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Rajan-Babu IS, Dolzhenko E, Eberle MA, Friedman JM. Sequence composition changes in short tandem repeats: heterogeneity, detection, mechanisms and clinical implications. Nat Rev Genet 2024:10.1038/s41576-024-00696-z. [PMID: 38467784 DOI: 10.1038/s41576-024-00696-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/19/2024] [Indexed: 03/13/2024]
Abstract
Short tandem repeats (STRs) are a class of repetitive elements, composed of tandem arrays of 1-6 base pair sequence motifs, that comprise a substantial fraction of the human genome. STR expansions can cause a wide range of neurological and neuromuscular conditions, known as repeat expansion disorders, whose age of onset, severity, penetrance and/or clinical phenotype are influenced by the length of the repeats and their sequence composition. The presence of non-canonical motifs, depending on the type, frequency and position within the repeat tract, can alter clinical outcomes by modifying somatic and intergenerational repeat stability, gene expression and mutant transcript-mediated and/or protein-mediated toxicities. Here, we review the diverse structural conformations of repeat expansions, technological advances for the characterization of changes in sequence composition, their clinical correlations and the impact on disease mechanisms.
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Affiliation(s)
- Indhu-Shree Rajan-Babu
- Department of Medical Genetics, The University of British Columbia, and Children's & Women's Hospital, Vancouver, British Columbia, Canada.
| | | | | | - Jan M Friedman
- Department of Medical Genetics, The University of British Columbia, and Children's & Women's Hospital, Vancouver, British Columbia, Canada
- BC Children's Hospital Research Institute, Vancouver, British Columbia, Canada
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2
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Sanchez-Flores M, Corral-Juan M, Gasch-Navalón E, Cirillo D, Sanchez I, Matilla-Dueñas A. Novel genotype-phenotype correlations, differential cerebellar allele-specific methylation, and a common origin of the (ATTTC) n insertion in spinocerebellar ataxia type 37. Hum Genet 2024; 143:211-232. [PMID: 38396267 PMCID: PMC11043136 DOI: 10.1007/s00439-024-02644-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2023] [Accepted: 01/17/2024] [Indexed: 02/25/2024]
Abstract
Spinocerebellar ataxia subtype 37 (SCA37) is a rare disease originally identified in ataxia patients from the Iberian Peninsula with a pure cerebellar syndrome. SCA37 patients carry a pathogenic intronic (ATTTC)n repeat insertion flanked by two polymorphic (ATTTT)n repeats in the Disabled-1 (DAB1) gene leading to cerebellar dysregulation. Herein, we determine the precise configuration of the pathogenic 5'(ATTTT)n-(ATTTC)n-3'(ATTTT)n SCA37 alleles by CRISPR-Cas9 and long-read nanopore sequencing, reveal their epigenomic signatures in SCA37 lymphocytes, fibroblasts, and cerebellar samples, and establish new molecular and clinical correlations. The 5'(ATTTT)n-(ATTTC)n-3'(ATTTT)n pathogenic allele configurations revealed repeat instability and differential methylation signatures. Disease age of onset negatively correlated with the (ATTTC)n, and positively correlated with the 3'(ATTTT)n. Geographic origin and gender significantly correlated with age of onset. Furthermore, significant predictive regression models were obtained by machine learning for age of onset and disease evolution by considering gender, the (ATTTC)n, the 3'(ATTTT)n, and seven CpG positions differentially methylated in SCA37 cerebellum. A common 964-kb genomic region spanning the (ATTTC)n insertion was identified in all SCA37 patients analysed from Portugal and Spain, evidencing a common origin of the SCA37 mutation in the Iberian Peninsula originating 859 years ago (95% CI 647-1378). In conclusion, we demonstrate an accurate determination of the size and configuration of the regulatory 5'(ATTTT)n-(ATTTC)n-3'(ATTTT)n repeat tract, avoiding PCR bias amplification using CRISPR/Cas9-enrichment and nanopore long-read sequencing, resulting relevant for accurate genetic diagnosis of SCA37. Moreover, we determine novel significant genotype-phenotype correlations in SCA37 and identify differential cerebellar allele-specific methylation signatures that may underlie DAB1 pathogenic dysregulation.
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Affiliation(s)
- Marina Sanchez-Flores
- Neurogenetics Unit, Department of Neuroscience, Germans Trias i Pujol Research Institute (IGTP), Universitat Autònoma de Barcelona-Can Ruti Campus, Carretera de Can Ruti, Camí de les Escoles s/n, 08916, Badalona, Spain
| | - Marc Corral-Juan
- Neurogenetics Unit, Department of Neuroscience, Germans Trias i Pujol Research Institute (IGTP), Universitat Autònoma de Barcelona-Can Ruti Campus, Carretera de Can Ruti, Camí de les Escoles s/n, 08916, Badalona, Spain
| | - Esther Gasch-Navalón
- Neurogenetics Unit, Department of Neuroscience, Germans Trias i Pujol Research Institute (IGTP), Universitat Autònoma de Barcelona-Can Ruti Campus, Carretera de Can Ruti, Camí de les Escoles s/n, 08916, Badalona, Spain
| | | | - Ivelisse Sanchez
- Neurogenetics Unit, Department of Neuroscience, Germans Trias i Pujol Research Institute (IGTP), Universitat Autònoma de Barcelona-Can Ruti Campus, Carretera de Can Ruti, Camí de les Escoles s/n, 08916, Badalona, Spain
| | - Antoni Matilla-Dueñas
- Neurogenetics Unit, Department of Neuroscience, Germans Trias i Pujol Research Institute (IGTP), Universitat Autònoma de Barcelona-Can Ruti Campus, Carretera de Can Ruti, Camí de les Escoles s/n, 08916, Badalona, Spain.
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3
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Kumar M, Tyagi N, Faruq M. The molecular mechanisms of spinocerebellar ataxias for DNA repeat expansion in disease. Emerg Top Life Sci 2023; 7:289-312. [PMID: 37668011 DOI: 10.1042/etls20230013] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2023] [Revised: 08/01/2023] [Accepted: 08/16/2023] [Indexed: 09/06/2023]
Abstract
Spinocerebellar ataxias (SCAs) are a heterogenous group of neurodegenerative disorders which commonly inherited in an autosomal dominant manner. They cause muscle incoordination due to degeneration of the cerebellum and other parts of nervous system. Out of all the characterized (>50) SCAs, 14 SCAs are caused due to microsatellite repeat expansion mutations. Repeat expansions can result in toxic protein gain-of-function, protein loss-of-function, and/or RNA gain-of-function effects. The location and the nature of mutation modulate the underlying disease pathophysiology resulting in varying disease manifestations. Potential toxic effects of these mutations likely affect key major cellular processes such as transcriptional regulation, mitochondrial functioning, ion channel dysfunction and synaptic transmission. Involvement of several common pathways suggests interlinked function of genes implicated in the disease pathogenesis. A better understanding of the shared and distinct molecular pathogenic mechanisms in these diseases is required to develop targeted therapeutic tools and interventions for disease management. The prime focus of this review is to elaborate on how expanded 'CAG' repeats contribute to the common modes of neurotoxicity and their possible therapeutic targets in management of such devastating disorders.
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Affiliation(s)
- Manish Kumar
- CSIR-Institute of Genomics and Integrative Biology, Mall Road, Delhi 110007, India
| | - Nishu Tyagi
- CSIR-Institute of Genomics and Integrative Biology, Mall Road, Delhi 110007, India
| | - Mohammed Faruq
- CSIR-Institute of Genomics and Integrative Biology, Mall Road, Delhi 110007, India
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4
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Yonenobu Y, Beck G, Kido K, Maeda N, Yamashita R, Inoue K, Saito Y, Hasegawa M, Ito H, Hasegawa K, Morii E, Iwaki T, Murayama S, Mochizuki H. Neuropathology of spinocerebellar ataxia type 8: Common features and unique tauopathy. Neuropathology 2023; 43:351-361. [PMID: 36703300 DOI: 10.1111/neup.12894] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2022] [Revised: 01/04/2023] [Accepted: 01/05/2023] [Indexed: 01/28/2023]
Abstract
Spinocerebellar ataxia type 8 (SCA8) is a neurodegenerative condition that presents with several neurological symptoms, such as cerebellar ataxia, parkinsonism, and cognitive impairment. It is caused by a CTA/CTG repeat expansion on chromosome 13q21 (ataxin 8 opposite strand [ATXN8OS]). However, the pathological significance of this expansion remains unclear. Moreover, abnormal CTA/CTG repeat expansions in ATXN8OS have also been reported in other neurodegenerative diseases, including progressive supranuclear palsy. In this study, we analyzed all available autopsy cases in Japan to investigate common pathological features and profiles of tau pathology in each case. Severe neuronal loss in the substantia nigra and prominent loss of Purkinje cells, atrophy of the molecular layer, and proliferation of Bergmann glia in the cerebellum were common features. Regarding tauopathy, one case presented with progressive supranuclear palsy-like 4-repeat tauopathy in addition to mild Alzheimer-type 3- and 4-repeat tauopathy. Another case showed 3- and 4-repeat tauopathy accentuated in the brainstem. The other two cases lacked tauopathy after extensive immunohistochemical studies. The present study confirmed common pathological features of SCA8 as degeneration of the substantia nigra in addition to the cerebellum. Our study also confirmed unique tauopathy in two of four cases, indicating the necessity to further collect autopsy cases.
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Affiliation(s)
- Yuki Yonenobu
- Department of Neurology, Osaka University Graduate School of Medicine, Suita, Japan
| | - Goichi Beck
- Department of Neurology, Osaka University Graduate School of Medicine, Suita, Japan
| | - Kansuke Kido
- Department of Pathology, Osaka University Graduate School of Medicine, Suita, Japan
| | - Norihisa Maeda
- Department of Neuropathology, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan
| | - Rika Yamashita
- Department of Neurology, Osaka University Graduate School of Medicine, Suita, Japan
| | - Kimiko Inoue
- Department of Neurology and Rehabilitation Medicine, National Hospital Organization, Osaka Toneyama Medical Center, Toyonaka, Japan
| | - Yuko Saito
- Department of Neurology and Neuropathology (Brain Bank for Aging Research), Tokyo Metropolitan Geriatric Hospital and Institute of Gerontology, Tokyo, Japan
| | - Masato Hasegawa
- Dementia Research Project, Tokyo Metropolitan Institute of Medical Science, Tokyo, Japan
| | - Hidefumi Ito
- Department of Neurology, Wakayama Medical University, Wakayama City, Japan
| | - Kazuko Hasegawa
- Department of Neurology, National Hospital Organization, Sagamihara National Hospital, Sagamihara, Japan
| | - Eiichi Morii
- Department of Pathology, Osaka University Graduate School of Medicine, Suita, Japan
| | - Toru Iwaki
- Department of Neuropathology, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan
| | - Shigeo Murayama
- Department of Neurology, Osaka University Graduate School of Medicine, Suita, Japan
- Department of Neurology and Neuropathology (Brain Bank for Aging Research), Tokyo Metropolitan Geriatric Hospital and Institute of Gerontology, Tokyo, Japan
- Brain Bank for Neurodevelopmental, Neurological and Psychiatric Disorders, Molecular Research Center for Children's Mental Development, United Graduate School of Child Development, Osaka University, Suita, Japan
| | - Hideki Mochizuki
- Department of Neurology, Osaka University Graduate School of Medicine, Suita, Japan
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Liu M, Niu X, Liu H, Chen J. Germline EGFR mutations in lung cancer (Review). Oncol Lett 2023; 26:282. [PMID: 37274482 PMCID: PMC10236141 DOI: 10.3892/ol.2023.13868] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2023] [Accepted: 04/17/2023] [Indexed: 06/06/2023] Open
Abstract
Lung cancer is the leading cause of cancer-related death and familial lung cancer is a potential contributing factor. Epidermal growth factor receptor (EGFR) mutations are important events in carcinogenesis. The present study summarized the common germline mutations of EGFR, including T790M, V843I, R776H and P848L, and provided detailed information regarding each mutation site and potential treatment strategies. Individuals with germline mutations may develop lung cancer upon exposure to environmental stimuli such as smoking, air pollution or radiological contamination, or due to the occurrence of another somatic mutation. The present study recommends regular physical examinations as well as population-wide germline mutation screening for early detection and diagnosis of lung cancer.
