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Wang N, Jiao K, He J, Zhu B, Cheng N, Sun J, Chen L, Chen W, Gong L, Qiao K, Xi J, Wu Q, Zhao C, Zhu W. Diagnosis of Challenging Spinal Muscular Atrophy Cases with Long-Read Sequencing. J Mol Diagn 2024; 26:364-373. [PMID: 38490302 DOI: 10.1016/j.jmoldx.2024.02.004] [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: 09/21/2023] [Revised: 01/17/2024] [Accepted: 02/07/2024] [Indexed: 03/17/2024] Open
Abstract
Spinal muscular atrophy (SMA) is an autosomal recessive neuromuscular disorder primarily caused by the deletion or mutation of the survival motor neuron 1 (SMN1) gene. This study assesses the diagnostic potential of long-read sequencing (LRS) in three patients with SMA. For Patient 1, who has a heterozygous SMN1 deletion, LRS unveiled a missense mutation in SMN1 exon 5. In Patient 2, an Alu/Alu-mediated rearrangement covering the SMN1 promoter and exon 1 was identified through a blend of multiplex ligation-dependent probe amplification, LRS, and PCR across the breakpoint. The third patient, born to a consanguineous family, bore four copies of hybrid SMN genes. LRS determined the genomic structures, indicating two distinct hybrids of SMN2 exon 7 and SMN1 exon 8. However, a discrepancy was found between the SMN1/SMN2 ratio interpretations by LRS (0:2) and multiplex ligation-dependent probe amplification (0:4), which suggested a limitation of LRS in SMA diagnosis. In conclusion, this newly adapted long PCR-based third-generation sequencing introduces an additional avenue for SMA diagnosis.
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Affiliation(s)
- Ningning Wang
- Department of Neurology, Huashan Hospital, Fudan University, Shanghai, China; National Center for Neurological Disorders, Shanghai, China; Huashan Rare Disease Center, Huashan Hospital, Shanghai Medical College, Fudan University, Shanghai, China
| | - Kexin Jiao
- Department of Neurology, Huashan Hospital, Fudan University, Shanghai, China; National Center for Neurological Disorders, Shanghai, China; Huashan Rare Disease Center, Huashan Hospital, Shanghai Medical College, Fudan University, Shanghai, China
| | - Jin He
- Department of Neurology and Institute of Neurology of First Affiliated Hospital, Institute of Neuroscience, and Fujian Key Laboratory of Molecular Neurology, Fujian Medical University, Fuzhou, China
| | - Bochen Zhu
- Department of Neurology, Huashan Hospital, Fudan University, Shanghai, China; National Center for Neurological Disorders, Shanghai, China; Huashan Rare Disease Center, Huashan Hospital, Shanghai Medical College, Fudan University, Shanghai, China
| | - Nachuan Cheng
- Department of Neurology, Huashan Hospital, Fudan University, Shanghai, China; National Center for Neurological Disorders, Shanghai, China; Huashan Rare Disease Center, Huashan Hospital, Shanghai Medical College, Fudan University, Shanghai, China
| | - Jian Sun
- Department of Neurology, Huashan Hospital, Fudan University, Shanghai, China; National Center for Neurological Disorders, Shanghai, China; Huashan Rare Disease Center, Huashan Hospital, Shanghai Medical College, Fudan University, Shanghai, China
| | - Lan Chen
- Department of Neurology, Nantong First People's Hospital, Nantong, China
| | - Wanjin Chen
- Department of Neurology and Institute of Neurology of First Affiliated Hospital, Institute of Neuroscience, and Fujian Key Laboratory of Molecular Neurology, Fujian Medical University, Fuzhou, China
| | - Lingyun Gong
- Department of Neurology, Huashan Hospital, Fudan University, Shanghai, China; National Center for Neurological Disorders, Shanghai, China; Huashan Rare Disease Center, Huashan Hospital, Shanghai Medical College, Fudan University, Shanghai, China
| | - Kai Qiao
- Department of Neurology, Huashan Hospital, Fudan University, Shanghai, China; National Center for Neurological Disorders, Shanghai, China; Huashan Rare Disease Center, Huashan Hospital, Shanghai Medical College, Fudan University, Shanghai, China
| | - Jianying Xi
- Department of Neurology, Huashan Hospital, Fudan University, Shanghai, China; National Center for Neurological Disorders, Shanghai, China; Huashan Rare Disease Center, Huashan Hospital, Shanghai Medical College, Fudan University, Shanghai, China
| | - Qihan Wu
- Shanghai Ministry of Science and Technology Key Laboratory of Health and Disease Genomics, National Health Commission Key Lab of Reproduction Regulation, Shanghai Institute for Biomedical and Pharmaceutical Technologies, Shanghai, China
| | - Chongbo Zhao
- Department of Neurology, Huashan Hospital, Fudan University, Shanghai, China; National Center for Neurological Disorders, Shanghai, China; Huashan Rare Disease Center, Huashan Hospital, Shanghai Medical College, Fudan University, Shanghai, China
| | - Wenhua Zhu
- Department of Neurology, Huashan Hospital, Fudan University, Shanghai, China; National Center for Neurological Disorders, Shanghai, China; Huashan Rare Disease Center, Huashan Hospital, Shanghai Medical College, Fudan University, Shanghai, China.
