In recent years, it has become increasingly clear that misfolded proteins can cause damage not just in the cell where they originally misfold. Since scientists first discovered that prion proteins can be infectious, traveling from cell to cell and even organism to organism to organism – causing Scrapie in sheep, mad cow disease in cows and Creutzfeldt-Jacob disease in humans – the list of misfolded proteins that can spread reads like a who's who of neurodegenerative disease: Alzheimer's and Parkinson's disease, amyotrophic lateral sclerosis (ALS) and frontotemporal lobe dementia.