Table 1. Etiologic classification of human prion diseases.

Etiology	Mechanism	Disease
Sporadic	Somatic mutation or spontaneous conversion of PrPC into PrPSc ?	Sporadic Creutzfeldt-Jakob disease
	Somatic mutation or spontaneous conversion of PrPC into PrPSc ?	Sporadic fatal insomnia
	Unknown	Variable protease-sensitive prionopathy
Hereditary	Germ-line mutations in the PRNP gene	Familial Creutzfeldt-Jakob disease
	Germ-line mutations in the PRNP gene	Fatal familial insomnia
	Germ-line mutations in the PRNP gene	Gerstmann–Sträussler-Scheinker disease
Acquired	Infection through ritualistic cannibalism	Kuru
	Zoonotic infection with bovine prions	Variant Creutzfeldt-Jakob disease
	Infection from prion-contaminated human growth hormone, dura mater grafts, etc.	Iatrogenic Creutzfeldt-Jakob disease