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Qu Y, Bai J, Jiao H, Qi H, Huang W, OuYang S, Peng X, Jin Y, Wang H, Song F. Variants located in intron 6 of SMN1 lead to misdiagnosis in genetic detection and screening for SMA. Heliyon 2024; 10:e28015. [PMID: 38515714 PMCID: PMC10955315 DOI: 10.1016/j.heliyon.2024.e28015] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2023] [Revised: 02/28/2024] [Accepted: 03/11/2024] [Indexed: 03/23/2024] Open
Abstract
Accurate genetic diagnosis is necessary for guiding the treatment of spinal muscular atrophy (SMA). An updated consensus for the diagnosis and management of SMA was published in 2018. However, clinicians should remain alert to some pitfalls of genetic testing that can occur when following a routine diagnosis. In this study, we report the diagnosis of three unrelated individuals who were initially misdiagnosed as carrying a homozygous deletion of SMN1 exon 7. MLPA (P060 and P021) and qPCR were used to detect the copy number of SMN. SMN1 variants were identified by SMN1 clone and next-generation sequencing (NGS). Transcription of SMN1 variants was detected using qRT-PCR and ex vivo splicing analysis. Among the three individuals, one was identified as a patient with SMA carrying a heterozygous deletion and a pathogenic variant (c.835-17_835-14delCTTT) of SMN1, one was a healthy carrier only carrying a heterozygous deletion of SMN1 exon 7, and the third was a patient with nemaline myopathy 2 carrying a heterozygous deletion of SMN1 exon 7. The misdiagnosis of these individuals was attributed to the presence of the c.835-17_835-14delCTTT or c.835-17C > G variants in SMN1 intron 6, which affect the amplification of SMN1 exon 7 during MLPA-P060 and qPCR testing. However, MLPA-P021 and NGS analyses were unaffected by these variants. These results support that additional detection methods should be employed in cases where the SMN1 copy number is ambiguous to minimize the misdiagnosis of SMA.
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Affiliation(s)
- Yujin Qu
- Department of Medical Genetics, Capital Institute of Pediatrics, Beijing, China
| | - Jinli Bai
- Department of Medical Genetics, Capital Institute of Pediatrics, Beijing, China
| | - Hui Jiao
- Department of Neurology, Children’s Hospital Affiliated to Capital Institute of Pediatrics, Beijing, China
| | - Hong Qi
- Prenatal Diagnosis Center, Beijing Haidian District Maternal and Child Health Care Hospital, Beijing, China
| | - Wenchen Huang
- Department of Medical Genetics, Capital Institute of Pediatrics, Beijing, China
| | - Shijia OuYang
- Department of Medical Genetics, Capital Institute of Pediatrics, Beijing, China
| | - Xiaoyin Peng
- Department of Neurology, Children’s Hospital Affiliated to Capital Institute of Pediatrics, Beijing, China
| | - Yuwei Jin
- Department of Medical Genetics, Capital Institute of Pediatrics, Beijing, China
| | - Hong Wang
- Department of Medical Genetics, Capital Institute of Pediatrics, Beijing, China
| | - Fang Song
- Department of Medical Genetics, Capital Institute of Pediatrics, Beijing, China
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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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4
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Bai J, Qu Y, OuYang S, Jiao H, Wang Y, Li J, Huang W, Zhao Y, Peng X, Wang D, Jin Y, Wang H, Song F. Novel Alu-mediated deletions of the SMN1 gene were identified by ultra-long read sequencing technology in patients with spinal muscular atrophy. Neuromuscul Disord 2023; 33:382-390. [PMID: 37023488 DOI: 10.1016/j.nmd.2023.03.001] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2022] [Revised: 02/20/2023] [Accepted: 03/01/2023] [Indexed: 03/11/2023]
