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Brain. 2016 Mar;139(Pt 3):674-91. doi: 10.1093/brain/awv352. Epub 2015 Dec 22.

Loss-of-function mutations in SCN4A cause severe foetal hypokinesia or 'classical' congenital myopathy.

Author information

1
1 Dubowitz Neuromuscular Centre, UCL Institute of Child Health, London, WC1N 1EH, UK.
2
2 MRC Centre for Neuromuscular Diseases, UCL Institute of Neurology, London, WC1N 3BG, UK.
3
3 Institute for Neuroscience and Muscle Research, Children's Hospital at Westmead, Westmead, New South Wales, 2145, Australia 4 Discipline of Paediatrics and Child Health, Faculty of Medicine, The University of Sydney, Sydney, New South Wales, 2006, Australia.
4
5 Department of Pediatrics, Child and Family Research Institute, Centre for Molecular Medicine and Therapeutics, University of British Columbia, 4480 Oak Street, Vancouver, B.C. V6H 3V4, Canada.
5
4 Discipline of Paediatrics and Child Health, Faculty of Medicine, The University of Sydney, Sydney, New South Wales, 2006, Australia.
6
8 Copenhagen Neuromuscular Center, Rigshospitalet, University of Copenhagen, DK2100 Copenhagen, Denmark.
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9 Department of Clinical Neuroscience for Children, Oslo University Hospital, 0424, Oslo, Norway 10 Unit for Hereditary Neuromuscular Disorders, Oslo University Hospital, 0424, Oslo, Norway.
8
11 Genetic Health Queensland, Royal Brisbane & Women's Hospital & Griffith University, Brisbane, Australia.
9
12 The Harry Perkins Institute of Medical Research, Centre for Medical Research, The University of Western Australia, Perth, 6009, Western Australia, Australia.
10
13 Department of Child Health, University Hospital Wales, Cardiff, CF14 4XW, UK.
11
14 Neurophysiology Department, Great Ormond Street Hospital for Children NHS Foundation Trust, Great Ormond Street, London WC1N 3JH, UK.
12
15 Department of Clinical Neurophysiology, Rigshospitalet, University of Copenhagen, DK2100 Copenhagen, Denmark.
13
16 Children's Clinic, St.Olavs hospital, Trondheim University Hospital, 7006 Trondheim, Norway.
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17 Department of Pathology, University Hospital of North Norway, 9038 Tromsø, Norway.
15
18 The Danish National Rehabilitation Center for Neuromuscular Diseases, Aarhus, 8000 Denmark.
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19 Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, V5A 1S6, Canada.
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20 Department Molecular Genetics, Pathwest, QEII Medical Centre, Nedlands 6009, Western Australia, Australia.
18
1 Dubowitz Neuromuscular Centre, UCL Institute of Child Health, London, WC1N 1EH, UK 2 MRC Centre for Neuromuscular Diseases, UCL Institute of Neurology, London, WC1N 3BG, UK.
19
21 Department of Human Genetics, Radboud University Medical Center, Nijmegen, 6500HB, The Netherlands.
20
1 Dubowitz Neuromuscular Centre, UCL Institute of Child Health, London, WC1N 1EH, UK 2 MRC Centre for Neuromuscular Diseases, UCL Institute of Neurology, London, WC1N 3BG, UK f.muntoni@ucl.ac.uk.

Abstract

Congenital myopathies are a clinically and genetically heterogeneous group of muscle disorders characterized by congenital or early-onset hypotonia and muscle weakness, and specific pathological features on muscle biopsy. The phenotype ranges from foetal akinesia resulting in in utero or neonatal mortality, to milder disorders that are not life-limiting. Over the past decade, more than 20 new congenital myopathy genes have been identified. Most encode proteins involved in muscle contraction; however, mutations in ion channel-encoding genes are increasingly being recognized as a cause of this group of disorders. SCN4A encodes the α-subunit of the skeletal muscle voltage-gated sodium channel (Nav1.4). This channel is essential for the generation and propagation of the muscle action potential crucial to muscle contraction. Dominant SCN4A gain-of-function mutations are a well-established cause of myotonia and periodic paralysis. Using whole exome sequencing, we identified homozygous or compound heterozygous SCN4A mutations in a cohort of 11 individuals from six unrelated kindreds with congenital myopathy. Affected members developed in utero- or neonatal-onset muscle weakness of variable severity. In seven cases, severe muscle weakness resulted in death during the third trimester or shortly after birth. The remaining four cases had marked congenital or neonatal-onset hypotonia and weakness associated with mild-to-moderate facial and neck weakness, significant neonatal-onset respiratory and swallowing difficulties and childhood-onset spinal deformities. All four surviving cohort members experienced clinical improvement in the first decade of life. Muscle biopsies showed myopathic features including fibre size variability, presence of fibrofatty tissue of varying severity, without specific structural abnormalities. Electrophysiology suggested a myopathic process, without myotonia. In vitro functional assessment in HEK293 cells of the impact of the identified SCN4A mutations showed loss-of-function of the mutant Nav1.4 channels. All, apart from one, of the mutations either caused fully non-functional channels, or resulted in a reduced channel activity. Each of the affected cases carried at least one full loss-of-function mutation. In five out of six families, a second loss-of-function mutation was present on the trans allele. These functional results provide convincing evidence for the pathogenicity of the identified mutations and suggest that different degrees of loss-of-function in mutant Nav1.4 channels are associated with attenuation of the skeletal muscle action potential amplitude to a level insufficient to support normal muscle function. The results demonstrate that recessive loss-of-function SCN4A mutations should be considered in patients with a congenital myopathy.

KEYWORDS:

SCN4A; congenital myopathy; foetal akinesia; foetal hypokinesia; loss-of-function mutation

PMID:
26700687
PMCID:
PMC4766374
DOI:
10.1093/brain/awv352
[Indexed for MEDLINE]
Free PMC Article

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