Many different diseases of animals and humans are caused by the pathological form of the prion protein (PrP). In animals, these disorders include scrapie of sheep and goats, "mad cow" disease, and chronic wasting disease of elk and deer. In humans, these maladies include kuru, Creutzfeldt–Jakob disease (CJD), Gerstmann–Sträussler–Scheinker disease (GSS), and fatal familial insomnia (FFI).
Once formed, pathological PrP promotes the misfolding of the normal prion protein into a diseased state. This self-propagating process allows for the exponential increase and accumulation of misfolded PrP in cells, resulting in a disruption of cell function and ultimately cell death.