201
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Abstract
There is compelling evidence for the direct involvement of mitochondria in certain neurodegenerative disorders, such as Morbus Parkinson, FRDA (Friedreich's ataxia), ALS (amyotrophic lateral sclerosis), and temporal lobe epilepsy with Ammon's horn sclerosis. This evidence includes the direct genetic evidence of pathogenic mutations in mitochondrial proteins in inherited Parkinsonism {such as PARK6, with mutations in the mitochondrial PINK1 [PTEN (phosphatase and tensin homologue deleted on chromosome 10)-induced kinase 1]} and in FRDA (with mutations in the mitochondrial protein frataxin). Moreover, there is functional evidence of impairment of the respiratory chain in sporadic forms of Parkinsonism, ALS, and temporal lobe epilepsy with Ammon's horn sclerosis. In the sporadic forms of the above-mentioned neurodegenerative disorders, increased oxidative stress appears to be the crucial initiating event that affects respiratory chain function and starts a vicious cycle finally leading to neuronal cell death. We suggest that the critical factor that determines the survival of neurons in neurodegenerative disorders is the degree of mitochondrial DNA damage and the maintenance of an appropriate mitochondrial DNA copy number. Evidence for a depletion of intact copies of the mitochondrial genome has been provided in all above-mentioned neurodegenerative disorders including ALS and temporal lobe epilepsy with Ammon's horn sclerosis. In the present study, we critically review the available data.
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202
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Condò I, Ventura N, Malisan F, Rufini A, Tomassini B, Testi R. In vivo maturation of human frataxin. Hum Mol Genet 2007; 16:1534-40. [PMID: 17468497 DOI: 10.1093/hmg/ddm102] [Citation(s) in RCA: 95] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The defective expression of frataxin causes the hereditary neurodegenerative disorder Friedreich's ataxia (FRDA). Human frataxin is synthesized as a 210 amino acid precursor protein, which needs proteolytic processing into mitochondria to be converted into the functional mature form. In vitro processing of human frataxin was previously described to yield a 155 amino acid mature form, corresponding to residues 56-210 (frataxin(56-210)). Here, we studied the maturation of frataxin by in vivo overexpression in human cells. Our data show that the main form of mature frataxin is generated by a proteolytic cleavage between Lys80 and Ser81, yielding a 130 amino acid protein (frataxin(81-210)). This maturation product corresponds to the endogenous frataxin detected in human heart, peripheral blood lymphocytes or dermal fibroblasts. Moreover, we demonstrate that frataxin(81-210) is biologically functional, as it rescues aconitase defects in frataxin-deficient cells derived from FRDA patients. Importantly, our data indicate that frataxin(56-210) can be produced in vivo when the primary 80-81 maturation site is unavailable, suggesting the existence of proteolytic mechanisms that can actively control the size of the mature product, with possible functional implications.
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Affiliation(s)
- Ivano Condò
- Laboratory of Signal Transduction, Department of Experimental Medicine and Biochemical Sciences, University of Rome Tor Vergata, Rome, Italy
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203
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Lim F, Palomo GM, Mauritz C, Giménez-Cassina A, Illana B, Wandosell F, Díaz-Nido J. Functional recovery in a Friedreich's ataxia mouse model by frataxin gene transfer using an HSV-1 amplicon vector. Mol Ther 2007; 15:1072-8. [PMID: 17375064 DOI: 10.1038/sj.mt.6300143] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
There is currently no effective treatment for Friedreich's ataxia (FA), the most common of the hereditary ataxias. The disease is caused by mutations in FRDA that drastically reduce expression levels of the mitochondrial protein frataxin. In FA animal models, a key difficulty is obtaining the precise levels of frataxin expression in the appropriate tissues to provoke pathology without early lethality. To develop strategies to circumvent these problems, conditional frataxin transgenic mice have been generated. We now show that frataxin expression can be eliminated in neurons from these loxP[frda] mice by infection with CRE-expressing herpes simplex virus type 1 (HSV-1) amplicon vectors. We have also achieved in vivo delivery by stereotaxic injection of these CRE-expressing vectors into the brainstem of loxP[frda] mice to generate a localized gene knockout model. These mice develop a behavioral deficit in the rotarod assay detectable after 4 weeks, and when re-injected with HSV-1 amplicon vectors expressing human frataxin complementary DNA (cDNA) exhibit behavioral recovery as early as 4 weeks after the second injection. To the best of our knowledge, this is the first proof of principle of recovery of neurological function by a therapeutic agent aimed at correcting frataxin deficiency.
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Affiliation(s)
- Filip Lim
- Departamento de Biología Molecular, Centro de Biología Molecular Severo Ochoa (CSIC-UAM), Universidad Autónoma de, Madrid, Madrid, Spain.
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204
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Shan Y, Napoli E, Cortopassi G. Mitochondrial frataxin interacts with ISD11 of the NFS1/ISCU complex and multiple mitochondrial chaperones. Hum Mol Genet 2007; 16:929-41. [PMID: 17331979 DOI: 10.1093/hmg/ddm038] [Citation(s) in RCA: 116] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The neurodegenerative disorder Friedreich's ataxia (FRDA) is caused by mutations in frataxin, a mitochondrial protein whose function remains controversial. Using co-immunoprecipitation and mass spectrometry we identified multiple interactors of mitochondrial frataxin in mammalian cells. One interactor was mortalin/GRP75, a homolog of the yeast ssq1 chaperone that integrates iron-sulfur clusters into imported mitochondrial proteins. Another interactor was ISD11, recently identified as a component of the eukaryotic complex Nfs1/ISCU, an essential component of iron-sulfur cluster biogenesis. Interactions between frataxin and ISD11, and frataxin and GRP75 were confirmed by co-immunoprecipitation experiments in both directions. Immunofluorescence analysis demonstrated that ISD11 co-localized with both frataxin and with mitochondria. The point mutations I154F and W155R in frataxin cause FRDA and are clustered to one surface of the protein, and these mutations decrease the interaction of frataxin with ISD11. The frataxin/ISD11 interaction was also decreased by the chelator EDTA, and was increased by supplementation with nickel but not other metal ions. Nickel supplementation rescued the defective interaction of mutant frataxin I154F and W155R with ISD11. Upon ISD11 depletion by siRNA in HEK293T cells, the amount of the Nfs1/ISCU protein complex declined, as did the activity of the iron-sulfur cluster enzyme aconitase, while the cellular iron content was increased, as seen in tissues from FRDA patients. Furthermore, ISD11 mRNA levels were decreased in FRDA patient cells. These data suggest that frataxin binds the iron-sulfur biogenesis Nfs1/ISCU complex through ISD11, that the interaction is nickel-dependent, and that multiple consequences of frataxin deficiency are duplicated by ISD11 deficiency.
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Affiliation(s)
- Yuxi Shan
- VM:Molecular Biosciences, 1311 Haring Hall, Davis, CA 95616, USA
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205
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Trushina E, McMurray CT. Oxidative stress and mitochondrial dysfunction in neurodegenerative diseases. Neuroscience 2007; 145:1233-48. [PMID: 17303344 DOI: 10.1016/j.neuroscience.2006.10.056] [Citation(s) in RCA: 323] [Impact Index Per Article: 19.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2006] [Revised: 10/24/2006] [Accepted: 10/27/2006] [Indexed: 11/16/2022]
Abstract
In recent years, it has become increasingly clear that mitochondrial dysfunction and oxidative damage are major contributors to neuronal loss. Free radicals, typically generated from mitochondrial respiration, cause oxidative damage of nucleic acids, lipids, carbohydrates and proteins. Despite enormous amount of effort, however, the mechanism by which oxidative damage causes neuronal death is not well understood. Emerging data from a number of neurodegenerative diseases suggest that there may be common features of toxicity that are related to oxidative damage. In this review, while focusing on Huntington's disease (HD), we discuss similarities among HD, Friedreich ataxia and xeroderma pigmentosum, which provide insight into shared mechanisms of neuronal death.
