FUNCTIONAL CHARACTERIZATION OF THE D188V MUTATION IN SCN1A CAUSING GENERALIZED EPILEPSY WITH FEBRILE SEIZURES PLUS (GEFS).
Abstract number :
D.04
Submission category :
Year :
2002
Submission ID :
2592
Source :
www.aesnet.org
Presentation date :
12/7/2002 12:00:00 AM
Published date :
Dec 1, 2002, 06:00 AM
Authors :
Patrick Cossette, Andrew Loukas, Ronald G. Lafreniere, Daniel Rochefort, David S. Ragsdale, Robert J. Dunn, Guy A. Rouleau. Neurology, McGill University Health Center, Montreal, Quebec, Canada; Neurology, Montreal Neurological Institute, Montreal, Quebec,
RATIONALE: Mutations in the alpha 1 subunit of the voltage-gated sodium channel (SCN1A) have been increasingly recognized as an important cause of epilepsy in humans, with mutations found in patients with generalized epilepsy and febrile seizure (GEFS), febrile seizures associated partial epilepsy, and severe myoclonic epilepsy of infancy. However, functional consequences of these mutations remain largely unknown. The aim of this study is to determine the effects of the D188V mutation on voltage-gated sodium channel function in vitro.
METHODS: We identified a mutation (D188V) in the SCN1A gene segregating with GEFS in a large kindred. We used site-directed mutagenesis to introduce this mutation into cDNA encoding rat SCN2A. We coexpressed wild type or mutant alpha subunits along with the auxiliary beta 1 subunit in human embryonic kidney (HEK 293) cells. Functional properties of the sodium channels were examined by whole cell patch clamp recording.
RESULTS: The D188V mutation does not affect the voltage dependence of SCN1A activation, steady state availability or inactivation time course. In turn, mutant channels have shown a decreased in channel refractoriness during high frequency activation compared to the wild-type. Whole cell sodium currents normally decrease in amplitude progressively over the course of high frequency trains of channel activity, and this frequency-dependent current rundown is thought to play a significant role in dampening hyperexcitability associated with seizures. Therefore, this decreased sodium current rundown caused by the D188V mutation is expected to increase neuronal excitability.
CONCLUSIONS: In vitro analysis of D188V mutation expressed in HEK cells have shown a reduction in frequency dependent rundown of voltage-gated sodium currents, compatible with an increase in membrane hyperexcitability. This mechanism could be central in the pathophysiology of the epilepsies caused by mutations in sodium channels in humans.
[Supported by: Canadian Institute for Health Research, Xenon Genetics]