SCN1A and Febrile seizure (within the age range of 3 months to 6 years): Monoallelic variation of the alpha subunit of the sodium channel (SCN1A) gene is a well-established cause of a spectrum of seizure disorders that include simple febrile seizures, febrile seizures plus (FS+) and genetic epilepsy with febrile seizures plus (GEFS+).