In Dravet syndrome patients with SCN1A mutations, 95% are de novo and 5% are inherited. Carrier relatives are either unaffected or mildly affected with genetic epilepsy with febrile seizures plus phenotypes. Germline and somatic mosaicism have been reported.
Approximately 75% of patients with Dravet syndrome have mutations or copy number variants in SCN1A. A small percentage of females with a Dravet syndrome-like phenotype have mutations in the PCDH19 gene. These females usually have clusters of seizures with fever as opposed to the prolonged status epilepticus with fever that occurs in SCN1A-related Dravet syndrome.
A family history of epilepsy and/or febrile seizures is present in 30-50% of patients. In some children with Dravet syndrome, the family history is consistent with genetic epilepsy with febrile seizures plus.