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Affiliation(s)
- E Trushina
- Department of Molecular Pharmacology and Experimental Therapeutics, Mayo Clinic, 200 First Street SW, Rochester, MN 55905, USA
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206
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Palau F, Espinós C. Autosomal recessive cerebellar ataxias. Orphanet J Rare Dis 2006; 1:47. [PMID: 17112370 PMCID: PMC1664553 DOI: 10.1186/1750-1172-1-47] [Citation(s) in RCA: 111] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2006] [Accepted: 11/17/2006] [Indexed: 02/06/2023] Open
Abstract
Autosomal recessive cerebellar ataxias (ARCA) are a heterogeneous group of rare neurological disorders involving both central and peripheral nervous system, and in some case other systems and organs, and characterized by degeneration or abnormal development of cerebellum and spinal cord, autosomal recessive inheritance and, in most cases, early onset occurring before the age of 20 years. This group encompasses a large number of rare diseases, the most frequent in Caucasian population being Friedreich ataxia (estimated prevalence 2–4/100,000), ataxia-telangiectasia (1–2.5/100,000) and early onset cerebellar ataxia with retained tendon reflexes (1/100,000). Other forms ARCA are much less common. Based on clinicogenetic criteria, five main types ARCA can be distinguished: congenital ataxias (developmental disorder), ataxias associated with metabolic disorders, ataxias with a DNA repair defect, degenerative ataxias, and ataxia associated with other features. These diseases are due to mutations in specific genes, some of which have been identified, such as frataxin in Friedreich ataxia, α-tocopherol transfer protein in ataxia with vitamin E deficiency (AVED), aprataxin in ataxia with oculomotor apraxia (AOA1), and senataxin in ataxia with oculomotor apraxia (AOA2). Clinical diagnosis is confirmed by ancillary tests such as neuroimaging (magnetic resonance imaging, scanning), electrophysiological examination, and mutation analysis when the causative gene is identified. Correct clinical and genetic diagnosis is important for appropriate genetic counseling and prognosis and, in some instances, pharmacological treatment. Due to autosomal recessive inheritance, previous familial history of affected individuals is unlikely. For most ARCA there is no specific drug treatment except for coenzyme Q10 deficiency and abetalipoproteinemia.
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Affiliation(s)
- Francesc Palau
- Genetics and Molecular Medicine Unit, Instituto de Biomedicina, CSIC, Jaume Roig, 11 46010 Valencia, Spain
- Centre for Biomedical Research on Rare Diseases (CIBERER), Instituto de Salud Carlos III, Valencia, Spain
| | - Carmen Espinós
- Genetics and Molecular Medicine Unit, Instituto de Biomedicina, CSIC, Jaume Roig, 11 46010 Valencia, Spain
- Centre for Biomedical Research on Rare Diseases (CIBERER), Instituto de Salud Carlos III, Valencia, Spain
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207
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Correia A, Adinolfi S, Pastore A, Gomes C. Conformational stability of human frataxin and effect of Friedreich's ataxia-related mutations on protein folding. Biochem J 2006; 398:605-11. [PMID: 16787388 PMCID: PMC1559467 DOI: 10.1042/bj20060345] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2006] [Revised: 06/06/2006] [Accepted: 06/21/2006] [Indexed: 11/17/2022]
Abstract
The neurodegenerative disorder FRDA (Friedreich's ataxia) results from a deficiency in frataxin, a putative iron chaperone, and is due to the presence of a high number of GAA repeats in the coding regions of both alleles of the frataxin gene, which impair protein expression. However, some FRDA patients are heterozygous for this triplet expansion and contain a deleterious point mutation on the other allele. In the present study, we investigated whether two particular FRDA-associated frataxin mutants, I154F and W155R, result in unfolded protein as a consequence of a severe structural modification. A detailed comparison of the conformational properties of the wild-type and mutant proteins combining biophysical and biochemical methodologies was undertaken. We show that the FRDA mutants retain the native fold under physiological conditions, but are differentially destabilized as reflected both by their reduced thermodynamic stability and a higher tendency towards proteolytic digestion. The I154F mutant has the strongest effect on fold stability as expected from the fact that the mutated residue contributes to the hydrophobic core formation. Functionally, the iron-binding properties of the mutant frataxins are found to be partly impaired. The apparently paradoxical situation of having clinically aggressive frataxin variants which are folded and are only significantly less stable than the wild-type form in a given adverse physiological stress condition is discussed and contextualized in terms of a mechanism determining the pathology of FRDA heterozygous.
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Affiliation(s)
- Ana R. Correia
- *Instituto Tecnologia Química e Biológica, Universidade Nova de Lisboa, Av. República 127, 2780-756 Oeiras, Portugal
| | - Salvatore Adinolfi
- †National Institute for Medical Research, Medical Research Council, London, U.K
| | - Annalisa Pastore
- †National Institute for Medical Research, Medical Research Council, London, U.K
| | - Cláudio M. Gomes
- *Instituto Tecnologia Química e Biológica, Universidade Nova de Lisboa, Av. República 127, 2780-756 Oeiras, Portugal
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208
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Bencze KZ, Kondapalli KC, Cook JD, McMahon S, Millán-Pacheco C, Pastor N, Stemmler TL. The structure and function of frataxin. Crit Rev Biochem Mol Biol 2006; 41:269-91. [PMID: 16911956 PMCID: PMC2859089 DOI: 10.1080/10409230600846058] [Citation(s) in RCA: 126] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
Frataxin, a highly conserved protein found in prokaryotes and eukaryotes, is required for efficient regulation of cellular iron homeostasis. Humans with a frataxin deficiency have the cardio- and neurodegenerative disorder Friedreich's ataxia, commonly resulting from a GAA trinucleotide repeat expansion in the frataxin gene. While frataxin's specific function remains a point of controversy, the general consensus is that the protein assists in controlling cellular iron homeostasis by directly binding iron. This review focuses on the structural and biochemical aspects of iron binding by the frataxin orthologs and outlines molecular attributes that may help explain the protein's role in different cellular pathways.
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Affiliation(s)
- Krisztina Z Bencze
- Department of Biochemistry and Molecular Biology, Wayne State University, School of Medicine, Detroit, Michigan 48201, USA
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209
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Abstract
Friedreich ataxia is the most common hereditary ataxia. The signs and symptoms of the disorder derive from decreased expression of the protein frataxin, which is involved in iron metabolism. Frataxin chaperones iron for iron-sulfur cluster biogenesis and detoxifies iron in the mitochondrial matrix. Decreased expression of frataxin is associated with impairments of iron-sulfur cluster biogenesis and heme synthesis, as well as with mitochondrial dysfunction and oxidative stress. Compounds currently in clinical trials are directed toward improving mitochondrial function and lessening oxidative stress. Iron chelators and compounds that increase frataxin expression are under evaluation. Further elucidation of frataxin's function should lead to additional therapeutic approaches.
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Affiliation(s)
- Robert B Wilson
- Department of Pathology and Laboratory Medicine, University of Pennsylvania, Philadelphia, PA 19106, USA.
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210
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Yilmaz MB, Koç AF, Kasap H, Güzel AI, Sarica Y, Süleymanova D. GAA repeat polymorphism in Turkish Friedreich's ataxia patients. Int J Neurosci 2006; 116:565-74. [PMID: 16644517 DOI: 10.1080/00207450600592099] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
Friedreich's ataxia (FRDA), the most common subtype of early onset hereditary spinocerebellar ataxia (SCA), is an autosomal recessive neurodegenerative disorder caused by unstable GAA tri-nucleotide expansions in the first intron of FRDA gene located at 9q13-q21.1 position. Results of GAA repeat polymorphism in 80 Turkish SCA patients and 38 family members of 11 typical FRDA patients were reported. GAA triplet repeat size ranged from approximately 7 to 34 in normal alleles and from approximately 66 to 1300 in mutant alleles. Twenty six patients were homozygous for GAA expansion and size of expanded alleles differed from approximately 425 to 1300 repeats. Children 2 and 6 years old (showing no ataxia symptoms) of one family had homozygous GAA expansions reaching approximately 925 repeats. All 11 families studied had at least 1 afflicted child and 9 parents and 2 siblings were carrier (heterozygous) with mutant alleles ranging from 66 to 850 repeats. Family studies confirmed the meiotic instability and stronger effect of expansion in the smaller alleles on phenotype and a negative correlation between GAA repeat expansion size and onset-age of the disease.
