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Wang L, Ji Y, Chen Y, Bai J, Gao P, Feng P. A splicing silencer in SMN2 intron 6 is critical in spinal muscular atrophy. Hum Mol Genet 2023; 32:971-983. [PMID: 36255739 DOI: 10.1093/hmg/ddac260] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2022] [Revised: 10/10/2022] [Accepted: 10/14/2022] [Indexed: 11/14/2022] Open
Abstract
Spinal muscular atrophy (SMA) is a fatal neuromuscular disease caused by homozygous deletions or mutations of the SMN1 gene. SMN2 is a paralogous gene of SMN1 and a modifying gene of SMA. A better understanding of how SMN2 exon 7 splicing is regulated helps discover new therapeutic targets for SMA therapy. Based on an antisense walk method to map exonic and intronic splicing silencers (ESSs and ISSs) in SMN2 exon 7 and the proximal regions of its flanking introns, we identified one ISS (ISS6-KH) at upstream of the branch point site in intron 6. By using mutagenesis-coupled RT-PCR with SMN1/2 minigenes, immunochromatography, overexpression and siRNA-knockdown, we found this ISS consists of a bipartite hnRNP A1 binding cis-element and a poly-U sequence located between the proximal hnRNP A1 binding site (UAGCUA) and the branch site. Both HuR and hnRNP C1 proteins promote exon 7 skipping through the poly-U stretch. Mutations or deletions of these motifs lead to efficient SMN2 exon 7 inclusion comparable to SMN1 gene. Furthermore, we identified an optimal antisense oligonucleotide that binds the intron six ISS and causes striking exon 7 inclusion in the SMN2 gene in patient fibroblasts and SMA mouse model. Our findings demonstrate that this novel ISS plays an important role in SMN2 exon 7 skipping and highlight a new therapeutic target for SMA therapy.
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Affiliation(s)
- Li Wang
- Jiangsu Key Laboratory for Molecular and Medical Biotechnology, College of Life Sciences, Nanjing Normal University, Nanjing 210023, China
| | - Yinfeng Ji
- Jiangsu Key Laboratory for Molecular and Medical Biotechnology, College of Life Sciences, Nanjing Normal University, Nanjing 210023, China
| | - Yuqing Chen
- Jiangsu Key Laboratory for Molecular and Medical Biotechnology, College of Life Sciences, Nanjing Normal University, Nanjing 210023, China
| | - Jialin Bai
- Jiangsu Key Laboratory for Molecular and Medical Biotechnology, College of Life Sciences, Nanjing Normal University, Nanjing 210023, China
| | - Peng Gao
- Jiangsu Key Laboratory for Molecular and Medical Biotechnology, College of Life Sciences, Nanjing Normal University, Nanjing 210023, China
| | - Pengchao Feng
- Nanjing Antisense Biopharmaceutical Co., Ltd, Nanjing 210046, China
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Miccio A, Antoniou P, Ciura S, Kabashi E. Novel genome-editing-based approaches to treat motor neuron diseases: Promises and challenges. Mol Ther 2022; 30:47-53. [PMID: 33823304 PMCID: PMC8753272 DOI: 10.1016/j.ymthe.2021.04.003] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2021] [Revised: 03/30/2021] [Accepted: 03/31/2021] [Indexed: 01/07/2023] Open
Abstract
Motor neuron diseases are untreatable with common pharmacological approaches. Spinal muscular atrophy (SMA) is caused by SMN1 gene mutations leading to lowered SMN expression. Symptoms are alleviated in infants with a higher copy number of the SMN2 gene, which, however, displays a splicing defect resulting in low SMN levels. Amyotrophic lateral sclerosis (ALS) is caused by a number of mutations, with C9orf72 repeat expansions the most common genetic cause and SOD1 gain-of-function mutations the first genetic cause identified for this disease. Genetic therapies based on oligonucleotides that enhance SMN2 splicing and SMN production or lower SOD1 expression have shown promise in initial clinical trials for individuals with SMA and ALS harboring SOD1 mutations, respectively. Gene addition/silencing approaches using adeno-associated viruses (AAVs) are also currently under clinical investigation in trials for SMA and ALS. Here we provide a brief overview of these efforts and their advantages and challenges. We also review genome editing approaches aimed at correcting the disease-causing mutations or modulating the expression of genetic modifiers, e.g., by repairing SOD1 mutations or the SMN2 splicing defect or deleting C9orf72 expanded repeats. These studies have shown promising results to approach therapeutic trials that should significantly lower the progression of these deadly disorders.
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Affiliation(s)
- Annarita Miccio
- Laboratory of Chromatin and Gene Regulation during Development, Imagine Institute, Université de Paris, INSERM UMR 1163, 75015, Paris, France,Corresponding author: Annarita Miccio, Laboratory of Chromatin and Gene Regulation during Development, Imagine Institute, Université de Paris, INSERM UMR 1163, 75015, Paris, France.
| | - Panagiotis Antoniou
- Laboratory of Chromatin and Gene Regulation during Development, Imagine Institute, Université de Paris, INSERM UMR 1163, 75015, Paris, France
| | - Sorana Ciura
- Laboratory of Translational Research for Neurological Disorders, Imagine Institute, Université de Paris, INSERM UMR 1163, 75015, Paris, France
| | - Edor Kabashi
- Laboratory of Translational Research for Neurological Disorders, Imagine Institute, Université de Paris, INSERM UMR 1163, 75015, Paris, France,Corresponding author: Edor Kabashi, Laboratory of Translational Research for Neurological Disorders, Imagine Institute, Université de Paris, INSERM UMR 1163, 75015, Paris, France.
