Gene therapy for Dravet syndrome: promises and impact on disease trigger and secondary modifications

Dravet syndrome is a severe epileptic syndrome that begins during the first year of life of otherwise healthy babies. Over the years, the seizure burden changes, and pathology evolves in strong association with behavioral alterations, including cognitive delay and autistic traits. Initially, this aspect was considered a direct consequence of epilepsy severity, and DS was defined as an epileptic encephalopathy. Increasing evidence suggests that these two aspects of the disease, epilepsy and behavioral impairment, might not be so strictly connected. DS is mostly caused by heterozygous loss-of-function mutations in the SCN1A gene, which encodes for the alpha-subunit of the voltage-gated sodium channel Nav1.1, responsible for GABAergic interneuron excitability. Interneuron dysfunction is evident at symptom onset in Dravet murine models, but their activity appears to recover in the chronic phase of the disease, when a series of secondary modifications arise and likely drive the phenotype. Given that the genetic basis of the disease is clear, innovative therapies based on the restoration of sufficient expression levels of Nav1.1 to re-establish functional neuronal activity are being developed. In this work, we review such therapeutic approaches, with a specific focus on the existing evidence of their ability to address not only epilepsy but also behavioral alterations, and to recover secondary modifications.