2, CMTX5), hereditary sensory neuropathy type 3 (HSAN3), Friedreich's ataxia, leukodystrophies, sphingolipidoses, ceroid-lipofuscinoses and neurodegeneration with brain iron accumulation. We review current knowledge about the underlying genetic predispositions, the most urgent open questions and how this may affect our management of this heterogeneous group of disorders in the future.
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Affiliation(s)
- Teresa Neuhann
- Medizinisch Genetisches Zentrum, Munich, Bayerstrasse 3-5, Munich 80335, Germany.
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122
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Parkinson MH, Boesch S, Nachbauer W, Mariotti C, Giunti P. Clinical features of Friedreich's ataxia: classical and atypical phenotypes. J Neurochem 2013; 126 Suppl 1:103-17. [PMID: 23859346 DOI: 10.1111/jnc.12317] [Citation(s) in RCA: 168] [Impact Index Per Article: 15.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2013] [Revised: 05/15/2013] [Accepted: 05/15/2013] [Indexed: 11/27/2022]
Abstract
One hundred and fifty years since Nikolaus Friedreich's first description of the degenerative ataxic syndrome which bears his name, his description remains at the core of the classical clinical phenotype of gait and limb ataxia, poor balance and coordination, leg weakness, sensory loss, areflexia, impaired walking, dysarthria, dysphagia, eye movement abnormalities, scoliosis, foot deformities, cardiomyopathy and diabetes. Onset is typically around puberty with slow progression and shortened life-span often related to cardiac complications. Inheritance is autosomal recessive with the vast majority of cases showing an unstable intronic GAA expansion in both alleles of the frataxin gene on chromosome 9q13. A small number of cases are caused by a compound heterozygous expansion with a point mutation or deletion. Understanding of the underlying molecular biology has enabled identification of atypical phenotypes with late onset, or atypical features such as retained reflexes. Late-onset cases tend to have slower progression and are associated with smaller GAA expansions. Early-onset cases tend to have more rapid progression and a higher frequency of non-neurological features such as diabetes, cardiomyopathy, scoliosis and pes cavus. Compound heterozygotes, including those with large deletions, often have atypical features. In this paper, we review the classical and atypical clinical phenotypes of Friedreich's ataxia.
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Affiliation(s)
- Michael H Parkinson
- Department of Molecular Neuroscience, UCL Institute of Neurology, London, UK
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123
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González-Cabo P, Palau F. Mitochondrial pathophysiology in Friedreich's ataxia. J Neurochem 2013; 126 Suppl 1:53-64. [PMID: 23859341 DOI: 10.1111/jnc.12303] [Citation(s) in RCA: 60] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2013] [Revised: 04/09/2013] [Accepted: 05/08/2013] [Indexed: 12/01/2022]
Abstract
Neurological examination indicates that Friedreich's ataxia corresponds to a mixed sensory and cerebellar ataxia, which affects the proprioceptive pathways. Neuropathology and pathophysiology of Friedreich's ataxia involves the peripheral sensory nerves, dorsal root ganglia, posterior columns, the spinocerebellar, and corticospinal tracts of the spinal cord, gracile and cuneate nuclei, dorsal nuclei of Clarke, and the dentate nucleus. Involvement of the myocardium and pancreatic islets of Langerhans indicates that it is also a systemic disease. The pathophysiology of the disease is the consequence of frataxin deficiency in the mitochondria and cells. Some of the biological consequences are currently recognized such as the effects on iron-sulfur cluster biogenesis or the oxidative status, but others deserve to be studied in depth. Among physiological aspects of mitochondria that have been associated with neurodegeneration and may be interesting to investigate in Friedreich's ataxia we can include mitochondrial dynamics and movement, communication with other organelles especially the endoplasmic reticulum, calcium homeostasis, apoptosis, and mitochondrial biogenesis and quality control. Changes in the mitochondrial physiology and transport in peripheral and central axons and mitochondrial metabolic functions such as bioenergetics and energy delivery in the synapses are also relevant functions to be considered. Thus, to understand the general pathophysiology of the disease and fundamental pathogenic mechanisms such as dying-back axonopathy, and determine molecular, cellular and tissue therapeutic targets, we need to discover the effect of frataxin depletion on mitochondrial properties and on specific cell susceptibility in the nervous system and other affected organs.
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Affiliation(s)
- Pilar González-Cabo
- Program in Rare and Genetic Diseases, Centro de Investigación Príncipe Felipe, Valencia, Spain
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124
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Perdomini M, Hick A, Puccio H, Pook MA. Animal and cellular models of Friedreich ataxia. J Neurochem 2013; 126 Suppl 1:65-79. [PMID: 23859342 DOI: 10.1111/jnc.12219] [Citation(s) in RCA: 60] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2012] [Revised: 02/01/2013] [Accepted: 02/04/2013] [Indexed: 11/30/2022]
Abstract
The development and use of animal and cellular models of Friedreich ataxia (FRDA) are essential requirements for the understanding of FRDA disease mechanisms and the investigation of potential FRDA therapeutic strategies. Although animal and cellular models of lower organisms have provided valuable information on certain aspects of FRDA disease and therapy, it is intuitive that the most useful models are those of mammals and mammalian cells, which are the closest in physiological terms to FRDA patients. To date, there have been considerable efforts put into the development of several different FRDA mouse models and relevant FRDA mouse and human cell line systems. We summarize the principal mammalian FRDA models, discuss the pros and cons of each system, and describe the ways in which such models have been used to address two of the fundamental, as yet unanswered, questions regarding FRDA. Namely, what is the exact pathophysiology of FRDA and what is the detailed genetic and epigenetic basis of FRDA?
