(Cooper, 2016). E xamining 100 patients with Dravet syndrome (87 of whom had SCN1A mutations) over a follow-up period averaging 17 years, the authors reported that 17 patients died (17%). Ten of those were caused by SUDEP, 4 by status epilepticus, 2 by drowning, and 1 by asphyxia. Taking into account the follow-up time period, this represents a mortality rate of 16 per 1000 person-years, compared to the SUDEP mortality rate of 5 per 1000 person-years for adults with refractory epilepsy. (Note that a mortality rate of 16 per 1000 person-years means that in a population of 1000 people, 16 deaths would be expected in a given year. It is a more accurate way of expressing mortality than simple percentages because it takes time into account.)

Cooper, M.S., et. al. Mortality in Dravet syndrome. Epilepsy Research. Oct 26;128:43-47. doi: 10.1016/j.eplepsyres.2016.10.006. https://www.ncbi.nlm.nih.gov/pubmed/27810515