Epilepsy is a common disorder of aberrant neuronal excitability that has long-term consequences for health and intellectual and social development. Many antiepileptic medications have undesirable side effects and only target the symptoms of epilepsy leading to ineffective seizure control. Our long-term goal is to facilitate the development of more effective epilepsy treatments through a better understanding of the factors that affect neuronal excitability. Mutations in the voltage-gated sodium channel gene SCN1A, a critical regulator of neuronal excitability, have been identified in two forms of dominant idiopathic generalized epilepsy: Generalized Epilepsy with Febrile Seizures Plus (GEFSP2) and Severe Myoclonic Epilepsy of Infancy (SMEI). GEFSP2 is characterized by febrile (fever induced) seizures that persist beyond the age of six and the development of adult epilepsy. SMEI is a severe, debilitating childhood epilepsy characterized by febrile and afebrile seizures, mental retardation and ataxia. Many loss-of-function SCN1A mutations have been identified in SMEI patients, suggesting an important relationship between SCN1A expression levels and neuronal excitability. We hypothesize that sequence variation in critical SCN1A regulatory elements can also lead to altered expression and represent an important, but as yet unexplored, component of severe childhood epilepsies. We will test this hypothesis by functional analysis of SCN1A promoter variants identified in patients and in unaffected controls. By multi-species sequence analysis, we have identified 9 evolutionarily conserved non-coding sequences (> 143 bp in length) in the SCN1A gene. We hypothesize that these represent additional regulatory elements. The biological functions of these regions will be examined using a combination of in vitro assays and by targeted deletion in the mouse. To further investigate the relationship between SCN1A expression and seizure susceptibility, we will develop a series of mouse lines with 10-80% of endogenous Scnla expression levels. These expression levels will be generated by crossing well-characterized Scnla BAG transgenic lines to available heterozygous Scnla knock-out mice. This study will provide new, clinically relevant insights into the regulation of SCN1A and the mechanisms that determine neuronal excitability.