A novel epileptic encephalopathy mutation in KCNB1 disrupts Kv2.1 ion selectivity, expression, and localization.
The epileptic encephalopathies are a group of highly heterogeneous genetic disorders. The majority of disease-causing mutations alter genes encoding voltage-gated ion channels, neurotransmitter receptors, or synaptic proteins. We have identified a novel de novo pathogenic K+ channel variant in an idiopathic epileptic encephalopathy family. Here, we report the effects of this mutation on channel function and heterologous expression in cell lines. We present a case report of infantile epileptic encephalopathy in a young girl, and trio-exome sequencing to determine the genetic etiology of her disorder. The patient was heterozygous for a de novo missense variant in the coding region of the KCNB1 gene, c.1133T>C. The variant encodes a V378A mutation in the α subunit of the Kv2.1 voltage-gated K+ channel, which is expressed at high levels in central neurons and is an important regulator of neuronal excitability. We found that expression of the V378A variant results in voltage-activated currents that are sensitive to the selective Kv2 channel blocker guangxitoxin-1E. These voltage-activated Kv2.1 V378A currents were nonselective among monovalent cations. Striking cell background-dependent differences in expression and subcellular localization of the V378A mutation were observed in heterologous cells. Further, coexpression of V378A subunits and wild-type Kv2.1 subunits reciprocally affects their respective trafficking characteristics. A recent study reported epileptic encephalopathy-linked missense variants that render Kv2.1 a tonically activated, nonselective cation channel that is not voltage activated. Our findings strengthen the correlation between mutations that result in loss of Kv2.1 ion selectivity and development of epileptic encephalopathy. However, the strong voltage sensitivity of currents from the V378A mutant indicates that the loss of voltage-sensitive gating seen in all other reported disease mutants is not required for an epileptic encephalopathy phenotype. In addition to electrophysiological differences, we suggest that defects in expression and subcellular localization of Kv2.1 V378A channels could contribute to the pathophysiology of this KCNB1 variant.
Center for Pediatric Genomic Medicine, Department of Pathology and Laboratory Medicine, and Department of Pediatrics, Children's Mercy Hospital, Kansas City, MO 64108.
Isabelle
I
Thiffault
Department of Neurobiology, Physiology and Behavior, Department of Physiology and Membrane Biology, and Department of Anesthesiology and Pain Medicine, University of California, Davis, Davis, CA 95616.
David J
DJ
Speca
Department of Neurobiology, Physiology and Behavior, Department of Physiology and Membrane Biology, and Department of Anesthesiology and Pain Medicine, University of California, Davis, Davis, CA 95616.
Daniel C
DC
Austin
Department of Neurobiology, Physiology and Behavior, Department of Physiology and Membrane Biology, and Department of Anesthesiology and Pain Medicine, University of California, Davis, Davis, CA 95616.
Melanie M
MM
Cobb
Department of Neurobiology, Physiology and Behavior, Department of Physiology and Membrane Biology, and Department of Anesthesiology and Pain Medicine, University of California, Davis, Davis, CA 95616.
Kenneth S
KS
Eum
Center for Pediatric Genomic Medicine, Department of Pathology and Laboratory Medicine, and Department of Pediatrics, Children's Mercy Hospital, Kansas City, MO 64108.
Nicole P
NP
Safina
Center for Pediatric Genomic Medicine, Department of Pathology and Laboratory Medicine, and Department of Pediatrics, Children's Mercy Hospital, Kansas City, MO 64108.
Lauren
L
Grote
Center for Pediatric Genomic Medicine, Department of Pathology and Laboratory Medicine, and Department of Pediatrics, Children's Mercy Hospital, Kansas City, MO 64108.
Emily G
EG
Farrow
Center for Pediatric Genomic Medicine, Department of Pathology and Laboratory Medicine, and Department of Pediatrics, Children's Mercy Hospital, Kansas City, MO 64108.
Neil
N
Miller
Center for Pediatric Genomic Medicine, Department of Pathology and Laboratory Medicine, and Department of Pediatrics, Children's Mercy Hospital, Kansas City, MO 64108 Center for Pediatric Genomic Medicine, Department of Pathology and Laboratory Medicine, and Department of Pediatrics, Children's Mercy Hospital, Kansas City, MO 64108 University of Missouri-Kansas City School of Medicine, Kansas City, MO 64108.
Sarah
S
Soden
Center for Pediatric Genomic Medicine, Department of Pathology and Laboratory Medicine, and Department of Pediatrics, Children's Mercy Hospital, Kansas City, MO 64108 Center for Pediatric Genomic Medicine, Department of Pathology and Laboratory Medicine, and Department of Pediatrics, Children's Mercy Hospital, Kansas City, MO 64108 Center for Pediatric Genomic Medicine, Department of Pathology and Laboratory Medicine, and Department of Pediatrics, Children's Mercy Hospital, Kansas City, MO 64108 University of Missouri-Kansas City School of Medicine, Kansas City, MO 64108.
Stephen F
SF
Kingsmore
Department of Neurobiology, Physiology and Behavior, Department of Physiology and Membrane Biology, and Department of Anesthesiology and Pain Medicine, University of California, Davis, Davis, CA 95616 Department of Neurobiology, Physiology and Behavior, Department of Physiology and Membrane Biology, and Department of Anesthesiology and Pain Medicine, University of California, Davis, Davis, CA 95616 jsack@ucdavis.edu jtrimmer@ucdavis.edu csaunders@cmh.edu.
James S
JS
Trimmer
Center for Pediatric Genomic Medicine, Department of Pathology and Laboratory Medicine, and Department of Pediatrics, Children's Mercy Hospital, Kansas City, MO 64108 Center for Pediatric Genomic Medicine, Department of Pathology and Laboratory Medicine, and Department of Pediatrics, Children's Mercy Hospital, Kansas City, MO 64108 University of Missouri-Kansas City School of Medicine, Kansas City, MO 64108 jsack@ucdavis.edu jtrimmer@ucdavis.edu csaunders@cmh.edu.
Carol J
CJ
Saunders
Department of Neurobiology, Physiology and Behavior, Department of Physiology and Membrane Biology, and Department of Anesthesiology and Pain Medicine, University of California, Davis, Davis, CA 95616 Department of Neurobiology, Physiology and Behavior, Department of Physiology and Membrane Biology, and Department of Anesthesiology and Pain Medicine, University of California, Davis, Davis, CA 95616 jsack@ucdavis.edu jtrimmer@ucdavis.edu csaunders@cmh.edu.
Jon T
JT
Sack
D000200:Action Potentials; D000818:Animals; D016466:CHO Cells; D019556:COS Cells; D002522:Chlorocebus aethiops; D006224:Cricetinae; D003412:Cricetulus; D004827:Epilepsy / Q000175:diagnosis / Q000235:genetics*; D005260:Female; D006801:Humans; D015640:Ion Channel Gating; D020125:Mutation, Missense; D011188:Potassium / Q000378:metabolism; D021381:Protein Transport; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051669:Shab Potassium Channels / Q000235:genetics / Q000378:metabolism*
C496988:KCNB1 protein, human; D012333:RNA, Messenger; D051669:Shab Potassium Channels; D011188:Potassium