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Affiliation(s)
- Morgane Perdomini
- Translational Medecine and Neurogenetics, IGBMC-Institut de Génétique et de Biologie Moléculaire et Cellulaire, Illkirch, France
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125
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Gottesfeld JM, Rusche JR, Pandolfo M. Increasing frataxin gene expression with histone deacetylase inhibitors as a therapeutic approach for Friedreich's ataxia. J Neurochem 2013; 126 Suppl 1:147-54. [PMID: 23859350 PMCID: PMC3766837 DOI: 10.1111/jnc.12302] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2013] [Revised: 04/19/2013] [Accepted: 04/19/2013] [Indexed: 01/08/2023]
Abstract
The genetic defect in Friedreich's ataxia (FRDA) is the expansion of a GAA·TCC triplet in the first intron of the FXN gene, which encodes the mitochondrial protein frataxin. Previous studies have established that the repeats reduce transcription of this essential gene, with a concomitant decrease in frataxin protein in affected individuals. As the repeats do not alter the FXN protein coding sequence, one therapeutic approach would be to increase transcription of pathogenic FXN genes. Histone posttranslational modifications near the expanded repeats are consistent with heterochromatin formation and FXN gene silencing. In an effort to find small molecules that would reactivate this silent gene, histone deacetylase inhibitors were screened for their ability to up-regulate FXN gene expression in patient cells and members of the pimelic 2-aminobenzamide family of class I histone deacetylase inhibitors were identified as potent inducers of FXN gene expression and frataxin protein. Importantly, these molecules up-regulate FXN expression in human neuronal cells derived from patient-induced pluripotent stem cells and in two mouse models for the disease. Preclinical studies of safety and toxicity have been completed for one such compound and a phase I clinical trial in FRDA patients has been initiated. Furthermore, medicinal chemistry efforts have identified improved compounds with superior pharmacological properties.
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Affiliation(s)
- Joel M. Gottesfeld
- Department of Molecular Biology, The Scripps Research Institute, La Jolla, California 92037 USA
| | | | - Massimo Pandolfo
- Université Libre de Bruxelles - Hôpital Erasme, 1070 Brussels, Belgium
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126
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Lane DJR, Huang MLH, Ting S, Sivagurunathan S, Richardson DR. Biochemistry of cardiomyopathy in the mitochondrial disease Friedreich's ataxia. Biochem J 2013; 453:321-36. [PMID: 23849057 DOI: 10.1042/bj20130079] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
FRDA (Friedreich's ataxia) is a debilitating mitochondrial disorder leading to neural and cardiac degeneration, which is caused by a mutation in the frataxin gene that leads to decreased frataxin expression. The most common cause of death in FRDA patients is heart failure, although it is not known how the deficiency in frataxin potentiates the observed cardiomyopathy. The major proposed biochemical mechanisms for disease pathogenesis and the origins of heart failure in FRDA involve metabolic perturbations caused by decreased frataxin expression. Additionally, recent data suggest that low frataxin expression in heart muscle of conditional frataxin knockout mice activates an integrated stress response that contributes to and/or exacerbates cardiac hypertrophy and the loss of cardiomyocytes. The elucidation of these potential mechanisms will lead to a more comprehensive understanding of the pathogenesis of FRDA, and will contribute to the development of better treatments and therapeutics.
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Affiliation(s)
- Darius J R Lane
- Molecular Pharmacology and Pathology Program, Department of Pathology and Bosch Institute, Blackburn Building, D06, University of Sydney, Sydney, NSW 2006, Australia
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127
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Cnop M, Mulder H, Igoillo-Esteve M. Diabetes in Friedreich ataxia. J Neurochem 2013; 126 Suppl 1:94-102. [PMID: 23859345 DOI: 10.1111/jnc.12216] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2012] [Accepted: 01/06/2013] [Indexed: 12/20/2022]
Abstract
Diabetes is a common metabolic disorder in patients with Friedreich ataxia. In this Supplement article, we review the clinical data on diabetes in Friedreich ataxia, and the experimental data from rodent and in vitro models of the disease. Increased body adiposity and insulin resistance are frequently present in Friedreich ataxia, but pancreatic β cell dysfunction and death are a conditio sine qua non for the loss of glucose tolerance and development of diabetes. The loss of frataxin function in mitochondria accounts for these pathogenic processes in Friedreich ataxia. Mitochondria are essential for the sensing of nutrients by the β cell and for the generation of signals that trigger and amplify insulin secretion, known as stimulus-secretion coupling. Moreover, in the intrinsic pathway of apoptosis, pro-apoptotic signals converge on mitochondria, resulting in mitochondrial Bax translocation, membrane permeabilization, cytochrome c release and caspase cleavage. How and at which level frataxin deficiency impacts on these processes in β cells is only partially understood. A better understanding of the molecular mechanisms mediating β cell demise in Friedreich ataxia will pave the way for new therapeutic approaches.
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Affiliation(s)
- Miriam Cnop
- Laboratory of Experimental Medicine, Université Libre de Bruxelles, Brussels, Belgium.
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128
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Pastore A, Puccio H. Frataxin: a protein in search for a function. J Neurochem 2013; 126 Suppl 1:43-52. [PMID: 23859340 DOI: 10.1111/jnc.12220] [Citation(s) in RCA: 143] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2012] [Revised: 01/18/2013] [Accepted: 01/23/2013] [Indexed: 01/01/2023]
Abstract
Reduced levels of the protein frataxin cause the neurodegenerative disease Friedreich's ataxia. Pathology is associated with disruption of iron-sulfur cluster biosynthesis, mitochondrial iron overload, and oxidative stress. Frataxin is a highly conserved iron-binding protein present in most organisms. Despite the intense interest generated since the determination of its pathology, identification of the cellular function of frataxin has so far remained elusive. In this review, we revisit the most significant milestones that have led us to our current understanding of frataxin and its functions. The picture that emerges is that frataxin is a crucial element of one of the most essential cellular machines specialized in iron-sulfur cluster biogenesis. Future developments, therefore, can be expected from further advancements in our comprehension of this machine.
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129
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Bayot A, Reichman S, Lebon S, Csaba Z, Aubry L, Sterkers G, Husson I, Rak M, Rustin P. Cis-silencing of PIP5K1B evidenced in Friedreich's ataxia patient cells results in cytoskeleton anomalies. Hum Mol Genet 2013; 22:2894-904. [PMID: 23552101 DOI: 10.1093/hmg/ddt144] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Friedreich's ataxia (FRDA) is a progressive neurodegenerative disease characterized by ataxia, variously associating heart disease, diabetes mellitus and/or glucose intolerance. It results from intronic expansion of GAA triplet repeats at the FXN locus. Homozygous expansions cause silencing of the FXN gene and subsequent decreased expression of the encoded mitochondrial frataxin. Detailed analyses in fibroblasts and neuronal tissues from FRDA patients have revealed profound cytoskeleton anomalies. So far, however, the molecular mechanism underlying these cytoskeleton defects remains unknown. We show here that gene silencing spreads in cis over the PIP5K1B gene in cells from FRDA patients (circulating lymphocytes and primary fibroblasts), correlating with expanded GAA repeat size. PIP5K1B encodes phosphatidylinositol 4-phosphate 5-kinase β type I (pip5k1β), an enzyme functionally linked to actin cytoskeleton dynamics that phosphorylates phosphatidylinositol 4-phosphate [PI(4)P] to generate phosphatidylinositol-4,5-bisphosphate [PI(4,5)P2]. Accordingly, loss of pip5k1β function in FRDA cells was accompanied by decreased PI(4,5)P2 levels and was shown instrumental for destabilization of the actin network and delayed cell spreading. Knockdown of PIP5K1B in control fibroblasts using shRNA reproduced abnormal actin cytoskeleton remodeling, whereas over-expression of PIP5K1B, but not FXN, suppressed this phenotype in FRDA cells. In addition to provide new insights into the consequences of the FXN gene expansion, these findings raise the question whether PIP5K1B silencing may contribute to the variable manifestation of this complex disease.
