PRNP and Creutzfeldt Jacob disease: Sporadic CJD (sCJD), the most common form, comprising about 85% of cases, includes six major clinicopathological subtypes that are primarily determined by the genotype at the polymorphic codon 129 (encoding methionine, M, or valine, V) of the prion protein gene (PRNP) and the type (1 or 2) of misfolded PrP (PrPSc) accumulating in the brain (e.g., MM1, VV1, MM2, etc.).