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Neurology. 2016 Nov 8;87(19):1975-1984. Epub 2016 Oct 12.

Dominant KCNA2 mutation causes episodic ataxia and pharmacoresponsive epilepsy.

Author information

1
From the School of Medicine and Robinson Research Institute (M.A.C., R.C., J.G.) and School of Biological Sciences (J.G.), The University of Adelaide; Epilepsy Research Centre, Department of Medicine (S.T.B., S. Micallef, S.F.B., I.E.S.), University of Melbourne, Austin Health, Heidelberg; Florey Institute of Neuroscience and Mental Health (M.L., S. Maljevic, E.V.G., S.P., I.E.S.), Melbourne; Division of Genetic Medicine, Department of Pediatrics (G.L.C., C.T.M., H.C.M.), University of Washington, Seattle; Department of Neurology (K.B.H., I.E.S.), Royal Children's Hospital; Neurosciences Group (K.B.H.), Murdoch Childrens Research Institute, Melbourne; Department of Paediatrics (K.B.H.), University of Melbourne, Royal Children's Hospital, Parkville, Australia; Department of Neurology and Epileptology (S. Maljevic, H.L.), Hertie Institute for Clinical Brain Research, University of Tübingen, Germany; The Walter and Eliza Hall Institute of Medical Research (M.B.); Department of Medical Biology (M.B.), The University of Melbourne, Parkville; and Department of Medicine, Royal Melbourne Hospital (S.P.), The University of Melbourne, Australia.
2
From the School of Medicine and Robinson Research Institute (M.A.C., R.C., J.G.) and School of Biological Sciences (J.G.), The University of Adelaide; Epilepsy Research Centre, Department of Medicine (S.T.B., S. Micallef, S.F.B., I.E.S.), University of Melbourne, Austin Health, Heidelberg; Florey Institute of Neuroscience and Mental Health (M.L., S. Maljevic, E.V.G., S.P., I.E.S.), Melbourne; Division of Genetic Medicine, Department of Pediatrics (G.L.C., C.T.M., H.C.M.), University of Washington, Seattle; Department of Neurology (K.B.H., I.E.S.), Royal Children's Hospital; Neurosciences Group (K.B.H.), Murdoch Childrens Research Institute, Melbourne; Department of Paediatrics (K.B.H.), University of Melbourne, Royal Children's Hospital, Parkville, Australia; Department of Neurology and Epileptology (S. Maljevic, H.L.), Hertie Institute for Clinical Brain Research, University of Tübingen, Germany; The Walter and Eliza Hall Institute of Medical Research (M.B.); Department of Medical Biology (M.B.), The University of Melbourne, Parkville; and Department of Medicine, Royal Melbourne Hospital (S.P.), The University of Melbourne, Australia. jozef.gecz@adelaide.edu.au scheffer@unimelb.edu.au.

Abstract

OBJECTIVE:

To identify the genetic basis of a family segregating episodic ataxia, infantile seizures, and heterogeneous epilepsies and to study the phenotypic spectrum of KCNA2 mutations.

METHODS:

A family with 7 affected individuals over 3 generations underwent detailed phenotyping. Whole genome sequencing was performed on a mildly affected grandmother and her grandson with epileptic encephalopathy (EE). Segregating variants were filtered and prioritized based on functional annotations. The effects of the mutation on channel function were analyzed in vitro by voltage clamp assay and in silico by molecular modeling. KCNA2 was sequenced in 35 probands with heterogeneous phenotypes.

RESULTS:

The 7 family members had episodic ataxia (5), self-limited infantile seizures (5), evolving to genetic generalized epilepsy (4), focal seizures (2), and EE (1). They had a segregating novel mutation in the shaker type voltage-gated potassium channel KCNA2 (CCDS_827.1: c.765_773del; p.255_257del). A rare missense SCN2A (rs200884216) variant was also found in 2 affected siblings and their unaffected mother. The p.255_257del mutation caused dominant negative loss of channel function. Molecular modeling predicted repositioning of critical arginine residues in the voltage-sensing domain. KCNA2 sequencing revealed 1 de novo mutation (CCDS_827.1: c.890G>A; p.Arg297Gln) in a girl with EE, ataxia, and tremor.

CONCLUSIONS:

A KCNA2 mutation caused dominantly inherited episodic ataxia, mild infantile-onset seizures, and later generalized and focal epilepsies in the setting of normal intellect. This observation expands the KCNA2 phenotypic spectrum from EE often associated with chronic ataxia, reflecting the marked variation in severity observed in many ion channel disorders.

PMID:
27733563
PMCID:
PMC5109949
DOI:
10.1212/WNL.0000000000003309
[Indexed for MEDLINE]
Free PMC Article

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