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Affiliation(s)
- Aurélien Bayot
- Hôpital Robert Debré, INSERM UMR 676 Faculté de Médecine Denis Diderot, Université Paris 7, 75019 Paris, France.
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130
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Gomes CM, Santos R. Neurodegeneration in Friedreich's ataxia: from defective frataxin to oxidative stress. OXIDATIVE MEDICINE AND CELLULAR LONGEVITY 2013; 2013:487534. [PMID: 23936609 PMCID: PMC3725840 DOI: 10.1155/2013/487534] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/26/2013] [Accepted: 06/14/2013] [Indexed: 02/08/2023]
Abstract
Friedreich's ataxia is the most common inherited autosomal recessive ataxia and is characterized by progressive degeneration of the peripheral and central nervous systems and cardiomyopathy. This disease is caused by the silencing of the FXN gene and reduced levels of the encoded protein, frataxin. Frataxin is a mitochondrial protein that functions primarily in iron-sulfur cluster synthesis. This small protein with an α / β sandwich fold undergoes complex processing and imports into the mitochondria, generating isoforms with distinct N-terminal lengths which may underlie different functionalities, also in respect to oligomerization. Missense mutations in the FXN coding region, which compromise protein folding, stability, and function, are found in 4% of FRDA heterozygous patients and are useful to understand how loss of functional frataxin impacts on FRDA physiopathology. In cells, frataxin deficiency leads to pleiotropic phenotypes, including deregulation of iron homeostasis and increased oxidative stress. Increasing amount of data suggest that oxidative stress contributes to neurodegeneration in Friedreich's ataxia.
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Affiliation(s)
- Cláudio M. Gomes
- Instituto Tecnologia Química e Biológica, Universidade Nova de Lisboa, Avenida da República, 2784-505 Oeiras, Portugal
| | - Renata Santos
- Development of the Nervous System, IBENS, Ecole Normale Supérieure, 46 rue d'Ulm, 75230 Paris Cedex 05, France
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131
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Analysis of the visual system in Friedreich ataxia. J Neurol 2013; 260:2362-9. [DOI: 10.1007/s00415-013-6978-z] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2013] [Revised: 05/20/2013] [Accepted: 05/25/2013] [Indexed: 10/26/2022]
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132
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Hasuike Y, Nagai T, Yorifuji S, Tanaka S, Matsumoto A, Yahiro M, Kaibe S, Kida A, Tokuyama M, Nagasawa Y, Otaki Y, Kuragano T, Nakanishi T. The mitochondrial protein frataxin is downregulated in hemodialysis patients. Clin Exp Nephrol 2013; 17:424-30. [PMID: 23180044 DOI: 10.1007/s10157-012-0737-9] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2012] [Accepted: 11/04/2012] [Indexed: 10/27/2022]
Abstract
BACKGROUND The mitochondrial protein frataxin regulates iron metabolism for heme and iron sulfur cluster synthesis in the mitochondria and could be associated with the regulation of oxidative stress. To clarify the expression of frataxin and its association with uremia, we evaluated the mRNA and protein levels of frataxin in the polymorphonuclear leukocytes (PMNLs) of patients on hemodialysis (HD). METHODS Uremic patients on HD (n = 18) and healthy control subjects (n = 18) were investigated. PMNLs were isolated by differential centrifugation. The mRNA levels of frataxin in isolated leukocytes were quantified by TaqMan real-time polymerase chain reaction. Frataxin protein expression in the cell lysate was evaluated using SDS-polyacrylamide gel electrophoresis and Western blotting. RESULTS The frataxin/glyceraldehyde-3-phosphate dehydrogenase mRNA ratio in PMNLs from uremic patients was significantly lower than that in control subjects. Frataxin protein expression in uremic patients was also significantly lower than that in controls. Multiple regression analysis showed that frataxin mRNA levels were independently associated with the serum levels of both the oxidative stress marker malondialdehyde and the proinflammatory cytokine tumor necrosis factor-α. CONCLUSION The downregulation of frataxin seems to be linked with uremic status, which is usually associated with chronic inflammation and the acceleration of oxidative stress. Mitochondrial iron regulation may play a role in several comorbidities and in the poor prognosis in uremic patients. Further investigation is needed to elucidate whether reduced frataxin levels are linked to the pathological status of uremic patients and whether uremic substances affect frataxin expression.
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Affiliation(s)
- Yukiko Hasuike
- Division of Kidney and Dialysis, Department of Internal Medicine, Hyogo College of Medicine, 1-1 Mukogawa-cho, Nishinomiya, 663-8501, Japan.
