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Chi Y, Qiao Y, Ma Y. Spinal muscular atrophy caused by compound heterozygous SMN1 mutations: two cases and literature review. Neurol Sci 2024:10.1007/s10072-024-07651-0. [PMID: 38972959 DOI: 10.1007/s10072-024-07651-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/25/2023] [Accepted: 06/11/2024] [Indexed: 07/09/2024]
Abstract
Spinal muscular atrophy (SMA) is a rare neuromuscular disease, which is characterized by the degeneration of motor neurons, leading to symmetrical muscle weakness and atrophy. Description of two novel SMN1 mutations (patient1: c.683T > A, p.Leu228Ter; patient2: c.347 T > C, p.Ile116 Thr). We reported two patients with SMN1 mutations with the clinical features, and provided a literature review of the previously reported 22 cases. Two SMA patients showed progressive proximal lower limb weakness and milder clinical symptom. In a total of 22 cases, the most commonly observed SMN1 gene alteration was missense mutation (55%), followed by splicing defect (27%), nonsense (9%) and frameshift (9%). We discuss the possible decisive role of these intragenic mutations in the phenotypic results, which enriched the SMN 1 fine mutation database.
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Affiliation(s)
- Yuewei Chi
- Department of Neurology, Shengjing Hospital of China Medical University, Shenyang, Liaoning, 110000, China
| | - Yue Qiao
- Department of Neurology, Shengjing Hospital of China Medical University, Shenyang, Liaoning, 110000, China
| | - Ying Ma
- Department of Neurology, Shengjing Hospital of China Medical University, Shenyang, Liaoning, 110000, China.
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2
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Li S, Han X, Zhang L, Xu Y, Chang C, Gao L, Zhan J, Hua R, Mao A, Wang Y. An Effective and Universal Long-Read Sequencing-Based Approach for SMN1 2 + 0 Carrier Screening through Family Trio Analysis. Clin Chem 2023; 69:1295-1306. [PMID: 37932106 DOI: 10.1093/clinchem/hvad152] [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: 07/05/2023] [Accepted: 08/28/2023] [Indexed: 11/08/2023]
Abstract
BACKGROUND Population-wide carrier screening for spinal muscular atrophy (SMA) is recommended by professional organizations to facilitate informed reproductive options. However, genetic screening for SMN1 2 + 0 carriers, accounting for 3%-8% of all SMA carriers, has been challenging due to the large gene size and long distance between the 2 SMN genes. METHODS Here we repurposed a previously developed long-read sequencing-based approach, termed comprehensive analysis of SMA (CASMA), to identify SMN1 2 + 0 carriers through haplotype analysis in family trios (CASMA-trio). Bioinformatics pipelines were developed for accurate haplotype analysis and SMN1 2 + 0 deduction. Seventy-nine subjects from 24 families composed of, at the minimum, 3 were enrolled, and CASMA-trio was employed to determine whether an index subject with 2 SMN1 copies was a 2 + 0 carrier in these families. For the proof-of-principle, SMN2 2 + 0 was also analyzed. RESULTS Among the 16 subjects with 2 SMN1 copies, CASMA-trio identified 5 subjects from 4 families as SMN1 2 + 0 carriers, which was consistent with pedigree analysis involving an affected proband. CASMA-trio also identified SMN2 2 + 0 in six out of 43 subjects with 2 SMN2 copies. Additionally, CASMA-trio successfully determined the distribution pattern of SMN1 and SMN2 genes on 2 alleles in all 79 subjects. CONCLUSIONS CASMA-trio represents an effective and universal approach for SMN1 2 + 0 carriers screening, as it does not reply on the presence of an affected proband, certain single-nucleotide polymorphisms, ethnicity-specific haplotypes, or complicated single-nucleotide polymorphism analysis across 3 generations. Incorporating CASMA-trio into existing SMA carrier screening programs will greatly reduce residual risk ratio.
