SCN1A and encephalopathy, progressive, early-onset, with brain edema and/or leukoencephalopathy: Reduced Nav1.1 function slows depolarization, decreases action potential amplitude, and directly impairs inhibitory neuronal firing, while its inactivation or reduced expression prolongs action potential depolarization, lowers the threshold for repetitive firing, triggers neuronal hyperexcitability, and leads to epilepsy (e.g., Dravet syndrome) and neurodevelopmental deficits (Black and Waxman, 2013).