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133
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Plasterer HL, Deutsch EC, Belmonte M, Egan E, Lynch DR, Rusche JR. Development of frataxin gene expression measures for the evaluation of experimental treatments in Friedreich's ataxia. PLoS One 2013; 8:e63958. [PMID: 23691127 PMCID: PMC3656936 DOI: 10.1371/journal.pone.0063958] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2012] [Accepted: 04/09/2013] [Indexed: 11/18/2022] Open
Abstract
BACKGROUND Friedreich ataxia is a progressive neurodegenerative disorder caused by GAA triplet repeat expansions or point mutations in the FXN gene and, ultimately, a deficiency in the levels of functional frataxin protein. Heterozygous carriers of the expansion express approximately 50% of normal frataxin levels yet manifest no clinical symptoms, suggesting that therapeutic approaches that increase frataxin may be effective even if frataxin is raised only to carrier levels. Small molecule HDAC inhibitor compounds increase frataxin mRNA and protein levels, and have beneficial effects in animal models of FRDA. METHODOLOGY/PRINCIPAL FINDINGS To gather data supporting the use of frataxin as a therapeutic biomarker of drug response we characterized the intra-individual stability of frataxin over time, determined the contribution of frataxin from different components of blood, compared frataxin measures in different cell compartments, and demonstrated that frataxin increases are achieved in peripheral blood mononuclear cells. Frataxin mRNA and protein levels were stable with repeated sampling over four and 15 weeks. In the 15-week study, the average CV was 15.6% for protein and 18% for mRNA. Highest levels of frataxin in blood were in erythrocytes. As erythrocytes are not useful for frataxin assessment in many clinical trial situations, we confirmed that PBMCs and buccal swabs have frataxin levels equivalent to those of whole blood. In addition, a dose-dependent increase in frataxin was observed when PBMCs isolated from patient blood were treated with HDACi. Finally, higher frataxin levels predicted less severe neurological dysfunction and were associated with slower rates of neurological change. CONCLUSIONS/SIGNIFICANCE Our data support the use of frataxin as a biomarker of drug effect. Frataxin levels are stable over time and as such a 1.5 to 2-fold change would be detectable over normal biological fluctuations. Additionally, our data support buccal cells or PBMCs as sources for measuring frataxin protein in therapeutic trials.
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Affiliation(s)
| | - Eric C. Deutsch
- Departments of Neurology and Pediatrics, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
- Divisions of Neurology and Pediatrics, Children’s Hospital of Philadelphia, Philadelphia, Pennsylvania, United States of America
| | - Matthew Belmonte
- Repligen Corporation, Waltham, Massachusetts, United States of America
| | - Elizabeth Egan
- Repligen Corporation, Waltham, Massachusetts, United States of America
| | - David R. Lynch
- Departments of Neurology and Pediatrics, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
- Divisions of Neurology and Pediatrics, Children’s Hospital of Philadelphia, Philadelphia, Pennsylvania, United States of America
| | - James R. Rusche
- Repligen Corporation, Waltham, Massachusetts, United States of America
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134
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Triple Therapy with Darbepoetin Alfa, Idebenone, and Riboflavin in Friedreich’s Ataxia: an Open-Label Trial. THE CEREBELLUM 2013; 12:713-20. [DOI: 10.1007/s12311-013-0482-y] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
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135
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Harms MB, Cady J, Zaidman C, Cooper P, Bali T, Allred P, Cruchaga C, Baughn M, Libby RT, Pestronk A, Goate A, Ravits J, Baloh RH. Lack of C9ORF72 coding mutations supports a gain of function for repeat expansions in amyotrophic lateral sclerosis. Neurobiol Aging 2013; 34:2234.e13-9. [PMID: 23597494 DOI: 10.1016/j.neurobiolaging.2013.03.006] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2012] [Revised: 02/25/2013] [Accepted: 03/11/2013] [Indexed: 12/13/2022]
Abstract
Hexanucleotide repeat expansions in C9ORF72 are a common cause of familial and apparently sporadic amyotrophic lateral sclerosis (ALS) and frontal temporal dementia (FTD). The mechanism by which expansions cause neurodegeneration is unknown, but current evidence supports both loss-of-function and gain-of-function mechanisms. We used pooled next-generation sequencing of the C9ORF72 gene in 389 ALS patients to look for traditional loss-of-function mutations. Although rare variants were identified, none were likely to be pathogenic, suggesting that mutations other than the repeat expansion are not a common cause of ALS, and providing supportive evidence for a gain-of-function mechanism. We also show by repeat-primed PCR genotyping that the C9ORF72 expansion frequency varies by geographical region within the United States, with an unexpectedly high frequency in the Mid-West. Finally we also show evidence of somatic instability of the expansion size by Southern blot, with the largest expansions occurring in brain tissue.
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Affiliation(s)
- Matthew B Harms
- Department of Neurology, Washington University School of Medicine, St. Louis, MO, USA
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136
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Saccà F, Marsili A, Puorro G, Antenora A, Pane C, Tessa A, Scoppettuolo P, Nesti C, Brescia Morra V, De Michele G, Santorelli FM, Filla A. Clinical use of frataxin measurement in a patient with a novel deletion in the FXN gene. J Neurol 2013; 260:1116-21. [PMID: 23196337 DOI: 10.1007/s00415-012-6770-5] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2012] [Revised: 11/11/2012] [Accepted: 11/16/2012] [Indexed: 10/27/2022]
Abstract
Friedreich ataxia (FRDA) is caused by a GAA expansion in the first intron of the FXN gene, which encodes frataxin. Four percent of patients harbor a point mutation on one allele and a GAA expansion on the other. We studied an Italian patient presenting with symptoms suggestive of FRDA, and carrying a single expanded 850 GAA allele. As a second diagnostic step, frataxin was measured in peripheral blood mononuclear cells, and proved to be in the pathological range (2.95 pg/μg total protein, 12.7 % of control levels). Subsequent sequencing revealed a novel deletion in exon 5a (c.572delC) which predicted a frameshift at codon 191 and a premature truncation of the protein at codon 194 (p.T191IfsX194). FXN/mRNA expression was reduced to 69.2 % of control levels. Clinical phenotype was atypical with absent dysarthria, and rapid disease progression. L-Buthionine-sulphoximine treatment of the proband's lymphoblasts showed a severe phenotype as compared to classic FRDA.
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Affiliation(s)
- Francesco Saccà
- Department of Neurological Sciences, University Federico II, Via Pansini 5, 80131 Naples, NA, Italy.