Abstract
Spinal muscular atrophy (SMA) is a neuromuscular disease caused by biallelic variants of the survival motor neuron 1 (SMN1) gene. In this study, our aim was to make a molecular diagnosis in two patients with SMA carrying only one SMN1 copy number. Using ultra-long read sequencing (Ultra-LRS), 1415 bp deletion and 3348 bp deletion of the SMN1 gene were identified in patient 1 and the father of patient 2, respectively. Ultra-LRS revealed two novel deletions, starting from the SMN1 promoter to intron 1. It also accurately provided the location of the deletion breakpoints in the SMN1 gene: chr5 g.70,924,798-70,926,212 for a 1415 bp deletion; chr5 g.70,922,695-70,926,042 for a 3348 bp deletion. By analyzing the breakpoint junctions, we identified that these genomic sequences were composed of Alu sequences, including AluJb, AluYm1, AluSq, and AluYm1, indicating that Alu-mediated rearrangements are a mechanism of SMN1 deletion events. In addition, full-length SMN1 transcripts and SMN protein in patient 1 were significantly decreased (p < 0.01), suggesting that a 1415 bp deletion that included the transcription and translation initiation sites of the SMN1 gene had severe consequences for SMN expression. Ultra-LRS can easily distinguish highly homozygous genes compared to other detection technologies, which is useful for detecting SMN1 intragenic mutations, to quickly discover structural rearrangements and to precisely present the breakpoint positions.
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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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6
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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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Azad AK, Huang CK, Jin H, Zou H, Yanakakis L, Du J, Fiddler M, Naeem R, Goldstein Y. Enhanced Carrier Screening for Spinal Muscular Atrophy: Detection of Silent (SMN1: 2 + 0) Carriers Utilizing a Novel TaqMan Genotyping Method. Lab Med 2021; 51:408-415. [PMID: 31875889 DOI: 10.1093/labmed/lmz088] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
BACKGROUND Individuals whose copies of the survival motor neuron 1 (SMN1) gene exist on the same chromosome are considered silent carriers for spinal muscular atrophy (SMA). Conventional screening for SMA only determines SMN1 copy number without any information regarding how those copies are arranged. A single nucleotide variant (SNV) rs143838139 is highly linked with the silent carrier genotype, so testing for this SNV can more accurately assess risk to a patient of having an affected child. METHODS Using a custom-designed SNV-specific Taqman genotyping assay, we determined and validated a model for silent-carrier detection in the laboratory. RESULTS An initial cohort of 21 pilot specimens demonstrated results that were 100% concordant with a reference laboratory method; this cohort was utilized to define the reportable range. An additional 177 specimens were utilized for a broader evaluation of clinical validity and reproducibility. Allelic-discrimination analysis demonstrated tight clustering of genotype groupings and excellent reproducibility, with a coefficient of variation for all genotypes ranging from 1% to 4%. CONCLUSION The custom-developed Taqman SNV genotyping assay we tested provides a rapid, accurate, and cost-effective method for routine SMA silent-carrier screening and considerably improves detection rates of residual risk for SMA carriers.
