The phenotypic spectrum of SCN8A encephalopathy

Jan Larsen, Gemma L. Carvill, Elena Gardella, Gerhard Kluger, Gudrun Schmiedel, Nina Barisic, Christel Depienne, Eva Brilstra, Yuan Mang, Jens Erik Klint Nielsen, Martin Kirkpatrick, David Goudie, Rebecca Goldman, Johanna A. Jähn, Birgit Jepsen, Deepak Gill, Miriam Döcker, Saskia Biskup, Jacinta M. McMahon, Bobby KoelemanMandy Harris, Kees Braun, Carolien G F De Kovel, Carla Marini, Nicola Specchio, Tania Djémié, Sarah Weckhuysen, Niels Tommerup, Monica Troncoso, Ledia Troncoso, Andrea Bevot, Markus Wolff, Helle Hjalgrim, Renzo Guerrini, Ingrid E. Scheffer*, Heather C. Mefford, Rikke S. Møller

*Corresponding author for this work

Research output: Contribution to journalArticle

146 Scopus citations

Abstract

Objective: SCN8A encodes the sodium channel voltage-gated a8-subunit (Nav1.6). SCN8A mutations have recently been associated with epilepsy and neurodevelopmental disorders. We aimed to delineate the phenotype associated with SCN8A mutations. Methods: We used high-throughput sequence analysis of the SCN8A gene in 683 patients with a range of epileptic encephalopathies. In addition, we ascertained cases with SCN8A mutations from other centers. A detailed clinical history was obtained together with a review of EEG and imaging data. Results: Seventeen patients with de novo heterozygous mutations of SCN8A were studied. Seizure onset occurred at a mean age of 5 months (range: 1 day to 18 months); in general, seizures were not triggered by fever. Fifteen of 17 patients had multiple seizure types including focal, tonic, clonic, myoclonic and absence seizures, and epileptic spasms; seizures were refractory to antiepileptic therapy. Development was normal in 12 patients and slowed after seizure onset, often with regression; 5 patients had delayed development from birth. All patients developed intellectual disability, ranging from mild to severe. Motor manifestations were prominent including hypotonia, dystonia, hyperreflexia, and ataxia. EEG findings comprised moderate to severe background slowing with focal or multifocal epileptiform discharges. Conclusion: SCN8A encephalopathy presents in infancy with multiple seizure types including focal seizures and spasms in some cases. Outcome is often poor and includes hypotonia and movement disorders. The majority of mutations arise de novo, although we observed a single case of somatic mosaicism in an unaffected parent.

Original languageEnglish (US)
Pages (from-to)480-489
Number of pages10
JournalNeurology
Volume84
Issue number5
DOIs
StatePublished - 2015

ASJC Scopus subject areas

  • Clinical Neurology

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