Prion disease

Prion diseases are unusual because they can be genetic, infectious, or idiopathic. Genetic (inherited) prion diseases result from rare mutations in PRNP, the gene that codes for PrP. Unlike conventional infectious diseases, which are spread by agents with a DNA or RNA genome (such as viruses or bacteria), prion diseases are transmitted by prions, the active material of which is solely abnormal PrP. Infection can occur when the organism is exposed to prions through consuming contaminated food or via iatrogenic means (such as treatment with biological material that is accidentally contaminated with prions). The variant form of Creutzfeldt–Jakob disease in humans is caused by exposure to BSE prions. While prion diseases spread relatively easily among animals, transmission to humans is very rare. Most people who develop prion disease were never exposed to an infected animal or contaminated material; in the majority of cases, there is no identifiable cause. Sporadic prion diseases occur in the absence of a mutation in the gene for PrP or a source of infection.