It is known that in vivo human Tau protein [17], [20], human prion protein (PrP) and its pathogenic mutants [16], [21], [22], and human copper, zinc superoxide dismutase (SOD1) pathogenic mutants [18], [23], [24] have the tendency to form fibril deposits in a variety of tissues and they are associated with Alzheimer disease, prion disease, and ALS, respectively, while the rabbit PrP [13], [25], [26] and hen egg white lysozyme [27] do not readily form fibrils and are unlikely to cause neurodegenerative diseases. The gene discussed is PRNP; the disease is Alzheimer disease.