A definitive diagnosis of CJD can only be made after neuropathological examination of brain tissue and demonstration of spongiform degeneration of the brain, accompanied by extensive neuronal loss and accumulation of PrPRES, a misfolded and protease-resistant form of the normal cellular prion protein (PrPC) [11], [12]. The gene discussed is PRNP; the disease is Creutzfeldt Jacob disease.