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Bozorg Qomi S, Asghari A, Salmaninejad A, Mojarrad M. Spinal Muscular Atrophy and Common Therapeutic Advances. Fetal Pediatr Pathol 2019; 38:226-238. [PMID: 31060440 DOI: 10.1080/15513815.2018.1520374] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
BACKGROUND Spinal muscular atrophy (SMA) is an autosomal recessive destructive motor neuron disease which is characterized primarily by the degeneration of α-motor neurons in the ventral gray horn of the spinal cord. It mainly affects children and represents the most common reason of inherited infant mortality. MATERIAL AND METHODS We provide an overview of the recent therapeutic strategies for the treatment of SMA together with available and developing therapeutic strategies. For this purpose, Google Scholar and PubMed databases were searched for literature on SMA, therapy and treatment. Titles were reviewed and 96 were selected and assessed in this paper. RESULT Over the last two decades, different therapeutic strategies have been proposed for SMA. Some methods are in the pre-clinical, others the clinical phase. CONCLUSION By emergence of the new approaches, especially in gene therapy, effective treatment in the close future is probable.
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Affiliation(s)
- Saeed Bozorg Qomi
- a Department of Medical Genetics, School of Medicine, Mashhad University of Medical Sciences , Mashhad , Iran.,b Medical Genetics Research Center, School of Medicine, Mashhad University of Medical Sciences , Mashhad , Iran
| | - Amir Asghari
- c Department of Medical Physiology, School of Medicine, Mashhad University of Medical Sciences , Mashhad , Iran
| | - Arash Salmaninejad
- d Drug Applied Research Center, Student Research Committee, Tabriz University of Medical Sciences , Tabriz , Iran
| | - Majid Mojarrad
- a Department of Medical Genetics, School of Medicine, Mashhad University of Medical Sciences , Mashhad , Iran.,b Medical Genetics Research Center, School of Medicine, Mashhad University of Medical Sciences , Mashhad , Iran
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Zhou M, Hu Z, Qiu L, Zhou T, Feng M, Hu Q, Zeng B, Li Z, Sun Q, Wu Y, Liu X, Wu L, Liang D. Seamless Genetic Conversion of SMN2 to SMN1 via CRISPR/Cpf1 and Single-Stranded Oligodeoxynucleotides in Spinal Muscular Atrophy Patient-Specific Induced Pluripotent Stem Cells. Hum Gene Ther 2018; 29:1252-1263. [PMID: 29598153 DOI: 10.1089/hum.2017.255] [Citation(s) in RCA: 45] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Spinal muscular atrophy (SMA) is a kind of neuromuscular disease characterized by progressive motor neuron loss in the spinal cord. It is caused by mutations in the survival motor neuron 1 (SMN1) gene. SMN1 has a paralogous gene, survival motor neuron 2 (SMN2), in humans that is present in almost all SMA patients. The generation and genetic correction of SMA patient-specific induced pluripotent stem cells (iPSCs) is a viable, autologous therapeutic strategy for the disease. Here, c-Myc-free and non-integrating iPSCs were generated from the urine cells of an SMA patient using an episomal iPSC reprogramming vector, and a unique crRNA was designed that does not have similar sequences (≤3 mismatches) anywhere in the human reference genome. In situ gene conversion of the SMN2 gene to an SMN1-like gene in SMA-iPSCs was achieved using CRISPR/Cpf1 and single-stranded oligodeoxynucleotide with a high efficiency of 4/36. Seamlessly gene-converted iPSC lines contained no exogenous sequences and retained a normal karyotype. Significantly, the SMN expression and gems localization were rescued in the gene-converted iPSCs and their derived motor neurons. This is the first report of an efficient gene conversion mediated by Cpf1 homology-directed repair in human cells and may provide a universal gene therapeutic approach for most SMA patients.
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Affiliation(s)
- Miaojin Zhou
- 1 Center for Medical Genetics, School of Life Sciences, Central South University , Hunan, China
| | - Zhiqing Hu
- 1 Center for Medical Genetics, School of Life Sciences, Central South University , Hunan, China
| | - Liyan Qiu
- 1 Center for Medical Genetics, School of Life Sciences, Central South University , Hunan, China
| | - Tao Zhou
- 1 Center for Medical Genetics, School of Life Sciences, Central South University , Hunan, China
| | - Mai Feng
- 1 Center for Medical Genetics, School of Life Sciences, Central South University , Hunan, China
| | - Qian Hu
- 1 Center for Medical Genetics, School of Life Sciences, Central South University , Hunan, China
| | - Baitao Zeng
- 1 Center for Medical Genetics, School of Life Sciences, Central South University , Hunan, China
| | - Zhuo Li
- 1 Center for Medical Genetics, School of Life Sciences, Central South University , Hunan, China
| | - Qianru Sun
- 1 Center for Medical Genetics, School of Life Sciences, Central South University , Hunan, China
| | - Yong Wu
- 1 Center for Medical Genetics, School of Life Sciences, Central South University , Hunan, China
| | - Xionghao Liu
- 1 Center for Medical Genetics, School of Life Sciences, Central South University , Hunan, China
| | - Lingqian Wu
- 1 Center for Medical Genetics, School of Life Sciences, Central South University , Hunan, China
- 2 Hunan Jiahui Genetics Hospital, Changsha, Hunan, China
| | - Desheng Liang
- 1 Center for Medical Genetics, School of Life Sciences, Central South University , Hunan, China
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Nelson CE, Robinson-Hamm JN, Gersbach CA. Genome engineering: a new approach to gene therapy for neuromuscular disorders. Nat Rev Neurol 2017; 13:647-661. [DOI: 10.1038/nrneurol.2017.126] [Citation(s) in RCA: 50] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
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Long C, Amoasii L, Bassel-Duby R, Olson EN. Genome Editing of Monogenic Neuromuscular Diseases: A Systematic Review. JAMA Neurol 2017; 73:1349-1355. [PMID: 27668807 DOI: 10.1001/jamaneurol.2016.3388] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Importance Muscle weakness, the most common symptom of neuromuscular disease, may result from muscle dysfunction or may be caused indirectly by neuronal and neuromuscular junction abnormalities. To date, more than 780 monogenic neuromuscular diseases, linked to 417 different genes, have been identified in humans. Genome-editing methods, especially the CRISPR (clustered regularly interspaced short palindromic repeats)-Cas9 (CRISPR-associated protein 9) system, hold clinical potential for curing many monogenic disorders, including neuromuscular diseases such as Duchenne muscular dystrophy, spinal muscular atrophy, amyotrophic lateral sclerosis, and myotonic dystrophy type 1. Objectives To provide an overview of genome-editing approaches; to summarize published reports on the feasibility, efficacy, and safety of current genome-editing methods as they relate to the potential correction of monogenic neuromuscular diseases; and to highlight scientific and clinical opportunities and obstacles toward permanent correction of disease-causing mutations responsible for monogenic neuromuscular diseases by genome editing. Evidence Review PubMed and Google Scholar were searched for articles published from June 30, 1989, through June 9, 2016, using the following keywords: genome editing, CRISPR-Cas9, neuromuscular disease, Duchenne muscular dystrophy, spinal muscular atrophy, amyotrophic lateral sclerosis, and myotonic dystrophy type 1. The following sources were reviewed: 341 articles describing different approaches to edit mammalian genomes; 330 articles describing CRISPR-Cas9-mediated genome editing in cell culture lines (in vitro) and animal models (in vivo); 16 websites used to generate single-guide RNA; 4 websites for off-target effects; and 382 articles describing viral and nonviral delivery systems. Articles describing neuromuscular diseases, including Duchenne muscular dystrophy, spinal muscular atrophy, amyotrophic lateral sclerosis, and myotonic dystrophy type 1, were also reviewed. Findings Multiple proof-of-concept studies reveal the feasibility and efficacy of genome-editing-meditated correction of monogenic neuromuscular diseases in cultured cells and animal models. Conclusions and Relevance Genome editing is a rapidly evolving technology with enormous translational potential once efficacy, delivery, and safety issues are addressed. The clinical impact of this technology is that genome editing can permanently correct disease-causing mutations and circumvent the hurdles of traditional gene- and cell-based therapies.
