The most common prion disease is Creutzfeldt-Jacob disease (CJD), usually sporadic (sCJD), but in up to 15% familial due to mutations in the prion gene. CJD presents with myoclonis, ataxia, and rapidly progressive dementia with an average age of onset of 67 years. Fatal Familial Insomnia (FFI) is a related uniformly fatal prion disease, with mean onset of dysautonomia and insomnia at 56 years and mean duration of 13 months.