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Affiliation(s)
- M Bertan Yilmaz
- Department of Medical Biology and Genetics Medical School Cukurova University, Adana, Turkey
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211
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Kraft S, Furtado S, Ranawaya R, Parboosingh J, Bleoo S, McElligott K, Bridge P, Spacey S, Das S, Suchowersky O. Adult onset spinocerebellar ataxia in a Canadian movement disorders clinic. Can J Neurol Sci 2006; 32:450-8. [PMID: 16408574 DOI: 10.1017/s0317167100004431] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
BACKGROUND The spinocerebellar ataxias (SCAs) are a genetically and clinically heterogeneous group of neurodegenerative disorders. Relative frequencies vary within different ethnic groups and geographical locations. OBJECTIVES 1) To determine the frequencies of hereditary and sporadic adult onset SCAs in the Movement Disorders population; 2) to assess if the fragile X mental retardation gene 1 (FMR1) premutation is found in this population. METHODS A retrospective chart review of individuals with a diagnosis of adult onset SCA was carried out. Testing for SCA types 1, 2, 3, 6, 7, and 8, Dentatorubral-pallidoluysian atrophy (DRPLA), Friedreich ataxia and the FMR1 expansion was performed. RESULTS A total of 69 patients in 60 families were identified. Twenty-one (35%) of the families displayed autosomal dominant and two (3.3%) showed autosomal recessive (AR) pattern of inheritance. A positive but undefined family history was noted in nine (15%). The disorder appeared sporadic in 26 patients (43.3%). In the AD families, the most common mutation was SCA3 (23.8%) followed by SCA2 (14.3%) and SCA6 (14.3%). The SCA1 and SCA8 were each identified in 4.8%. FA was found in a pseudodominant pedigree, and one autosomal recessive pedigree. One sporadic patient had a positive test (SCA3).Dentatorubral-pallidoluysian atrophy and FMR1 testing was negative. CONCLUSION A positive family history was present in 53.3% of our adult onset SCA patients. A specific genetic diagnosis could be given in 61.9% of dominant pedigrees with SCA3 being the most common mutation, followed by SCA2 and SCA6. The yield in sporadic cases was low. The fragile X premutation was not found to be responsible for SCA.
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Affiliation(s)
- Scott Kraft
- Movement Disorsders program, Department of Clinical Neurosciences, University of Calgary, Calgary, Alberta, Canada
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212
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Friedreich's ataxia and other autosomal recessive ataxias. NEURODEGENER DIS 2005. [DOI: 10.1017/cbo9780511544873.049] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022] Open
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213
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van de Warrenburg BPC, Sinke RJ, Kremer B. Recent advances in hereditary spinocerebellar ataxias. J Neuropathol Exp Neurol 2005; 64:171-80. [PMID: 15804048 DOI: 10.1093/jnen/64.3.171] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
In recent years, molecular genetic research has unraveled a major part of the genetic background of autosomal dominant and recessive spinocerebellar ataxias. These advances have also allowed insight in (some of) the pathophysiologic pathways assumed to be involved in these diseases. For the clinician, the expanding number of genes and genetic loci in these diseases and the enormous clinical heterogeneity of specific ataxia subtypes complicate management of ataxia patients. In this review, the clinical and neuropathologic features of the recently identified spinocerebellar ataxias are described, and the various molecular mechanisms that have been demonstrated to be involved in these disorders are discussed.
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214
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Nair M, Adinolfi S, Pastore C, Kelly G, Temussi P, Pastore A. Solution structure of the bacterial frataxin ortholog, CyaY: mapping the iron binding sites. Structure 2005; 12:2037-48. [PMID: 15530368 DOI: 10.1016/j.str.2004.08.012] [Citation(s) in RCA: 107] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2004] [Revised: 08/05/2004] [Accepted: 08/31/2004] [Indexed: 11/26/2022]
Abstract
CyaY is the bacterial ortholog of frataxin, a small mitochondrial iron binding protein thought to be involved in iron sulphur cluster formation. Loss of frataxin function leads to the neurodegenerative disorder Friedreich's ataxia. We have solved the solution structure of CyaY and used the structural information to map iron binding onto the protein surface. Comparison of the behavior of wild-type CyaY with that of a mutant indicates that specific binding with a defined stoichiometry does not require aggregation and that the main binding site, which hosts both Fe(2+) and Fe(3+), occupies a highly anionic surface of the molecule. This function is conserved across species since the corresponding region of human frataxin is also able to bind iron, albeit with weaker affinity. The presence of secondary binding sites on CyaY, but not on frataxin, hints at a possible polymerization mechanism. We suggest mutations that may provide further insights into the frataxin function.
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Affiliation(s)
- Margie Nair
- Division of Molecular Structure, The Ridgeway, London, NW7 1AA, United Kingdom
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215
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Gómez M, Clark RM, Nath SK, Bhatti S, Sharma R, Alonso E, Rasmussen A, Bidichandani SI. Genetic admixture of European FRDA genes is the cause of Friedreich ataxia in the Mexican population. Genomics 2005; 84:779-84. [PMID: 15475256 DOI: 10.1016/j.ygeno.2004.07.014] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2004] [Accepted: 07/25/2004] [Indexed: 10/26/2022]
Abstract
Friedreich ataxia accounts for approximately 75% of European recessive ataxia patients. Approximately 98% of pathogenic chromosomes have large expansions of a GAA triplet repeat in the FRDA gene (E alleles), and strong linkage disequilibrium among polymorphisms spanning the FRDA locus indicates a common origin for all European E alleles. In contrast, we found that only 14 of 151 (9.3%) Mexican Mestizo patients with recessive ataxia were homozygous for E alleles. Analysis of polymorphisms spanning the FRDA locus revealed that all Mestizo E alleles had the common European haplotype, indicating that they share a single origin. Genetic admixture levels were determined, which revealed that the relative contributions to the Mestizo FRDA gene pool by Native American and European genes were 76-87% and 13-24%, respectively, commensurate with the observed low prevalence of Friedreich ataxia in Mestizos. This indicates that Friedreich ataxia in Mexican Mestizos is due to genetic admixture of European mutant FRDA genes in the Native American gene pool that existed prior to contact with Europeans.
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Affiliation(s)
- Mariluz Gómez
- Department of Biochemistry & Molecular Biology, University of Oklahoma Health Sciences Center, 975 NE, 10th Street, BRC458, Oklahoma City, OK 73104, USA
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216
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Subramony SH. GENETICS OF INHERITED ATAXIAS. Continuum (Minneap Minn) 2005. [DOI: 10.1212/01.con.0000293702.31088.0d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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217
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Lynch DR, Farmer JM, Wilson RL, Balcer LJ. Performance measures in Friedreich ataxia: Potential utility as clinical outcome tools. Mov Disord 2005; 20:777-82. [PMID: 15747359 DOI: 10.1002/mds.20449] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
Although several neuroprotective agents have been proposed as potential therapies in Friedreich ataxia (FA), clinical trials of their efficacy are limited by a lack of sensitive outcome measures. We assessed whether performance measures (nine-hole peg test, the timed 25-foot walk, and low-contrast letter acuity) provide valid measures of disease status in FA. Scores for each measure correlated significantly with neurologic disability and disease duration. Rank correlations between scores for performance measures were moderate in magnitude, suggesting that the each test captures separate yet related dimensions of neurological function in FA. Linear regression models demonstrated that scores from the nine-hole peg test and the timed 25-foot walk (after reciprocal transformation) were predicted by age and triplet repeat length in patients with FA. In addition, comparison of the temporal courses of change for each performance measure demonstrated that scores from the timed 25-foot walk change early in the course of FA, nine-hole peg test scores change slowly over the full course of the disorder, and low-contrast letter acuity scores change in the later stages of the disease. Thus, a composite scale derived from these performance measures may provide the best overall measure for assessing disease progression throughout the illness.
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Affiliation(s)
- David R Lynch
- Department of Neurology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104-4318, USA.
