At the moment about 1500 pathogenic mutations of SCN1A have been described [23] and the majority of them, over 900, are associated with the Severe Myoclonic Epilepsy of Infancy (SMEI), a rare and grave form of epilepsy described for the first time by Charlotte Dravet in 1978 renamed Dravet syndrome in 1989 [24]. This evidence concerns the gene SCN1A and encephalopathy, progressive, early-onset, with brain edema and/or leukoencephalopathy.