A Knock-In Model of Human Epilepsy in Drosophila Reveals a Novel Cellular Mechanism Associated with Heat-Induced Seizure

Over 40 missense mutations in the human SCN1A sodium channel gene are linked to an epilepsy syndrome termed genetic epilepsy with febrile seizures plus (GEFS+). Inheritance of GEFS+ is dominant, but the underlying cellular mechanisms remain poorly understood. Here we report that knock-in of a GEFS+ SCN1A mutation (K1270T) into the Drosophila sodium channel gene, para, causes a semidominant temperature-induced seizure phenotype. Electrophysiological studies of GABAergic interneurons in the brains of adult GEFS+ flies reveal a novel cellular mechanism underlying heat-induced seizures: the deactivation threshold for persistent sodium currents reversibly shifts to a more negative voltage when the temperature is elevated. This leads to sustained depolarizations in GABAergic neurons and reduced inhibitory activity in the central nervous system. Furthermore, our data indicate a natural temperature-dependent shift in sodium current deactivation (exacerbated by mutation) may contribute to febrile seizures in GEFS+ and perhaps normal individuals.