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Affiliation(s)
- Chengzu Long
- Department of Molecular Biology, Senator Paul D. Wellstone Muscular Dystrophy Cooperative Research Center and Hamon Center for Regenerative Science and Medicine, The University of Texas Southwestern Medical Center, Dallas
| | - Leonela Amoasii
- Department of Molecular Biology, Senator Paul D. Wellstone Muscular Dystrophy Cooperative Research Center and Hamon Center for Regenerative Science and Medicine, The University of Texas Southwestern Medical Center, Dallas
| | - Rhonda Bassel-Duby
- Department of Molecular Biology, Senator Paul D. Wellstone Muscular Dystrophy Cooperative Research Center and Hamon Center for Regenerative Science and Medicine, The University of Texas Southwestern Medical Center, Dallas
| | - Eric N Olson
- Department of Molecular Biology, Senator Paul D. Wellstone Muscular Dystrophy Cooperative Research Center and Hamon Center for Regenerative Science and Medicine, The University of Texas Southwestern Medical Center, Dallas
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8
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In vitro gene manipulation of spinal muscular atrophy fibroblast cell line using gene-targeting fragment for restoration of SMN protein expression. Gene Ther 2015; 23:10-7. [DOI: 10.1038/gt.2015.92] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2015] [Revised: 06/17/2015] [Accepted: 08/05/2015] [Indexed: 11/08/2022]
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Corti S, Nizzardo M, Simone C, Falcone M, Nardini M, Ronchi D, Donadoni C, Salani S, Riboldi G, Magri F, Menozzi G, Bonaglia C, Rizzo F, Bresolin N, Comi GP. Genetic correction of human induced pluripotent stem cells from patients with spinal muscular atrophy. Sci Transl Med 2013; 4:165ra162. [PMID: 23253609 DOI: 10.1126/scitranslmed.3004108] [Citation(s) in RCA: 148] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Spinal muscular atrophy (SMA) is among the most common genetic neurological diseases that cause infant mortality. Induced pluripotent stem cells (iPSCs) generated from skin fibroblasts from SMA patients and genetically corrected have been proposed to be useful for autologous cell therapy. We generated iPSCs from SMA patients (SMA-iPSCs) using nonviral, nonintegrating episomal vectors and used a targeted gene correction approach based on single-stranded oligonucleotides to convert the survival motor neuron 2 (SMN2) gene into an SMN1-like gene. Corrected iPSC lines contained no exogenous sequences. Motor neurons formed by differentiation of uncorrected SMA-iPSCs reproduced disease-specific features. These features were ameliorated in motor neurons derived from genetically corrected SMA-iPSCs. The different gene splicing profile in SMA-iPSC motor neurons was rescued after genetic correction. The transplantation of corrected motor neurons derived from SMA-iPSCs into an SMA mouse model extended the life span of the animals and improved the disease phenotype. These results suggest that generating genetically corrected SMA-iPSCs and differentiating them into motor neurons may provide a source of motor neurons for therapeutic transplantation for SMA.