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218
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Badhwar A, Jansen A, Andermann F, Pandolfo M, Andermann E. Striking intrafamilial phenotypic variability and spastic paraplegia in the presence of similar homozygous expansions of the FRDA1 gene. Mov Disord 2004; 19:1424-31. [PMID: 15514925 DOI: 10.1002/mds.20264] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
We report on a Friedreich's ataxia (FA) family with 3 affected siblings with markedly different phenotypic presentations, including one with spastic paraplegia. Molecular analysis showed midsize GAA repeat expansion sizes in all 3 individuals. Gait spasticity in FA, although rare, has been described in a few patients who are compound heterozygotes for a point mutation, or who had GAA expansions of less than 200 repeats. The occurrence of spastic paraplegia in our family, in the presence of homozygous midsize GAA repeat expansions, is an unusual finding. Spasticity can be the main feature in both sporadic and familial patients with FA, either as an isolated finding, or in addition to other neurological abnormalities, and should be included as a rare feature in the clinical spectrum of FA. This family also demonstrates that in FA, marked intrafamilial phenotypic variability can arise in the presence of similar GAA expansion sizes. Therefore, in familial FA, the disease course in relatives therefore cannot be predicted solely from repeat length. Factors such as somatic mosaicism, repeat interruptions, modifying mutations and environmental factors must also be considered.
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Affiliation(s)
- Amanpreet Badhwar
- Neurogenetics Unit, Montreal Neurological Hospital and Institute, McGill University, Montreal, Quebec, Canada
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219
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Sharma R, De Biase I, Gómez M, Delatycki MB, Ashizawa T, Bidichandani SI. Friedreich ataxia in carriers of unstable borderline GAA triplet-repeat alleles. Ann Neurol 2004; 56:898-901. [PMID: 15562408 DOI: 10.1002/ana.20333] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Friedreich ataxia patients are homozygous for expanded GAA triplet-repeats containing 66 to 1,700 triplets. We report two patients with delayed-onset, hyperreflexia and gradually progressive disease. Both were heterozygous for large expansions and also carried alleles with 44 and 66 triplet-repeats, respectively. Due to somatic instability, 15% (GAA-44) and 75% (GAA-66) of cells contained alleles with >/=66 triplet-repeats, constituting a plausible mechanism for their mild phenotype. A sibling with a stable GAA-37 allele and a large expansion was clinically normal. Instability of borderline alleles confers a risk for Friedreich ataxia, and the range of pathogenic alleles is broader than previously recognized.
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Affiliation(s)
- Rajesh Sharma
- Department of Biochemistry & Molecular Biology, University of Oklahoma Health Sciences Center, Oklahoma City, OK, USA
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De Michele G, Coppola G, Cocozza S, Filla A. A pathogenetic classification of hereditary ataxias: is the time ripe? J Neurol 2004; 251:913-22. [PMID: 15316795 DOI: 10.1007/s00415-004-0484-2] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2004] [Accepted: 03/23/2004] [Indexed: 01/30/2023]
Abstract
Harding's classification takes credits for defining the homogeneous phenotypes that have been essential for the genetic linkage studies and it is still useful for didactic purposes. The advances in pathogenetic knowledge make it now possible to modify Harding's classification. Five main pathogenetic mechanisms may be distinguished: 1) mitochondrial; 2) metabolic; 3) defective DNA repair; 4) abnormal protein folding and degradation; 5) channelopathies. The present attempt to classify ataxia disorders according to their pathogenetic mechanism is a work in progress, since the pathogenesis of several disorders is still unknown. A pathogenetic classification may be useful in clinical practice and when new therapeutic strategies become available.
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Affiliation(s)
- Giuseppe De Michele
- Dipartimento di Scienze Neurologiche, Università degli Studi di Napoli Federico II, Via Pansini 5, 80131, Napoli, Italy
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221
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Spacey SD, Szczygielski BI, Young SP, Hukin J, Selby K, Snutch TP. Malaysian siblings with friedreich ataxia and chorea: a novel deletion in the frataxin gene. Can J Neurol Sci 2004; 31:383-6. [PMID: 15376485 DOI: 10.1017/s0317167100003498] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
BACKGROUND Friedrich ataxia (FRDA1) is most often the result of a homozygous GAA repeat expansion in the first intron of the frataxin gene (FRDA gene). This condition is seen in individuals of European, North African, Middle Eastern and Indian descent and has not been reported in Southeast Asian populations. Approximately 4% of FRDA1 patients are compound heterozygotes. These patients have a GAA expansion on one allele and a point mutation on the other and have been reported to have an atypical phenotype. OBJECTIVE To describe a novel dinucleotide deletion in the FRDA gene in two Malaysian siblings with FRDA1. SETTING Tertiary referral university hospital setting. PATIENTS AND METHODS A previously healthy 10-year-old Malaysian boy, presented with fever, lethargy, headaches, dysarthria, dysphagia, vertigo and ataxia which developed over a one week period. His neurological exam revealed evidence of dysarthria and ataxia, mild generalized weakness and choreoform movements of the tongue and hands. His reflexes were absent and Babinski sign was present bilaterally. A nine-year-old sister was found to have mild ataxia but was otherwise neurologically intact. RESULTS Molecular genetic studies demonstrated that both siblings were compound heterozygotes with a GAA expansion on one allele and a novel dinucleotide deletion on the other allele. CONCLUSIONS We describe a novel dinucleotide deletion in the first exon of the FRDA gene in two siblings with FRDA1. Additionally this is the first report of FRDA1 occurring in a family of southeast Asian descent, it demonstrates intrafamilial phenotypic variability, and confirms that atypical phenotypes are associated with compound heterozygosity.
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Affiliation(s)
- Siân D Spacey
- Division of Neurology, Biotechnology Laboratory, Brain Research Center, University of British Columbia, Canada
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222
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Affiliation(s)
- Franco Taroni
- Laboratory of Cell Pathology, IRCCS-Istituto Nazionale Neurologico Carlo Besta, via Celoria 11, 20133 Milan, Italy
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223
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Monticelli A, Giacchetti M, De Biase I, Pianese L, Turano M, Pandolfo M, Cocozza S. New clues on the origin of the Friedreich ataxia expanded alleles from the analysis of new polymorphisms closely linked to the mutation. Hum Genet 2004; 114:458-63. [PMID: 14767759 DOI: 10.1007/s00439-004-1089-7] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2003] [Accepted: 01/09/2004] [Indexed: 10/26/2022]
Abstract
Friedreich's ataxia (FRDA) is an autosomal recessive neurodegenerative disorder commonly caused by large expansions of a GAA repeat in the first intron of the frataxin gene, FRDA. The expansion of the triplet repeat is localized within an Alu sequence. FRDA GAA-repeat alleles can be divided into three classes depending on their lengths: short normal alleles (SN), long normal alleles (LN) and expanded pathological alleles (E). We made an accurate analysis of the Alu sequence containing the GAA repeat. We found a new single-nucleotide polymorphism (SNP) that is the closest one to the GAA repeat. We studied this new SNP and the polymorphic polyA region contiguous to the GAA triplets in two populations with different frequencies of FRDA. We found that, while both E and LN alleles seem to be genetically homogeneous and likely related, SN represents a more heterogeneous class of alleles. Indeed, one SNP variation (T) was more frequently associated with (GAA)(8) alleles, whereas the other one (C) with (GAA)(9) repeat(s). The long normal and expanded alleles presented the C haplotype. The same correlation was described for polyA-tract polymorphisms. Thus, 14A was commonly associated with (GAA)(8) alleles and 17A with (GAA)(9) alleles. The long normal alleles more frequently showed the 17A haplotype. Our data seem to suggest that all the E alleles come from LN alleles, while LN alleles come from a defined subclass of SN alleles.