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Affiliation(s)
- Shuyuan Li
- International Peace Maternity and Child Health Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai 200030, China
- Shanghai Key Laboratory of Embryo Original Diseases, Shanghai 200030, China
- Institute of Birth Defects and Rare Diseases, School of Medicine, Shanghai Jiao Tong University, Shanghai 200030, China
| | - Xu Han
- International Peace Maternity and Child Health Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai 200030, China
- Shanghai Key Laboratory of Embryo Original Diseases, Shanghai 200030, China
- Institute of Birth Defects and Rare Diseases, School of Medicine, Shanghai Jiao Tong University, Shanghai 200030, China
| | - Liang Zhang
- International Peace Maternity and Child Health Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai 200030, China
- Shanghai Key Laboratory of Embryo Original Diseases, Shanghai 200030, China
- Institute of Birth Defects and Rare Diseases, School of Medicine, Shanghai Jiao Tong University, Shanghai 200030, China
| | - Yan Xu
- International Peace Maternity and Child Health Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai 200030, China
- Shanghai Key Laboratory of Embryo Original Diseases, Shanghai 200030, China
- Institute of Birth Defects and Rare Diseases, School of Medicine, Shanghai Jiao Tong University, Shanghai 200030, China
| | - Chunxin Chang
- International Peace Maternity and Child Health Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai 200030, China
- Shanghai Key Laboratory of Embryo Original Diseases, Shanghai 200030, China
- Institute of Birth Defects and Rare Diseases, School of Medicine, Shanghai Jiao Tong University, Shanghai 200030, China
| | - Li Gao
- International Peace Maternity and Child Health Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai 200030, China
- Shanghai Key Laboratory of Embryo Original Diseases, Shanghai 200030, China
- Institute of Birth Defects and Rare Diseases, School of Medicine, Shanghai Jiao Tong University, Shanghai 200030, China
| | - Jiahan Zhan
- Berry Genomics Corporation, Beijing 102200, China
| | - Renyi Hua
- International Peace Maternity and Child Health Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai 200030, China
- Shanghai Key Laboratory of Embryo Original Diseases, Shanghai 200030, China
- Institute of Birth Defects and Rare Diseases, School of Medicine, Shanghai Jiao Tong University, Shanghai 200030, China
| | - Aiping Mao
- Berry Genomics Corporation, Beijing 102200, China
| | - Yanlin Wang
- International Peace Maternity and Child Health Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai 200030, China
- Shanghai Key Laboratory of Embryo Original Diseases, Shanghai 200030, China
- Institute of Birth Defects and Rare Diseases, School of Medicine, Shanghai Jiao Tong University, Shanghai 200030, China
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Votsi C, Koutsou P, Ververis A, Georghiou A, Nicolaou P, Tanteles G, Christodoulou K. Spinal muscular atrophy type I associated with a novel SMN1 splicing variant that disrupts the expression of the functional transcript. Front Neurol 2023; 14:1241195. [PMID: 37799281 PMCID: PMC10548546 DOI: 10.3389/fneur.2023.1241195] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2023] [Accepted: 08/31/2023] [Indexed: 10/07/2023] Open
Abstract
Introduction Spinal muscular atrophy (SMA) is an autosomal recessive neuromuscular disorder caused by pathogenic variants in the SMN1 gene. The majority of SMA patients harbor a homozygous deletion of SMN1 exon 7 (95%). Heterozygosity for a conventional variant and a deletion is rare (5%) and not easily detected, due to the highly homologous SMN2 gene interference. SMN2 mainly produces a truncated non-functional protein (SMN-d7) instead of the full-length functional (SMN-FL). We hereby report a novel SMN1 splicing variant in an infant with severe SMA. Methods MLPA was used for SMN1/2 exon dosage determination. Sanger sequencing approaches and long-range PCR were employed to search for an SMN1 variant. Conventional and improved Real-time PCR assays were developed for the qualitative and quantitative SMN1/2 RNA analysis. Results The novel SMN1 splice-site variant c.835-8_835-5delinsG, was identified in compound heterozygosity with SMN1 exons 7/8 deletion. RNA studies revealed complete absence of SMN1 exon 7, thus confirming a disruptive effect of the variant on SMN1 splicing. No expression of the functional SMN1-FL transcript, remarkable expression of the SMN1-d7 and increased levels of the SMN2-FL/SMN2-d7 transcripts were observed. Discussion We verified the occurrence of a non-deletion SMN1 variant and supported its pathogenicity, thus expanding the SMN1 variants spectrum. We discuss the updated SMA genetic findings in the Cypriot population, highlighting an increased percentage of intragenic variants compared to other populations.