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Affiliation(s)
- Stefania Corti
- Dino Ferrari Centre, Neuroscience Section, Department of Pathophysiology and Transplantation, University of Milan, Neurology Unit, IRCCS Foundation Ca' Granda Ospedale Maggiore Policlinico, Milan 20135, Italy
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Wadman RI, Bosboom WMJ, van der Pol WL, van den Berg LH, Wokke JHJ, Iannaccone ST, Vrancken AFJE. Drug treatment for spinal muscular atrophy types II and III. Cochrane Database Syst Rev 2012:CD006282. [PMID: 22513940 DOI: 10.1002/14651858.cd006282.pub4] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
BACKGROUND Spinal muscular atrophy (SMA) is caused by degeneration of anterior horn cells, which leads to progressive muscle weakness. Children with SMA type II do not develop the ability to walk without support and have a shortened life expectancy, whereas children with SMA type III develop the ability to walk and have a normal life expectancy. There are no known efficacious drug treatments that influence the disease course of SMA. This is an update of a review first published in 2009. OBJECTIVES To evaluate whether drug treatment is able to slow or arrest the disease progression of SMA types II and III and to assess if such therapy can be given safely. Drug treatment for SMA type I is the topic of a separate updated Cochrane review. SEARCH METHODS We searched the Cochrane Neuromuscular Disease Group Specialized Register (8 March 2011), Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2011, Issue 1), MEDLINE (January 1991 to February 2011), EMBASE (January 1991 to February 2011) and ISI Web of Knowledge (January 1991 to March 8 2011). We also searched clinicaltrials.gov to identify as yet unpublished trials (8 March 2011). SELECTION CRITERIA We sought all randomised or quasi-randomised trials that examined the efficacy of drug treatment for SMA types II and III. Participants had to fulfil the clinical criteria and have a deletion or mutation of the survival motor neuron 1 (SMN1) gene (5q11.2-13.2) that was confirmed by genetic analysis.The primary outcome measure was to be change in disability score within one year after the onset of treatment. Secondary outcome measures within one year after the onset of treatment were to be change in muscle strength, ability to stand or walk, change in quality of life, time from the start of treatment until death or full time ventilation and adverse events attributable to treatment during the trial period. DATA COLLECTION AND ANALYSIS Two authors independently reviewed and extracted data from all potentially relevant trials. Pooled relative risks and pooled standardised mean differences were to be calculated to assess treatment efficacy. Risk of bias was systematically analysed. MAIN RESULTS Six randomised placebo-controlled trials on treatment for SMA types II and III were found and included in the review: the four in the original review and two trials added in this update. The treatments were creatine (55 participants), phenylbutyrate (107 participants), gabapentin (84 participants), thyrotropin releasing hormone (9 participants), hydroxyurea (57 participants), and combination therapy with valproate and acetyl-L-carnitine (61 participants). None of these studies were completely free of bias. All studies had adequate blinding, sequence generation and reports of primary outcomes.None of the included trials showed any statistically significant effects on the outcome measures in participants with SMA types II and III. One participant died due to suffocation in the hydroxyurea trial and one participant died in the creatine trial. No participants in any of the other four trials died or reached the state of full time ventilation. Serious side effects were infrequent. AUTHORS' CONCLUSIONS There is no proven efficacious drug treatment for SMA types II and III.
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Affiliation(s)
- Renske I Wadman
- Department of Neurology, University Medical Center Utrecht, Utrecht, Netherlands.
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Wadman RI, Bosboom WMJ, van der Pol WL, van den Berg LH, Wokke JHJ, Iannaccone ST, Vrancken AFFJE. Drug treatment for spinal muscular atrophy type I. Cochrane Database Syst Rev 2012:CD006281. [PMID: 22513939 DOI: 10.1002/14651858.cd006281.pub4] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
BACKGROUND Spinal muscular atrophy (SMA) is caused by degeneration of anterior horn cells of the spinal cord, which leads to progressive muscle weakness. Children with SMA type I will never be able to sit without support and usually die by the age of two years. There are no known efficacious drug treatments that influence the course of the disease. This is an update of a review first published in 2009. OBJECTIVES To evaluate whether drug treatment is able to slow or arrest the disease progression of SMA type I, and to assess if such therapy can be given safely. Drug treatment for SMA types II and III is the topic of a separate updated Cochrane review. SEARCH METHODS We searched the Cochrane Neuromuscular Disease Group Specialized Register (8 March 2011), CENTRAL (The Cochrane Library 2011, Issue 1), MEDLINE (January 1991 to February 2011), EMBASE (January 1991 to February 2011) and ISI Web of Knowledge (January 1991 to 8 March 2011). We searched the Clinical Trials Registry of the U.S. National Institute of Health (www.ClinicalTrials.gov) (8 March 2011) to identify additional trials that had not yet been published. SELECTION CRITERIA We sought all randomised or quasi-randomised trials that examined the efficacy of drug treatment for SMA type I. Participants had to fulfil the clinical criteria and have a deletion or mutation of the SMN1 gene (5q11.2-13.2) confirmed by genetic analysis.The primary outcome measure was time from birth until death or full time ventilation. Secondary outcome measures were development of rolling, sitting or standing within one year after the onset of treatment, and adverse events attributable to treatment during the trial period. DATA COLLECTION AND ANALYSIS Two authors (RW and AV) independently reviewed and extracted data from all potentially relevant trials. For included studies, pooled relative risks and standardised mean differences were to be calculated to assess treatment efficacy. MAIN RESULTS One small randomised controlled study comparing riluzole treatment to placebo for 10 SMA type 1 children was identified and included in the original review. No further trials were identified for the update in 2011. Regarding the primary outcome measure, three of seven children treated with riluzole were still alive at the ages of 30, 48 and 64 months, whereas all three children in the placebo group died; but the difference was not statistically significant. Regarding the secondary outcome measures, none of the children in the riluzole or placebo group developed the ability to roll, sit or stand, and no adverse effects were observed. For several reasons the overall quality of the study was low, mainly because the study was too small to detect an effect and because of baseline differences. Follow-up of the 10 included children was complete. AUTHORS' CONCLUSIONS No drug treatment for SMA type I has been proven to have significant efficacy.
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Affiliation(s)
- Renske I Wadman
- Department of Neurology, University Medical Center Utrecht, Utrecht, Netherlands.
