SCN1A and epilepsy: However, SCN1A IVS5-91 G>A intronic polymorphism of the same gene has been reported to show a population-specific association with carbamazepine and multiple drug-resistance epilepsy.[37–39] It is now well established that various AEDs mediate their action through GABA binding.[40] It is also hypothesized that target receptor sites are somehow altered in the epileptic brain so that they are much less sensitive to the administered AEDs.