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Affiliation(s)
- Minghui Liu
- Department of Lung Cancer Surgery, Tianjin Medical University General Hospital, Heping, Tianjin 300052, P.R. China
| | - Xiaoyu Niu
- Department of Lung Cancer Surgery, Tianjin Medical University General Hospital, Heping, Tianjin 300052, P.R. China
| | - Hongyu Liu
- Tianjin Key Laboratory of Lung Cancer Metastasis and Tumor Microenvironment, Tianjin Lung Cancer Institute, Tianjin Medical University General Hospital, Heping, Tianjin 300052, P.R. China
| | - Jun Chen
- Department of Lung Cancer Surgery, Tianjin Medical University General Hospital, Heping, Tianjin 300052, P.R. China
- Tianjin Key Laboratory of Lung Cancer Metastasis and Tumor Microenvironment, Tianjin Lung Cancer Institute, Tianjin Medical University General Hospital, Heping, Tianjin 300052, P.R. China
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6
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Kurosaki T, Ashizawa T. The genetic and molecular features of the intronic pentanucleotide repeat expansion in spinocerebellar ataxia type 10. Front Genet 2022; 13:936869. [PMID: 36199580 PMCID: PMC9528567 DOI: 10.3389/fgene.2022.936869] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2022] [Accepted: 08/25/2022] [Indexed: 11/13/2022] Open
Abstract
Spinocerebellar ataxia type 10 (SCA10) is characterized by progressive cerebellar neurodegeneration and, in many patients, epilepsy. This disease mainly occurs in individuals with Indigenous American or East Asian ancestry, with strong evidence supporting a founder effect. The mutation causing SCA10 is a large expansion in an ATTCT pentanucleotide repeat in intron 9 of the ATXN10 gene. The ATTCT repeat is highly unstable, expanding to 280–4,500 repeats in affected patients compared with the 9–32 repeats in normal individuals, one of the largest repeat expansions causing neurological disorders identified to date. However, the underlying molecular basis of how this huge repeat expansion evolves and contributes to the SCA10 phenotype remains largely unknown. Recent progress in next-generation DNA sequencing technologies has established that the SCA10 repeat sequence has a highly heterogeneous structure. Here we summarize what is known about the structure and origin of SCA10 repeats, discuss the potential contribution of variant repeats to the SCA10 disease phenotype, and explore how this information can be exploited for therapeutic benefit.
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Affiliation(s)
- Tatsuaki Kurosaki
- Department of Biochemistry and Biophysics, School of Medicine and Dentistry, University of Rochester, Rochester, NY, United States
- Center for RNA Biology, University of Rochester, Rochester, NY, United States
- *Correspondence: Tatsuaki Kurosaki, ; Tetsuo Ashizawa,
| | - Tetsuo Ashizawa
- Stanley H. Appel Department of Neurology, Houston Methodist Research Institute and Weil Cornell Medical College at Houston Methodist Houston, TX, United States
- *Correspondence: Tatsuaki Kurosaki, ; Tetsuo Ashizawa,
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7
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Arning L, Nguyen HP. Huntington disease update: new insights into the role of repeat instability in disease pathogenesis. MED GENET-BERLIN 2021; 33:293-300. [PMID: 38835439 PMCID: PMC11006308 DOI: 10.1515/medgen-2021-2101] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2021] [Accepted: 11/16/2021] [Indexed: 06/06/2024]
Abstract
The causative mutation for Huntington disease (HD), an expanded trinucleotide repeat sequence in the first exon of the huntingtin gene (HTT) is naturally polymorphic and inevitably associated with disease symptoms above 39 CAG repeats. Although symptomatic medical therapies for HD can improve the motor and non-motor symptoms for affected patients, these drugs do not stop the ongoing neurodegeneration and progression of the disease, which results in severe motor and cognitive disability and death. To date, there is still an urgent need for the development of effective disease-modifying therapies to slow or even stop the progression of HD. The increasing ability to intervene directly at the roots of the disease, namely HTT transcription and translation of its mRNA, makes it necessary to understand the pathogenesis of HD as precisely as possible. In addition to the long-postulated toxicity of the polyglutamine-expanded mutant HTT protein, there is increasing evidence that the CAG repeat-containing RNA might also be directly involved in toxicity. Recent studies have identified cis- (DNA repair genes) and trans- (loss/duplication of CAA interruption) acting variants as major modifiers of age at onset (AO) and disease progression. More and more extensive data indicate that somatic instability functions as a driver for AO as well as disease progression and severity, not only in HD but also in other polyglutamine diseases. Thus, somatic expansions of repetitive DNA sequences may be essential to promote respective repeat lengths to reach a threshold leading to the overt neurodegenerative symptoms of trinucleotide diseases. These findings support somatic expansion as a potential therapeutic target in HD and related repeat expansion disorders.
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Affiliation(s)
- Larissa Arning
- Department of Human Genetics, Medical Faculty, Ruhr-University Bochum, Bochum 44780, Germany
| | - Huu Phuc Nguyen
- Department of Human Genetics, Medical Faculty, Ruhr-University Bochum, Bochum 44780, Germany
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8
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Perez BA, Shorrock HK, Banez‐Coronel M, Zu T, Romano LEL, Laboissonniere LA, Reid T, Ikeda Y, Reddy K, Gomez CM, Bird T, Ashizawa T, Schut LJ, Brusco A, Berglund JA, Hasholt LF, Nielsen JE, Subramony SH, Ranum LPW. CCG•CGG interruptions in high-penetrance SCA8 families increase RAN translation and protein toxicity. EMBO Mol Med 2021; 13:e14095. [PMID: 34632710 PMCID: PMC8573593 DOI: 10.15252/emmm.202114095] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2021] [Revised: 09/09/2021] [Accepted: 09/10/2021] [Indexed: 12/28/2022] Open
Abstract
Spinocerebellar ataxia type 8 (SCA8), a dominantly inherited neurodegenerative disorder caused by a CTG•CAG expansion, is unusual because most individuals that carry the mutation do not develop ataxia. To understand the variable penetrance of SCA8, we studied the molecular differences between highly penetrant families and more common sporadic cases (82%) using a large cohort of SCA8 families (n = 77). We show that repeat expansion mutations from individuals with multiple affected family members have CCG•CGG interruptions at a higher frequency than sporadic SCA8 cases and that the number of CCG•CGG interruptions correlates with age at onset. At the molecular level, CCG•CGG interruptions increase RNA hairpin stability, and in cell culture experiments, increase p-eIF2α and polyAla and polySer RAN protein levels. Additionally, CCG•CGG interruptions, which encode arginine interruptions in the polyGln frame, increase toxicity of the resulting proteins. In summary, SCA8 CCG•CGG interruptions increase polyAla and polySer RAN protein levels, polyGln protein toxicity, and disease penetrance and provide novel insight into the molecular differences between SCA8 families with high vs. low disease penetrance.
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Affiliation(s)
- Barbara A Perez
- Center for NeuroGeneticsUniversity of FloridaGainesvilleFLUSA
- Department of Molecular Genetics and MicrobiologyUniversity of FloridaGainesvilleFLUSA
| | - Hannah K Shorrock
- Center for NeuroGeneticsUniversity of FloridaGainesvilleFLUSA
- Department of Molecular Genetics and MicrobiologyUniversity of FloridaGainesvilleFLUSA
| | - Monica Banez‐Coronel
- Center for NeuroGeneticsUniversity of FloridaGainesvilleFLUSA
- Department of Molecular Genetics and MicrobiologyUniversity of FloridaGainesvilleFLUSA
| | - Tao Zu
- Center for NeuroGeneticsUniversity of FloridaGainesvilleFLUSA
- Department of Molecular Genetics and MicrobiologyUniversity of FloridaGainesvilleFLUSA
| | - Lisa EL Romano
- Center for NeuroGeneticsUniversity of FloridaGainesvilleFLUSA
- Department of Molecular Genetics and MicrobiologyUniversity of FloridaGainesvilleFLUSA
| | - Lauren A Laboissonniere
- Center for NeuroGeneticsUniversity of FloridaGainesvilleFLUSA
- Department of Molecular Genetics and MicrobiologyUniversity of FloridaGainesvilleFLUSA
| | - Tammy Reid
- Center for NeuroGeneticsUniversity of FloridaGainesvilleFLUSA
- Department of Molecular Genetics and MicrobiologyUniversity of FloridaGainesvilleFLUSA
| | - Yoshio Ikeda
- Department of NeurologyGunma UniversityMaebashiJapan
| | - Kaalak Reddy
- RNA InstituteUniversity at Albany–SUNYAlbanyNYUSA
| | | | - Thomas Bird
- Department of NeurologyUniversity of WashingtonSeattleWAUSA
- Geriatrics Research SectionVA Puget Sound Health Care SystemSeattleWAUSA
| | - Tetsuo Ashizawa
- Department of NeurologyHouston Methodist Research InstituteHoustonTXUSA
| | | | - Alfredo Brusco
- Department of Medical SciencesUniversity of TorinoTorinoItaly
- Medical Genetics Units“Città della Salute e della Scienza” University HospitalTorinoItaly
| | - J Andrew Berglund
- Center for NeuroGeneticsUniversity of FloridaGainesvilleFLUSA
- RNA InstituteUniversity at Albany–SUNYAlbanyNYUSA
| | - Lis F Hasholt
- Institute of Cellular and Molecular MedicineUniversity of CopenhagenCopenhagenDenmark
| | - Jorgen E Nielsen
- Department of NeurologyRigshospitaletUniversity of CopenhagenCopenhagenDenmark
| | - SH Subramony
- Center for NeuroGeneticsUniversity of FloridaGainesvilleFLUSA
- McKnight Brain InstituteUniversity of FloridaGainesvilleFLUSA
| | - Laura PW Ranum
- Center for NeuroGeneticsUniversity of FloridaGainesvilleFLUSA
- Department of Molecular Genetics and MicrobiologyUniversity of FloridaGainesvilleFLUSA
- McKnight Brain InstituteUniversity of FloridaGainesvilleFLUSA
- Genetics InstituteUniversity of FloridaGainesvilleFLUSA
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Chintalaphani SR, Pineda SS, Deveson IW, Kumar KR. An update on the neurological short tandem repeat expansion disorders and the emergence of long-read sequencing diagnostics. Acta Neuropathol Commun 2021; 9:98. [PMID: 34034831 PMCID: PMC8145836 DOI: 10.1186/s40478-021-01201-x] [Citation(s) in RCA: 62] [Impact Index Per Article: 20.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2021] [Accepted: 05/17/2021] [Indexed: 12/14/2022] Open
Abstract
BACKGROUND Short tandem repeat (STR) expansion disorders are an important cause of human neurological disease. They have an established role in more than 40 different phenotypes including the myotonic dystrophies, Fragile X syndrome, Huntington's disease, the hereditary cerebellar ataxias, amyotrophic lateral sclerosis and frontotemporal dementia. MAIN BODY STR expansions are difficult to detect and may explain unsolved diseases, as highlighted by recent findings including: the discovery of a biallelic intronic 'AAGGG' repeat in RFC1 as the cause of cerebellar ataxia, neuropathy, and vestibular areflexia syndrome (CANVAS); and the finding of 'CGG' repeat expansions in NOTCH2NLC as the cause of neuronal intranuclear inclusion disease and a range of clinical phenotypes. However, established laboratory techniques for diagnosis of repeat expansions (repeat-primed PCR and Southern blot) are cumbersome, low-throughput and poorly suited to parallel analysis of multiple gene regions. While next generation sequencing (NGS) has been increasingly used, established short-read NGS platforms (e.g., Illumina) are unable to genotype large and/or complex repeat expansions. Long-read sequencing platforms recently developed by Oxford Nanopore Technology and Pacific Biosciences promise to overcome these limitations to deliver enhanced diagnosis of repeat expansion disorders in a rapid and cost-effective fashion. CONCLUSION We anticipate that long-read sequencing will rapidly transform the detection of short tandem repeat expansion disorders for both clinical diagnosis and gene discovery.
