**4.4 Etiology**

DS is a channelopathy due to mutation in the SCN1A gene which encodes the alpha 1 subunit of the voltage-gated sodium (Nav1.1) channel reported in 80% of patients [50]. Almost half of SCN1A mutations are truncations, and most DS SCN1A mutations are de novo [51]. SCN1A mutations are not pathognomonic of DS; it could be observed in a spectrum of febrile epilepsy syndromes, which ranges from genetic epilepsy with febrile seizures plus (GEFS+) to DS. The mutations in the SCN1A gene also constitute a risk factor for SUDEP by causing cardiac and respiratory dysfunctions [52]. Another gene implicated in DS is GABRA1 [53].