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Wadman RI, Bosboom WM, van den Berg LH, Wokke JH, Iannaccone ST, Vrancken AF. Drug treatment for spinal muscular atrophy type I. Cochrane Database Syst Rev 2011:CD006281. [PMID: 22161399 DOI: 10.1002/14651858.cd006281.pub3] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
BACKGROUND Spinal muscular atrophy (SMA) is caused by degeneration of anterior horn cells of the spinal cord, which leads to progressive muscle weakness. Children with SMA type I will never be able to sit without support and usually die by the age of two years. There are no known efficacious drug treatments that influence the course of the disease. This is an update of a review first published in 2009. OBJECTIVES To evaluate whether drug treatment is able to slow or arrest the disease progression of SMA type I, and to assess if such therapy can be given safely. Drug treatment for SMA types II and III is the topic of a separate updated Cochrane review. SEARCH METHODS We searched the Cochrane Neuromuscular Disease Group Specialized Register (8 March 2011), CENTRAL (The Cochrane Library 2011, Issue 1), MEDLINE (January 1991 to February 2011), EMBASE (January 1991 to February 2011) and ISI Web of Knowledge (January 1991 to 8 March 2011). We searched the Clinical Trials Registry of the U.S. National Institute of Health (www.ClinicalTrials.gov) (8 March 2011) to identify additional trials that had not yet been published. SELECTION CRITERIA We sought all randomised or quasi-randomised trials that examined the efficacy of drug treatment for SMA type I. Participants had to fulfil the clinical criteria and have a deletion or mutation of the SMN1 gene (5q11.2-13.2) confirmed by genetic analysis.The primary outcome measure was time from birth until death or full time ventilation. Secondary outcome measures were development of rolling, sitting or standing within one year after the onset of treatment, and adverse events attributable to treatment during the trial period. DATA COLLECTION AND ANALYSIS Two authors (RW and AV) independently reviewed and extracted data from all potentially relevant trials. For included studies, pooled relative risks and standardised mean differences were to be calculated to assess treatment efficacy. MAIN RESULTS One small randomised controlled study comparing riluzole treatment to placebo for 10 SMA type 1 children was identified and included in the original review. No further trials were identified for the update in 2011. Regarding the primary outcome measure, three of seven children treated with riluzole were still alive at the ages of 30, 48 and 64 months, whereas all three children in the placebo group died; but the difference was not statistically significant. Regarding the secondary outcome measures, none of the children in the riluzole or placebo group developed the ability to roll, sit or stand, and no adverse effects were observed. For several reasons the overall quality of the study was low, mainly because the study was too small to detect an effect and because of baseline differences. Follow-up of the 10 included children was complete. AUTHORS' CONCLUSIONS No drug treatment for SMA type I has been proven to have significant efficacy.
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Affiliation(s)
- Renske I Wadman
- Department of Neurology, University Medical Center Utrecht, Rudolf Magnus Institute for Neuroscience, Universiteitsweg 100, Utrecht, Netherlands, 3584 CG
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Wadman RI, Bosboom WM, van den Berg LH, Wokke JH, Iannaccone ST, Vrancken AF. Drug treatment for spinal muscular atrophy types II and III. Cochrane Database Syst Rev 2011:CD006282. [PMID: 22161400 DOI: 10.1002/14651858.cd006282.pub3] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
BACKGROUND Spinal muscular atrophy (SMA) is caused by degeneration of anterior horn cells, which leads to progressive muscle weakness. Children with SMA type II do not develop the ability to walk without support and have a shortened life expectancy, whereas children with SMA type III develop the ability to walk and have a normal life expectancy. There are no known efficacious drug treatments that influence the disease course of SMA. This is an update of a review first published in 2009. OBJECTIVES To evaluate whether drug treatment is able to slow or arrest the disease progression of SMA types II and III and to assess if such therapy can be given safely. Drug treatment for SMA type I is the topic of a separate updated Cochrane review. SEARCH METHODS We searched the Cochrane Neuromuscular Disease Group Specialized Register (8 March 2011), Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2011, Issue 1), MEDLINE (January 1991 to February 2011), EMBASE (January 1991 to February 2011) and ISI Web of Knowledge (January 1991 to March 8 2011). We also searched clinicaltrials.gov to identify as yet unpublished trials (8 March 2011). SELECTION CRITERIA We sought all randomised or quasi-randomised trials that examined the efficacy of drug treatment for SMA types II and III. Participants had to fulfil the clinical criteria and have a deletion or mutation of the survival motor neuron 1 (SMN1) gene (5q11.2-13.2) that was confirmed by genetic analysis.The primary outcome measure was to be change in disability score within one year after the onset of treatment. Secondary outcome measures within one year after the onset of treatment were to be change in muscle strength, ability to stand or walk, change in quality of life, time from the start of treatment until death or full time ventilation and adverse events attributable to treatment during the trial period. DATA COLLECTION AND ANALYSIS Two authors independently reviewed and extracted data from all potentially relevant trials. Pooled relative risks and pooled standardised mean differences were to be calculated to assess treatment efficacy. Risk of bias was systematically analysed. MAIN RESULTS Six randomised placebo-controlled trials on treatment for SMA types II and III were found and included in the review: the four in the original review and two trials added in this update. The treatments were creatine (55 participants), phenylbutyrate (107 participants), gabapentin (84 participants), thyrotropin releasing hormone (9 participants), hydroxyurea (57 participants), and combination therapy with valproate and acetyl-L-carnitine (61 participants). None of these studies were completely free of bias. All studies had adequate blinding, sequence generation and reports of primary outcomes.None of the included trials showed any statistically significant effects on the outcome measures in participants with SMA types II and III. One participant died due to suffocation in the hydroxyurea trial and one participant died in the creatine trial. No participants in any of the other four trials died or reached the state of full time ventilation. Serious side effects were infrequent. AUTHORS' CONCLUSIONS There is no proven efficacious drug treatment for SMA types II and III.
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Affiliation(s)
- Renske I Wadman
- Department of Neurology, University Medical Center Utrecht, Rudolf Magnus Institute for Neuroscience, Universiteitsweg 100, Utrecht, Netherlands, 3584 CG
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Zhong Q, Bhattacharya S, Kotsopoulos S, Olson J, Taly V, Griffiths AD, Link DR, Larson JW. Multiplex digital PCR: breaking the one target per color barrier of quantitative PCR. LAB ON A CHIP 2011; 11:2167-74. [PMID: 21584334 DOI: 10.1039/c1lc20126c] [Citation(s) in RCA: 220] [Impact Index Per Article: 16.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Quantitative polymerase chain reactions (qPCR) based on real-time PCR constitute a powerful and sensitive method for the analysis of nucleic acids. However, in qPCR, the ability to multiplex targets using differently colored fluorescent probes is typically limited to 4-fold by the spectral overlap of the fluorophores. Furthermore, multiplexing qPCR assays requires expensive instrumentation and most often lengthy assay development cycles. Digital PCR (dPCR), which is based on the amplification of single target DNA molecules in many separate reactions, is an attractive alternative to qPCR. Here we report a novel and easy method for multiplexing dPCR in picolitre droplets within emulsions-generated and read out in microfluidic devices-that takes advantage of both the very high numbers of reactions possible within emulsions (>10(6)) as well as the high likelihood that the amplification of only a single target DNA molecule will initiate within each droplet. By varying the concentration of different fluorogenic probes of the same color, it is possible to identify the different probes on the basis of fluorescence intensity. Adding multiple colors increases the number of possible reactions geometrically, rather than linearly as with qPCR. Accurate and precise copy numbers of up to sixteen per cell were measured using a model system. A 5-plex assay for spinal muscular atrophy was demonstrated with just two fluorophores to simultaneously measure the copy number of two genes (SMN1 and SMN2) and to genotype a single nucleotide polymorphism (c.815A>G, SMN1). Results of a pilot study with SMA patients are presented.