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Affiliation(s)
- Sanjog R. Chintalaphani
- School of Medicine, University of New South Wales, Sydney, 2052 Australia
- Kinghorn Centre for Clinical Genomics, Garvan Institute of Medical Research, Darlinghurst, NSW 2010 Australia
| | - Sandy S. Pineda
- Garvan-Weizmann Centre for Cellular Genomics, Garvan Institute of Medical Research, Darlinghurst, NSW 2010 Australia
- Brain and Mind Centre, University of Sydney, Camperdown, NSW 2050 Australia
| | - Ira W. Deveson
- Kinghorn Centre for Clinical Genomics, Garvan Institute of Medical Research, Darlinghurst, NSW 2010 Australia
- Faculty of Medicine, St Vincent’s Clinical School, University of New South Wales, Sydney, NSW 2010 Australia
| | - Kishore R. Kumar
- Kinghorn Centre for Clinical Genomics, Garvan Institute of Medical Research, Darlinghurst, NSW 2010 Australia
- Molecular Medicine Laboratory and Neurology Department, Central Clinical School, Concord Repatriation General Hospital, University of Sydney, Concord, NSW 2137 Australia
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10
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Monckton DG. The Contribution of Somatic Expansion of the CAG Repeat to Symptomatic Development in Huntington's Disease: A Historical Perspective. J Huntingtons Dis 2021; 10:7-33. [PMID: 33579863 PMCID: PMC7990401 DOI: 10.3233/jhd-200429] [Citation(s) in RCA: 33] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
The discovery in the early 1990s of the expansion of unstable simple sequence repeats as the causative mutation for a number of inherited human disorders, including Huntington’s disease (HD), opened up a new era of human genetics and provided explanations for some old problems. In particular, an inverse association between the number of repeats inherited and age at onset, and unprecedented levels of germline instability, biased toward further expansion, provided an explanation for the wide symptomatic variability and anticipation observed in HD and many of these disorders. The repeats were also revealed to be somatically unstable in a process that is expansion-biased, age-dependent and tissue-specific, features that are now increasingly recognised as contributory to the age-dependence, progressive nature and tissue specificity of the symptoms of HD, and at least some related disorders. With much of the data deriving from affected individuals, and model systems, somatic expansions have been revealed to arise in a cell division-independent manner in critical target tissues via a mechanism involving key components of the DNA mismatch repair pathway. These insights have opened new approaches to thinking about how the disease could be treated by suppressing somatic expansion and revealed novel protein targets for intervention. Exciting times lie ahead in turning these insights into novel therapies for HD and related disorders.
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Affiliation(s)
- Darren G Monckton
- Institute of Molecular, Cell and Systems Biology, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, UK
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11
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Antisense Transcription across Nucleotide Repeat Expansions in Neurodegenerative and Neuromuscular Diseases: Progress and Mysteries. Genes (Basel) 2020; 11:genes11121418. [PMID: 33261024 PMCID: PMC7760973 DOI: 10.3390/genes11121418] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2020] [Revised: 11/24/2020] [Accepted: 11/24/2020] [Indexed: 12/14/2022] Open
Abstract
Unstable repeat expansions and insertions cause more than 30 neurodegenerative and neuromuscular diseases. Remarkably, bidirectional transcription of repeat expansions has been identified in at least 14 of these diseases. More remarkably, a growing number of studies has been showing that both sense and antisense repeat RNAs are able to dysregulate important cellular pathways, contributing together to the observed clinical phenotype. Notably, antisense repeat RNAs from spinocerebellar ataxia type 7, myotonic dystrophy type 1, Huntington's disease and frontotemporal dementia/amyotrophic lateral sclerosis associated genes have been implicated in transcriptional regulation of sense gene expression, acting either at a transcriptional or posttranscriptional level. The recent evidence that antisense repeat RNAs could modulate gene expression broadens our understanding of the pathogenic pathways and adds more complexity to the development of therapeutic strategies for these disorders. In this review, we cover the amazing progress made in the understanding of the pathogenic mechanisms associated with repeat expansion neurodegenerative and neuromuscular diseases with a focus on the impact of antisense repeat transcription in the development of efficient therapies.
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12
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Hashem V, Tiwari A, Bewick B, Teive HAG, Moscovich M, Schüele B, Bushara K, Bower M, Rasmussen A, Tsai YC, Clark T, McFarland K, Ashizawa T. Pulse-Field capillary electrophoresis of repeat-primed PCR amplicons for analysis of large repeats in Spinocerebellar Ataxia Type 10. PLoS One 2020; 15:e0228789. [PMID: 32160188 PMCID: PMC7065784 DOI: 10.1371/journal.pone.0228789] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2019] [Accepted: 01/23/2020] [Indexed: 12/13/2022] Open
Abstract
Large expansions of microsatellite DNA cause several neurological diseases. In Spinocerebellar ataxia type 10 (SCA10), the repeat interruptions change disease phenotype; an (ATTCC)n or a (ATCCT)n/(ATCCC)n interruption within the (ATTCT)n repeat is associated with the robust phenotype of ataxia and epilepsy while mostly pure (ATTCT)n may have reduced penetrance. Large repeat expansions of SCA10, and many other microsatellite expansions, can exceed 10,000 base pairs (bp) in size. Conventional next generation sequencing (NGS) technologies are ineffective in determining internal sequence contents or size of these expanded repeats. Using repeat primed PCR (RP-PCR) in conjunction with a high-sensitivity pulsed-field capillary electrophoresis fragment analyzer (FEMTO-Pulse, Agilent, Santa Clara, CA) (RP-FEMTO hereafter), we successfully determined sequence content of large expansion repeats in genomic DNA of SCA10 patients and transformed yeast artificial chromosomes containing SCA10 repeats. This RP-FEMTO is a simple and economical methodology which could complement emerging NGS for very long sequence reads such as Single Molecule, Real-Time (SMRT) and nanopore sequencing technologies.
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Affiliation(s)
- Vera Hashem
- Department of Neurology, Houston Methodist Research Institute, Houston, Texas, United States of America
| | - Anjana Tiwari
- Department of Neurology, Houston Methodist Research Institute, Houston, Texas, United States of America
| | - Brittani Bewick
- Department of Neurology, Houston Methodist Research Institute, Houston, Texas, United States of America
| | - Helio A. G. Teive
- Movement Disorders Unit, Neurology Service, Department of Internal Medicine, Hospital de Clinicas, Federal University of Paraná, Curitiba, PR, Brazil
| | - Mariana Moscovich
- Department of Internal Medicine, Federal University of Paraná, Curitiba, Paraná, Brazil
| | - Birgitt Schüele
- Department of Pathology, Stanford University School of Medicine, Stanford, California, United States of America
| | - Khalaf Bushara
- Department of Neurology, University of Minnesota Medical Center, Minneapolis, Minnesota, United States of America
| | - Matt Bower
- Institute of Human Genetics, University of Minnesota Medical Center, Minneapolis, Minnesota, United States of America
| | - Astrid Rasmussen
- Oklahoma Medical Research Foundation, Oklahoma City, OK, USA
- Instituto Nacional de Ciencias Medicas y Nutricion Salvador Zubiran, Mexico City, CDMX, Mexico
| | - Yu-Chih Tsai
- Pacific Biosciences of California, Inc, Menlo Park, California, United States of America
| | - Tyson Clark
- Pacific Biosciences of California, Inc, Menlo Park, California, United States of America
| | - Karen McFarland
- Department of Neurology and The McKnight Brain Institute, University of Florida, Gainesville, Florida, United States of America
| | - Tetsuo Ashizawa
- Department of Neurology, Houston Methodist Research Institute, Houston, Texas, United States of America
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13
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Genetic and clinical analyses of spinocerebellar ataxia type 8 in mainland China. J Neurol 2019; 266:2979-2986. [DOI: 10.1007/s00415-019-09519-2] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2019] [Revised: 08/19/2019] [Accepted: 08/19/2019] [Indexed: 02/01/2023]
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14
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Abstract
The spinocerebellar ataxias (SCAs) are a genetically heterogeneous group of autosomal dominantly inherited progressive disorders, the clinical hallmark of which is loss of balance and coordination accompanied by slurred speech; onset is most often in adult life. Genetically, SCAs are grouped as repeat expansion SCAs, such as SCA3/Machado-Joseph disease (MJD), and rare SCAs that are caused by non-repeat mutations, such as SCA5. Most SCA mutations cause prominent damage to cerebellar Purkinje neurons with consecutive cerebellar atrophy, although Purkinje neurons are only mildly affected in some SCAs. Furthermore, other parts of the nervous system, such as the spinal cord, basal ganglia and pontine nuclei in the brainstem, can be involved. As there is currently no treatment to slow or halt SCAs (many SCAs lead to premature death), the clinical care of patients with SCA focuses on managing the symptoms through physiotherapy, occupational therapy and speech therapy. Intense research has greatly expanded our understanding of the pathobiology of many SCAs, revealing that they occur via interrelated mechanisms (including proteotoxicity, RNA toxicity and ion channel dysfunction), and has led to the identification of new targets for treatment development. However, the development of effective therapies is hampered by the heterogeneity of the SCAs; specific therapeutic approaches may be required for each disease.
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15
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Loureiro JR, Oliveira CL, Mota C, Castro AF, Costa C, Loureiro JL, Coutinho P, Martins S, Sequeiros J, Silveira I. Mutational mechanism for DAB1 (ATTTC) n insertion in SCA37: ATTTT repeat lengthening and nucleotide substitution. Hum Mutat 2019; 40:404-412. [PMID: 30588707 DOI: 10.1002/humu.23704] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2018] [Revised: 11/28/2018] [Accepted: 12/22/2018] [Indexed: 12/20/2022]
Abstract
Dynamic mutations by microsatellite instability are the molecular basis of a growing number of neuromuscular and neurodegenerative diseases. Repetitive stretches in the human genome may drive pathogenicity, either by expansion above a given threshold, or by insertion of abnormal tracts in nonpathogenic polymorphic repetitive regions, as is the case in spinocerebellar ataxia type 37 (SCA37). We have recently established that this neurodegenerative disease is caused by an (ATTTC)n insertion within an (ATTTT)n in a noncoding region of DAB1. We now investigated the mutational mechanism that originated the (ATTTC)n insertion within an ancestral (ATTTT)n . Approximately 3% of nonpathogenic (ATTTT)n alleles are interspersed by AT-rich motifs, contrarily to mutant alleles that are composed of pure (ATTTT)n and (ATTTC)n stretches. Haplotype studies in unaffected chromosomes suggested that the primary mutational mechanism, leading to the (ATTTC)n insertion, was likely one or more T>C substitutions in an (ATTTT)n pure allele of approximately 200 repeats. Then, the (ATTTC)n expanded in size, originating a deleterious allele in DAB1 that leads to SCA37. This is likely the mutational mechanism in three similar (TTTCA)n insertions responsible for familial myoclonic epilepsy. Because (ATTTT)n tracts are frequent in the human genome, many loci could be at risk for this mutational process.
