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Jha NN, Kim JK, Monani UR. Motor neuron biology and disease: A current perspective on infantile-onset spinal muscular atrophy. FUTURE NEUROLOGY 2018; 13:161-172. [PMID: 31396020 DOI: 10.2217/fnl-2018-0008] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Infantile-onset spinal muscular atrophy (SMA) is a prototypical disease in which to investigate selective neurodegenerative phenotypes. Caused by low levels of the ubiquitously expressed Survival Motor Neuron (SMN) protein, the disease mainly targets the spinal motor neurons. This selective phenotype remains largely unexplained, but has not hindered the development of SMN repletion as a means to a treatment. Here we chronicle recent advances in the area of SMA biology. We provide a brief background to the disease, highlight major advances that have shaped our current understanding of SMA, trace efforts to treat the condition, discuss the outcome of two promising new therapies and conclude by considering contemporary as well as new challenges stemming from recent successes within the field.
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Affiliation(s)
- Narendra N Jha
- Department of Pathology & Cell Biology, 630 W. 168 St., Columbia University Medical Center, New York, NY 10032.,Center for Motor Neuron Biology & Disease, 630 W. 168 St., Columbia University Medical Center, New York, NY 10032
| | - Jeong-Ki Kim
- Department of Pathology & Cell Biology, 630 W. 168 St., Columbia University Medical Center, New York, NY 10032.,Center for Motor Neuron Biology & Disease, 630 W. 168 St., Columbia University Medical Center, New York, NY 10032
| | - Umrao R Monani
- Department of Pathology & Cell Biology, 630 W. 168 St., Columbia University Medical Center, New York, NY 10032.,Department of Neurology, 630 W. 168 St., Columbia University Medical Center, New York, NY 10032.,Center for Motor Neuron Biology & Disease, 630 W. 168 St., Columbia University Medical Center, New York, NY 10032
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Petit F, Cuisset JM, Rouaix-Emery N, Cancés C, Sablonnière B, Bieth E, Moerman A, Sukno S, Hardy N, Holder-Espinasse M, Manouvrier-Hanu S, Vallée L. Insights into genotype-phenotype correlations in spinal muscular atrophy: a retrospective study of 103 patients. Muscle Nerve 2011; 43:26-30. [PMID: 21171094 DOI: 10.1002/mus.21832] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
Spinal muscular atrophy (SMA) is an autosomal recessive disorder associated with homozygous deletion of the survival motor neuron 1 gene (SMN1). Its centromeric copy gene, SMN2, is the major modifying factor. However, the genotype-phenotype correlation is incomplete and is therefore not useful in clinical practice. We studied a cohort of 103 patients in order to refine this correlation. In addition to standard disease severity data, we collected three additional criteria: age at death; brainstem involvement; and loss of ambulation. Gene dosage analysis was conducted by multiplex ligation-dependent probe amplification (MLPA). SMN2 copynumber was highly correlated with survival duration in SMA type I and ambulation conservation or loss in type III. Among SMA severity groups, it was not significantly different in cases with brainstem involvement. Although the SMN2 copynumber could provide prognostic indications, clinical discrepancies still exist among patients, suggesting the existence of unidentified modifying factors.
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Affiliation(s)
- Florence Petit
- Service de Génétique Clinique, CHU Hôpital Jeanne de Flandre, Lille, France
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Abstract
Motor neurons are large, highly polarised cells with very long axons and a requirement for precise spatial and temporal gene expression. Neurodegenerative disorders characterised by selective motor neuron vulnerability include various forms of amyotrophic lateral sclerosis (ALS) and spinal muscular atrophy (SMA). A rapid expansion in knowledge on the pathophysiology of motor neuron degeneration has occurred in recent years, largely through the identification of genes leading to familial forms of ALS and SMA. The major emerging theme is that motor neuron degeneration can result from mutation in genes that encode factors important for ribonucleoprotein biogenesis and RNA processing, including splicing regulation, transcript stabilisation, translational repression and localisation of mRNA. Complete understanding of how these pathways interact and elucidation of specialised mechanisms for mRNA targeting and processing in motor neurons are likely to produce new targets for therapy in ALS and related disorders.
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Bäumer D, Lee S, Nicholson G, Davies JL, Parkinson NJ, Murray LM, Gillingwater TH, Ansorge O, Davies KE, Talbot K. Alternative splicing events are a late feature of pathology in a mouse model of spinal muscular atrophy. PLoS Genet 2009; 5:e1000773. [PMID: 20019802 PMCID: PMC2787017 DOI: 10.1371/journal.pgen.1000773] [Citation(s) in RCA: 195] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2009] [Accepted: 11/16/2009] [Indexed: 11/24/2022] Open
Abstract
Spinal muscular atrophy is a severe motor neuron disease caused by inactivating mutations in the SMN1 gene leading to reduced levels of full-length functional SMN protein. SMN is a critical mediator of spliceosomal protein assembly, and complete loss or drastic reduction in protein leads to loss of cell viability. However, the reason for selective motor neuron degeneration when SMN is reduced to levels which are tolerated by all other cell types is not currently understood. Widespread splicing abnormalities have recently been reported at end-stage in a mouse model of SMA, leading to the proposition that disruption of efficient splicing is the primary mechanism of motor neuron death. However, it remains unclear whether splicing abnormalities are present during early stages of the disease, which would be a requirement for a direct role in disease pathogenesis. We performed exon-array analysis of RNA from SMN deficient mouse spinal cord at 3 time points, pre-symptomatic (P1), early symptomatic (P7), and late-symptomatic (P13). Compared to littermate control mice, SMA mice showed a time-dependent increase in the number of exons showing differential expression, with minimal differences between genotypes at P1 and P7, but substantial variation in late-symptomatic (P13) mice. Gene ontology analysis revealed differences in pathways associated with neuronal development as well as cellular injury. Validation of selected targets by RT-PCR confirmed the array findings and was in keeping with a shift between physiologically occurring mRNA isoforms. We conclude that the majority of splicing changes occur late in SMA and may represent a secondary effect of cell injury, though we cannot rule out significant early changes in a small number of transcripts crucial to motor neuron survival.
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Affiliation(s)
- Dirk Bäumer
- MRC Functional Genomics Unit, Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
| | - Sheena Lee
- MRC Functional Genomics Unit, Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
| | - George Nicholson
- Department of Statistics, University of Oxford, Oxford, United Kingdom
| | - Joanna L. Davies
- Department of Statistics, University of Oxford, Oxford, United Kingdom
| | - Nicholas J. Parkinson
- MRC Functional Genomics Unit, Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
| | - Lyndsay M. Murray
- Centre for Integrative Physiology and Euan MacDonald Centre for Motor Neuron Disease Research, University of Edinburgh Medical School, Edinburgh, United Kingdom
| | - Thomas H. Gillingwater
- Centre for Integrative Physiology and Euan MacDonald Centre for Motor Neuron Disease Research, University of Edinburgh Medical School, Edinburgh, United Kingdom
| | - Olaf Ansorge
- Department of Neuropathology, John Radcliffe Hospital, Oxford, United Kingdom
| | - Kay E. Davies
- MRC Functional Genomics Unit, Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
| | - Kevin Talbot
- MRC Functional Genomics Unit, Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
- Department of Clinical Neurology, University of Oxford, John Radcliffe Hospital, Oxford, United Kingdom
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