Dravet syndrome (DS), previously known as severe myoclonic epilepsy of infancy (SMEI), is an autosomal dominant genetic disorder which causes a catastrophic form of epilepsy, with prolonged seizures that are often triggered by hot temperatures or fever. It is very difficult to treat with anticonvulsant medications. It often begins before one year of age, with six months being the age that seizures, char-ac-ter-ized by prolonged convulsions and triggered by fever, usually begin. Seizures are the most common form of DS. DS is diagnosed clinically and genetic testing is recommended if there is any doubt. Due to drug-refractory epilepsy in DS, many other therapies are being explored to prolong the life expectancy of patients.

Reference
Wiki: Severe myoclonic epilepsy