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Affiliation(s)
- Joana R Loureiro
- Genetics of Cognitive Dysfunction Laboratory, i3S-Instituto de Investigação e Inovação em Saúde, Universidade do Porto, Porto, Portugal.,IBMC- Institute for Molecular and Cell Biology, Universidade do Porto, Porto, Portugal.,ICBAS, Universidade do Porto, Porto, Portugal
| | - Cláudia L Oliveira
- Genetics of Cognitive Dysfunction Laboratory, i3S-Instituto de Investigação e Inovação em Saúde, Universidade do Porto, Porto, Portugal.,IBMC- Institute for Molecular and Cell Biology, Universidade do Porto, Porto, Portugal
| | - Carolina Mota
- Genetics of Cognitive Dysfunction Laboratory, i3S-Instituto de Investigação e Inovação em Saúde, Universidade do Porto, Porto, Portugal.,IBMC- Institute for Molecular and Cell Biology, Universidade do Porto, Porto, Portugal
| | - Ana F Castro
- Genetics of Cognitive Dysfunction Laboratory, i3S-Instituto de Investigação e Inovação em Saúde, Universidade do Porto, Porto, Portugal.,IBMC- Institute for Molecular and Cell Biology, Universidade do Porto, Porto, Portugal
| | - Cristina Costa
- Department of Neurology, Hospital Prof. Doutor Fernando Fonseca, Amadora, Portugal
| | - José L Loureiro
- IBMC- Institute for Molecular and Cell Biology, Universidade do Porto, Porto, Portugal.,UnIGENe, i3S-Instituto de Investigação e Inovação em Saúde, Universidade do Porto, Porto, Portugal.,Department of Neurology, Hospital São Sebastião, Feira, Portugal
| | - Paula Coutinho
- IBMC- Institute for Molecular and Cell Biology, Universidade do Porto, Porto, Portugal.,UnIGENe, i3S-Instituto de Investigação e Inovação em Saúde, Universidade do Porto, Porto, Portugal
| | - Sandra Martins
- Population Genetics & Evolution, i3S-Instituto de Investigação e Inovação em Saúde, Universidade do Porto, Porto, Portugal.,IPATIMUP - Institute of Molecular Pathology and Immunology, University of Porto, Porto, Portugal
| | - Jorge Sequeiros
- IBMC- Institute for Molecular and Cell Biology, Universidade do Porto, Porto, Portugal.,ICBAS, Universidade do Porto, Porto, Portugal.,UnIGENe, i3S-Instituto de Investigação e Inovação em Saúde, Universidade do Porto, Porto, Portugal
| | - Isabel Silveira
- Genetics of Cognitive Dysfunction Laboratory, i3S-Instituto de Investigação e Inovação em Saúde, Universidade do Porto, Porto, Portugal.,IBMC- Institute for Molecular and Cell Biology, Universidade do Porto, Porto, Portugal
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16
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Pešović J, Perić S, Brkušanin M, Brajušković G, Rakočević-Stojanović V, Savić-Pavićević D. Repeat Interruptions Modify Age at Onset in Myotonic Dystrophy Type 1 by Stabilizing DMPK Expansions in Somatic Cells. Front Genet 2018; 9:601. [PMID: 30546383 PMCID: PMC6278776 DOI: 10.3389/fgene.2018.00601] [Citation(s) in RCA: 32] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2018] [Accepted: 11/15/2018] [Indexed: 12/19/2022] Open
Abstract
CTG expansions in DMPK gene, causing myotonic dystrophy type 1 (DM1), are characterized by pronounced somatic instability. A large proportion of variability of somatic instability is explained by expansion size and patient's age at sampling, while individual-specific differences are attributed to additional factors. The age at onset is extremely variable in DM1, and inversely correlates with the expansion size and individual-specific differences in somatic instability. Three to five percent of DM1 patients carry repeat interruptions and some appear with later age at onset than expected for corresponding expansion size. Herein, we characterized somatic instability of interrupted DMPK expansions and the effect on age at onset in our previously described patients. Repeat-primed PCR showed stable structures of different types and patterns of repeat interruptions in blood cells over time and buccal cells. Single-molecule small-pool PCR quantification of somatic instability and mathematical modeling showed that interrupted expansions were characterized by lower level of somatic instability accompanied by slower progression over time. Mathematical modeling demonstrated that individual-specific differences in somatic instability had greater influence on age at onset in patients with interrupted expansions. Therefore, repeat interruptions have clinical importance for disease course in DM1 patients due to stabilizing effect on DMPK expansions in somatic cells.
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Affiliation(s)
- Jovan Pešović
- Center for Human Molecular Genetics, Faculty of Biology, University of Belgrade, Belgrade, Serbia
| | - Stojan Perić
- School of Medicine, University of Belgrade, Belgrade, Serbia.,Neurology Clinic, Clinical Center of Serbia, Belgrade, Serbia
| | - Miloš Brkušanin
- Center for Human Molecular Genetics, Faculty of Biology, University of Belgrade, Belgrade, Serbia
| | - Goran Brajušković
- Center for Human Molecular Genetics, Faculty of Biology, University of Belgrade, Belgrade, Serbia
| | - Vidosava Rakočević-Stojanović
- School of Medicine, University of Belgrade, Belgrade, Serbia.,Neurology Clinic, Clinical Center of Serbia, Belgrade, Serbia
| | - Dušanka Savić-Pavićević
- Center for Human Molecular Genetics, Faculty of Biology, University of Belgrade, Belgrade, Serbia
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17
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Wang M, Guo S, Yao W, Wang J, Tao J, Zhou Y, Ying B. Identification of Abnormal 51 CTA/CTG Expansion as Probably the Shortest Pathogenic Allele for Spinocerebellar Ataxia-8 in China. Neurosci Bull 2018; 34:859-862. [PMID: 29943235 DOI: 10.1007/s12264-018-0247-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2018] [Accepted: 05/20/2018] [Indexed: 02/05/2023] Open
Affiliation(s)
- Minjin Wang
- Department of Laboratory Medicine, West China Hospital, Sichuan University, Chengdu, 610041, China
| | - Shuo Guo
- Department of Laboratory Medicine, West China Hospital, Sichuan University, Chengdu, 610041, China
| | - Wencong Yao
- Department of Laboratory Medicine, West China Hospital, Sichuan University, Chengdu, 610041, China
| | - Jun Wang
- Department of Laboratory Medicine, West China Hospital, Sichuan University, Chengdu, 610041, China
| | - Jianxia Tao
- Department of Laboratory Medicine, West China Hospital, Sichuan University, Chengdu, 610041, China
| | - Yanbing Zhou
- Department of Laboratory Medicine, West China Hospital, Sichuan University, Chengdu, 610041, China
| | - Binwu Ying
- Department of Laboratory Medicine, West China Hospital, Sichuan University, Chengdu, 610041, China.
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18
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Tomé S, Dandelot E, Dogan C, Bertrand A, Geneviève D, Péréon Y, Simon M, Bonnefont JP, Bassez G, Gourdon G. Unusual association of a unique CAG interruption in 5' of DM1 CTG repeats with intergenerational contractions and low somatic mosaicism. Hum Mutat 2018; 39:970-982. [PMID: 29664219 DOI: 10.1002/humu.23531] [Citation(s) in RCA: 32] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2017] [Revised: 03/23/2018] [Accepted: 04/10/2018] [Indexed: 11/11/2022]
Abstract
Myotonic dystrophy type 1 (DM1) is a dominant multisystemic disorder associated with high variability of symptoms and anticipation. DM1 is caused by an unstable CTG repeat expansion that usually increases in successive generations and tissues. DM1 family pedigrees have shown that ∼90% and 10% of transmissions result in expansions and contractions of the CTG repeat, respectively. To date, the mechanisms of CTG repeat contraction remain poorly documented in DM1. In this report, we identified two new DM1 families with apparent contractions and no worsening of DM1 symptoms in two and three successive maternal transmissions. A new and unique CAG interruption was found in 5' of the CTG expansion in one family, whereas multiple 5' CCG interruptions were detected in the second family. We showed that these interruptions are associated with maternal intergenerational contractions and low somatic mosaicism in blood. By specific triplet-prime PCR, we observed that CTG repeat changes (contractions/expansions) occur preferentially in 3' of the interruptions for both families.
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Affiliation(s)
- Stéphanie Tomé
- Laboratory CTGDM, Inserm UMR1163, Paris, France; Institut Imagine, Université Paris-Descartes-Sorbonne Paris-Cité, Paris, France
| | - Elodie Dandelot
- Laboratory CTGDM, Inserm UMR1163, Paris, France; Institut Imagine, Université Paris-Descartes-Sorbonne Paris-Cité, Paris, France
| | - Céline Dogan
- Neuromuscular Reference Center, AP-HP, Hôpital Pitié-Salpêtrière, F-75013, Paris, France
| | - Alexis Bertrand
- Laboratory CTGDM, Inserm UMR1163, Paris, France; Institut Imagine, Université Paris-Descartes-Sorbonne Paris-Cité, Paris, France
| | - David Geneviève
- Molecular Genetic Laboratory, Necker Hospital, Paris, France.,Département de Génétique Médicale, Maladies Rares et Médecine Personnalisée, CHU Montpellier, Université Montpellier, Montpellier, France
| | - Yann Péréon
- Centre for Neuromuscular Diseases, Hôtel-Dieu Hospital, Nantes, France
| | -
- Pauline Arnaud: Department of genetic, Bichat Hospital, Paris, France, Raphaële Chasserieau: Centre for Neuromuscular Diseases, Hôtel-Dieu Hospital, Nantes, France, Pascal Cintas: Neuromuscular Reference Center, Purpan Hospital, Toulouse, France, Ana-maria Cobo Esteban: Neuromuscular Reference Center, Marin Hospital, Hendaye, France, Marie-Carmen Cruz: Neuromuscular Reference Center, Purpan Hospital, Toulouse, France, Dalil Hamroun: Centre Hospitalo-Universitaire de Montpellier, Montpellier, France, Armelle Magot: Neuromuscular Reference Center, Hôtel-Dieu Hospital, Nantes, France, Alexandra Nadaj-Pakleza Neuromuscular Reference Center, Larrey Hospital, Angers, France, Anne-catherine Aube-Gauthier Neuromuscular Reference Center, Larrey Hospital, Angers, France, Andoni Urtizberea: Neuromuscular Reference Center, Marin Hospital, Hendaye, France
| | - Marie Simon
- Molecular Genetic Laboratory, Necker Hospital, Paris, France
| | | | - Guillaume Bassez
- Sorbonne Université, Inserm, UMRS974, Neuromuscular Reference center, AP-HP, Hôpital Pitié-Salpêtrière, F-75013, Paris, France
| | - Geneviève Gourdon
- Laboratory CTGDM, Inserm UMR1163, Paris, France; Institut Imagine, Université Paris-Descartes-Sorbonne Paris-Cité, Paris, France
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19
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Abstract
Frontotemporal dementia (FTD) is a neurodegenerative disorder characterized by progressive changes in behavior, personality, and language with involvement of the frontal and temporal regions of the brain. About 40% of FTD cases have a positive family history, and about 10% of these cases are inherited in an autosomal-dominant pattern. These gene defects present with distinct clinical phenotypes. As the diagnosis of FTD becomes more recognizable, it will become increasingly important to keep these gene mutations in mind. In this chapter, we review the genes with known associations to FTD. We discuss protein functions, mutation frequencies, clinical phenotypes, imaging characteristics, and pathology associated with these genes.
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Affiliation(s)
- Jessica Deleon
- Memory and Aging Center, Department of Neurology, University of California, San Francisco, CA, United States
| | - Bruce L Miller
- Memory and Aging Center, Department of Neurology, University of California, San Francisco, CA, United States.