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137
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Söderberg CAG, Rajan S, Shkumatov AV, Gakh O, Schaefer S, Ahlgren EC, Svergun DI, Isaya G, Al-Karadaghi S. The molecular basis of iron-induced oligomerization of frataxin and the role of the ferroxidation reaction in oligomerization. J Biol Chem 2013; 288:8156-8167. [PMID: 23344952 PMCID: PMC3605634 DOI: 10.1074/jbc.m112.442285] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2012] [Revised: 01/22/2013] [Indexed: 11/06/2022] Open
Abstract
The role of the mitochondrial protein frataxin in iron storage and detoxification, iron delivery to iron-sulfur cluster biosynthesis, heme biosynthesis, and aconitase repair has been extensively studied during the last decade. However, still no general consensus exists on the details of the mechanism of frataxin function and oligomerization. Here, using small-angle x-ray scattering and x-ray crystallography, we describe the solution structure of the oligomers formed during the iron-dependent assembly of yeast (Yfh1) and Escherichia coli (CyaY) frataxin. At an iron-to-protein ratio of 2, the initially monomeric Yfh1 is converted to a trimeric form in solution. The trimer in turn serves as the assembly unit for higher order oligomers induced at higher iron-to-protein ratios. The x-ray crystallographic structure obtained from iron-soaked crystals demonstrates that iron binds at the trimer-trimer interaction sites, presumably contributing to oligomer stabilization. For the ferroxidation-deficient D79A/D82A variant of Yfh1, iron-dependent oligomerization may still take place, although >50% of the protein is found in the monomeric state at the highest iron-to-protein ratio used. This demonstrates that the ferroxidation reaction controls frataxin assembly and presumably the iron chaperone function of frataxin and its interactions with target proteins. For E. coli CyaY, the assembly unit of higher order oligomers is a tetramer, which could be an effect of the much shorter N-terminal region of this protein. The results show that understanding of the mechanistic features of frataxin function requires detailed knowledge of the interplay between the ferroxidation reaction, iron-induced oligomerization, and the structure of oligomers formed during assembly.
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Affiliation(s)
- Christopher A G Söderberg
- Center for Molecular Protein Science, Institute for Chemistry and Chemical Engineering, Lund University, P. O. Box 124, SE-221 00 Lund, Sweden
| | - Sreekanth Rajan
- Center for Molecular Protein Science, Institute for Chemistry and Chemical Engineering, Lund University, P. O. Box 124, SE-221 00 Lund, Sweden
| | - Alexander V Shkumatov
- European Molecular Biology Laboratory (EMBL), Hamburg Unit c/o DESY, Notkestrasse 85, D-22603 Hamburg, Germany
| | - Oleksandr Gakh
- Departments of Pediatric and Adolescent Medicine and Biochemistry and Molecular Biology, Mayo Clinic, College of Medicine, Rochester, Minnesota 55905
| | - Susanne Schaefer
- Center for Molecular Protein Science, Institute for Chemistry and Chemical Engineering, Lund University, P. O. Box 124, SE-221 00 Lund, Sweden
| | - Eva-Christina Ahlgren
- Center for Molecular Protein Science, Institute for Chemistry and Chemical Engineering, Lund University, P. O. Box 124, SE-221 00 Lund, Sweden
| | - Dmitri I Svergun
- European Molecular Biology Laboratory (EMBL), Hamburg Unit c/o DESY, Notkestrasse 85, D-22603 Hamburg, Germany
| | - Grazia Isaya
- Departments of Pediatric and Adolescent Medicine and Biochemistry and Molecular Biology, Mayo Clinic, College of Medicine, Rochester, Minnesota 55905.
| | - Salam Al-Karadaghi
- Center for Molecular Protein Science, Institute for Chemistry and Chemical Engineering, Lund University, P. O. Box 124, SE-221 00 Lund, Sweden.
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Epigenetics in Friedreich's Ataxia: Challenges and Opportunities for Therapy. GENETICS RESEARCH INTERNATIONAL 2013; 2013:852080. [PMID: 23533785 PMCID: PMC3590757 DOI: 10.1155/2013/852080] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/03/2012] [Accepted: 01/10/2013] [Indexed: 11/17/2022]
Abstract
Friedreich's ataxia (FRDA) is an autosomal recessive neurodegenerative disorder caused by homozygous expansion of a GAA·TTC trinucleotide repeat within the first intron of the FXN gene, leading to reduced FXN transcription and decreased levels of frataxin protein. Recent advances in FRDA research have revealed the presence of several epigenetic modifications that are either directly or indirectly involved in this FXN gene silencing. Although epigenetic marks may be inherited from one generation to the next, modifications of DNA and histones can be reversed, indicating that they are suitable targets for epigenetic-based therapy. Unlike other trinucleotide repeat disorders, such as Huntington disease, the large expansions of GAA·TTC repeats in FRDA do not produce a change in the frataxin amino acid sequence, but they produce reduced levels of normal frataxin. Therefore, transcriptional reactivation of the FXN gene provides a good therapeutic option. The present paper will initially focus on the epigenetic changes seen in FRDA patients and their role in the silencing of FXN gene and will be concluded by considering the potential epigenetic therapies.
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139
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140
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Li H, Gakh O, Smith DY, Ranatunga WK, Isaya G. Missense mutations linked to friedreich ataxia have different but synergistic effects on mitochondrial frataxin isoforms. J Biol Chem 2013; 288:4116-27. [PMID: 23269675 PMCID: PMC3567662 DOI: 10.1074/jbc.m112.435263] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2012] [Revised: 12/21/2012] [Indexed: 12/25/2022] Open
Abstract
Friedreich ataxia is an early-onset multisystemic disease linked to a variety of molecular defects in the nuclear gene FRDA. This gene normally encodes the iron-binding protein frataxin (FXN), which is critical for mitochondrial iron metabolism, global cellular iron homeostasis, and antioxidant protection. In most Friedreich ataxia patients, a large GAA-repeat expansion is present within the first intron of both FRDA alleles, that results in transcriptional silencing ultimately leading to insufficient levels of FXN protein in the mitochondrial matrix and probably other cellular compartments. The lack of FXN in turn impairs incorporation of iron into iron-sulfur cluster and heme cofactors, causing widespread enzymatic deficits and oxidative damage catalyzed by excess labile iron. In a minority of patients, a typical GAA expansion is present in only one FRDA allele, whereas a missense mutation is found in the other allele. Although it is known that the disease course for these patients can be as severe as for patients with two expanded FRDA alleles, the underlying pathophysiological mechanisms are not understood. Human cells normally contain two major mitochondrial isoforms of FXN (FXN(42-210) and FXN(81-210)) that have different biochemical properties and functional roles. Using cell-free systems and different cellular models, we show that two of the most clinically severe FXN point mutations, I154F and W155R, have unique direct and indirect effects on the stability, biogenesis, or catalytic activity of FXN(42-210) and FXN(81-210) under physiological conditions. Our data indicate that frataxin point mutations have complex biochemical effects that synergistically contribute to the pathophysiology of Friedreich ataxia.
