Current classification of sporadic (s) CJD, the most common form, includes six major disease subtypes that are primarily determined by the combination of the genotype at the polymorphic codon 129 of PRNP, encoding for methionine (M) or valine (V), with either one of two types (1 and 2) of misfolded prion protein (PrPSc) that differ in the size (21 and 19 kDa) of their protease-resistant core [55, 56, 58, 59]. The gene discussed is PRNP; the disease is Creutzfeldt Jacob disease.