**1. Introduction**

Epilepsy is one of the chronic brain disorders characterized by recurrent seizures due to abnormal excessive electrical discharges of cerebral neurons [1]. It is believed that genetic factors play a crucial role in the etiopathogenesis of epilepsy. So far ~1000 genes have been proved to be associated with epilepsy, among which genes encoding VGIC predominate [2].

VGICs are pore-forming membrane proteins. Their functions include establishing APs and maintaining homeostasis by gating the ionic flow traversing the cell membrane, managing the ionic flow across cells and regulating Ca2+ signal transduction, which are essential to the neuroexcitability, so VGICs are potentially involved in epileptogenesis [2]. The association of VGIC genes and epilepsy might provide insights into the etiopathogenesis underlying epilepsy. Pathophysiological studies illuminated that two key defects are (i) a neuronal disinhibition induced by loss-of-function of VGIC gene expressed specifically in inhibitory interneurons (for example, Nav1.1 and P/Q VGCCs) or (ii) dysfunction of axon initial segments, the neuronal structure in which APs are generated and many VGICs (such as Nav1.2 and Kv7) are mainly localized (**Figure 1**). Moreover, clinically originated studies identified novel genes, defined their neuronal functions, and sometimes established novel physiological principles [2].

### **Figure 1.**

*Neuronal localization of some relevant voltage-gated ion channels. A schematic view of an excitatory pyramidal (orange), an inhibitory (green) neuron, and their synaptic connections is shown. Distinctive intracellular compartments are targeted by different populations of VGICs. Examples of which as mentioned in this chapter are shown here: in the somatodendritic compartment, Nav, Cav (L- and T-type), TRP, BK, and Kv channels; at axon initial segments (AIS) and nodes of Ranvier in pyramidal neurons, Nav1.2, Kv7 channels; at AIS of inhibitory neurons, Nav1.1; in the somatodendritic compartment of inhibitory neurons, BK and Nav1.6; in the presynaptic terminals, Cav P/Q type. GOF represents the gain-of-function mutation of VGICs-induced human epilepsy. LOF represents the loss-of-function mutation of VGICs.*

In this chapter, we summarize the epilepsy-associated VGIC genes, the mutations, corresponding phenotypes, and functional changes, aiming to provide clues for evaluating the relationship between VGIC genes and epileptogenesis.