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Affiliation(s)
- Antonella Monticelli
- Dipartimento di Biologia e Patologia Cellulare e Molecolare, L. Califano Università Federico II, Via S. Pansini 5, 80131 Naples, Italy
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224
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Schöls L, Meyer C, Schmid G, Wilhelms I, Przuntek H. Therapeutic strategies in Friedreich’s ataxia. ACTA ACUST UNITED AC 2004:135-45. [PMID: 15354399 DOI: 10.1007/978-3-7091-0579-5_16] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/18/2023]
Abstract
Friedreich's ataxia is caused by a pronounced lack of frataxin, a mitochondrial protein of not fully understood function. Lack of frataxin homologues in yeast and mice leads to increased sensitivity to oxidative stress, depletion of proteins with iron-sulfur clusters like respiratory chain complexes I-III and aconitase, and to iron accumulation in mitochondria. Similar effects have been demonstrated in human disease with increased markers of oxidative DNA damage in urine and impaired oxidative phosphorylation in in vivo exercise studies using 31 Phosphorus magnetic resonance spectroscopy (31P-MRS). Therapeutical trials mainly focus on antioxidative treatment with coenzyme Q10 or its short-chain variant idebenone. Promising effects on cardiac hypertrophy in uncontrolled preliminary studies contrast with minor effects in controlled trials and no effect of antioxidants on neurological deficits has been established. Preliminary encouraging 31P-MRS data exist for the treatment with L-carnitine but not with creatine. However, all these interventions may take effect too late in the pathogenic process. Alternative strategies aiming at an enhancement of frataxin by stem cell transplantation, gene transfer or frataxin supplementation are desirable. Additionally, more efficient biomarkers are needed to monitor treatment effects.
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Affiliation(s)
- L Schöls
- Center of Neurology and Hertie-Institute for Clinical Brain Research, University of Tübingen, Germany.
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225
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Abstract
There has been rapid progress in the understanding of several aspects of Friedreich's ataxia (FA) since the gene mutation was identified in 1996. At the clinical level, now it is possible to confirm that the majority of patients fullfilling clinical criteria for classic FA have the FA gene mutation but some do not, indicating genetic heterogeneity. Also, the phenotype associated with the FA mutation is much wider than that defined by clinical criteria and includes ataxia with retained or brisk reflexes as well as late onset ataxia with or without retained reflexes. It is now clear that the unstable GAA expansion that underlies FA causes a deficiency of the mitochondrial protein frataxin, leading to potentially harmful oxidative injury associated with excessive iron deposits in mitochondria. In addition, pathogenesis may involve a primary defect in synthesis of iron-sulfur cluster containing enzymes. Therapeutic attempts are already using anti-oxidant strategies and such efforts are likely to be enhanced by the rapid availability of animal models of the disease.
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Affiliation(s)
- Massimo Pandolfo
- Department of Neurology, Erasme Hospital, Brussels Free University, Brussels, Belgium
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226
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Pandolfo M. The molecular basis of Friedreich ataxia. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2003; 516:99-118. [PMID: 12611437 DOI: 10.1007/978-1-4615-0117-6_5] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/01/2023]
Affiliation(s)
- Massimo Pandolfo
- Centre Hospitalier de lé Université de Montréal, Hopital Notre-Dame, 1560 rue Sherbrooke Est, Montréal, Québec H2L 4M1 Canada
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227
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Affiliation(s)
- J M Cooper
- Department of Clinical Neuroscience, Royal Free & University College Medical School, London, NW3 2PF, United Kingdom
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228
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Abstract
Since the discovery of the gene mutation causing Friedreich's ataxia (FA), the rich spectrum of clinical manifestations of this autosomal recessive disorder is being increasingly recognized. Movement disorders besides ataxia, however, have not been fully characterized in patients with FA. We describe here two young male patients who, in addition to progressive ataxia, kinetic tremor and other typical features of FA, also manifest axial and limb dystonia. The primary purpose of this report is to draw attention to the broad spectrum of hyperkinetic movement disorders that can present as or be associated with FA.
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Affiliation(s)
- Jyh-Gong Gabriel Hou
- Parkinson's Disease Center and Movement Disorders Clinic, Department of Neurology, Baylor College of Medicine, 6550 Fannin, #1801, Houston, TX 77030, USA
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229
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Gasser T, Bressman S, Dürr A, Higgins J, Klockgether T, Myers RH. State of the art review: molecular diagnosis of inherited movement disorders. Movement Disorders Society task force on molecular diagnosis. Mov Disord 2003; 18:3-18. [PMID: 12518296 DOI: 10.1002/mds.10338] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
This review is designed to provide practical help for the clinical neurologist to make appropriate use of the possibilities of molecular diagnosis of inherited movement disorders. Huntington's disease, Parkinson's disease and parkinsonian syndromes, ataxias, Wilson disease, essential tremor, dystonias, and other genetic diseases associated with a variety of movement disorders are considered separately.
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Affiliation(s)
- Thomas Gasser
- Department of Neurology, Klinikum Grosshadern, Ludwig-Maximilians-University, Munich, Germany.
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230
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Lynch DR, Farmer JM, Rochestie D, Balcer LJ. Contrast letter acuity as a measure of visual dysfunction in patients with Friedreich ataxia. J Neuroophthalmol 2002; 22:270-4. [PMID: 12464730 DOI: 10.1097/00041327-200212000-00003] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
BACKGROUND Friedreich ataxia is a progressive neurodegenerative disorder affecting afferent cerebellar pathways and other neuronal systems, including afferent visual pathways. A systematic clinical outcome measure for examination of visual dysfunction in Friedreich ataxia has not been identified. We sought to identify a simple, reliable method for assessing clinical and subclinical visual dysfunction in patients with Friedreich ataxia. METHODS Contrast letter acuity was measured binocularly in Friedreich ataxia patients and age-matched visually asymptomatic volunteers (control group) using the Low-contrast Sloan Letter Charts at three different low-contrast levels (5.0%, 1.25%, and 0.6%). Binocular high-contrast visual acuity (100% level) was also determined for each participant. RESULTS Despite equal median binocular high-contrast visual acuities between the two groups, patients with Friedreich ataxia had significantly lower (worse) Low-contrast Sloan Letter Chart scores compared with controls, particularly at the lowest contrast levels (1.25% and 0.6%). Ambulation status significantly predicted Low-contrast Sloan Letter Charts scores in linear regression models accounting for patient age, suggesting a potential complementary role for Low-contrast Sloan Letter Chart testing in the assessment of disease status as well as visual function in Friedreich ataxia. CONCLUSIONS This study demonstrates that Low-contrast Sloan Letter Chart testing may provide a useful clinical outcome measure for Friedreich ataxia and other neuro-ophthalmologic disorders.
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Affiliation(s)
- David R Lynch
- Department of Neurology, University of Pennsylvania and The Children's Hospital of Philadelphia, 19104, USA.
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231
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Abstract
Over the past 15 years, molecular genetic advances have led to new approaches for evaluation of neurogenetic disease. New diagnostic tests are available, and in some cases new diseases have been defined. However, effective use of these new tests still relies on solid clinical assessment to prioritize testing and interpret results. This review presents applications of genetic advances to a series of neurogenetic disorders, emphasizing the specific uses of genetic testing and the clinical questions that may arise. The rapid expansion in molecular diagnostics and genomics has fundamentally changed the approach to neurogenetic illnesses. Use of molecular biologic techniques has elucidated new disease mechanisms and allowed the application of genetic concepts to classically nongenetic illnesses. This has led to a wealth of new clinical information and created new dilemmas in patient care. In addition, it has brought into common usage a series of clinical genetic terms, such as variable expressivity (the range of phenotypic features in which the same disease can manifest) and anticipation (the progressively earlier age of onset of a specific disease in a family). This review provides a practical approach for neurogenetic evaluation of individuals who are likely to present in neuro-ophthalmologic practices with inherited ataxias, myotonic dystrophy, oculopharyngeal dystrophy, and Parkinson disease.
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Affiliation(s)
- David R Lynch
- Department of Neurology, University of Pennsylvania School of Medicine, Philadelphia, USA.
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232
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Abstract
Increasing evidence implicates a role of iron in the pathogenesis of numerous neurodegenerative diseases due to its capacity to enhance production of toxic reactive radicals and to induce protein aggregation. The underlying mechanism of iron accumulation in areas of the brain specific for the respective disease, however, is still unknown. Recent molecular and biochemical studies provide new insights into the consequences of impairment of brain iron metabolism. This review summarizes our understanding of the regulation of iron in the brain and defines the current knowledge on the involvement of iron metabolism in neurodegenerative diseases with genetically determined iron accumulation in the brain.
