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Zwartkruis MM, de Pagter MS, Gommers D, Koopmans M, Ottenheim CPE, Kortooms JV, Albring M, Elferink MG, Wadman RI, Asselman FL, Cuppen I, van der Pol WL, Nelen MR, van Haaften GW, Groen EJN. A de novo deletion underlying spinal muscular atrophy: implications for carrier testing and genetic counseling. Hum Mol Genet 2025; 34:894-904. [PMID: 40094379 PMCID: PMC12056310 DOI: 10.1093/hmg/ddaf035] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2025] [Revised: 02/24/2025] [Accepted: 02/28/2025] [Indexed: 03/19/2025] Open
Abstract
Spinal muscular atrophy (SMA) is an autosomal recessive disease most commonly caused by homozygous deletion of the SMN1 gene. Parents of affected children are typically carriers, with a recurrence risk of 25% for future pregnancies. Their close relatives have up to 50% chance of being carriers. Carriers typically possess a single copy of the SMN1 gene; however, some parents carry two copies of SMN1. Current standard diagnostic carrier tests are unable to distinguish between silent carriers with two copies on one chromosome (2 + 0 genotype) and non-carriers (1 + 1 genotype), where a de novo deletion occurred. This distinction is crucial for recurrence risk assessment, which highlights the unsolved challenge to carrier testing and genetic counseling. We combined microsatellite marker analysis, SMN copy number analysis, Sanger sequencing, long-read sequencing and de novo assembly to investigate the cause of the absence of SMN1 in a pedigree with an SMA patient identified through newborn screening, whose parents each carried two SMN1 copies. Our analysis revealed that the father is a silent carrier, while de novo assembly of the SMN locus showed a 1.4 megabase (Mb) de novo deletion between mother and child. This deletion encompasses SMN1 and SMN2 and represents the first reported nucleotide-level resolved SMA-causing deletion to date. Our findings allowed informed counseling of at-risk relatives and illustrate the complexity of SMA carrier testing and counseling. This case underscores the feasibility of and need for advanced genetic testing for SMA carriership in select cases, to improve genetic counseling practices, risk assessment, and family planning.
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Affiliation(s)
- Maria M Zwartkruis
- Department of Neurology and Neurosurgery, UMC Utrecht Brain Center, University Medical Center Utrecht, Heidelberglaan 100, Utrecht 3584 CX, the Netherlands
- Department of Genetics, University Medical Center Utrecht, Heidelberglaan 100, Utrecht 3584 CX, the Netherlands
| | - Mirjam S de Pagter
- Department of Genetics, University Medical Center Utrecht, Heidelberglaan 100, Utrecht 3584 CX, the Netherlands
| | - Demi Gommers
- Department of Neurology and Neurosurgery, UMC Utrecht Brain Center, University Medical Center Utrecht, Heidelberglaan 100, Utrecht 3584 CX, the Netherlands
- Department of Genetics, University Medical Center Utrecht, Heidelberglaan 100, Utrecht 3584 CX, the Netherlands
| | - Marije Koopmans
- Department of Genetics, University Medical Center Utrecht, Heidelberglaan 100, Utrecht 3584 CX, the Netherlands
| | - Cecile P E Ottenheim
- Department of Human Genetics, Amsterdam UMC, University of Amsterdam, Meibergdreef 9, Amsterdam 1105 AZ, the Netherlands
| | - Joris V Kortooms
- Department of Neurology and Neurosurgery, UMC Utrecht Brain Center, University Medical Center Utrecht, Heidelberglaan 100, Utrecht 3584 CX, the Netherlands
| | - Mirjan Albring
- Department of Genetics, University Medical Center Utrecht, Heidelberglaan 100, Utrecht 3584 CX, the Netherlands
| | - Martin G Elferink
- Department of Genetics, University Medical Center Utrecht, Heidelberglaan 100, Utrecht 3584 CX, the Netherlands
| | - Renske I Wadman
- Department of Neurology and Neurosurgery, UMC Utrecht Brain Center, University Medical Center Utrecht, Heidelberglaan 100, Utrecht 3584 CX, the Netherlands
| | - Fay-Lynn Asselman
- Department of Neurology and Neurosurgery, UMC Utrecht Brain Center, University Medical Center Utrecht, Heidelberglaan 100, Utrecht 3584 CX, the Netherlands
| | - Inge Cuppen
- Department of Neurology and Neurosurgery, UMC Utrecht Brain Center, University Medical Center Utrecht, Heidelberglaan 100, Utrecht 3584 CX, the Netherlands
| | - W Ludo van der Pol
- Department of Neurology and Neurosurgery, UMC Utrecht Brain Center, University Medical Center Utrecht, Heidelberglaan 100, Utrecht 3584 CX, the Netherlands
| | - Marcel R Nelen
- Department of Genetics, University Medical Center Utrecht, Heidelberglaan 100, Utrecht 3584 CX, the Netherlands
| | - Gijs W van Haaften
- Department of Genetics, University Medical Center Utrecht, Heidelberglaan 100, Utrecht 3584 CX, the Netherlands
| | - Ewout J N Groen
- Department of Neurology and Neurosurgery, UMC Utrecht Brain Center, University Medical Center Utrecht, Heidelberglaan 100, Utrecht 3584 CX, the Netherlands
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Fasciculations in human hereditary disease. Acta Neurol Belg 2015; 115:91-5. [PMID: 25073774 DOI: 10.1007/s13760-014-0335-6] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2014] [Accepted: 07/13/2014] [Indexed: 12/11/2022]
Abstract
Fasciculations are a manifestation of peripheral nerve hyperexcitability in addition to myokymia, neuromyotonia, cramps, or tetany. Fasciculations occur in hereditary and non-hereditary diseases. Among the hereditary diseases, fasciculations are most frequently reported in familial amyotrophic lateral sclerosis (FALS), and spinal muscular atrophy (SMA). Among the non-hereditary diseases, fasciculations occur most frequently in peripheral nerve hyperexcitability syndromes (Isaac's syndrome, voltage-gated potassium channelopathy, cramp fasciculation syndrome, Morvan syndrome). If the cause of fasciculations remains unknown, they are called benign. Systematically reviewing the literature about fasciculations in hereditary disease shows that fasciculations can be a phenotypic feature in bulbospinal muscular atrophy (BSMA), GM2-gangliosidosis, triple-A syndrome, or hereditary neuropathy. Additionally, fasciculations have been reported in familial amyloidosis, spinocerebellar ataxias, Huntington's disease, Rett syndrome, central nervous system disease due to L1-cell adhesion molecule (L1CAM) mutations, Fabry's disease, or Gerstmann-Sträussler disease. Rarely, fasciculations may be a phenotypic feature in patients with mitochondrial disorders or other myopathies. Fasciculations are part of the phenotype in much more genetic disorders than commonly assumed. Fasciculations not only occur in motor neuron disease, but also in hereditary neuropathy, spinocerebellar ataxia, GM2-gangliosidosis, Huntington's disease, Rett syndrome, Fabry's disease, Gerstmann-Sträussler disease, mitochondrial disorders, or muscular dystrophies.
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