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Affiliation(s)
- Qun Zhong
- RainDance Technologies, Inc., 44 Hartwell Ave., Lexington, MA 02150, USA.
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15
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Chen TH, Tzeng CC, Wang CC, Wu SM, Chang JG, Yang SN, Hung CH, Jong YJ. Identification of bidirectional gene conversion between SMN1 and SMN2 by simultaneous analysis of SMN dosage and hybrid genes in a Chinese population. J Neurol Sci 2011; 308:83-7. [PMID: 21705024 DOI: 10.1016/j.jns.2011.06.002] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2011] [Accepted: 06/01/2011] [Indexed: 10/18/2022]
Abstract
Spinal muscular atrophy (SMA) is a neurodegenerative disease characterized by programmed motoneuron death. The survival motor neuron 1 (SMN1) gene is an SMA-determining gene and SMN2 represents an SMA-modifying gene. Here, we applied capillary electrophoresis to quantify the SMN gene dosage in 163 normal individuals, 94 SMA patients and 138 of their parents. We further quantified exons 7 and 8 in SMN1 and SMN2. We found that the SMA patients carried the highest SMN2 copies, which was inversely correlated with disease severity among its three subtypes. Increased SMN1 was significantly associated with decreased SMN2 in the normal group. We also observed that parents of type I SMA patients had significantly fewer SMN2 copies than those of types II and III patients. The hybrid SMN genes were detected in two normal individuals and one patient and her mother. These results imply that increased SMN2 copies in SMA patient group might be derived from SMN1-to-SMN2 conversion, whereas the trend that normal individuals with higher SMN1 copies simultaneously carry fewer SMN2 copies suggested a reverse conversion, SMN2-to-SMN1. Together with the identification of hybrid SMN genes, our data provided additional evidence to support that SMN1 and SMN2 gene loci are interchangeable between population groups.
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Affiliation(s)
- Tai-Heng Chen
- Department of Pediatrics, Kaohsiung Medical University Hospital, Kaohsiung Medical University, Kaohsiung, Taiwan
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16
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Wang CC, Jong YJ, Chang JG, Chen YL, Wu SM. Universal fluorescent multiplex PCR and capillary electrophoresis for evaluation of gene conversion between SMN1 and SMN2 in spinal muscular atrophy. Anal Bioanal Chem 2010; 397:2375-83. [PMID: 20563565 DOI: 10.1007/s00216-010-3761-1] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2010] [Revised: 04/15/2010] [Accepted: 04/15/2010] [Indexed: 12/24/2022]
Abstract
We have developed a capillary electrophoresis (CE) method with universal fluorescent multiplex PCR to simultaneously detect the SMN1 and SMN2 genes in exons 7 and 8. Spinal muscular atrophy (SMA) is a very frequent inherited disease caused by the absence of the SMN1 gene in approximately 94% of patients. Those patients have deletion of the SMN1 gene or gene conversion between SMN1 and SMN2. However, most methods only focus on the analysis of whole gene deletion, and ignore gene conversion. Simultaneous quantification of SMN1 and SMN2 in exons 7 and 8 is a good strategy for estimating SMN1 deletion or SMN1 to SMN2 gene conversion. This study established a CE separation allowing differentiation of all copy ratios of SMN1 to SMN2 in exons 7 and 8. Among 212 detected individuals, there were 23 SMA patients, 45 carriers, and 144 normal subjects. Three individuals had different ratios of SMN1 to SMN2 in two exons, including an SMA patient having two SMN2 copies in exon 7 but one SMN1 copy in exon 8. This method could provide more information about SMN1 deletion or SMN1 to SMN2 gene conversion for SMA genotyping and diagnosis.
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Affiliation(s)
- Chun-Chi Wang
- School of Pharmacy, College of Pharmacy, Kaohsiung Medical University, 100 Shih-Chuan 1st Road, Kaohsiung 807, Taiwan
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Bertoni C, Rustagi A, Rando TA. Enhanced gene repair mediated by methyl-CpG-modified single-stranded oligonucleotides. Nucleic Acids Res 2010; 37:7468-82. [PMID: 19854937 PMCID: PMC2794159 DOI: 10.1093/nar/gkp757] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Gene editing mediated by oligonucleotides has been shown to induce stable single base alterations in genomic DNA in both prokaryotic and eukaryotic organisms. However, the low frequencies of gene repair have limited its applicability for both basic manipulation of genomic sequences and for the development of therapeutic approaches for genetic disorders. Here, we show that single-stranded oligodeoxynucleotides (ssODNs) containing a methyl-CpG modification and capable of binding to the methyl-CpG binding domain protein 4 (MBD4) are able to induce >10-fold higher levels of gene correction than ssODNs lacking the specific modification. Correction was stably inherited through cell division and was confirmed at the protein, transcript and genomic levels. Downregulation of MBD4 expression using RNAi prevented the enhancement of gene correction efficacy obtained using the methyl-CpG-modified ssODN, demonstrating the specificity of the repair mechanism being recruited. Our data demonstrate that efficient manipulation of genomic targets can be achieved and controlled by the type of ssODN used and by modulation of the repair mechanism involved in the correction process. This new generation of ssODNs represents an important technological advance that is likely to have an impact on multiple applications, especially for gene therapy where permanent correction of the genetic defect has clear advantages over viral and other nonviral approaches currently being tested.