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Affiliation(s)
- D. Berg
- Department of Neurology, Bayerische Julius-Maximilians-Universi.at Wdot;urzburg
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233
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Pandolfo M. Frataxin deficiency and mitochondrial dysfunction. Mitochondrion 2002; 2:87-93. [PMID: 16120311 DOI: 10.1016/s1567-7249(02)00039-9] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2002] [Revised: 04/25/2002] [Accepted: 05/01/2002] [Indexed: 02/01/2023]
Abstract
Friedreich ataxia (FA) is an inherited recessive disorder characterized by progressive neurological disability and heart abnormalities. The Friedreich ataxia gene (FRDA) encodes a small mitochondrial protein, frataxin, which is produced in insufficient amounts in the disease as a consequence of a GAA triplet repeat expansion in the first intron of the gene. Frataxin deficiency leads to excessive free radical production, dysfunction of Fe-S center containing enzymes (in particular respiratory complexes I, II and III, and aconitase), and progressive iron accumulation in mitochondria. Frataxin may be a mitochondrial iron-binding protein that prevents this metal from participating in Fenton chemistry to generate toxic hydroxyl radicals. We investigated whether frataxin deficiency may in addition interfere with signaling pathways. First, we showed that exposure of FA fibroblasts to iron fails to produce the normally observed increase in expression of the stress defense protein manganese superoxide dismutase. This impaired induction involves a nuclear factor-kappaB-independent pathway that does not require free radical signaling intermediates. We also examined the role of frataxin in neuronal differentiation by using stably transfected clones of P19 embryonic carcinoma cells with antisense or sense frataxin constructs. We found that during retinoic acid-induced neurogenesis frataxin deficiency enhances apoptosis and reduces the number of terminally differentiated neuronal-like cells. The addition of the antioxidant N-acetyl-cysteine only rescues cells non-committed to the neuronal lineage, indicating that frataxin deficiency impairs differentiation mechanisms and survival responses through different mechanisms. Both studies suggest that some abnormalities in frataxin-deficient cells are related to free radical independent signaling pathways.
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Affiliation(s)
- Massimo Pandolfo
- Université Libre de Bruxelles-Hôpital Erasme, Service de Neurologie, Route de Lennik 808, B-1070 Brussels, Belgium.
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234
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Pandolfo M. Iron metabolism and mitochondrial abnormalities in Friedreich ataxia. Blood Cells Mol Dis 2002; 29:536-47; discussion 548-52. [PMID: 12547248 DOI: 10.1006/bcmd.2002.0591] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Friedreich ataxia is an autosomal recessive disease causing degeneration in the central and peripheral nervous system, cardiomyopathy, skeletal abnormalities and increased risk of diabetes. It is caused by deficiency of frataxin, a highly conserved nuclear-encoded mitochondrial protein. The genetic mutation found in 98% of Friedreich ataxia chromosomes is the unstable hyperexpansion of a GAA triplet repeat in the first intron of the gene. The expanded GAA repeat, by adopting an abnormal triple helical structure, impairs frataxin transcription. Longer repeats cause a more profound frataxin deficiency and are associated with earlier onset and increased severity of the disease. Yeast cells deficient in the frataxin homologue (Deltayfh1) become unable to carry out oxidative phosphorylation, lose mitochondrial DNA, accumulate iron in mitochondria, show unregulated high expression of high affinity iron uptake, and have an increased sensitivity to oxidative stress. Loss of respiratory competence in Deltayfh1 is iron-dependent. Additional properties of these cells include a deficiency of iron-sulfur cluster containing proteins (ISPs) and impaired iron efflux out of mitochondria. Evidence of oxidative stress, mitochondrial dysfunction, deficiency of multiple ISPs and iron deposits are also found in the human disease and in mouse models. The primary function of frataxin is still unknown, however much recent evidence suggests that it enhances iron-sulfur cluster synthesis and protects iron from free radical-generating reactions. The search for frataxin function stimulated more investigations on the role of mitochondria in cellular iron homeostasis. Their results suggest that these organelles may play a central role in controlling iron homeostasis, which is not surprising considering that they are the major cellular site where this metal is utilized. I propose a model, valid in yeast as well as in higher eukaryotes, in which iron transport into mitochondria is directly coupled to its uptake at the cell membrane and iron transport out of mitochondria depends on adequate iron-sulfur cluster synthesis. Regulatory mechanisms in the cytosol would then sense a post-mitochondrial iron pool. Much circumstantial evidence from genetically manipulated yeast and from human diseases supports this model.
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Affiliation(s)
- Massimo Pandolfo
- Service de Neurologie, Université Libre de Bruxelles-Hôpital Erasme, Route de Lennik 808, B-1070 Brussels, Belgium.
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235
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Abstract
Friedreich's ataxia (FA) is the most prevalent cerebellar ataxia in children and adults in Europe. FA is one of a growing number of diseases known to be caused by triplet-repeat expansions. The causative mutation is a GAA trinucleotide-repeat expansion in the first intron of the frataxin gene. The mitochondrial localisation of frataxin and decreased oxidation activity in vivo and in vitro show that FA is a mitochondrial disease. Frataxin is involved in iron metabolism and may protect mitochondria from oxidative damage. The understanding of the disease has only just begun and possible treatments are within reach. In this review I discuss the clinical knowledge of FA and recent developments that have helped to elucidate the pathogenesis of the disease and made the first therapeutic attempts possible.
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Affiliation(s)
- Alexandra Dürr
- INSERM U289 and Département de Génétique, Cytogénétique et Embryologie, Hôpital de la Salpêtrière, Paris, France.
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236
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Zhu D, Burke C, Leslie A, Nicholson GA. Friedreich's ataxia with chorea and myoclonus caused by a compound heterozygosity for a novel deletion and the trinucleotide GAA expansion. Mov Disord 2002; 17:585-9. [PMID: 12112211 DOI: 10.1002/mds.10175] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Friedreich's ataxia (FRDA) is the most common hereditary ataxia, affecting about 1 in 50,000 individuals. It is caused by mutations in the frataxin gene; 98% of cases have homozygous expansions of a GAA trinucleotide in intron 1 of the frataxin gene. The remaining 2% of patients are compound heterozygotes, who have a GAA repeat expansion in one allele and a point mutation in the other allele. FRDA patients with point mutation have been suggested to have atypical clinical features. We present a case of compound heterozygotes in a FRDA patient who has a deletion of one T in the start codon (ATG) of the frataxin gene and a GAA repeat expansion in the other allele. The patient presented with chorea and subsequently developed FRDA symptoms. The disease in this case is the result of both a failure of initiation of translation and the effect of the expansion. This novel mutation extends the range of point mutations seen in FRDA patients, and also broadens the spectrum of FRDA genotype associated with chorea.
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Affiliation(s)
- Danqing Zhu
- Neurobiology Department, ANZAC Research Institute, University of Sydney, Concord Hospital, Concord, NSW, Australia.
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237
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Abstract
Friedreich's ataxia is one of the most frequent hereditary ataxias of childhood. The disease is inherited in an autosomal recessive mode. The current state of knowledge concerning genetics, pathophysiology, pathology, clinical course, differential diagnosis, genotype-phenotype correlation, and therapy is presented.
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Affiliation(s)
- Jacek Pilch
- Department of Pediatric Neurology, Medical University of Silesia, Katowice, Poland.
