Although the etiology of prion disease has not been well elucidated, major evidence suggests that modification of prion protein (PrP) from a normal cellular protein (PrPc) to a disease-specific species called the pathological scrapie isoform (PrPsc) causes insolubility and protease resistance, resulting in the disruption of neuronal homeostasis. This evidence concerns the gene PRNP and prion disease.