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20
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Sequence configuration of spinocerebellar ataxia type 8 repeat expansions in a Japanese cohort of 797 ataxia subjects. J Neurol Sci 2017; 382:87-90. [PMID: 29111027 DOI: 10.1016/j.jns.2017.08.3256] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2017] [Revised: 08/04/2017] [Accepted: 08/28/2017] [Indexed: 11/23/2022]
Abstract
Spinocerebellar ataxia type 8 (SCA8), an autosomal dominant neurodegenerative disorder showing slowly progressive cerebellar ataxia, is caused by a tri-nucleotide CTG repeat expansion (CTGexp) in the SCA8 gene. As the CTGexp is not fully penetrant, the significance of screening CTGexp in ataxia subjects remains obscure. We tested SCA8 CTGexp in a cohort of 797 ataxia subjects, and if present, its sequence configuration was analyzed. CTGexp was found in 16 alleles from 14 individuals, 2 of which was homozygous for CTGexp. Nucleotide sequencing disclosed 3 types of CTGexp sequence configurations: uninterrupted CTGexp, tri-nucleotide CTA interruption and CCG interruption. The 2 individuals with homozygous expansions were both sporadic cases with clinical features compatible with SCA8, supporting gene dosage effect. Seven out of 14 CTGexp-positive subjects were also carriers of other SCA expansions [Machado-Joseph disease (n=1), SCA6 (n=3) and SCA31 (n=3)], whereas 7 others were not complicated with such major SCAs. Ages of onset in subjects with pure CTGexp tended to be earlier than those with interrupted CTGexp among the 7 subjects not complicated by major SCAs, suggesting that pure CTGexp have stronger pathogenic effect than interrupted CTGexps. The present study underscores importance of disclosing sequence configuration when testing SCA8.
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21
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Vincent JB. Unstable repeat expansion in major psychiatric disorders: two decades on, is dynamic DNA back on the menu? Psychiatr Genet 2017; 26:156-65. [PMID: 27270050 DOI: 10.1097/ypg.0000000000000141] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
For a period in the mid-1990s, soon after the discovery of the involvement of trinucleotide repeat expansions in fragile-X syndrome (both A and E), Huntington's disease, myotonic dystrophy, and a number of hereditary ataxias, there was a clear sense that this new disease mechanism might provide answers for psychiatric disorders. Given the then failures to replicate initial genetic linkage findings for schizophrenia (SCZ) and bipolar disorder (BD), a greater emphasis was placed on the role of complex and non-Mendelian mechanisms, and repeat instability appeared to have the potential to provide adequate explanations for numerous apparently non-Mendelian features such as anticipation, incomplete penetrance, sporadic occurrence, and nonconcordance of monozygotic twins. Initial molecular studies using a ligation-based amplification method (repeat expansion detection) appeared to support the involvement of CAG•CTG repeat expansion in SCZ and BD. However, subsequent studies that dissected the large repeats responsible for much of the positive signal showed that there were three main loci where CAG•CTG repeat expansion was occurring (on 13q21.33, 17q21.33-q22, and 18q21.2). None of the expansions at these loci appeared to segregate with SCZ or BD, and research into repeat expansions in psychiatric illness petered out in the early 2000s. The 13q expansion occurs within a noncoding RNA and appears to be associated with spinocerebellar ataxia 8 (SCA8), but with a still unexplained dichotomy in penetrance - either very high or very low. The 17q expansion occurs within an intron of the carbonic anhydrase-like gene, CA10. The 18q expansion is located within an intron of the TCF4 gene. Mutations in TCF4 are a known cause of Pitt-Hopkins syndrome. Also, pertinently, genome-wide association studies have shown a well-replicated association between TCF4 and SCZ. Two decades on, in 2016, it appears to be an appropriate juncture to reflect on what we have learned, and, with the arrival of newer technologies, whether there is any mileage to be made in revisiting the unstable DNA hypothesis for psychiatric illness.
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Affiliation(s)
- John B Vincent
- aMolecular Neuropsychiatry & Development (MiND) Lab, Centre for Addiction and Mental Health, Campbell Family Mental Health Research Institute bInstitute of Medical Science cDepartment of Psychiatry, University of Toronto, Toronto, Ontario, Canada
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22
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Landrian I, McFarland KN, Liu J, Mulligan CJ, Rasmussen A, Ashizawa T. Inheritance patterns of ATCCT repeat interruptions in spinocerebellar ataxia type 10 (SCA10) expansions. PLoS One 2017; 12:e0175958. [PMID: 28423040 PMCID: PMC5397023 DOI: 10.1371/journal.pone.0175958] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2016] [Accepted: 04/03/2017] [Indexed: 11/18/2022] Open
Abstract
Spinocerebellar ataxia type 10 (SCA10), an autosomal dominant cerebellar ataxia disorder, is caused by a non-coding ATTCT microsatellite repeat expansion in the ataxin 10 gene. In a subset of SCA10 families, the 5’-end of the repeat expansion contains a complex sequence of penta- and heptanucleotide interruption motifs which is followed by a pure tract of tandem ATCCT repeats of unknown length at its 3’-end. Intriguingly, expansions that carry these interruption motifs correlate with an epileptic seizure phenotype and are unstable despite the theory that interruptions are expected to stabilize expanded repeats. To examine the apparent contradiction of unstable, interruption-positive SCA10 expansion alleles and to determine whether the instability originates outside of the interrupted region, we sequenced approximately 1 kb of the 5’-end of SCA10 expansions using the ATCCT-PCR product in individuals across multiple generations from four SCA10 families. We found that the greatest instability within this region occurred in paternal transmissions of the allele in stretches of pure ATTCT motifs while the intervening interrupted sequences were stable. Overall, the ATCCT interruption changes by only one to three repeat units and therefore cannot account for the instability across the length of the disease allele. We conclude that the AT-rich interruptions locally stabilize the SCA10 expansion at the 5’-end but do not completely abolish instability across the entire span of the expansion. In addition, analysis of the interruption alleles across these families support a parsimonious single origin of the mutation with a shared distant ancestor.
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Affiliation(s)
- Ivette Landrian
- Department of Neurology, College of Medicine, and the McKnight Brain Institute, University of Florida, Gainesville, Florida, United States of America
| | - Karen N. McFarland
- Department of Neurology, College of Medicine, and the McKnight Brain Institute, University of Florida, Gainesville, Florida, United States of America
- Center for Translational Research in Neurodegenerative Disease, The University of Florida, Gainesville, Florida, United States of America
- * E-mail:
| | - Jilin Liu
- Department of Neurology, College of Medicine, and the McKnight Brain Institute, University of Florida, Gainesville, Florida, United States of America
| | - Connie J. Mulligan
- Department of Anthropology, College of Liberal Arts and Sciences, University of Florida, Gainesville, Florida, United States of America
- Genetics Institute, University of Florida, Gainesville, Florida, United States of America
| | - Astrid Rasmussen
- Arthritis and Clinical Immunology Research Program, Oklahoma Medical Research Foundation, Oklahoma City, Oklahoma, United States of America
| | - Tetsuo Ashizawa
- Department of Neurology, College of Medicine, and the McKnight Brain Institute, University of Florida, Gainesville, Florida, United States of America
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23
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Zhang N, Ashizawa T. RNA toxicity and foci formation in microsatellite expansion diseases. Curr Opin Genet Dev 2017; 44:17-29. [PMID: 28208060 DOI: 10.1016/j.gde.2017.01.005] [Citation(s) in RCA: 65] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2016] [Revised: 01/04/2017] [Accepted: 01/18/2017] [Indexed: 12/11/2022]
Abstract
More than 30 incurable neurological and neuromuscular diseases are caused by simple microsatellite expansions consisted of 3-6 nucleotides. These repeats can occur in non-coding regions and often result in a dominantly inherited disease phenotype that is characteristic of a toxic RNA gain-of-function. The expanded RNA adopts unusual secondary structures, sequesters various RNA binding proteins to form insoluble nuclear foci, and causes cellular defects at a multisystem level. Nuclear foci are dynamic in size, shape and colocalization of RNA binding proteins in different expansion diseases and tissue types. This review sets to provide new insights into the disease mechanisms of RNA toxicity and foci modulation, in light of recent advancement on bi-directional transcription, antisense RNA, repeat-associated non-ATG translation and beyond.
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Affiliation(s)
- Nan Zhang
- Neurosciences Research Program, Houston Methodist Research Institute, Houston, TX 77030, United States; Division of Cell and Molecular Biology, South Kensington Campus, Imperial College London, London SW7 2AZ, UK
| | - Tetsuo Ashizawa
- Neurosciences Research Program, Houston Methodist Research Institute, Houston, TX 77030, United States.
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24
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Arnheim N, Calabrese P. Germline Stem Cell Competition, Mutation Hot Spots, Genetic Disorders, and Older Fathers. Annu Rev Genomics Hum Genet 2016; 17:219-43. [PMID: 27070266 DOI: 10.1146/annurev-genom-083115-022656] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Some de novo human mutations arise at frequencies far exceeding the genome average mutation rate. Examples include the common mutations at one or a few sites in the genes that cause achondroplasia, Apert syndrome, multiple endocrine neoplasia type 2B, and Noonan syndrome. These mutations are recurrent, provide a gain of function, are paternally derived, and are more likely to be transmitted as the father ages. Recent experiments have tested whether the high mutation frequencies are due to an elevated mutation rate per cell division, as expected, or to an advantage of the mutant spermatogonial stem cells over wild-type stem cells. The evidence, which includes the surprising discovery of testis mutation clusters, rules out the former model but not the latter. We propose how the mutations might alter spermatogonial stem cell function and discuss how germline selection contributes to the paternal age effect, the human mutational load, and adaptive evolution.
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Affiliation(s)
- Norman Arnheim
- Molecular and Computational Biology Program, University of Southern California, Los Angeles, California 90089-2910; ,
| | - Peter Calabrese
- Molecular and Computational Biology Program, University of Southern California, Los Angeles, California 90089-2910; ,
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Loureiro JR, Oliveira CL, Silveira I. Unstable repeat expansions in neurodegenerative diseases: nucleocytoplasmic transport emerges on the scene. Neurobiol Aging 2015; 39:174-83. [PMID: 26923414 DOI: 10.1016/j.neurobiolaging.2015.12.007] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2015] [Revised: 12/07/2015] [Accepted: 12/15/2015] [Indexed: 12/12/2022]
Abstract
An astonishing number of neurological diseases result from expansion of unstable repetitive sequences causing alterations in key neuronal processes. Some are progressive late-onset conditions related to aging, such as the spinocerebellar ataxias. In several of these pathologies, the expanded repeat is transcribed, producing an expanded RNA repeat that causes neurodegeneration by a complex mechanism, comprising 3 main pathways. These include (1) accumulation in the nucleus of RNA foci, resulting from sequestration of RNA-binding proteins functioning in important neuronal cascades; (2) decrease in availability of RNA-binding proteins, such as splicing factors, causing alternative splicing misregulation with imbalance in the expression ratio of neuronal isoforms; and (3) generation of neurotoxic peptides, produced from repeat-associated non-ATG-initiated translation across the RNA repeat, in all reading frames. Recently, 2 pathologies characterized by impaired motor function, cognitive decline, or/and degeneration of motor neurons have been found that have broaden our understanding of these diseases. Moreover, the finding of compromised nucleocytoplasmic transport opens new avenues for research. This review will cover the amazing progress regarding these conditions.
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Affiliation(s)
- Joana R Loureiro
- Group Genetics of Cognitive Dysfunction, i3s- Instituto de Investigação e Inovação em Saúde, Universidade do Porto, Portugal; IBMC-Instituto de Biologia Molecular e Celular, Universidade do Porto, Portugal; ICBAS, Universidade do Porto, Portugal
| | - Claudia L Oliveira
- Group Genetics of Cognitive Dysfunction, i3s- Instituto de Investigação e Inovação em Saúde, Universidade do Porto, Portugal; IBMC-Instituto de Biologia Molecular e Celular, Universidade do Porto, Portugal; ICBAS, Universidade do Porto, Portugal
| | - Isabel Silveira
- Group Genetics of Cognitive Dysfunction, i3s- Instituto de Investigação e Inovação em Saúde, Universidade do Porto, Portugal; IBMC-Instituto de Biologia Molecular e Celular, Universidade do Porto, Portugal; ICBAS, Universidade do Porto, Portugal.