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Affiliation(s)
- Hongqiao Li
- From the Department of Pediatric and Adolescent Medicine and the Department of Biochemistry and Molecular Biology and the Mayo Clinic Children's Center, Mayo Clinic, Rochester, Minnesota 55905
| | - Oleksandr Gakh
- From the Department of Pediatric and Adolescent Medicine and the Department of Biochemistry and Molecular Biology and the Mayo Clinic Children's Center, Mayo Clinic, Rochester, Minnesota 55905
| | - Douglas Y. Smith
- From the Department of Pediatric and Adolescent Medicine and the Department of Biochemistry and Molecular Biology and the Mayo Clinic Children's Center, Mayo Clinic, Rochester, Minnesota 55905
| | - Wasantha K. Ranatunga
- From the Department of Pediatric and Adolescent Medicine and the Department of Biochemistry and Molecular Biology and the Mayo Clinic Children's Center, Mayo Clinic, Rochester, Minnesota 55905
| | - Grazia Isaya
- From the Department of Pediatric and Adolescent Medicine and the Department of Biochemistry and Molecular Biology and the Mayo Clinic Children's Center, Mayo Clinic, Rochester, Minnesota 55905
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Abstract
Friedreich ataxia is an autosomal recessive disorder that affects children and young adults. The mutation consists of a homozygous guanine-adenine-adenine trinucleotide repeat expansion that causes deficiency of frataxin, a small nuclear genome-encoded mitochondrial protein. Low frataxin levels lead to insufficient biosynthesis of iron-sulfur clusters that are required for mitochondrial electron transport and assembly of functional aconitase, and iron dysmetabolism of the entire cell. This review of the neuropathology of Friedreich ataxia stresses the critical role of hypoplasia and superimposed atrophy of dorsal root ganglia. Progressive destruction of dorsal root ganglia accounts for thinning of dorsal roots, degeneration of dorsal columns, transsynaptic atrophy of nerve cells in Clarke column and dorsal spinocerebellar fibers, atrophy of gracile and cuneate nuclei, and neuropathy of sensory nerves. The lesion of the dentate nucleus consists of progressive and selective atrophy of large glutamatergic neurons and grumose degeneration of corticonuclear synaptic terminals that contain γ-aminobutyric acid (GABA). Small GABA-ergic neurons and their projection fibers in the dentato-olivary tract survive. Atrophy of Betz cells and corticospinal tracts constitute a second intrinsic CNS lesion. In light of the selective vulnerability of organs and tissues to systemic frataxin deficiency, many questions about the pathogenesis of Friedreich ataxia remain.
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Affiliation(s)
- Arnulf H Koeppen
- Research Service, Veterans Affairs Medical Center, Albany, New York 12208, USA.
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Kasson TMD, Barry BA. Reactive oxygen and oxidative stress: N-formyl kynurenine in photosystem II and non-photosynthetic proteins. PHOTOSYNTHESIS RESEARCH 2012; 114:97-110. [PMID: 23161228 DOI: 10.1007/s11120-012-9784-z] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/03/2012] [Accepted: 10/31/2012] [Indexed: 06/01/2023]
Abstract
While light is the essential driving force for photosynthetic carbon fixation, high light intensities are toxic to photosynthetic organisms. Prolonged exposure to high light results in damage to the photosynthetic membrane proteins and suboptimal activity, a phenomenon called photoinhibition. The primary target for inactivation is the photosystem II (PSII) reaction center. PSII catalyzes the light-induced oxidation of water at the oxygen-evolving complex. Reactive oxygen species (ROS) are generated under photoinhibitory conditions and induce oxidative post translational modifications of amino acid side chains. Specific modification of tryptophan residues to N-formylkynurenine (NFK) occurs in the CP43 and D1 core polypeptides of PSII. The NFK modification has also been detected in other proteins, such as mitochondrial respiratory enzymes, and is formed by a non-random, ROS-targeted mechanism. NFK has been shown to accumulate in PSII during conditions of high light stress in vitro. This review provides a summary of what is known about the generation and function of NFK in PSII and other proteins. Currently, the role of ROS in photoinhibition is under debate. Furthermore, the triggers for the degradation and accelerated turnover of PSII subunits, which occur under high light, are not yet identified. Owing to its unique optical and Raman signal, NFK provides a new marker to use in the identification of ROS generation sites in PSII and other proteins. Also, the speculative hypothesis that NFK, and other oxidative modifications of tryptophan, play a role in the PSII damage and repair cycle is discussed. NFK may have a similar function during oxidative stress in other biologic systems.
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Affiliation(s)
- Tina M Dreaden Kasson
- School of Chemistry and Biochemistry and Petit Institute for Bioengineering and Bioscience, Georgia Institute of Technology, Atlanta, GA 30332, USA
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Martelli A, Friedman LS, Reutenauer L, Messaddeq N, Perlman SL, Lynch DR, Fedosov K, Schulz JB, Pandolfo M, Puccio H. Clinical data and characterization of the liver conditional mouse model exclude neoplasia as a non-neurological manifestation associated with Friedreich's ataxia. Dis Model Mech 2012; 5:860-9. [PMID: 22736457 PMCID: PMC3484868 DOI: 10.1242/dmm.009829] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2012] [Accepted: 06/06/2012] [Indexed: 01/01/2023] Open
Abstract
Friedreich's ataxia (FRDA) is the most common hereditary ataxia in the caucasian population and is characterized by a mixed spinocerebellar and sensory ataxia, hypertrophic cardiomyopathy and increased incidence of diabetes. FRDA is caused by impaired expression of the FXN gene coding for the mitochondrial protein frataxin. During the past ten years, the development of mouse models of FRDA has allowed better understanding of the pathophysiology of the disease. Among the mouse models of FRDA, the liver conditional mouse model pointed to a tumor suppressor activity of frataxin leading to the hypothesis that individuals with FRDA might be predisposed to cancer. In the present work, we investigated the presence and the incidence of neoplasia in the largest FRDA patient cohorts from the USA, Australia and Europe. As no predisposition to cancer could be observed in both cohorts, we revisited the phenotype of the liver conditional mouse model. Our results show that frataxin-deficient livers developed early mitochondriopathy, iron-sulfur cluster deficits and intramitochondrial dense deposits, classical hallmarks observed in frataxin-deficient tissues and cells. With age, a minority of mice developed structures similar to the ones previously associated with tumor formation. However, these peripheral structures contained dying, frataxin-deficient hepatocytes, whereas the inner liver structure was composed of a pool of frataxin-positive cells, due to inefficient Cre-mediated recombination of the Fxn gene, that contributed to regeneration of a functional liver. Together, our data demonstrate that frataxin deficiency and tumorigenesis are not associated.
