Loss of function SCN1A mutations are associated with a broad spectrum of phenotypes in people that vary in severity, from ‘just’ febrile seizures, or epilepsy with febrile seizures plus (GEFS+), which are both relatively milder, to Dravet syndrome, the most severe (Catterall et al., 2010; Mantegazza & Broccoli, 2019). Here, SCN1A is linked to Dravet syndrome.