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Affiliation(s)
- Carmen Bertoni
- Department of Neurology and Neurological Sciences, Stanford University School of Medicine, Stanford, CA 94305, USA.
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18
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Abstract
Spinal muscular atrophy is a leading genetic cause of infantile death and occurs in approximately 1/6000 live births. SMA is caused by the loss of Survival Motor Neuron-1 (SMN1), however, all patients retain at least one copy of a nearly identical gene called SMN2. While SMN2 and SMN1 are comprised of identical coding sequences, the majority of SMN2 transcripts are alternatively spliced, encoding a truncated protein that is unstable and nonfunctional. Considerable effort has focused upon modulating the SMN2 alternative splicing event since this would produce more wild-type protein. Recently we reported the development of an optimized trans-splicing system that involved the coexpression of a SMN2 trans-splicing RNA and an antisense RNA that blocks a downstream splice site in SMN2 pre-mRNA. Here, we demonstrate that in vivo delivery of the optimized trans-splicing vector increases an important SMN-dependent activity, snRNP assembly, in disease-relevant tissue in the SMA mouse model. A single injection of the vector into the intracerebral-ventricular space in SMA neonates also lessens the severity of the SMA phenotype in a severe SMA mouse model, extending survival approximately 70%. Collectively, these results provide the first in vivo demonstration that SMN2 trans-splicing leads to a lessening of the severity of the SMA phenotype and provide evidence for the power of this strategy for reprogramming genetic diseases at the pre-mRNA level.
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Abstract
AbstractProgress in understanding the genetic basis and pathophysiology of spinal muscular atrophy (SMA), along with continuous efforts in finding a way to increase survival motor neuron (SMN) protein levels have resulted in several strategies that have been proposed as potential directions for efficient drug development. Here we provide an overview on the current status of the following approaches: 1) activation of SMN2 gene and increasing full length SMN2 transcript level, 2) modulating SMN2 splicing, 3) stabilizing SMN mRNA and SMN protein, 4) development of neurotrophic, neuroprotective and anabolic compounds and 5) stem cell and gene therapy. The new preclinical advances warrant a cautious optimism for emergence of an effective treatment in the very near future.
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Bosboom WMJ, Vrancken AFJE, van den Berg LH, Wokke JHJ, Iannaccone ST. Drug treatment for spinal muscular atrophy types II and III. Cochrane Database Syst Rev 2009:CD006282. [PMID: 19160275 DOI: 10.1002/14651858.cd006282.pub2] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
BACKGROUND Spinal muscular atrophy (SMA) is caused by degeneration of anterior horn cells, which leads to progressive muscle weakness. Children with SMA type II do not develop the ability to walk without support and have a shortened life expectancy, whereas children with SMA type III develop the ability to walk and have a normal life expectancy. There are no known efficacious drug treatments that influence the disease course of SMA. OBJECTIVES To evaluate if drug treatment is able to slow or arrest the disease progression of SMA type II and III, and to assess if such therapy can be given safely. Drug treatment for SMA type I will be the topic of a separate Cochrane review. SEARCH STRATEGY We searched the Cochrane Neuromuscular Disease Group Trials Register (September 30 2008), The Cochrane Library (Issue 3, 2008), MEDLINE (January 1966 to June 2008), EMBASE (January 1980 to June 2008), ISI (January 1988 to June 2008), and ACP Journal Club (January 1991 to June 2008). SELECTION CRITERIA We sought all randomized or quasi-randomized trials that examined the efficacy of drug treatment for SMA type II and III. Participants had to fulfil the clinical criteria and, in studies including genetic analysis to confirm the diagnosis, have a deletion or mutation of the SMN1 gene (5q11.2-13.2)The primary outcome measure was to be change in disability score within one year after the onset of treatment. Secondary outcome measures within one year after the onset of treatment were to be change in muscle strength, ability to stand or walk, change in quality of life, time from the start of treatment until death or full time ventilation, and adverse events attributable to treatment during the trial period. DATA COLLECTION AND ANALYSIS Two authors independently reviewed and extracted data from all potentially relevant trials. Pooled relative risks and pooled weighted standardized mean differences were to be calculated to assess treatment efficacy MAIN RESULTS Four randomized placebo-controlled trials on treatment for SMA type II and III were found and included in the review. The treatments were creatine, phenylbutyrate, gabapentin and thyrotropin releasing hormone. None of these trials showed any effect on the outcome measures in patients with SMA type II and III. None of the patients in any of the four trials died or reached the state of full time ventilation and serious side effects were infrequent. AUTHORS' CONCLUSIONS There is no proven efficacious drug treatment for SMA type II and III.
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Affiliation(s)
- Wendy M J Bosboom
- Department of Neurology, Sint Lucas Andreas Hospital, Jan Tooropstraat 164, Amsterdam, Netherlands, 1061 AE.
