Prions cause a variety of CNS illnesses, such as Creutzfeldt–Jakob disease. In this British kindred, a prion-associated process was associated with chronic diarrhea and autonomic dysfunction, a finding that extends the known disorders caused by these aberrant proteins. The prion diseases are transmissible, fatal, neurodegenerative disorders that may be inherited or acquired or that may occur spontaneously as sporadic Creutzfeldt–Jakob disease. 1 The transmissible agent, or prion, is thought to comprise misfolded and aggregated forms of the normal cell-surface prion protein. Prion propagation is thought to occur by means of seeded protein polymerization, a process involving the binding and templated misfolding of normal cellular prion protein. Similar processes are increasingly recognized as relevant to other, more common neurodegenerative diseases. In prion and other neurodegenerative disorders, the aggregates of misfolded protein in the central nervous system are highly heterogeneous, occurring . . .