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Affiliation(s)
- Alain Martelli
- Translational Medecine and Neurogenetics, Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC), 67404 Illkirch, France
- INSERM, U596, 67404 Illkirch, France
- CNRS, UMR7104, 67404 Illkirch, France
- Université de Strasbourg, 67404 Illkirch, France
- Collège de France, Chaire de génétique humaine, 67404 Illkirch, France
| | - Lisa S. Friedman
- Department of Neurology, University of Pennsylvania, Philadelphia, PA 19104, USA
- Department of Pediatrics, University of Pennsylvania, Philadelphia, PA 19104, USA
- Division of Neurology, The Children’s Hospital of Philadelphia, Philadelphia, PA 19104, USA
| | - Laurence Reutenauer
- Translational Medecine and Neurogenetics, Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC), 67404 Illkirch, France
- INSERM, U596, 67404 Illkirch, France
- CNRS, UMR7104, 67404 Illkirch, France
- Université de Strasbourg, 67404 Illkirch, France
- Collège de France, Chaire de génétique humaine, 67404 Illkirch, France
| | - Nadia Messaddeq
- Translational Medecine and Neurogenetics, Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC), 67404 Illkirch, France
- INSERM, U596, 67404 Illkirch, France
- CNRS, UMR7104, 67404 Illkirch, France
- Université de Strasbourg, 67404 Illkirch, France
- Collège de France, Chaire de génétique humaine, 67404 Illkirch, France
| | - Susan L. Perlman
- University of California Los Angeles (UCLA), Los Angeles, CA 90095, USA
| | - David R. Lynch
- Department of Neurology, University of Pennsylvania, Philadelphia, PA 19104, USA
- Department of Pediatrics, University of Pennsylvania, Philadelphia, PA 19104, USA
- Division of Neurology, The Children’s Hospital of Philadelphia, Philadelphia, PA 19104, USA
| | - Kathrin Fedosov
- Department of Neurology, University Hospital Aachen, 52074 Aachen, Germany
| | - Jörg B. Schulz
- Department of Neurology, University Hospital Aachen, 52074 Aachen, Germany
| | - Massimo Pandolfo
- Laboratoire de Neurologie Expérimentale, Hôpital Erasme, Université Libre de Bruxelles, 1070 Brussels, Belgium
| | - Hélène Puccio
- Translational Medecine and Neurogenetics, Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC), 67404 Illkirch, France
- INSERM, U596, 67404 Illkirch, France
- CNRS, UMR7104, 67404 Illkirch, France
- Université de Strasbourg, 67404 Illkirch, France
- Collège de France, Chaire de génétique humaine, 67404 Illkirch, France
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Regner SR, Wilcox N, Friedman LS, Seyer L, Schadt K, Brigatti KW, Perlman S, Delatycki M, Wilmot GR, Gomez CM, Bushara KO, Mathews KD, Subramony S, Ashizawa T, Ravina B, Brocht A, Farmer JM, Lynch DR. Friedreich ataxia clinical outcome measures: natural history evaluation in 410 participants. J Child Neurol 2012; 27:1152-8. [PMID: 22752494 PMCID: PMC3674496 DOI: 10.1177/0883073812448462] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Friedreich ataxia is an autosomal recessive neurodegenerative disorder characterized by ataxia, dysarthria, and areflexia. The authors report the progress of a large international noninterventional cohort (n = 410), tracking the natural history of disease progression using the neurologic examination-based Friedreich Ataxia Rating Scale. The authors analyzed the rate of progression with cross-sectional analysis and longitudinal analysis over a 2-year period. The Friedreich Ataxia Rating Scale captured disease progression when used at 1 and 2 years following initial evaluation, with a lower ratio of standard deviation of change to mean change over 2 years of evaluation. However, modeling of disease progression identified substantial ceiling effects in the Friedreich Ataxia Rating Scale, suggesting this measure is most useful in subjects before maximal deficit is approached.
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Affiliation(s)
- Sean R. Regner
- Department of Neurology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania
- Department of Pediatrics, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania
- Children’s Hospital of Philadelphia, Philadelphia, Pennsylvania
| | - Nicholas Wilcox
- Children’s Hospital of Philadelphia, Philadelphia, Pennsylvania
| | - Lisa S. Friedman
- Department of Neurology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania
- Department of Pediatrics, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania
- Children’s Hospital of Philadelphia, Philadelphia, Pennsylvania
| | - Lauren Seyer
- Department of Neurology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania
- Department of Pediatrics, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania
- Children’s Hospital of Philadelphia, Philadelphia, Pennsylvania
| | - Kim Schadt
- Department of Neurology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania
- Department of Pediatrics, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania
- Children’s Hospital of Philadelphia, Philadelphia, Pennsylvania
| | - Karlla W. Brigatti
- Department of Neurology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania
- Department of Pediatrics, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania
- Children’s Hospital of Philadelphia, Philadelphia, Pennsylvania
| | - Susan Perlman
- Department of Neurology, David Geffen School of Medicine at UCLA, Los Angeles, California
| | - Martin Delatycki
- Murdoch Children’s Research Institute, Melbourne, Victoria, Australia
| | | | | | - Khalaf O. Bushara
- Department of Neurology, University of Minnesota, Minneapolis, Minnesota
| | | | - S.H. Subramony
- Department of Neurology, University of Florida, Gainesville, Florida
| | - Tetsuo Ashizawa
- Department of Neurology, University of Florida, Gainesville, Florida
| | - Bernard Ravina
- Department of Neurology, University of Rochester, Rochester, New York
| | - Alicia Brocht
- Department of Neurology, University of Rochester, Rochester, New York
| | - Jennifer M. Farmer
- Department of Neurology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania
- Department of Pediatrics, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania
- Children’s Hospital of Philadelphia, Philadelphia, Pennsylvania
- Friedreich Ataxia Research Alliance, Downingtown, Pennsylvania
| | - David R. Lynch
- Department of Neurology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania
- Department of Pediatrics, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania
- Children’s Hospital of Philadelphia, Philadelphia, Pennsylvania
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145
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Abstract
Friedreich ataxia is the most common inherited ataxia, with a wide phenotypic spectrum. It is generally caused by GAA expansions on both alleles of FXN, but a small percentage of patients are compound heterozygotes for a pathogenic expansion and a point mutation. Two recent diagnostic innovations are further characterizing individuals with the phenotype but without the classic genotypes. First, lateral-flow immunoassay is able to quantify the frataxin protein, thereby further characterizing these atypical individuals as likely affected or not affected, and providing some correlation to phenotype. It also holds promise as a biomarker for clinical trials in which the investigative agent increases frataxin. Second, gene dosage analysis and the identification of affected individuals with gene deletions introduce a novel genetic mechanism of disease. Both tests are now clinically available and suggest a new diagnostic paradigm for the disorder. Genetic counseling issues and future diagnostic testing approaches are considered as well.
