Purpose:  A questionnaire survey was conducted in Japan to investigate the causes and prevalence of death related to Dravet syndrome.

Methods:  A questionnaire was delivered to 246 hospitals at which physicians were treating childhood epilepsy to gain information about the total number of patients with Dravet syndrome and their prevalence of early death.

Key Findings:  Responses to the survey were collected from 91 hospitals, and a total of 63 of 623 patients with Dravet syndrome died. Data from 59 of these patients were analyzed. The patients’ ages at death ranged from 13 months to 24 years and 11 months, with a median age of 6 years and 8 months. The analysis showed that the risk of mortality remained high up to approximately 12 years of age. The causes of mortality included sudden death in 31 patients (53%), acute encephalopathy with status epilepticus (SE) in 21 patients (36%), drowning in 6 patients (10%), and acute hepatopathy in one patient (1%). The incidence of sudden death reached a first peak at 1–3 years of age and reached a second peak at 18 years and older. In contrast, the incidence of acute encephalopathy with SE reached a sharp peak at 6 years of age. Seven of 10 patients who underwent an SCN1A mutation analysis exhibited positive mutations without a specific mutation site.

Significance:  In the present study, the prevalence of Dravet syndrome–related mortality was 10.1%. The incidence of sudden death and acute encephalopathy with SE was the highest in infancy (1–3 years) and at early school ages (with a peak at 6 years), respectively. After approximately 12 years of age, the risk of mortality declined sharply. Neither the treatment nor the number of seizures was associated with any cause of mortality. In addition, it is difficult to predict which factors lead to a fatal outcome.