SCN1B and epilepsy: The disease penetrance of SCN1B p.C121W and p.I70_E74del mutations for GEFS+ is found to be 62–76% [5,6,44].There is also variable expressivity, and family members that share the same SCN1B variant may be seizure-free, with febrile seizures, or with epilepsy (most frequently FS+).