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Bosboom WMJ, Vrancken AFJE, van den Berg LH, Wokke JHJ, Iannaccone ST. Drug treatment for spinal muscular atrophy type I. Cochrane Database Syst Rev 2009:CD006281. [PMID: 19160274 DOI: 10.1002/14651858.cd006281.pub2] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
BACKGROUND Spinal muscular atrophy (SMA) is caused by degeneration of anterior horn cells, which leads to progressive muscle weakness. Children with SMA type I will never be able to sit without support and usually die by the age of two years. There are no known efficacious drug treatments that influence the disease course. OBJECTIVES To evaluate if drug treatment is able to slow or arrest the disease progression of SMA type I, and to assess if such therapy can be given safely. Drug treatment for SMA type II and III will be will be the topic of a separate Cochrane review. SEARCH STRATEGY We searched the Cochrane Neuromuscular Disease Group Trials Register (September 30 2008, The Cochrane Library (Issue 3, 2008), MEDLINE (January 1966 to June 2008), EMBASE (January 1980 to June 2008), ISI (January 1988 to June 2008), and ACP Journal Club (January 1991 to June 2008). SELECTION CRITERIA All randomized or quasi-randomized trials that examined the efficacy of drug treatment for SMA type 1 were sought. Participants had to fulfil clinical criteria and, in studies including genetic analysis to confirm the diagnosis, have a deletion or mutation of the SMN1 gene (5q11.2-13.2)The primary outcome measure was to be time from birth until death or full time ventilation. Secondary outcome measures were to be development of rolling, sitting or standing within one year after the onset of treatment, and adverse events attributable to treatment during the trial period. DATA COLLECTION AND ANALYSIS Two authors (WB and AV) independently reviewed and extracted data from all potentially relevant trials. For included studies pooled relative risks and pooled weighted standardized mean differences were to be calculated to assess treatment efficacy MAIN RESULTS One small randomized-controlled study comparing riluzole treatment to placebo for SMA type 1 was identified and included in the review. Regarding the primary outcome measure three of seven children treated with riluzole were still alive at the age of 30, 48 and 64 months, whereas all three children in the placebo group died, but the difference was not statistically significant. Regarding the secondary outcome measures none of the patients in the riluzole or placebo group developed the ability to roll, sit or stand, and no adverse effects were observed. AUTHORS' CONCLUSIONS No drug treatment for SMA type I has been proven to have significant efficacy.
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Affiliation(s)
- Wendy M J Bosboom
- Department of Neurology, Sint Lucas Andreas Hospital, Jan Tooropstraat 164, Amsterdam, Netherlands, 1061 AE.
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Development of a single vector system that enhances trans-splicing of SMN2 transcripts. PLoS One 2008; 3:e3468. [PMID: 18941511 PMCID: PMC2565107 DOI: 10.1371/journal.pone.0003468] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2008] [Accepted: 09/20/2008] [Indexed: 11/20/2022] Open
Abstract
RNA modalities are developing as a powerful means to re-direct pathogenic pre-mRNA splicing events. Improving the efficiency of these molecules in vivo is critical as they move towards clinical applications. Spinal muscular atrophy (SMA) is caused by loss of SMN1. A nearly identical copy gene called SMN2 produces low levels of functional protein due to alternative splicing. We previously reported a trans-splicing RNA (tsRNA) that re-directed SMN2 splicing. Now we show that reducing the competition between endogenous splices sites enhanced the efficiency of trans-splicing. A single vector system was developed that expressed the SMN tsRNA and a splice-site blocking antisense (ASO-tsRNA). The ASO-tsRNA vector significantly elevated SMN levels in primary SMA patient fibroblasts, within the central nervous system of SMA mice and increased SMN-dependent in vitro snRNP assembly. These results demonstrate that the ASO-tsRNA strategy provides insight into the trans-splicing mechanism and a means of significantly enhancing trans-splicing activity in vivo.
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Simic G. Pathogenesis of proximal autosomal recessive spinal muscular atrophy. Acta Neuropathol 2008; 116:223-34. [PMID: 18629520 DOI: 10.1007/s00401-008-0411-1] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2008] [Revised: 07/02/2008] [Accepted: 07/02/2008] [Indexed: 02/06/2023]
Abstract
Although it is known that deletions or mutations of the SMN1 gene on chromosome 5 cause decreased levels of the SMN protein in subjects with proximal autosomal recessive spinal muscular atrophy (SMA), the exact sequence of pathological events leading to selective motoneuron cell death is not fully understood yet. In this review, new findings regarding the dual cellular role of the SMN protein (translocation of beta-actin to axonal growth cones and snRNP biogenesis/pre-mRNA splicing) were integrated with recent data obtained by detailed neuropathological examination of SMA and control subjects. A presumptive series of 10 pathogenetic events for SMA is proposed as follows: (1) deletions or mutations of the SMN1 gene, (2) increased SMN mRNA decay and reduction in full-length functional SMN protein, (3) impaired motoneuron axono- and dendrogenesis, (4) failure of motoneurons to form synapses with corticospinal fibers from upper motoneurons, (5) abnormal motoneuron migration towards ventral spinal roots, (6) inappropriate persistence of motoneuron apoptosis due to impaired differentiation and motoneuron displacement, (7) substantial numbers of motoneurons continuing to migrate abnormally ("heterotopic motoneurons") and entering into the ventral roots, (8) attracted glial cells following these heterotopic motoneurons, which form the glial bundles of ventral roots, (9) impaired axonal transport of actin, causing remaining motoneurons to become chromatolytic, and (10) eventual death of all apoptotic, heterotopic and chromatolytic neurons, with apoptosis being more rapid and predominating in the earlier stages, with death of heterotopic and chromatolytic neurons occurring more slowly by necrosis during the later stages of SMA. According to this model, the motoneuron axonopathy is more important for pathogenesis than the ubiquitous nuclear splicing deficit. It is also supposed that individually variable levels of SMN protein, together with influences of other phenotype modifier genes and their products, cause the clinical SMA spectrum through differential degree of motoneuron functional loss.
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Affiliation(s)
- Goran Simic
- Department of Neuroscience, Croatian Institute for Brain Research, School of Medicine, Zagreb University, Salata 12, 10000, Zagreb, Croatia.
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25
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Abstract
Spinal muscular atrophy is an autosomal recessive neurodegenerative disease characterised by degeneration of spinal cord motor neurons, atrophy of skeletal muscles, and generalised weakness. It is caused by homozygous disruption of the survival motor neuron 1 (SMN1) gene by deletion, conversion, or mutation. Although no medical treatment is available, investigations have elucidated possible mechanisms underlying the molecular pathogenesis of the disease. Treatment strategies have been developed to use the unique genomic structure of the SMN1 gene region. Several candidate treatment agents have been identified and are in various stages of development. These and other advances in medical technology have changed the standard of care for patients with spinal muscular atrophy. In this Seminar, we provide a comprehensive review that integrates clinical manifestations, molecular pathogenesis, diagnostic strategy, therapeutic development, and evidence from clinical trials.
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Affiliation(s)
- Mitchell R Lunn
- Department of Medicine, Stanford University School of Medicine, Stanford, CA, USA
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