PRNP and Creutzfeldt Jacob disease: There are three major subtypes of CJD i.e. Sporadic CJD, which occurs for reasons unbeknown to science (85% of known cases), Genetic or Familial CJD which is characterized by the presence of mutations in the human prion protein (PRNP) gene (10–15% cases) and Iatrogenic CJD that occurs via accidental transmission through medical and surgical procedures (1–2% cases).