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Affiliation(s)
- Abul Kalam Azad
- Department of Pathology, Montefiore Medical Center at Albert Einstein College of Medicine, Bronx, New York
| | - Chih-Kang Huang
- Department of Pathology, Montefiore Medical Center at Albert Einstein College of Medicine, Bronx, New York
| | - Hong Jin
- Department of Pathology, Montefiore Medical Center at Albert Einstein College of Medicine, Bronx, New York
| | | | | | - Juan Du
- Department of Pathology, Montefiore Medical Center at Albert Einstein College of Medicine, Bronx, New York
| | | | - Rizwan Naeem
- Department of Pathology, Montefiore Medical Center at Albert Einstein College of Medicine, Bronx, New York
| | - Yitz Goldstein
- Department of Pathology, Montefiore Medical Center at Albert Einstein College of Medicine, Bronx, New York
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Detection of SMN1 to SMN2 gene conversion events and partial SMN1 gene deletions using array digital PCR. Neurogenetics 2021; 22:53-64. [PMID: 33415588 DOI: 10.1007/s10048-020-00630-5] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2020] [Accepted: 11/26/2020] [Indexed: 12/15/2022]
Abstract
Proximal spinal muscular atrophy (SMA), a leading genetic cause of infant death worldwide, is an early-onset motor neuron disease characterized by loss of α-motor neurons and associated muscle atrophy. SMA is caused by deletion or other disabling mutations of survival motor neuron 1 (SMN1) but retention of one or more copies of the paralog SMN2. Within the SMA population, there is substantial variation in SMN2 copy number (CN); in general, those individuals with SMA who have a high SMN2 CN have a milder disease. Because SMN2 functions as a disease modifier, its accurate CN determination may have clinical relevance. In this study, we describe the development of array digital PCR (dPCR) to quantify SMN1 and SMN2 CNs in DNA samples using probes that can distinguish the single nucleotide difference between SMN1 and SMN2 in exon 8. This set of dPCR assays can accurately and reliably measure the number of SMN1 and SMN2 copies in DNA samples. In a cohort of SMA patient-derived cell lines, the assay confirmed a strong inverse correlation between SMN2 CN and disease severity. We can detect SMN1-SMN2 gene conversion events in DNA samples by comparing CNs at exon 7 and exon 8. Partial deletions of SMN1 can also be detected with dPCR by comparing CNs at exon 7 or exon 8 with those at intron 1. Array dPCR is a practical technique to determine, accurately and reliably, SMN1 and SMN2 CNs from SMA samples as well as identify gene conversion events and partial deletions of SMN1.
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9
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Rouzier C, Chaussenot A, Paquis-Flucklinger V. Molecular diagnosis and genetic counseling for spinal muscular atrophy (SMA). Arch Pediatr 2020; 27:7S9-7S14. [DOI: 10.1016/s0929-693x(20)30270-0] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
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10
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Resolving misalignment interference for NGS-based clinical diagnostics. Hum Genet 2020; 140:477-492. [PMID: 32915251 DOI: 10.1007/s00439-020-02216-5] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2020] [Accepted: 07/31/2020] [Indexed: 01/18/2023]
Abstract
Next-generation sequencing (NGS) is an incredibly useful tool for genetic disease diagnosis. However, the most commonly used bioinformatics methods for analyzing sequence reads insufficiently discriminate genomic regions with extensive sequence identity, such as gene families and pseudogenes, complicating diagnostics. This problem has been recognized for specific genes, including many involved in human disease, and diagnostic labs must perform additional costly steps to guarantee accurate diagnosis in these cases. Here we report a new data analysis method based on the comparison of read depth between highly homologous regions to identify misalignment. Analyzing six clinically important genes-CYP21A2, GBA, HBA1/2, PMS2, and SMN1-each exhibiting misalignment issues related to homology, we show that our technique can correctly identify potential misalignment events and be used to make appropriate calls. Combined with long-range PCR and/or MLPA orthogonal testing, our clinical laboratory can improve variant calling with minimal additional cost. We propose an accurate and cost-efficient NGS testing procedure that will benefit disease diagnostics, carrier screening, and research-based population studies.
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Dual Mechanism of a New SMN1 Variant (c.835G>C, p.Gly279Arg) by Interrupting Exon 7 Skipping and YG Oligomerization in Causation of Spinal Muscular Atrophy. J Mol Neurosci 2020; 71:112-121. [PMID: 32812185 DOI: 10.1007/s12031-020-01631-7] [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: 03/10/2020] [Accepted: 06/08/2020] [Indexed: 10/23/2022]
Abstract
Spinal muscular atrophy (SMA) is an autosomal recessive neuromuscular disorder caused by deletion or subtle variant of survival motor neuron 1 (SMN1) gene. By multiplex ligation-dependent probe amplification, genomic sequencing, and T-A cloning on cDNA level, we identified one novel SMN1 subtle variant c.835G>C (p.Gly279Arg) in a non-homozygous patient with type 1 SMA. Full-length SMN1 (fl-SMN1) transcripts in the peripheral bloods of the patient were significantly decreased compared with those in healthy individuals and the carries (p < 0.05). And two fragments of SMN1 transcripts including fl-SMN1 and △7-SMN1 were observed by RT-PCR, which indicated Exon 7 skipping of SMN1 gene. To further evaluate its splicing effects on Exon 7, we performed ex vivo splicing analysis, which showed that the mutant mini gene with c.835G>C reduced Exon 7 inclusion to 54%. In addition, self-oligomerization between mutant SMN protein with the c.835G>C (p.Gly279Arg) and wild SMN was decreased in self-interaction assays. Our study clearly demonstrates that the c.835G>C (p.Gly279Arg) variant can lead to a decrease in fl-SMN1 transcripts by interrupting correct splicing of SMN1. What is more, the variant also affects SMN self-oligomerization via amino acid substitution from Gly to Arg at amino acid position of 279. This work presents the first evidence that it does exit double-hit events for the novel variant, which is crucial to understanding a severe SMA phenotype (type 1).
