Nav1.1 dysfunction in genetic epilepsy with febrile seizures-plus or Dravet syndrome

Authors

  • Linda Volkers,

    1. Division of Biomedical Genetics, Department of Medical Genetics, University Medical Center Utrecht, Utrecht, The Netherlands
    2. Division Heart & Lungs, Department of Medical Physiology, University Medical Center Utrecht, Yalelaan 50, 3584 CM Utrecht, The Netherlands
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  • Kristopher M. Kahlig,

    1. Department of Medicine, Vanderbilt University, Nashville, TN, USA
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    • K.M.K., N.E.V., B.P.C.K. and M.B.R. contributed equally to this work.

  • Nienke E. Verbeek,

    1. Division of Biomedical Genetics, Department of Medical Genetics, University Medical Center Utrecht, Utrecht, The Netherlands
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    • K.M.K., N.E.V., B.P.C.K. and M.B.R. contributed equally to this work.

  • Joost H. G. Das,

    1. Division of Biomedical Genetics, Department of Medical Genetics, University Medical Center Utrecht, Utrecht, The Netherlands
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  • Marjan J. A. van Kempen,

    1. Division of Biomedical Genetics, Department of Medical Genetics, University Medical Center Utrecht, Utrecht, The Netherlands
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  • Hans Stroink,

    1. Department of Neurology, Canisius-Wilhelmina Hospital, Nijmegen, The Netherlands
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  • Paul Augustijn,

    1. SEIN – The Epilepsy Institutes of the Netherlands Foundation, Heemstede, The Netherlands
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  • Onno van Nieuwenhuizen,

    1. Department of Pediatrics Neurology, University Medical Center Utrecht, Utrecht, The Netherlands
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  • Dick Lindhout,

    1. Division of Biomedical Genetics, Department of Medical Genetics, University Medical Center Utrecht, Utrecht, The Netherlands
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  • Alfred L. George Jr,

    1. Department of Medicine, Vanderbilt University, Nashville, TN, USA
    2. Department of Pharmacology, Vanderbilt University, Nashville, TN, USA
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  • Bobby P. C. Koeleman,

    1. Division of Biomedical Genetics, Department of Medical Genetics, University Medical Center Utrecht, Utrecht, The Netherlands
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    • K.M.K., N.E.V., B.P.C.K. and M.B.R. contributed equally to this work.

  • Martin B. Rook

    1. Division Heart & Lungs, Department of Medical Physiology, University Medical Center Utrecht, Yalelaan 50, 3584 CM Utrecht, The Netherlands
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    • K.M.K., N.E.V., B.P.C.K. and M.B.R. contributed equally to this work.


Dr Martin B. Rook, as above.
E-mail: m.b.rook@umcutrecht.nl

Abstract

Relatively few SCN1A mutations associated with genetic epilepsy with febrile seizures-plus (GEFS+) and Dravet syndrome (DS) have been functionally characterized. In contrast to GEFS+, many mutations detected in DS patients are predicted to have complete loss of function. However, functional consequences are not immediately apparent for DS missense mutations. Therefore, we performed a biophysical analysis of three SCN1A missense mutations (R865G, R946C and R946H) we detected in six patients with DS. Furthermore, we compared the functionality of the R865G DS mutation with that of a R859H mutation detected in a GEFS+ patient; the two mutations reside in the same voltage sensor domain of Nav1.1. The four mutations were co-expressed with β1 and β2 subunits in tsA201 cells, and characterized using the whole-cell patch clamp technique. The two DS mutations, R946C and R946H, were nonfunctional. However, the novel voltage sensor mutants R859H (GEFS+) and R865G (DS) produced sodium current densities similar to those in wild-type channels. Both mutants had negative shifts in the voltage dependence of activation, slower recovery from inactivation, and increased persistent current. Only the GEFS+ mutant exhibited a loss of function in voltage-dependent channel availability. Our results suggest that the R859H mutation causes GEFS+ by a mixture of biophysical defects in Nav1.1 gating. Interestingly, while loss of Nav1.1 function is common in DS, the R865G mutation may cause DS by overall gain-of-function defects.

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