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Subramony S, Moscovich M, Ashizawa T. Genetics and Clinical Features of Inherited Ataxias. Mov Disord 2015. [DOI: 10.1016/b978-0-12-405195-9.00062-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
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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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Kim JS, Son TO, Youn J, Ki CS, Cho JW. Non-Ataxic Phenotypes of SCA8 Mimicking Amyotrophic Lateral Sclerosis and Parkinson Disease. J Clin Neurol 2013; 9:274-9. [PMID: 24285970 PMCID: PMC3840139 DOI: 10.3988/jcn.2013.9.4.274] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2012] [Revised: 03/06/2013] [Accepted: 03/06/2013] [Indexed: 12/13/2022] Open
Abstract
Background Spinocerebellar ataxia (SCA) type 8 (SCA8) is an inherited neurodegenerative disorder caused by the expansion of untranslated CTA/CTG triplet repeats on 13q21. The phenomenology of SCA8 is relatively varied when compared to the other types of SCAs and its spectrum is not well established. Case Report Two newly detected cases of SCA8 with the nonataxic phenotype and unusual clinical manifestations such as dopaminergic-treatment-responsive parkinsonism and amyotrophic lateral sclerosis (ALS) are described herein. Family A expressed good dopaminergic treatment-responsive parkinsonism as an initial manifestation and developed mild cerebellar ataxia with additional movements, including dystonic gait and unusual oscillatory movement of the trunk, during the disease course. The proband of family B presented as probable ALS with cerebellar atrophy on brain MRI, with a positive family history (a brother with typical cerebellar ataxia) and genetic confirmation for SCA8. Conclusions Our findings support that the non-ataxic phenotypes could be caused by a mutation of the SCA8 locus which might affect neurons other than the cerebellum.
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Affiliation(s)
- Ji Sun Kim
- Department of Neurology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea. ; Department of Neurology, Soonchunhyang University Hospital, Soonchunhyang University School of Medicine, Seoul, Korea
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Martindale JE, Seneca S, Wieczorek S, Sequeiros J. Spinocerebellar ataxias: an example of the challenges associated with genetic databases for dynamic mutations. Hum Mutat 2012; 33:1359-65. [PMID: 22753119 DOI: 10.1002/humu.22156] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2012] [Accepted: 06/21/2012] [Indexed: 11/08/2022]
Abstract
Locus-specific databases are an important source of information for diagnostic laboratories and a valued means of improving quality of genetic testing. Although increasingly frequent, databases for oligonucleotide repeat expansions are still scarce, due to factors that make them different and the building of databases much more difficult. Definition of what constitutes "the repeat" to measure is not a simple matter and correct sizing is not always straightforward. Reference ranges and penetrance classes are not easy to establish. Acceptable margins of error depend on the disease and allele-size distribution, and vary according to size range and pathogenic significance. Inter- and intralaboratorial variance is well documented and allele distribution may vary among populations. The spinocerebellar ataxias, used only as an example of those difficulties, are also a highly heterogeneous group, which includes loci with both pathogenic repeat expansions and point mutations or insertions/deletions. They display a variable, but often overlapping phenotype, where genotype-phenotype correlation is difficult or nonexistent. Standard (Human Genome Variation Society) nomenclature is not appropriate for oligonucleotide repeats, as established at harmonization among all EMQN (European Molecular Genetics Network) external quality assessment (EQA) schemes for "repeat disorders." Curation of such databases is a difficult task, but one that needs to be addressed adequately and without much delay.
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Affiliation(s)
- Joanne E Martindale
- European Molecular Genetics Network (EMQN), spinocerebellar ataxias (SCAs) External Quality Assessment (EQA) Scheme organizer (JS) and assessors, Manchester, UK
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Rademakers R, Neumann M, Mackenzie IR. Advances in understanding the molecular basis of frontotemporal dementia. Nat Rev Neurol 2012; 8:423-34. [PMID: 22732773 DOI: 10.1038/nrneurol.2012.117] [Citation(s) in RCA: 297] [Impact Index Per Article: 24.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Frontotemporal dementia (FTD) is a clinical syndrome with a heterogeneous molecular basis. Until recently, the underlying cause was known in only a minority of cases that were associated with abnormalities of the tau protein or gene. In 2006, however, mutations in the progranulin gene were discovered as another important cause of familial FTD. That same year, TAR DNA-binding protein 43 (TDP-43) was identified as the pathological protein in the most common subtypes of FTD and amyotrophic lateral sclerosis (ALS). Since then, substantial efforts have been made to understand the functions and regulation of progranulin and TDP-43, as well as their roles in neurodegeneration. More recently, other DNA/RNA binding proteins (FET family proteins) have been identified as the pathological proteins in most of the remaining cases of FTD. In 2011, abnormal expansion of a hexanucleotide repeat in the gene C9orf72 was found to be the most common genetic cause of both FTD and ALS. All common FTD-causing genes have seemingly now been discovered and the main pathological proteins identified. In this Review, we highlight recent advances in understanding the molecular aspects of FTD, which will provide the basis for improved patient care through the development of more-targeted diagnostic tests and therapies.
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Affiliation(s)
- Rosa Rademakers
- Department of Neuroscience, Mayo Clinic Florida, Jacksonville, FL 32224, USA
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The spinocerebellar ataxias: clinical aspects and molecular genetics. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2012; 724:351-74. [PMID: 22411256 DOI: 10.1007/978-1-4614-0653-2_27] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Spinocerebellar ataxias (SCAs) are a highly heterogeneous group of inherited neurological disorders, based on clinical characterization alone with variable degrees of cerebellar ataxia often accompanied by additional cerebellar and noncerebellar symptoms which in most cases defy differentiation. Molecular causative deficits in at least 31 genes underlie the clinical symptoms in the SCAs by triggering cerebellar and, very frequently, brain stem dysfunction. The identification of the causative molecular deficits enables the molecular diagnosis of the different SCA subtypes and facilitates genetic counselling. Recent scientific advances are shedding light into developing therapeutic strategies. The scope of this chapter is to provide updated details of the spinocerebellar ataxias with particular emphasis on those aspects aimed at facilitating the clinical and genetic diagnoses.
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Ikeda Y, Ranum LPW, Day JW. Clinical and genetic features of spinocerebellar ataxia type 8. HANDBOOK OF CLINICAL NEUROLOGY 2012; 103:493-505. [PMID: 21827909 DOI: 10.1016/b978-0-444-51892-7.00031-0] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Affiliation(s)
- Yoshio Ikeda
- Department of Genetics, Cell Biology, and Development, University of Minnesota, Minneapolis, MN 55455, USA
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Affiliation(s)
- Tetsuo Ashizawa
- Department of Neurology, Evelyn & WIlliam L. McKinght Brain Institute, University of Florida, Gainesville, FL, USA.
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Marelli C, Cazeneuve C, Brice A, Stevanin G, Dürr A. Autosomal dominant cerebellar ataxias. Rev Neurol (Paris) 2011; 167:385-400. [PMID: 21546047 DOI: 10.1016/j.neurol.2011.01.015] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2010] [Accepted: 01/27/2011] [Indexed: 12/30/2022]
Abstract
Cerebellar ataxias with autosomal dominant transmission (ADCA) are far rarer than sporadic cases of cerebellar ataxia. The identification of genes involved in dominant forms has confirmed the genetic heterogeneity of these conditions and of the underlying mechanisms and pathways. To date, at least 28 genetic loci and, among them, 20 genes have been identified. In many instances, the phenotype is not restricted to cerebellar dysfunction but includes more complex multisystemic neurological deficits. Seven ADCA (SCA1, 2, 3, 6, 7, 17, and dentatorubro-pallido-luysian atrophy) are caused by repeat expansions in the corresponding proteins; phenotype-genotype correlations have shown that repeat size influences the progression of the disease, its severity and clinical differences among patients, including the phenomenon of anticipation between generations. All other ADCA are caused either by non-coding repeat expansions, conventional mutations or large rearrangements in genes with different functions. This review will focus on the genetic features of ADCA and on the clinical differences among the different forms.
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Affiliation(s)
- C Marelli
- Département de génétique et cytogénétique, consultation de génétique clinique, CHU Pitié-Salpêtrière, AP-HP, 47, boulevard de l'Hôpital, 75013 Paris, France
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Repeat associated non-ATG translation initiation: one DNA, two transcripts, seven reading frames, potentially nine toxic entities! PLoS Genet 2011; 7:e1002018. [PMID: 21423665 PMCID: PMC3053344 DOI: 10.1371/journal.pgen.1002018] [Citation(s) in RCA: 89] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
Diseases associated with unstable repetitive elements in the DNA, RNA, and amino acids have consistently revealed scientific surprises. Most diseases are caused by expansions of trinucleotide repeats, which ultimately lead to diseases like Huntington's disease, myotonic dystrophy, fragile X syndrome, and a series of spinocerebellar ataxias. These repeat mutations are dynamic, changing through generations and within an individual, and the repeats can be bi-directionally transcribed. Unsuspected modes of pathogenesis involve aberrant loss of protein expression; aberrant over-expression of non-mutant proteins; toxic-gain-of-protein function through expanded polyglutamine tracts that are encoded by expanded CAG tracts; and RNA-toxic-gain-of-function caused by transcripts harboring expanded CUG, CAG, or CGG tracts. A recent advance reveals that RNA transcripts with expanded CAG repeats can be translated in the complete absence of a starting ATG, and this Repeat Associated Non-ATG translation (RAN-translation) occurs across expanded CAG repeats in all reading frames (CAG, AGC, and GCA) to produce homopolymeric proteins of long polyglutamine, polyserine, and polyalanine tracts. Expanded CTG tracts expressing CUG transcripts also show RAN-translation occurring in all three frames (CUG, UGC, and GCU), to produce polyleucine, polycysteine, and polyalanine. These RAN-translation products can be toxic. Thus, one unstable (CAG)•(CTG) DNA can produce two expanded repeat transcripts and homopolymeric proteins with reading frames (the AUG-directed polyGln and six RAN-translation proteins), yielding a total of potentially nine toxic entities. The occurrence of RAN-translation in patient tissues expands our horizons of modes of disease pathogenesis. Moreover, since RAN-translation counters the canonical requirements of translation initiation, many new questions are now posed that must be addressed. This review covers RAN-translation and some of the pertinent questions.
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Abstract
Cerebellar ataxias with autosomal dominant transmission are rare, but identification of the associated genes has provided insight into the mechanisms that could underlie other forms of genetic or non-genetic ataxias. In many instances, the phenotype is not restricted to cerebellar dysfunction but includes complex multisystemic neurological deficits. The designation of the loci, SCA for spinocerebellar ataxia, indicates the involvement of at least two systems: the spinal cord and the cerebellum. 11 of 18 known genes are caused by repeat expansions in the corresponding proteins, sharing the same mutational mechanism. All other SCAs are caused by either conventional mutations or large rearrangements in genes with different functions, including glutamate signalling (SCA5/SPTBN2) and calcium signalling (SCA15/16/ITPR1), channel function (SCA13/KCNC3, SCA14/PRKCG, SCA27/FGF14), tau regulation (SCA11/TTBK2), and mitochondrial activity (SCA28/AFG3L2) or RNA alteration (SCA31/BEAN-TK2). The diversity of underlying mechanisms that give rise to the dominant cerebellar ataxias need to be taken into account to identify therapeutic targets.
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Affiliation(s)
- Alexandra Durr
- Université Pierre et Marie Curie-Paris, Centre de Recherche de l'Institut du Cerveau et de la Moelle Epinière, UMR-S975, Paris, France.