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Affiliation(s)
- Christina Votsi
- Neurogenetics Department, The Cyprus Institute of Neurology and Genetics, Nicosia, Cyprus
| | - Pantelitsa Koutsou
- Neurogenetics Department, The Cyprus Institute of Neurology and Genetics, Nicosia, Cyprus
| | - Antonis Ververis
- Neurogenetics Department, The Cyprus Institute of Neurology and Genetics, Nicosia, Cyprus
| | - Anthi Georghiou
- Neurogenetics Department, The Cyprus Institute of Neurology and Genetics, Nicosia, Cyprus
| | - Paschalis Nicolaou
- Neurogenetics Department, The Cyprus Institute of Neurology and Genetics, Nicosia, Cyprus
| | - George Tanteles
- Clinical Genetics Department, The Cyprus Institute of Neurology and Genetics, Nicosia, Cyprus
| | - Kyproula Christodoulou
- Neurogenetics Department, The Cyprus Institute of Neurology and Genetics, Nicosia, Cyprus
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Vezain M, Thauvin-Robinet C, Vial Y, Coutant S, Drunat S, Urtizberea JA, Rolland A, Jacquin-Piques A, Fehrenbach S, Nicolas G, Lecoquierre F, Saugier-Veber P. Retrotransposon insertion as a novel mutational cause of spinal muscular atrophy. Hum Genet 2023; 142:125-138. [PMID: 36138164 DOI: 10.1007/s00439-022-02473-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2022] [Accepted: 07/15/2022] [Indexed: 01/18/2023]
Abstract
Spinal muscular atrophy (SMA) is an autosomal recessive neuromuscular disorder resulting from biallelic alterations of the SMN1 gene: deletion, gene conversion or, in rare cases, intragenic variants. The disease severity is mainly influenced by the copy number of SMN2, a nearly identical gene, which produces only low amounts of full-length (FL) mRNA. Here we describe the first example of retrotransposon insertion as a pathogenic SMN1 mutational event. The 50-year-old patient is clinically affected by SMA type III with a diagnostic odyssey spanning nearly 30 years. Despite a mild disease course, he carries a single SMN2 copy. Using Exome Sequencing and Sanger sequencing, we characterized a SINE-VNTR-Alu (SVA) type F retrotransposon inserted in SMN1 intron 7. Using RT-PCR and RNASeq experiments on lymphoblastoid cell lines, we documented the dramatic decrease of FL transcript production in the patient compared to subjects with the same SMN1 and SMN2 copy number, thus validating the pathogenicity of this SVA insertion. We described the mutant FL-SMN1-SVA transcript characterized by exon extension and showed that it is subject to degradation by nonsense-mediated mRNA decay. The stability of the SMN-SVA protein may explain the mild course of the disease. This observation exemplifies the role of retrotransposons in human genetic disorders.
