Functional analysis of novel KCNQ2 mutations found in patients with Benign Familial Neonatal Convulsions

Benign Familial Neonatal Convulsions (BFNC) are a rare epilepsy disorder with an autosomal-dominant inheritance. It is linked to mutations in the potassium channel genes KCNQ2 and KCNQ3. These encode for Kv7.2 and Kv7.3 potassium ion channels, which produce an M-current that regulates the potential...

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Bibliographic Details
Published in:Neuroscience letters 2009-10, Vol.462 (1), p.24-29
Main Authors: Volkers, Linda, Rook, Martin B., Das, Joost H.G., Verbeek, Nienke E., Groenewegen, W. Antoinette, van Kempen, Marjan J.A., Lindhout, Dick, Koeleman, Bobby P.C.
Format: Article
Language:English
Subjects:
Benign
Benign Familial Neonatal Convulsions
BFNC
Biological and medical sciences
Cell Line
Cell Membrane - physiology
Endoplasmic Reticulum - metabolism
Epilepsy, Benign Neonatal - genetics
Family
Female
Fluorescent Antibody Technique
Fundamental and applied biological sciences. Psychology
Green Fluorescent Proteins
Humans
KCNQ2
KCNQ2 Potassium Channel - genetics
KCNQ2 Potassium Channel - metabolism
KCNQ3 Potassium Channel - metabolism
Kv7.2
Loss-of-function
Membrane Potentials - physiology
Microscopy, Confocal
Microscopy, Fluorescence
Mutation
Mutation, Missense
Patch-Clamp Techniques
Potassium - metabolism
Time Factors
Transfection
Vertebrates: nervous system and sense organs
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Summary:Benign Familial Neonatal Convulsions (BFNC) are a rare epilepsy disorder with an autosomal-dominant inheritance. It is linked to mutations in the potassium channel genes KCNQ2 and KCNQ3. These encode for Kv7.2 and Kv7.3 potassium ion channels, which produce an M-current that regulates the potential firing action in neurons through modulation of the membrane potential. We report on the biophysical and biochemical properties of V589X, T359K and P410fs12X mutant-KCNQ2 ion channels that were detected in three BFNC families. Mutant KCNQ2 cDNAs were co-expressed with WT-KCNQ2 and KCNQ3 cDNAs in HEK293 cells to mimic heterozygous expression of the KCNQ2 mutations in BFNC patients. The resulting potassium currents were measured using patch-clamp techniques and showed an approximately 75% reduction in current and a depolarized shift in the voltage dependence of activation. Furthermore, the time-constant of activation of M-currents in cells expressing T359K and P410fs12X was slower compared to cells expressing only wild-type proteins. Immunofluorescent labeling of HEK293 cells stably expressing GFP-tagged KCNQ2-WT or mutant α-subunits indicated cell surface expression of WT, V589X and T359K mutants, suggesting a loss-of-function, while P410fs12X was predominantly retained in the ER and sub-cellular compartments outside the ER suggesting an effectively haplo-insufficient effect.
ISSN:0304-3940
1872-7972
DOI:10.1016/j.neulet.2009.06.064