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37
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Braida C, Stefanatos RK, Adam B, Mahajan N, Smeets HJ, Niel F, Goizet C, Arveiler B, Koenig M, Lagier-Tourenne C, Mandel JL, Faber CG, de Die-Smulders CE, Spaans F, Monckton DG. Variant CCG and GGC repeats within the CTG expansion dramatically modify mutational dynamics and likely contribute toward unusual symptoms in some myotonic dystrophy type 1 patients. Hum Mol Genet 2010; 19:1399-412. [DOI: 10.1093/hmg/ddq015] [Citation(s) in RCA: 118] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
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38
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Understanding what determines the frequency and pattern of human germline mutations. Nat Rev Genet 2009; 10:478-88. [PMID: 19488047 DOI: 10.1038/nrg2529] [Citation(s) in RCA: 95] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Surprising findings about human germline mutation have come from applying new technologies to detect rare mutations in germline DNA, from analysing DNA sequence divergence between humans and closely related species, and from investigating human polymorphic variation. In this Review we discuss how these approaches affect our current understanding of the roles of sex, age, mutation hot spots, germline selection and genomic factors in determining human nucleotide substitution mutation patterns and frequencies. To enhance our understanding of mutation and disease, more extensive molecular data on the human germ line with regard to mutation origin, DNA repair, epigenetic status and the effect of newly arisen mutations on gamete development are needed.
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Musova Z, Mazanec R, Krepelova A, Ehler E, Vales J, Jaklova R, Prochazka T, Koukal P, Marikova T, Kraus J, Havlovicova M, Sedlacek Z. Highly unstable sequence interruptions of the CTG repeat in the myotonic dystrophy gene. Am J Med Genet A 2009; 149A:1365-74. [DOI: 10.1002/ajmg.a.32987] [Citation(s) in RCA: 117] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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Gupta A, Jankovic J. Spinocerebellar ataxia 8: variable phenotype and unique pathogenesis. Parkinsonism Relat Disord 2009; 15:621-6. [PMID: 19559641 DOI: 10.1016/j.parkreldis.2009.06.001] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/09/2009] [Revised: 06/01/2009] [Accepted: 06/02/2009] [Indexed: 12/16/2022]
Abstract
Spinocerebellar ataxia 8 (SCA8), a triplet repeat expansion disorder, is genetically distinct from the other inherited ataxias, but its unusually variable phenotype can make its diagnosis difficult. In this review we describe 3 new cases of genetically verified SCA8 to highlight the broad clinical spectrum of symptoms observed with this disorder and to draw attention to the features of myoclonus and migraine headaches, which in the context of cerebellar ataxia warrants the clinician to consider SCA8 as a potential diagnosis. We also address the controversy surrounding the genetic testing approach for diagnosing SCA8. Finally, we evaluate the evidence that SCA8 may affect calcium channel function and that the presentation of episodic ataxia and migraines suggests a clinical and pathogenic overlap of SCA8 with the channelopathies.
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Affiliation(s)
- Amitabh Gupta
- Department of Neurology, University of Toronto, Toronto, ON, Canada M5T 2S8
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41
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Ikeda Y, Daughters RS, Ranum LPW. Bidirectional expression of the SCA8 expansion mutation: one mutation, two genes. THE CEREBELLUM 2009; 7:150-8. [PMID: 18418692 DOI: 10.1007/s12311-008-0010-7] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
Spinocerebellar ataxia type 8 (SCA8) is a dominantly inherited, slowly progressive neurodegenerative disorder caused by a CTG.CAG repeat expansion located on chromosome 13q21. The expansion mutation was isolated directly from the DNA of a single patient using RAPID cloning and subsequently shown to co-segregate with disease in additional ataxia families including a seven-generation kindred (the MN-A family). The size-dependent penetrance of the repeat found in the large MN-A kindred makes it appear as though some parts of the family have a dominant disorder while other parts of this same family have recessive or sporadic forms of ataxia. While the linkage and size-dependent penetrance of the SCA8 CTG.CAG expansion in the MN-A family argue that the SCA8 expansion causes ataxia, the reduced penetrance in other SCA8 families and the discovery of expansions in the general population have led to a controversy surrounding whether or not the SCA8 expansion is pathogenic. A recently reported mouse model in which SCA8 BAC-expansion but not BAC-control lines develop a progressive neurological phenotype now demonstrates the pathogenicity of the (CTG.CAG)(n) expansion. These mice show a loss of cerebellar GABAergic inhibition and, similar to human patients, have 1C2-positive intranuclear inclusions in Purkinje cells and other neurons. Additional studies demonstrate that the SCA8 expansion is expressed in both directions (CUG and CAG) and that a novel gene expressed in the CAG direction encodes a pure polyglutamine expansion protein (ataxin 8, ATXN8). Moreover, the expression of non-coding (CUG)(n) expansion transcripts (ataxin 8 opposite strand, ATXN8OS) and the discovery of intranuclear polyglutamine inclusions suggest SCA8 pathogenesis may involve toxic gain-of-function mechanisms at both the protein and RNA levels. Our data, combined with the recently reported antisense transcripts spanning the DM1 repeat expansion in the CAG direction and the growing number of reports of antisense transcripts expressed throughout the mammalian genome, raises the possibility that bidirectional expression across pathogenic microsatellite expansions may occur in other expansion disorders, and that potential pathogenic effects of mutations expressed from both strands should be considered.
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Affiliation(s)
- Yoshio Ikeda
- Department of Genetics, Cell Biology, and Development, University of Minnesota, Minneapolis, MN 55455, USA
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Chen IC, Lin HY, Lee GC, Kao SH, Chen CM, Wu YR, Hsieh-Li HM, Su MT, Lee-Chen GJ. Spinocerebellar ataxia type 8 larger triplet expansion alters histone modification and induces RNA foci. BMC Mol Biol 2009; 10:9. [PMID: 19203395 PMCID: PMC2647542 DOI: 10.1186/1471-2199-10-9] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2008] [Accepted: 02/10/2009] [Indexed: 11/17/2022] Open
Abstract
BACKGROUND Spinocerebellar ataxia type 8 (SCA8) involves the expression of an expanded CTG/CAG combined repeats (CR) from opposite strands producing CUG expansion transcripts (ataxin 8 opposite strand, ATXN8OS) and a polyglutamine expansion protein (ataxin 8, ATXN8). The pathogenesis of SCA8 is complex and the spectrum of clinical presentations is broad. RESULTS Using stably induced cell models expressing 0, 23, 88 and 157 CR, we study the role of ATXN8OS transcripts in SCA8 pathogenesis. In the absence of doxycycline, the stable ATXN8OS CR cell lines exhibit low levels of ATXN8OS expression and a repeat length-related increase in staurosporine sensitivity and in the number of annexin positive cells. A repeat length-dependent repression of ATXN8OS expression was also notable. Addition of doxycycline leads to 25 approximately 50 times more ATXN8OS RNA expression with a repeat length-dependent increase in fold of ATXN8OS RNA induction. ChIP-PCR assay using anti-dimethyl-histone H3-K9 and anti-acetyl-histone H3-K14 antibodies revealed increased H3-K9 dimethylation and reduced H3-K14 acetylation around the ATXN8OS cDNA gene in 157 CR line. The repeat length-dependent increase in induction fold is probably due to the increased RNA stability as demonstrated by monitoring ATXN8OS RNA decay in cells treated with the transcriptional inhibitor, actinomycin D. In cells stably expressing ATXN8OS, RNA FISH experiments further revealed ribonuclear foci formation in cells carrying expanded 88 and 157 CR. CONCLUSION The present study demonstrates that the expanded CUG-repeat tracts are toxic to human cells and may affect ATXN8OS RNA expression and stability through epigenetic and post-transcriptional mechanisms.
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Affiliation(s)
- I-Cheng Chen
- Department of Life Science, National Taiwan Normal University, Taipei 116, Taiwan
| | - Hsuan-Yuan Lin
- Department of Life Science, National Taiwan Normal University, Taipei 116, Taiwan
| | - Ghin-Chueh Lee
- Department of Life Science, National Taiwan Normal University, Taipei 116, Taiwan
| | - Shih-Huan Kao
- Department of Life Science, National Taiwan Normal University, Taipei 116, Taiwan
| | - Chiung-Mei Chen
- Department of Neurology, Chang Gung Memorial Hospital, Chang-Gung University College of Medicine, Taipei 105, Taiwan
| | - Yih-Ru Wu
- Department of Neurology, Chang Gung Memorial Hospital, Chang-Gung University College of Medicine, Taipei 105, Taiwan
| | - Hsiu-Mei Hsieh-Li
- Department of Life Science, National Taiwan Normal University, Taipei 116, Taiwan
| | - Ming-Tsan Su
- Department of Life Science, National Taiwan Normal University, Taipei 116, Taiwan
| | - Guey-Jen Lee-Chen
- Department of Life Science, National Taiwan Normal University, Taipei 116, Taiwan
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Munhoz RP, Teive HA, Raskin S, Werneck LC. CTA/CTG expansions at the SCA 8 locus in multiple system atrophy. Clin Neurol Neurosurg 2008; 111:208-10. [PMID: 18980793 DOI: 10.1016/j.clineuro.2008.09.003] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2008] [Revised: 08/29/2008] [Accepted: 09/05/2008] [Indexed: 10/21/2022]
Abstract
OBJECTIVE Spinocerebellar ataxia type 8 (SCA 8) is an autosomal dominant disorder characterized by cerebellar ataxia with additional features, such as upper motor neuron signs, urinary incontinence and dysphagia. From a clinical standpoint, SCA 8 and the cerebellar form of multiple system atrophy (MSA-C) share several common features. METHODS We studied the presence of expanded SCA 8 alleles in 10 sporadic patients with probable MSA-C. RESULTS We found 1 patient with a heterozygous CTA/CTG repeat expansion in the pathological range. Clinically this subject presented no features that differed from the other subjects carrying smaller repeat sizes. CONCLUSIONS We believe that the association of SCA 8 repeat expansions with sporadic, atypical and heterogeneous phenotypes is debatable and should be interpreted with caution. Our personal conclusion is that testing in such patients may become a source of diagnostic confusion.
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Affiliation(s)
- Renato P Munhoz
- Department of Neurology, Hospital de Clínicas, Federal University of Paraná, Curitiba, PR, Brazil.
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A comparison of huntington disease and huntington disease-like 2 neuropathology. J Neuropathol Exp Neurol 2008; 67:366-74. [PMID: 18379432 DOI: 10.1097/nen.0b013e31816b4aee] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
Huntington disease-like 2 (HDL2) is an autosomal dominant disorder characterized by adult-onset, progressive motor abnormalities, psychiatric disturbances, and dementia ending in premature death. Clinically, it most closely resembles Huntington disease (HD), although a subset of affected individuals have parkinsonian features. Here, we systematically compare 5 HDL2 and 5 HD brains with the hypothesis that, reflecting the clinical presentation, the neuropathology of the 2 diseases would be similar. Gross and microscopic examination revealed prominent striatal neuron loss and astrocytic gliosis in a dorsal to ventral gradient in each disorder and cortical atrophy. Nuclear protein aggregates were as common in HDL2 as in HD, and the ultrastructural features of HDL2 and HD aggregates were similar. Electron microscopy also revealed degenerating neurons, some with evidence of autophagy, in both HDL2 and HD. Small ribonuclear foci, previously associated with potentially neurotoxic RNA transcripts in HDL2, rarely colocalized with protein aggregates in HDL2 brain, although the protein aggregates were stained by anti-TATA-box binding protein antibodies. Overall, the neuropathologic features of HDL2 and HD are very similar but not identical, suggesting that the pathogenetic mechanisms of the 2 diseases may partially overlap.