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Affiliation(s)
- Myriam Vezain
- INSERM UMR1245, UNIROUEN, Normandie Univ, F-76000, Rouen, France.,Department of Genetics, FHU G4 Génomique, Rouen University Hospital, F-76000, Rouen, France
| | - Christel Thauvin-Robinet
- INSERM UMR1231 GAD-Génétique des Anomalies du Développement, Bourgogne Franche-Comté University, F-21000 , Dijon, France.,Genetics Center, Fédération Hospitalo-Universitaire Médecine Translationnelle et Anomalies du Développement (TRANSLAD), Dijon-Burgundy University Hospital, F-21000, Dijon, France
| | - Yoann Vial
- INSERM UMR1245, UNIROUEN, Normandie Univ, F-76000, Rouen, France.,Department of Genetics, FHU G4 Génomique, Rouen University Hospital, F-76000, Rouen, France.,Genetics Department, AP-HP, Robert-Debré University Hospital, 48 boulevard Sérurier, 75019 , Paris, France
| | - Sophie Coutant
- INSERM UMR1245, UNIROUEN, Normandie Univ, F-76000, Rouen, France.,Department of Genetics, FHU G4 Génomique, Rouen University Hospital, F-76000, Rouen, France
| | - Séverine Drunat
- INSERM UMR 1141, PROTECT, Paris University, F-75019, Paris, France.,Genetics Department, AP-HP, Robert-Debré University Hospital, F-75019, Paris, France
| | - Jon Andoni Urtizberea
- Myology Institute, AP-HP Pitié-Salpêtrière University Hospital, F-75013, Paris, France
| | - Anne Rolland
- INSERM UMR1245, UNIROUEN, Normandie Univ, F-76000, Rouen, France.,Pediatrics Department, Valence Hospital, 179 boulevard du Maréchal Juin, 26000, Valence, France
| | - Agnès Jacquin-Piques
- Department of Neurology, Clinical Neurophysiology, Competence Center of Neuromuscular Diseases, Dijon-Burgundy University Hospital, F-21000, Dijon, France
| | - Séverine Fehrenbach
- Department of Genetics, FHU G4 Génomique, Rouen University Hospital, F-76000, Rouen, France
| | - Gaël Nicolas
- INSERM UMR1245, UNIROUEN, Normandie Univ, F-76000, Rouen, France.,Department of Genetics, FHU G4 Génomique, Rouen University Hospital, F-76000, Rouen, France
| | - François Lecoquierre
- INSERM UMR1245, UNIROUEN, Normandie Univ, F-76000, Rouen, France.,Department of Genetics, FHU G4 Génomique, Rouen University Hospital, F-76000, Rouen, France
| | - Pascale Saugier-Veber
- INSERM UMR1245, UNIROUEN, Normandie Univ, F-76000, Rouen, France. .,Department of Genetics, FHU G4 Génomique, Rouen University Hospital, F-76000, Rouen, France. .,Laboratoire de Génétique Moléculaire, UFR-Santé, 22 boulevard Gambetta, 76183, Rouen, France.
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Li S, Han X, Xu Y, Chang C, Gao L, Li J, Lu Y, Mao A, Wang Y. Comprehensive Analysis of Spinal Muscular Atrophy: SMN1 Copy Number, Intragenic Mutation, and 2 + 0 Carrier Analysis by Third-Generation Sequencing. J Mol Diagn 2022; 24:1009-1020. [PMID: 35659528 DOI: 10.1016/j.jmoldx.2022.05.001] [Citation(s) in RCA: 16] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2022] [Revised: 04/14/2022] [Accepted: 05/16/2022] [Indexed: 01/18/2023] Open
Abstract
Population-wide carrier screening for spinal muscular atrophy (SMA) is recommended by the American College of Medical Genetics and Genomics. However, the methods used currently mainly focus on SMN1 copy number and fail to identify carriers with pathogenic intragenic mutations and silent (2 + 0) carriers. We developed a method termed comprehensive analysis of SMA (CASMA) based on long-range PCR and third-generation sequencing of full-length and downstream regions of SMN1/2. The sensitivity and specificity of CASMA to detect SMA carriers with one copy of SMN1 were 100% (n = 101) and 99.2% (n = 236), respectively. CASMA confirmed three SMN1 intragenic mutations and pinpointed an inframe mutation c.661_666del to SMN2, which was misreported to SMN1 by allele-specific long-range nested PCR plus Sanger sequencing. CASMA also correctly predicted 8 of 16 samples (50%) with SMN1 duplication alleles. CASMA was expected to increase the detection rate of SMA carriers from 91% to 98% and decrease the residual risk ratio from 1:415 to 1:1868 after negative results of two SMN1 copies in the Chinese population. CASMA presents a comprehensive approach for identifying SMN1 and SMN2 copy number, intragenic mutations, and potential silent carriers that significantly reduces the residual risk ratio in SMA carrier screening and has great clinical utility.