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12
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Wadman RI, Jansen MD, Stam M, Wijngaarde CA, Curial CAD, Medic J, Sodaar P, Schouten J, Vijzelaar R, Lemmink HH, van den Berg LH, Groen EJN, van der Pol WL. Intragenic and structural variation in the SMN locus and clinical variability in spinal muscular atrophy. Brain Commun 2020; 2:fcaa075. [PMID: 32954327 PMCID: PMC7425299 DOI: 10.1093/braincomms/fcaa075] [Citation(s) in RCA: 24] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2020] [Revised: 04/17/2020] [Accepted: 04/22/2020] [Indexed: 11/15/2022] Open
Abstract
Clinical severity and treatment response vary significantly between patients with spinal muscular atrophy. The approval of therapies and the emergence of neonatal screening programmes urgently require a more detailed understanding of the genetic variants that underlie this clinical heterogeneity. We systematically investigated genetic variation other than SMN2 copy number in the SMN locus. Data were collected through our single-centre, population-based study on spinal muscular atrophy in the Netherlands, including 286 children and adults with spinal muscular atrophy Types 1–4, including 56 patients from 25 families with multiple siblings with spinal muscular atrophy. We combined multiplex ligation-dependent probe amplification, Sanger sequencing, multiplexed targeted resequencing and digital droplet polymerase chain reaction to determine sequence and expression variation in the SMN locus. SMN1, SMN2 and NAIP gene copy number were determined by multiplex ligation-dependent probe amplification. SMN2 gene variant analysis was performed using Sanger sequencing and RNA expression analysis of SMN by droplet digital polymerase chain reaction. We identified SMN1–SMN2 hybrid genes in 10% of spinal muscular atrophy patients, including partial gene deletions, duplications or conversions within SMN1 and SMN2 genes. This indicates that SMN2 copies can vary structurally between patients, implicating an important novel level of genetic variability in spinal muscular atrophy. Sequence analysis revealed six exonic and four intronic SMN2 variants, which were associated with disease severity in individual cases. There are no indications that NAIP1 gene copy number or sequence variants add value in addition to SMN2 copies in predicting the clinical phenotype in individual patients with spinal muscular atrophy. Importantly, 95% of spinal muscular atrophy siblings in our study had equal SMN2 copy numbers and structural changes (e.g. hybrid genes), but 60% presented with a different spinal muscular atrophy type, indicating the likely presence of further inter- and intragenic variabilities inside as well as outside the SMN locus. SMN2 gene copies can be structurally different, resulting in inter- and intra-individual differences in the composition of SMN1 and SMN2 gene copies. This adds another layer of complexity to the genetics that underlie spinal muscular atrophy and should be considered in current genetic diagnosis and counselling practices.
