After, often prolonged, febrile seizures or hemiconvulsions, therapy resistant afebrile seizures and neurological deterioration occur.[11] In at least 70% of children, Dravet syndrome is caused by a heterozygous mutation in the SCN1A-gene, [10], [12] encoding the alpha-subunit of the neuronal voltage gated sodium channel. This evidence concerns the gene SCN1A and encephalopathy, progressive, early-onset, with brain edema and/or leukoencephalopathy.