Di Berardino, Mainardi, Brusco et al. show that induction of Scn1a haploinsufficiency in mice at postnatal day (P)2, P30 or P60 elicits a classic Dravet syndrome phenotype. The gene discussed is SCN1A; the disease is encephalopathy, progressive, early-onset, with brain edema and/or leukoencephalopathy.