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Affiliation(s)
- Renske I Wadman
- UMC Utrecht Brain Center, Department of Neurology and Neurosurgery, University Medical Center Utrecht, 3584 CX Utrecht, the Netherlands
| | - Marc D Jansen
- UMC Utrecht Brain Center, Department of Neurology and Neurosurgery, University Medical Center Utrecht, 3584 CX Utrecht, the Netherlands
| | - Marloes Stam
- UMC Utrecht Brain Center, Department of Neurology and Neurosurgery, University Medical Center Utrecht, 3584 CX Utrecht, the Netherlands
| | - Camiel A Wijngaarde
- UMC Utrecht Brain Center, Department of Neurology and Neurosurgery, University Medical Center Utrecht, 3584 CX Utrecht, the Netherlands
| | - Chantall A D Curial
- UMC Utrecht Brain Center, Department of Neurology and Neurosurgery, University Medical Center Utrecht, 3584 CX Utrecht, the Netherlands
| | - Jelena Medic
- UMC Utrecht Brain Center, Department of Neurology and Neurosurgery, University Medical Center Utrecht, 3584 CX Utrecht, the Netherlands
| | - Peter Sodaar
- UMC Utrecht Brain Center, Department of Neurology and Neurosurgery, University Medical Center Utrecht, 3584 CX Utrecht, the Netherlands
| | - Jan Schouten
- MRC Holland BV, 1057 DL Amsterdam, the Netherlands
| | | | - Henny H Lemmink
- Department of Genetics, University Medical Center Groningen, 9713 GZ Groningen, the Netherlands
| | - Leonard H van den Berg
- UMC Utrecht Brain Center, Department of Neurology and Neurosurgery, University Medical Center Utrecht, 3584 CX Utrecht, the Netherlands
| | - Ewout J N Groen
- UMC Utrecht Brain Center, Department of Neurology and Neurosurgery, University Medical Center Utrecht, 3584 CX Utrecht, the Netherlands
| | - W Ludo van der Pol
- UMC Utrecht Brain Center, Department of Neurology and Neurosurgery, University Medical Center Utrecht, 3584 CX Utrecht, the Netherlands
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13
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Vijzelaar R, Snetselaar R, Clausen M, Mason AG, Rinsma M, Zegers M, Molleman N, Boschloo R, Yilmaz R, Kuilboer R, Lens S, Sulchan S, Schouten J. The frequency of SMN gene variants lacking exon 7 and 8 is highly population dependent. PLoS One 2019; 14:e0220211. [PMID: 31339938 PMCID: PMC6655720 DOI: 10.1371/journal.pone.0220211] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2019] [Accepted: 07/10/2019] [Indexed: 01/30/2023] Open
Abstract
Spinal Muscular Atrophy (SMA) is a disorder characterized by the degeneration of motor neurons in the spinal cord, leading to muscular atrophy. In the majority of cases, SMA is caused by the homozygous absence of the SMN1 gene. The disease severity of SMA is strongly influenced by the copy number of the closely related SMN2 gene. In addition, an SMN variant lacking exons 7 and 8 has been reported in 8% and 23% of healthy Swedish and Spanish individuals respectively. We tested 1255 samples from the 1000 Genomes Project using a new version of the multiplex ligation-dependent probe amplification (MLPA) P021 probemix that covers each SMN exon. The SMN variant lacking exons 7 and 8 was present in up to 20% of individuals in several Caucasian populations, while being almost completely absent in various Asian and African populations. This SMN1/2Δ7-8 variant appears to be derived from an ancient deletion event as the deletion size is identical in 99% of samples tested. The average total copy number of SMN1, SMN2 and the SMN1/2Δ7-8 variant combined was remarkably comparable in all populations tested, ranging from 3.64 in Asian to 3.75 in African samples.
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Affiliation(s)
| | | | | | | | | | | | | | | | | | | | - Sylvia Lens
- MRC Holland B.V., Amsterdam, The Netherlands
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14
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Li L, Zhou WJ, Fang P, Zhong ZY, Xie JS, Yan TZ, Zeng J, Tan XH, Xu XM. Evaluation and comparison of three assays for molecular detection of spinal muscular atrophy. Clin Chem Lab Med 2017; 55:358-367. [PMID: 27754957 DOI: 10.1515/cclm-2016-0275] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2016] [Accepted: 08/29/2016] [Indexed: 11/15/2022]
Abstract
BACKGROUND Spinal muscular atrophy (SMA) is mainly caused by deletions in SMA-related genes. The objective of this study was to develop gene-dosage assays for diagnosing SMA. METHODS A multiplex, quantitative PCR assay and a CNVplex assay were developed for determining the copy number of SMN1, SMN2, and NAIP. Reproducibility and specificity of the two assays were compared to a multiple ligation-dependent probe amplification (MLPA) assay. To evaluate reproducibility, 30 samples were analyzed three times using the three assays. A total of 317 samples were used to assess the specificity of the two assays. RESULTS The multiplex quantitative PCR (qPCR) assay had higher reproducibility. Intra-assay CVs were 3.01%-8.52% and inter-assay CVs were 4.12%-6.24%. The CNVplex assay had ratios that were closer to expected (0.49-0.5 for one copy, 1.03-1.0 for two copies, and 1.50-1.50 for three copies). Diagnostic accuracy rates for the two assays were 100%. CONCLUSIONS The multiplex qPCR assay was a simple, rapid, and cost-effective method for routine SMA diagnosis and carrier screening. The CNVplex assay could be used to detect SMAs with complicated gene structures. The assays were reliable and could be used as alternative methods for clinical diagnosis of SMA.
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