EIMFS is a severe, drug-resistant, early-onset epilepsy encephalopathy in which variants in the KCNT1, SCN1A, SCN8A, SCN2A, PLCB1, KCNT1, SLC25A22, TBC1D24 and SLC12A5 genes as well as 16p11.2 duplication have been reported. The gene discussed is SCN8A; the disease is epilepsy of infancy with migrating focal seizures.