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Affiliation(s)
- Shuyuan Li
- International Peace Maternity and Child Health Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai, China; Shanghai Key Laboratory of Embryo Original Diseases, Shanghai, China; Institute of Birth Defects and Rare Diseases, School of Medicine, Shanghai Jiao Tong University, Shanghai, China
| | - Xu Han
- International Peace Maternity and Child Health Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai, China; Shanghai Key Laboratory of Embryo Original Diseases, Shanghai, China; Institute of Birth Defects and Rare Diseases, School of Medicine, Shanghai Jiao Tong University, Shanghai, China
| | - Yan Xu
- International Peace Maternity and Child Health Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai, China; Shanghai Key Laboratory of Embryo Original Diseases, Shanghai, China; Institute of Birth Defects and Rare Diseases, School of Medicine, Shanghai Jiao Tong University, Shanghai, China
| | - Chunxin Chang
- International Peace Maternity and Child Health Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai, China; Shanghai Key Laboratory of Embryo Original Diseases, Shanghai, China; Institute of Birth Defects and Rare Diseases, School of Medicine, Shanghai Jiao Tong University, Shanghai, China
| | - Li Gao
- International Peace Maternity and Child Health Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai, China; Shanghai Key Laboratory of Embryo Original Diseases, Shanghai, China; Institute of Birth Defects and Rare Diseases, School of Medicine, Shanghai Jiao Tong University, Shanghai, China
| | - Jiaqi Li
- Berry Genomics Corporation, Beijing, China
| | - Yulin Lu
- Berry Genomics Corporation, Beijing, China
| | - Aiping Mao
- Berry Genomics Corporation, Beijing, China.
| | - Yanlin Wang
- International Peace Maternity and Child Health Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai, China; Shanghai Key Laboratory of Embryo Original Diseases, Shanghai, China; Institute of Birth Defects and Rare Diseases, School of Medicine, Shanghai Jiao Tong University, Shanghai, China.
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Dai M, Xu Y, Sun Y, Xiao B, Ying X, Liu Y, Jiang W, Zhang J, Liu X, Ji X. Revealing diverse alternative splicing variants of the highly homologous SMN1 and SMN2 genes by targeted long-read sequencing. Mol Genet Genomics 2022; 297:1039-1048. [PMID: 35612622 DOI: 10.1007/s00438-022-01874-6] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2021] [Accepted: 10/11/2021] [Indexed: 11/25/2022]
Abstract
The survival of motor neuron (SMN) genes, SMN1 and SMN2, are two highly homologous genes related to spinal muscular atrophy (SMA). Different patterns of alternative splicing have been observed in the SMN genes. In this study, the long-read sequencing technique for distinguishing SMN1 and SMN2 without any assembly were developed and applied to reveal multiple alternative splicing patterns and to comprehensively identify transcript variants of the SMN genes. In total, 36 types of transcript variants were identified, with an equal number of variants generated from both SMN1 and SMN2. Of these, 18 were novel SMN transcripts that have never been reported. The structures of SMN transcripts were revealed to be much more complicated and diverse than previously discovered. These novel transcripts were derived from diverse splicing events, including skipping of one or more exons, intron retention, and exon shortening or addition. SMN1 mainly produces FL-SMN1, SMN1Δ7, SMN1Δ5 and SMN1Δ3. The distribution of SMN2 transcripts was significantly different from those of SMN1, with the majority transcripts to be SMN2Δ7, followed by FL-SMN2, SMN2Δ3,5 and SMN2Δ5,7. Targeted long-read sequencing approach could accurately distinguish sequences of SMN1 from those of SMN2. Our study comprehensively addressed naturally occurring SMN1 and SMN2 transcript variants and splicing patterns in peripheral blood mononuclear cells (PBMCs). The novel transcripts identified in our study expanded knowledge of the diversity of transcript variants generated from the SMN genes and showed a much more comprehensive profile of the SMN splicing spectrum. Results in our study will provide valuable information for the study of low expression level of SMN proteins and SMA pathogenesis based on transcript levels.