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238
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Lynch DR, Lech G, Farmer JM, Balcer LJ, Bank W, Chance B, Wilson RB. Near infrared muscle spectroscopy in patients with Friedreich's ataxia. Muscle Nerve 2002; 25:664-673. [PMID: 11994959 DOI: 10.1002/mus.10077] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Friedreich's ataxia is a progressive neurodegenerative disorder of the afferent cerebellar pathways associated with mitochondrial dysfunction at the cellular level. We have used noninvasive continuous near infrared muscle spectroscopy (NIRS) to investigate the delivery and utilization of oxygen in response to exercise in this disorder. Patients performed an incremental treadmill walking protocol in which levels of muscle deoxygenation or oxygenation were continuously measured in the medial calf muscle. The kinetics of recovery from exercise-induced deoxygenation, called the half-time of recovery (t(1/2)) were determined. The t(1/2) was prolonged in patients with Friedreich's ataxia compared with controls, and the degree of prolongation correlated with the length of the shorter GAA repeat, a genetic measure that correlates with the age of onset of disease. The t(1/2) also correlated inversely with patient age and with the maximum treadmill speed attained. Several patients also displayed features consistent with inadequate oxygen utilization by muscle. These results suggest that NIRS may be an effective tool for monitoring the biochemical and functional features of Friedreich's ataxia in parallel.
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Affiliation(s)
- David R Lynch
- Department of Neurology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104, USA
- Department of Pediatrics, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104, USA
| | - Gwen Lech
- Department of Physiology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104, USA
| | - Jennifer M Farmer
- Department of Medicine, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104, USA
| | - Laura J Balcer
- Department of Neurology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104, USA
| | - William Bank
- Department of Neurology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104, USA
| | - Britton Chance
- Department of Physiology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104, USA
| | - Robert B Wilson
- Department of Pathology and Laboratory Medicine, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104, USA
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239
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Pianese L, Tammaro A, Turano M, De Biase I, Monticelli A, Cocozza S. Identification of a novel transcript of X25, the human gene involved in Friedreich ataxia. Neurosci Lett 2002; 320:137-40. [PMID: 11852181 DOI: 10.1016/s0304-3940(02)00048-4] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Friedreich ataxia (FRDA) is caused by a GAA triplet expansion in the first intron of the X25 gene. The X25 gene encodes a 210-amino acid protein, frataxin (A isoform). Here, we report the identification of a new transcript of the X25 gene generated by alternative splicing by the use of a second donor splice site in the intron 4. Full-length cDNA transcript sequence revealed an insertion of 8 bp between 4 and 5a exon sequence. This event leads to a frameshift in the mRNA reading frame and introduces a new stop codon at position 589. Therefore, this X25 transcript variant may encode a 196-amino acid protein, the A1 isoform, that structurally differs from the main A isoform of 210 amino acids after residue 160. In all human tissues analyzed, reverse transcription-polymerase chain reaction experiments demonstrated that the A1 isoform was expressed at low levels compared with the predominant A isoform. No difference in A and A1 isoform expression rate was detected between FRDA patients and normal controls. We did not find an A1 like splice variant in rodents.
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Affiliation(s)
- Luigi Pianese
- BioGeM, c/o Department of Molecular and Cellular Biology and Pathology, Federico II University, Via S. Pansini, 580131 Naples, Italy.
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240
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Gilbert F, Kauff N. Disease genes and chromosomes: disease maps of the human genome. Chromosome 9. GENETIC TESTING 2002; 5:157-74. [PMID: 11551106 DOI: 10.1089/109065701753145664] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Affiliation(s)
- F Gilbert
- Weill Medical College of Cornell University, New York, NY 10021, USA.
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241
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Berciano J, Mateo I, De Pablos C, Polo JM, Combarros O. Friedreich ataxia with minimal GAA expansion presenting as adult-onset spastic ataxia. J Neurol Sci 2002; 194:75-82. [PMID: 11809170 DOI: 10.1016/s0022-510x(01)00681-5] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Around a quarter of Friedreich ataxia (FA) patients, despite being homozygous for GAA expansion within the FRDA gene, show atypical presentations. Our aim is to describe the case of three brothers with long-term follow-up suffering from late onset FA manifested with spastic ataxia. The three patients belong to a family with occipital dysplasia (OD) and Chiari I malformation previously reported by us. We have carried out serial examinations since 1977. Electrophysiological and neuroimaging studies, and molecular genetic analyses of hereditary ataxias are available in all three patients. Onset of symptoms occurred between 25 and 35 years. The clinical picture consisted of progressive spastic gait, truncal and limb ataxia, dysarthria, nystagmus, hyperreflexia with knee and ankle clonus and extensor plantar response, and mild hypopallesthesia. Ages at present vary between 50 and 59. One patient is wheelchair-bound but the other two are able to walk with support. Leaving OD aside, skeletal anomalies are not prominent. All three patients showed cardiomyopathy. MR imaging revealed atrophy of the cerebellum and spinal cord. Motor and sensory nerve conduction velocities were normal. Central conduction time of both motor and sensory pathways was delayed or unobtainable. All three patients were homozygous for the GAA expansion, the smaller expanded allele ranging between 131 and 156 repeats. Four heterozygotic carriers were detected among non-ataxic relatives including one with OD; furthermore, an asymptomatic OD patient showed normal genotype. We conclude that adult onset spastic ataxia is a distinctive FA phenotype associated with minimal GAA expansion. This phenotype represents a new cause of selective distal degeneration of central sensory axons. The present concurrence of OD and FA reflects coincidental cosegregation of two different inherited disorders.
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Affiliation(s)
- J Berciano
- Service of Neurology, University Hospital Marqués de Valdecilla, 39008, Santander, Spain.
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242
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Miranda CJ, Santos MM, Ohshima K, Smith J, Li L, Bunting M, Cossée M, Koenig M, Sequeiros J, Kaplan J, Pandolfo M. Frataxin knockin mouse. FEBS Lett 2002; 512:291-7. [PMID: 11852098 DOI: 10.1016/s0014-5793(02)02251-2] [Citation(s) in RCA: 115] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Friedreich ataxia is the consequence of frataxin deficiency, most often caused by a GAA repeat expansion in intron 1 of the corresponding gene. Frataxin is a mitochondrial protein involved in iron homeostasis. As an attempt to generate a mouse model of the disease, we introduced a (GAA)(230) repeat within the mouse frataxin gene by homologous recombination. GAA repeat knockin mice were crossed with frataxin knockout mice to obtain double heterozygous mice expressing 25-36% of wild-type frataxin levels. These mice were viable and did not develop anomalies of motor coordination, iron metabolism or response to iron loading. Repeats were meiotically and mitotically stable.
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Affiliation(s)
- Carlos J Miranda
- Department of Medicine, Centre Hospitalier de l'Université de Montréal, Hôpital Notre-Dame, Pav de Seve--Y5608, 1560 rue Sherbrooke Est, H2L 4M1, Montréal, QC, Canada
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243
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Chapter 5 Mitochondrial Abnormalities in Neurodegenerative Disorders. ACTA ACUST UNITED AC 2002. [DOI: 10.1016/s1877-3419(09)70064-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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244
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McDaniel DO, Keats B, Vedanarayanan VV, Subramony SH. Sequence variation in GAA repeat expansions may cause differential phenotype display in Friedreich's ataxia. Mov Disord 2001; 16:1153-8. [PMID: 11748752 DOI: 10.1002/mds.1210] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
Friedreich's ataxia, the most common autosomal recessive inherited ataxia, is characterized by progressive gait and limb ataxia. Friedreich's ataxia is known for its occurrence within the first or second decade of life and is associated with hypertrophic cardiomyopathy, and in some cases with diabetes. Genetically, it is identified by the expression of an unstable trinucleotide GAA repeat expansion located in the first intron of the X25 gene on chromosome 9. Two brothers with very late adult-onset ataxia, and their unaffected sister, were examined for the clinical presentation of FA and for the presence of the mutated FA gene. The relationship of the expanded gene sequence to the severity of disease and age of onset were evaluated. Clinical examination revealed that the two brothers had mild ataxia and proprioceptive loss, with age of onset between 60 and 70 years of age. DNA from peripheral blood nucleated cells demonstrated a small homozygous expansion, with approximately 120-130 GAA repeats in the X25 gene in both patients. The expanded repeats were interrupted either with GAAGAG, GAAGGA, or GAAGAAAA sequences. The unaffected sister carried a normal FA genotype with 8-uninterrupted GAA repeat, observed by sequence analysis. In addition, the levels of FA gene transcript in both brothers were relatively lower than that in the unaffected sister. No detectable cardiomyopathy or diabetes was observed. Phenotypic diversity of FA is increasingly expanding. The age of onset and the structure of GAA repeat expansion plays an important role in determining the clinical features and the differential diagnosis of FA. The confirmation of the FA gene mutation in the atypical case, broadens the clinical spectrum of FA, and supports the idea that patients with even a mild form of ataxia of late adult onset should be considered for molecular testing.
