A common molecular hallmark of several neurodegenerative diseases is theaggregation of infectious isoforms or misfolded proteins, such as the prionprotein (PrPC) with its conformational isoform PrPSC inprion disease, β-amyloid plagues in Alzheimer’s disease (AD), andα-synuclein fibrils in Parkinson’s disease (PD). The gene discussed is PRNP; the disease is Alzheimer disease.