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Affiliation(s)
- Mengyao Dai
- Department of Paediatric Endocrinology/Genetics, Xinhua Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai, China
- Molecular Genetics Group, Shanghai Institute for Paediatric Research, Shanghai, China
- National Research Center for Translational Medicine, National Key Scientific Infrastructure for Translational Medicine (Shanghai), Shanghai Jiaotong University, Shanghai, China
- National Clinical Research Centre for Metabolic Diseases, State Key Laboratory of Medical Genomics, Shanghai Clinical Center for Endocrine and Metabolic Diseases, Shanghai Institute for Endocrine and Metabolic Diseases, Ruijin Hospital, Shanghai Jiaotong University School of Medicine, Shanghai, China
| | - Yan Xu
- Department of Paediatric Endocrinology/Genetics, Xinhua Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai, China
- Molecular Genetics Group, Shanghai Institute for Paediatric Research, Shanghai, China
- Department of Reproductive Genetics, International Peace Maternity and Child Health Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai, China
| | - Yu Sun
- Department of Paediatric Endocrinology/Genetics, Xinhua Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai, China
- Molecular Genetics Group, Shanghai Institute for Paediatric Research, Shanghai, China
| | - Bing Xiao
- Department of Paediatric Endocrinology/Genetics, Xinhua Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai, China
- Molecular Genetics Group, Shanghai Institute for Paediatric Research, Shanghai, China
| | - Xiaomin Ying
- Department of Paediatric Endocrinology/Genetics, Xinhua Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai, China
- Molecular Genetics Group, Shanghai Institute for Paediatric Research, Shanghai, China
| | - Yu Liu
- Department of Paediatric Endocrinology/Genetics, Xinhua Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai, China
- Molecular Genetics Group, Shanghai Institute for Paediatric Research, Shanghai, China
| | - Wenting Jiang
- Department of Paediatric Endocrinology/Genetics, Xinhua Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai, China
- Molecular Genetics Group, Shanghai Institute for Paediatric Research, Shanghai, China
| | - Jingmin Zhang
- Department of Paediatric Endocrinology/Genetics, Xinhua Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai, China
- Molecular Genetics Group, Shanghai Institute for Paediatric Research, Shanghai, China
| | - Xiaoqing Liu
- Department of Paediatric Endocrinology/Genetics, Xinhua Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai, China
- Molecular Genetics Group, Shanghai Institute for Paediatric Research, Shanghai, China
| | - Xing Ji
- Department of Paediatric Endocrinology/Genetics, Xinhua Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai, China.
- Molecular Genetics Group, Shanghai Institute for Paediatric Research, Shanghai, China.
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Butchbach MER. Genomic Variability in the Survival Motor Neuron Genes ( SMN1 and SMN2): Implications for Spinal Muscular Atrophy Phenotype and Therapeutics Development. Int J Mol Sci 2021; 22:ijms22157896. [PMID: 34360669 PMCID: PMC8348669 DOI: 10.3390/ijms22157896] [Citation(s) in RCA: 28] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2021] [Revised: 07/14/2021] [Accepted: 07/21/2021] [Indexed: 02/07/2023] Open
Abstract
Spinal muscular atrophy (SMA) is a leading genetic cause of infant death worldwide that is characterized by loss of spinal motor neurons leading to muscle weakness and atrophy. SMA results from the loss of survival motor neuron 1 (SMN1) gene but retention of its paralog SMN2. The copy numbers of SMN1 and SMN2 are variable within the human population with SMN2 copy number inversely correlating with SMA severity. Current therapeutic options for SMA focus on increasing SMN2 expression and alternative splicing so as to increase the amount of SMN protein. Recent work has demonstrated that not all SMN2, or SMN1, genes are equivalent and there is a high degree of genomic heterogeneity with respect to the SMN genes. Because SMA is now an actionable disease with SMN2 being the primary target, it is imperative to have a comprehensive understanding of this genomic heterogeneity with respect to hybrid SMN1–SMN2 genes generated by gene conversion events as well as partial deletions of the SMN genes. This review will describe this genetic heterogeneity in SMA and its impact on disease phenotype as well as therapeutic efficacy.
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Affiliation(s)
- Matthew E. R. Butchbach
- Center for Applied Clinical Genomics, Nemours Children’s Health Delaware, Wilmington, DE 19803, USA;
- Center for Pediatric Research, Nemours Children’s Health Delaware, Wilmington, DE 19803, USA
- Department of Biological Sciences, University of Delaware, Newark, DE 19716, USA
- Department of Pediatrics, Thomas Jefferson University, Philadelphia, PA 19107, USA
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