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Martins S, Coutinho P, Silveira I, Giunti P, Jardim LB, Calafell F, Sequeiros J, Amorim A. Cis-acting factors promoting the CAG intergenerational instability in Machado-Joseph disease. Am J Med Genet B Neuropsychiatr Genet 2008; 147B:439-46. [PMID: 17948873 DOI: 10.1002/ajmg.b.30624] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
In repeat expansion disorders, the size of pathological alleles is the most relevant factor accounting for the disease severity and age-at-onset, emphasizing the clinical significance of their underlying intergenerational instability. In one of these diseases, Machado-Joseph disease (MJD), the sex of transmitting progenitor and the C(987)GG/G(987)GG polymorphism are the best studied factors acting on intergenerational instability of expanded alleles. Here, we assessed the influence of other cis and inter-allelic acting factors, at the ATXN3 locus, through the analysis of MJD lineages, flanking STR-based haplotypes, the initial repeat size and parental age. A total of 100 transmissions of the expanded MJD allele were analyzed according to the sex of the transmitting parent. We have shown that independent origin mutations (identified by intragenic SNP-based haplotypes) behave differently, as the status of instability (contraction, no change or further expansion) is concerned. Indeed, 72% of expansions were associated to the worldwide spread TTACAC lineage, whereas the GTGGCA displayed 75% of all contractions observed. The analysis of flanking recombinant haplotypes did not suggest any further distant cis elements acting up- or downstream the ATXN3 locus. Considering the increased amplitude of expansions seen in older transmitting fathers, a repair-based mechanism may be suggested for the meiotic instability at this locus; furthermore, the lack of correlation between the initial repeat size and degree of instability did not support a replication-based mechanism. In summary, our findings point to different mechanisms of instability underlying male and female meioses, as well as contraction and expansion processes in MJD.
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Affiliation(s)
- Sandra Martins
- IPATIMUP-Instituto de Patologia e Imunologia Molecular da Universidade do Porto, Portugal.
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Gao R, Matsuura T, Coolbaugh M, Zühlke C, Nakamura K, Rasmussen A, Siciliano MJ, Ashizawa T, Lin X. Instability of expanded CAG/CAA repeats in spinocerebellar ataxia type 17. Eur J Hum Genet 2007; 16:215-22. [PMID: 18043721 DOI: 10.1038/sj.ejhg.5201954] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
Trinucleotide repeat expansions are dynamic mutations causing many neurological disorders, and their instability is influenced by multiple factors. Repeat configuration seems particularly important, and pure repeats are thought to be more unstable than interrupted repeats. But direct evidence is still lacking. Here, we presented strong support for this hypothesis from our studies on spinocerebellar ataxia type 17 (SCA17). SCA17 is a typical polyglutamine disease caused by CAG repeat expansion in TBP (TATA binding protein), and is unique in that the pure expanded polyglutamine tract is coded by either a simple configuration with long stretches of pure CAGs or a complex configuration containing CAA interruptions. By small pool PCR (SP-PCR) analysis of blood DNA from SCA17 patients of distinct racial backgrounds, we quantitatively assessed the instability of these two types of expanded alleles coding similar length of polyglutamine expansion. Mutation frequency in patients harboring pure CAG repeats is 2-3 folds of those with CAA interruptions. Interestingly, the pure CAG repeats showed both expansion and deletion while the interrupted repeats exhibited mostly deletion at a significantly lower frequency. These data strongly suggest that repeat configuration is a critical determinant for instability, and CAA interruptions might serve as a limiting element for further expansion of CAG repeats in SCA17 locus, suggesting a molecular basis for lack of anticipation in SCA17 families with interrupted CAG expansion.
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Affiliation(s)
- Rui Gao
- Department of Neurology, The University of Texas Medical Branch, Galveston, TX 77555-0653, USA
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Abstract
Myotonic dystrophy type 1 (DM1) is caused by a CTG expansion mutation located in the 3' untranslated portion of the dystrophica myotonin protein kinase gene. The identification and characterization of RNA-binding proteins that interact with expanded CUG repeats and the discovery that a similar transcribed but untranslated CCTG expansion in an intron causes myotonic dystrophy type 2 (DM2) have uncovered a new type of mechanism in which microsatellite expansion mutations cause disease through an RNA gain-of-function mechanism. This review discusses RNA pathogenesis in DM1 and DM2 and evidence that similar mechanisms may play a role in a growing number of dominant noncoding expansion disorders, including fragile X tremor ataxia syndrome (FXTAS), spinocerebellar ataxia type 8 (SCA8), SCA10, SCA12, and Huntington's disease-like 2 (HDL2).
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Affiliation(s)
- Laura P W Ranum
- Institute of Human Genetics and Department of Genetics, Cell Biology & Development, University of Minnesota, Minneapolis, Minnesota 55455, USA.
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Moseley ML, Zu T, Ikeda Y, Gao W, Mosemiller AK, Daughters RS, Chen G, Weatherspoon MR, Clark HB, Ebner TJ, Day JW, Ranum LPW. Bidirectional expression of CUG and CAG expansion transcripts and intranuclear polyglutamine inclusions in spinocerebellar ataxia type 8. Nat Genet 2006; 38:758-69. [PMID: 16804541 DOI: 10.1038/ng1827] [Citation(s) in RCA: 314] [Impact Index Per Article: 17.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2006] [Accepted: 05/22/2006] [Indexed: 11/08/2022]
Abstract
We previously reported that a (CTG)n expansion causes spinocerebellar ataxia type 8 (SCA8), a slowly progressive ataxia with reduced penetrance. We now report a transgenic mouse model in which the full-length human SCA8 mutation is transcribed using its endogenous promoter. (CTG)116 expansion, but not (CTG)11 control lines, develop a progressive neurological phenotype with in vivo imaging showing reduced cerebellar-cortical inhibition. 1C2-positive intranuclear inclusions in cerebellar Purkinje and brainstem neurons in SCA8 expansion mice and human SCA8 autopsy tissue result from translation of a polyglutamine protein, encoded on a previously unidentified antiparallel transcript (ataxin 8, ATXN8) spanning the repeat in the CAG direction. The neurological phenotype in SCA8 BAC expansion but not BAC control lines demonstrates the pathogenicity of the (CTG-CAG)n expansion. Moreover, the expression of noncoding (CUG)n expansion transcripts (ataxin 8 opposite strand, ATXN8OS) and the discovery of intranuclear polyglutamine inclusions suggests SCA8 pathogenesis involves toxic gain-of-function mechanisms at both the protein and RNA levels.
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Affiliation(s)
- Melinda L Moseley
- Department of Genetics, Cell Biology, and Development, University of Minnesota, Minneapolis, Minnesota 55455, USA
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49
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Matsuura T, Fang P, Pearson CE, Jayakar P, Ashizawa T, Roa BB, Nelson DL. Interruptions in the expanded ATTCT repeat of spinocerebellar ataxia type 10: repeat purity as a disease modifier? Am J Hum Genet 2006; 78:125-9. [PMID: 16385455 PMCID: PMC1380209 DOI: 10.1086/498654] [Citation(s) in RCA: 74] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2005] [Accepted: 09/30/2005] [Indexed: 11/03/2022] Open
Abstract
Spinocerebellar ataxia type 10 (SCA10) is one of numerous genetic disorders that result from simple repeat expansions. SCA10 is caused by expansion of an intronic ATTCT pentanucleotide repeat tract. It is clinically characterized by progressive ataxia, seizures, and anticipation, which can vary within and between families. We report two SCA10 families showing distinct frequencies of seizures and correlations of repeat length with age at onset. One family displayed uninterrupted ATTCT expansions, whereas the other showed multiple interruptions of the repeat by nonconsensus repeat units, which differed both in the length and/or sequence of the repeat unit. Disease-causing microsatellite expansions have been assumed to be composed of uninterrupted pure repeats. Our findings for SCA10 challenge this convention and suggest that the purity of the expanded repeat element may be a disease modifier.
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Affiliation(s)
- Tohru Matsuura
- Department of Molecular and Human Genetics and Baylor DNA Diagnostic Laboratory, Baylor College of Medicine, Houston; Program of Genetics and Genomic Biology, The Hospital for Sick Children, and Department of Molecular and Medical Genetics, University of Toronto, Toronto; Division of Genetics and Metabolism, Miami Children's Hospital, Miami; and Department of Neurology, University of Texas Medical Branch, Galveston, TX
| | - Ping Fang
- Department of Molecular and Human Genetics and Baylor DNA Diagnostic Laboratory, Baylor College of Medicine, Houston; Program of Genetics and Genomic Biology, The Hospital for Sick Children, and Department of Molecular and Medical Genetics, University of Toronto, Toronto; Division of Genetics and Metabolism, Miami Children's Hospital, Miami; and Department of Neurology, University of Texas Medical Branch, Galveston, TX
| | - Christopher E. Pearson
- Department of Molecular and Human Genetics and Baylor DNA Diagnostic Laboratory, Baylor College of Medicine, Houston; Program of Genetics and Genomic Biology, The Hospital for Sick Children, and Department of Molecular and Medical Genetics, University of Toronto, Toronto; Division of Genetics and Metabolism, Miami Children's Hospital, Miami; and Department of Neurology, University of Texas Medical Branch, Galveston, TX
| | - Parul Jayakar
- Department of Molecular and Human Genetics and Baylor DNA Diagnostic Laboratory, Baylor College of Medicine, Houston; Program of Genetics and Genomic Biology, The Hospital for Sick Children, and Department of Molecular and Medical Genetics, University of Toronto, Toronto; Division of Genetics and Metabolism, Miami Children's Hospital, Miami; and Department of Neurology, University of Texas Medical Branch, Galveston, TX
| | - Tetsuo Ashizawa
- Department of Molecular and Human Genetics and Baylor DNA Diagnostic Laboratory, Baylor College of Medicine, Houston; Program of Genetics and Genomic Biology, The Hospital for Sick Children, and Department of Molecular and Medical Genetics, University of Toronto, Toronto; Division of Genetics and Metabolism, Miami Children's Hospital, Miami; and Department of Neurology, University of Texas Medical Branch, Galveston, TX
| | - Benjamin B. Roa
- Department of Molecular and Human Genetics and Baylor DNA Diagnostic Laboratory, Baylor College of Medicine, Houston; Program of Genetics and Genomic Biology, The Hospital for Sick Children, and Department of Molecular and Medical Genetics, University of Toronto, Toronto; Division of Genetics and Metabolism, Miami Children's Hospital, Miami; and Department of Neurology, University of Texas Medical Branch, Galveston, TX
| | - David L. Nelson
- Department of Molecular and Human Genetics and Baylor DNA Diagnostic Laboratory, Baylor College of Medicine, Houston; Program of Genetics and Genomic Biology, The Hospital for Sick Children, and Department of Molecular and Medical Genetics, University of Toronto, Toronto; Division of Genetics and Metabolism, Miami Children's Hospital, Miami; and Department of Neurology, University of Texas Medical Branch, Galveston, TX
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Martins S, Seixas AI, Magalhães P, Coutinho P, Sequeiros J, Silveira I. Haplotype diversity and somatic instability in normal and expanded SCA8 alleles. Am J Med Genet B Neuropsychiatr Genet 2005; 139B:109-14. [PMID: 16184604 DOI: 10.1002/ajmg.b.30235] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Spinocerebellar ataxia type 8 (SCA8) is an autosomal dominant late-onset neurodegenerative disorder, belonging to the group of diseases caused by trinucleotide repeat expansions. SCA8 remains one of the most intriguing SCAs, regarding the reduced disease penetrance, and the high instability and poorly understood functional meaning of the (CTA)(n)(CTG)(n) expansion. We performed haplotype and sequencing analysis in a large region, encompassing the repeat, in four SCA8 and 20 control Portuguese families. The results from the haplotype study including the combined repeat and six SNP markers showed two different haplotypes, AG-Exp-GTTG and AG-Exp-CTTG, in the SCA8 families. Among the control population, these were also the most frequent, in a total of five haplotypes found unequally distributed throughout repeat sizes. From cloning fragments of control, unstable normal and expanded chromosomes, eleven different base substitutions were identified in exon A of the SCA8 gene. In some instances, somatic variability in repeat size or base composition was found for a same chromosome, regardless of its normal or expanded nature. In conclusion, our results in Portuguese families with ataxia show that SCA8 expansions arose in common backgrounds; in addition, this region seems to be unstable beyond the repeat.
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