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Affiliation(s)
- D O McDaniel
- Department of Surgery, The University of Mississippi Medical Center, Jackson, Mississippi 39216, USA.
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245
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Affiliation(s)
- M Pandolfo
- Département de Médecine, Université de Montréal, Centre Hospitalier de l'Université de Montréal, Hôpital Notre-Dame, Montréal, Québec, Canada.
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246
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Patel PI, Isaya G. Friedreich ataxia: from GAA triplet-repeat expansion to frataxin deficiency. Am J Hum Genet 2001; 69:15-24. [PMID: 11391483 PMCID: PMC1226030 DOI: 10.1086/321283] [Citation(s) in RCA: 96] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2001] [Accepted: 05/14/2001] [Indexed: 12/30/2022] Open
Affiliation(s)
- P I Patel
- Departments of Neurology and Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA.
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247
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Mäueler W, Bassili G, Hardt C, Keyl HG, Epplen JT. A complex containing at least one zinc dependent HeLa nuclear protein binds to the intronic (gaa)(n) block of the frataxin gene. Gene 2001; 270:131-43. [PMID: 11404010 DOI: 10.1016/s0378-1119(01)00487-5] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
We analyzed HeLa nuclear proteins binding to the (gaa)(n) harbouring intron 1 of nine frataxin alleles and characterized the structures of the repeats. Fragments with blocks longer than (gaa)(9) form spontaneously different intramolecular H-y topoisomeres in linear state. The observed triplexes depend on the length of the repeat. Interruption of the perfectly repeated (gaa)(n) block entails two structural regions. At least two HeLa nuclear proteins bind to the (gaa)(n) fragments resulting in a distinct major retarded complex as revealed by EMSA. One of these proteins is zinc dependent. Importantly, the fragment harbouring (gan)(121) binds additional proteins. Protein binding appears to be locus specific, and the binding affinity was found to be not random. The affinities of the different target fragments varied by a factor of four. Binding affinities of the fragments were not obviously correlated to differences in the composition of the repeats. DNase I footprinting revealed only weakly protected binding regions, but multiple HS sites in the repeat regions of the fragments. These findings and the fact, that DNA conformers observed in EMSA and electron microscopical experiments bind proteins, lead to the assumption that the proteins recognize, both, B-DNA and triple helical structures, but with different affinity. Possible functions of the proteins are discussed in the context of transformation of triple helical structures into B-DNA and the pathogenesis of FRDA.
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Affiliation(s)
- W Mäueler
- Department of Molecular Human Genetics, Ruhr-Universität, 44780, Bochum, Germany.
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248
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Cavadini P, Adamec J, Taroni F, Gakh O, Isaya G. Two-step processing of human frataxin by mitochondrial processing peptidase. Precursor and intermediate forms are cleaved at different rates. J Biol Chem 2000; 275:41469-75. [PMID: 11020385 DOI: 10.1074/jbc.m006539200] [Citation(s) in RCA: 91] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
We showed previously that maturation of the human frataxin precursor (p-fxn) involves two cleavages by the mitochondrial processing peptidase (MPP). This observation was not confirmed by another group, however, who reported only one cleavage. Here, we demonstrate conclusively that MPP cleaves p-fxn in two sequential steps, yielding a 18,826-Da intermediate (i-fxn) and a 17,255-Da mature (m-fxn) form, the latter corresponding to endogenous frataxin in human tissues. The two cleavages occur between residues 41-42 and 55-56, and both match the MPP consensus sequence RX downward arrow (X/S). Recombinant rat and yeast MPP catalyze the p --> i step 4 and 40 times faster, respectively, than the i --> m step. In isolated rat mitochondria, p-fxn undergoes a sequence of cleavages, p --> i --> m --> d(1) --> d(2), with d(1) and d(2) representing two C-terminal fragments of m-fxn produced by an unknown protease. The i --> m step is limiting, and the overall rate of p --> i --> m does not exceed the rate of m --> d(1) --> d(2), such that the levels of m-fxn do not change during incubations as long as 3 h. Inhibition of the i --> m step by a disease-causing frataxin mutation (W173G) leads to nonspecific degradation of i-fxn. Thus, the second of the two processing steps catalyzed by MPP limits the levels of mature frataxin within mitochondria.
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Affiliation(s)
- P Cavadini
- Department of Pediatric & Adolescent Medicine and Biochemistry & Molecular Biology, Mayo Clinic and Foundation, 200 First Street SW, Rochester, Minnesota 55905, USA
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249
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Sobrido MJ, Geschwind DH. Molecular Genetics and Inherited Ataxias: Redefining Phenotypes and Pathogenesis. Neuroscientist 2000. [DOI: 10.1177/107385840000600609] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Genetic research on inherited ataxias has transformed our understanding of these conditions. The availability of genetic testing has shown that a classification based solely on clinical and pathologic findings is not adequate, and molecular genetic analysis is now mandatory for diagnostic accuracy and prognostic purposes. The epidemiology of these disorders is also being rewritten under the light of molecular genetic analysis. In this review, we discuss some of the recent advances on the hereditary cerebellar degenerations without a known metabolic defect, focusing on genotype-phenotype correlations in the spinocerebellar ataxias (SCAs) and Friedreich’s ataxia (FRDA). Three main biochemical pathways seem to be involved in the pathogenesis of inherited ataxias: 1) expansion of (CAG)n repeats within genes coding for polyglutamine-containing proteins (SCAs); 2) impairment of mitochondrial function (FRDA); and 3) dysfunction of ion channels (episodic ataxias, EA1, EA2). It is likely that many neurodegenerative conditions will prove to share basic molecular mechanisms, and therefore, data provided by the investigation of a particular disease is likely to be relevant to our global understanding of spinocerebellar degenerations and other degenerative disorders of the nervous system. A better knowledge of the molecular and cellular routes leading to neurodegeneration will provide a key to the design of rational therapies.
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Affiliation(s)
- Maria J. Sobrido
- Department of Neurology, Neurogenetics Program, University of California, Los Angeles, School of Medicine, Los Angeles, California
| | - Daniel H. Geschwind
- Department of Neurology, Neurogenetics Program, University of California, Los Angeles, School of Medicine, Los Angeles, California,
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250
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Filla A, De Michele G, Coppola G, Federico A, Vita G, Toscano A, Uncini A, Pisanelli P, Barone P, Scarano V, Perretti A, Santoro L, Monticelli A, Cavalcanti F, Caruso G, Cocozza S. Accuracy of clinical diagnostic criteria for Friedreich's ataxia. Mov Disord 2000; 15:1255-8. [PMID: 11104216 DOI: 10.1002/1531-8257(200011)15:6<1255::aid-mds1031>3.0.co;2-c] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
The accuracy of the diagnostic criteria for Friedreich's ataxia proposed by Harding and by the Quebec Cooperative Study on Friedreich's Ataxia was studied in 142 patients with progressive unremitting ataxia of autosomal recessive inheritance or sporadic occurrence. Eighty-eight patients received the molecular diagnosis of Friedreich's ataxia. Traditional diagnostic criteria are characterized by high specificity, but they yield a high number of false-negative diagnoses. We suggest three levels of diagnostic certainty: (1) possible Friedreich's ataxia, defined as sporadic or recessive progressive ataxia with (a) lower limb areflexia and dysarthria, Babinski sign, or electrocardiographic repolarization abnormalities, or (b) with lower limb retained reflexes and electrocardiographic repolarization abnormalities (95% sensitivity and 88% positive predictive value); (2) probable Friedreich's ataxia as defined by Harding's criteria (63% sensitivity and 96% positive predictive value) or by Quebec Cooperative Study on Friedreich's Ataxia criteria (63% sensitivity and 98% positive predictive value); (3) definite diagnosis, molecularly confirmed.
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Affiliation(s)
- A Filla
- Department of Neurological Sciences, Federico II University, Naples, Italy
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