De novo gain-of-function and loss-of-function mutations of SCN8A in patients with intellectual disabilities and epilepsy.
SourceJournal of Medical Genetics, 52, 5, (2015), pp. 330-337
1 mei 2015
Article / Letter to editor
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Primary and Community Care
Journal of Medical Genetics
SubjectRadboudumc 0: Other Research DCMN: Donders Center for Medical Neuroscience; Radboudumc 11: Renal disorders RIMLS: Radboud Institute for Molecular Life Sciences; Radboudumc 12: Sensory disorders RIMLS: Radboud Institute for Molecular Life Sciences; Radboudumc 3: Disorders of movement DCMN: Donders Center for Medical Neuroscience; Radboudumc 7: Neurodevelopmental disorders DCMN: Donders Center for Medical Neuroscience; Radboudumc 9: Rare cancers RIHS: Radboud Institute for Health Sciences
BACKGROUND: Mutations of SCN8A encoding the neuronal voltage-gated sodium channel NaV1.6 are associated with early-infantile epileptic encephalopathy type 13 (EIEE13) and intellectual disability. Using clinical exome sequencing, we have detected three novel de novo SCN8A mutations in patients with intellectual disabilities, and variable clinical features including seizures in two patients. To determine the causality of these SCN8A mutations in the disease of those three patients, we aimed to study the (dys)function of the mutant sodium channels. METHODS: The functional consequences of the three SCN8A mutations were assessed using electrophysiological analyses in transfected cells. Genotype-phenotype correlations of these and other cases were related to the functional analyses. RESULTS: The first mutant displayed a 10 mV hyperpolarising shift in voltage dependence of activation (gain of function), the second did not form functional channels (loss of function), while the third mutation was functionally indistinguishable from the wildtype channel. CONCLUSIONS: Comparison of the clinical features of these patients with those in the literature suggests that gain-of-function mutations are associated with severe EIEE, while heterozygous loss-of-function mutations cause intellectual disability with or without seizures. These data demonstrate that functional analysis of missense mutations detected by clinical exome sequencing, both inherited and de novo, is valuable for clinical interpretation in the age of massive parallel sequencing.
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