Initial antiepileptic treatment fails in over 40% of people with epilepsy, resulting in significant personal, financial, and societal hardships. The objective of this proposal is to determine the influence of genetic alterations in sodium channel genes on response to carbamazepine (CBZ), one of the main first line treatments for epilepsy. It is hypothesized that single nucleotide polymorphisms (SNPs) in sodium channel genes which change the amino acid composition of the resultant channel (nonsynonymous SNPs) alter the channel's responsiveness to CBZ resulting in treatment failure in some people with epilepsy. To achieve the objective of this application the specific aims are to (1) Identify single nucleotide polymorphisms in sodium channel a- subunit genes expressed in the central nervous system that occur more frequently in patients with epilepsy unresponsive to initial CBZ therapy than in patients with CBZ-responsive epilepsy;and (2) Determine how SNPs in sodium channel a-subunit genes affect electrophysiological and pharmacological properties of sodium channels in vitro. To accomplish these aims, first nonsynonymous variations in sodium channel genes occurring people with epilepsy that is unresponsive to CBZ will be identified and the frequency of these SNPs will be compared between patients with epilepsy that is unresponsive to CBZ, patients with epilepsy that responds to CBZ, and gender and ethnicity matched controls. Subsequently, the functional consequences of these sodium channel SNPs will be studied in vitro with whole cell patch clamp techniques using heterologously expressed recombinant human sodium channels. The motivation of the proposed research is that once the influence of sodium channel SNPs on CBZ responsiveness is understood, more efficacious therapies for epilepsy can be developed both by providing a way to pre-select treatment tailored to individual patients and by promoting the development of more effective genetic based therapies. This work is innovative because it links phenotype (CBZ resistant epilepsy), genotype (sodium channel SNPs) and functionality (alteration in channel responsiveness to AEDs);it is also innovative because the design of the pharmacogenetic association study involves a consecutive cohort of newly diagnosed patients taking a single AED whose response to treatment will be rigorously assessed. It is expected that sodium channel gene polymorphisms will be identified that are clinically associated with CBZ failure and alter sodium channel CBZ responsiveness;this will lead to a future prospective study to test whether CBZ responsiveness can be predict pre-treatment in patients with newly diagnosed epilepsy. From the functionality studies, in vitro methods for screening new AEDs can be developed. These results will have a positive impact by advancing understanding of how failure of first-line CBZ treatment occurs. This is significant because it is expected to provide information needed to better treat patients with newly diagnosed epilepsy and will contribute to future genetic therapeutic approaches.
The proposed work is relevant to human health because it will advance understanding of how failure of initial drug treatment for epilepsy occurs. As a result, it is anticipated that people with partial onset epilepsy who are unlikely to respond to the most commonly used initial medication could be identified at the time of diagnosis and their therapy subsequently individualized. In addition, using the results of this work, new animal models of epilepsy and in vitro methods for screening potential antiepileptic medication can be developed, facilitating identification of novel treatments.
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