PRNP and human prion disease: These conformational disorders or protein misfolding diseases include Alzheimer's disease (AD) with extracellular plaques of amyloid-β protein (Aβ) and tangles of hyperphosphorylated tau protein in the cytoplasm of neurons; Parkinson's disease (PD) where the cytoplasm of neurons in the substantia nigra contains aggregates called Lewy bodies composed principally of the protein α-synuclein (α-syn); Huntington's disease; Amyotrophic Lateral Sclerosis; and transmissible spongiform encephalopathy characterized by an accumulation of aggregates of the prion protein (PrP) in the brain (Soto, 2003).