Genetic Defects of Voltage-Gated Sodium Channel α Subunit 1 in Dravet Syndrome and the Patients’ Response to Antiepileptic Drugs

Abstract

In the past decade, hundreds of mutations have been found in the SCN1A (sodium voltage-gated channel α subunit 1) gene in the epileptic patients. The functioning of the SCN1A gene products is intensively studied in the neuroscience field. The loss-of-function mutations of the SCN1A gene are the causative factor of Dravet syndrome, an intractable epilepsy syndrome. With the loss-of-function Na v 1.1 (the protein encoded by SCN1A gene), the selective dysfunction of the inhibitory parvalbumin (PV) interneurons impairs the balance of excitatory and inhibitory synaptic inputs to the downstream neurons, and causes the hyperexcitability of the neuronal network. The underlying mechanism is that the axon initial segments (AISs) of inhibitory parvalbumin interneurons predominantly express Na v 1.1, particularly in the proximal end of the AISs. The deficiency of Na v 1.1 weakens the excitability of the inhibitory parvalbumin neurons and leads to the hyperexcitability of the neuronal network. The sodium channel blockers, one category of the antiepileptic drugs (AEDs) that specifically block the activity of VGSCs, may potentially worsen the defect of Na v 1.1 of the PV interneurons in the patients with the SCN1A gene loss-of-function mutations, the clinical manifestation, and increase the seizure frequency of those patients.