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Affiliation(s)
- Karlla W. Brigatti
- Department of Neurology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania
- Department of Pediatrics, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania
- Children’s Hospital of Philadelphia, Philadelphia, Pennsylvania
| | - Eric C. Deutsch
- Department of Neurology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania
- Department of Pediatrics, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania
- Children’s Hospital of Philadelphia, Philadelphia, Pennsylvania
| | - David R. Lynch
- Department of Neurology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania
- Department of Pediatrics, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania
- Children’s Hospital of Philadelphia, Philadelphia, Pennsylvania
| | - Jennifer M. Farmer
- Department of Neurology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania
- Department of Pediatrics, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania
- Children’s Hospital of Philadelphia, Philadelphia, Pennsylvania
- Friedreich Ataxia Research Alliance, Downingtown, Pennsylvania
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146
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Abstract
Friedreich ataxia is a rare disorder characterized by an autosomal recessive pattern of inheritance. The disease is noted for a constellation of clinical symptoms, notably loss of coordination and a variety of neurologic and cardiac complications. More recently, scientists have focused their research on an array of general investigations of the underlying cellular basis for the disease, including mitochondrial biogenesis, iron-sulfur cluster synthesis, iron metabolism, antioxidant responses, and mitophagy. Combined with investigations that have explored the pathogenesis of the disease and the function of the protein frataxin, these studies have led to insights that will be key to identifying new therapeutic strategies for treating the disease.
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Affiliation(s)
- Massimo Pandolfo
- Université Libre de Bruxelles, Hôpital Erasme, Brussels, Belgium.
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147
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Abstract
Friedreich ataxia, the most common hereditary ataxia, affects approximately 1 per 29,000 white individuals. In about 98% of these individuals, it is due to homozygosity for a GAA trinucleotide repeat expansion in intron 1 of FXN; in the other 2%, it is due to compound heterozygosity for a GAA expansion and point mutation or deletion. The condition affects multiple sites in the central and peripheral nervous system as well as a number of other organ systems, resulting in multiple signs and symptoms. Onset of this autosomal recessive condition is usually in the first 2 decades of life. Major clinical features include progressive ataxia, absent lower limb reflexes, upgoing plantar responses, and peripheral sensory neuropathy. The main nonneurological sites of morbidity are the heart, resulting in cardiomyopathy, and the pancreas, resulting in diabetes mellitus. In this review, we provide an overview of the clinical features of Friedreich ataxia and discuss differential diagnoses.
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Affiliation(s)
- Martin B Delatycki
- Bruce Lefroy Centre for Genetic Health Research, Murdoch Childrens Research Institute, Parkville, VIC, Australia.
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148
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Schadt KA, Friedman LS, Regner SR, Mark GE, Lynch DR, Lin KY. Cross-sectional analysis of electrocardiograms in a large heterogeneous cohort of Friedreich ataxia subjects. J Child Neurol 2012; 27:1187-92. [PMID: 22752487 PMCID: PMC3674639 DOI: 10.1177/0883073812448461] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Electrocardiographic (ECG) findings in Friedreich ataxia and their relation to disease characteristics have not been well described. In this retrospective cross-sectional study, the authors reviewed baseline ECGs from 239 children and adults with Friedreich ataxia. ECG abnormalities--assessed in relation to participant age, sex, shorter guanine-adenine-adenine triplet repeat length, age of disease onset, and functional disability score--were found in 90% of subjects, including nonspecific ST-T wave changes (53%), right axis deviation (32%), left ventricular hypertrophy (19%), and right ventricular hypertrophy (13%). Female sex and shorter guanine-adenine-adenine repeat lengths were associated with a normal ECG (P = .004 and P = .003). Males and those of younger age were more likely to show ventricular hypertrophy (P = .006 and P = .026 for left ventricular hypertrophy and P < .001 and P = .001 for right). Neurologic status as measured by the functional disability score did not predict ECG abnormalities.
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Affiliation(s)
- Kimberly A. Schadt
- Department of Pediatrics, Division of Neurology, Children’s Hospital of Philadelphia, Pennsylvania,Department of Neurology, University of Pennsylvania, Philadelphia, Pennsylvania
| | - Lisa S. Friedman
- Department of Pediatrics, Division of Neurology, Children’s Hospital of Philadelphia, Pennsylvania,Department of Neurology, University of Pennsylvania, Philadelphia, Pennsylvania
| | - Sean R. Regner
- Department of Pediatrics, Division of Neurology, Children’s Hospital of Philadelphia, Pennsylvania,Department of Neurology, University of Pennsylvania, Philadelphia, Pennsylvania
| | - George E. Mark
- Department of Cardiology, Cooper University Hospital, Camden, New Jersey
| | - David R. Lynch
- Department of Pediatrics, Division of Neurology, Children’s Hospital of Philadelphia, Pennsylvania,Department of Neurology, University of Pennsylvania, Philadelphia, Pennsylvania
| | - Kimberly Y. Lin
- Department of Pediatrics, Division of Cardiology, Children’s Hospital of Philadelphia, Pennsylvania
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149
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Abstract
During the past 15 years, the pace of research advancement in Friedreich ataxia has been rapid. The abnormal gene has been discovered and its gene product characterized, leading to the development of new evidence-based therapies. Still, various unsettled issues remain that affect clinical trials. These include the level of frataxin deficiency needed to cause disease, the mechanism by which frataxin-deficient mitochondrial dysfunction leads to symptomatology, and the reason selected cells are most affected in Friedreich ataxia. In this review, we summarize these questions and propose testable hypotheses for their resolution.
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Affiliation(s)
- David R Lynch
- Department of Neurology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA.
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150
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Bettencourt C, Quintáns B, Ros R, Ampuero I, Yáñez Z, Pascual SI, de Yébenes JG, Sobrido MJ. Revisiting genotype-phenotype overlap in neurogenetics: Triplet-repeat expansions mimicking spastic paraplegias. Hum Mutat 2012; 33:1315-23. [DOI: 10.1002/humu.22148] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2012] [Accepted: 06/06/2012] [Indexed: 01/12/2023]
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