Certain types of cellular proteins have the property that when in an abnormal configuration, they will induce the corresponding normal protein to assume the same abnormal configuration. These proteins can set up a chain reaction leading to the progressive accumulation of abnormally configured proteins. This process is generally analogous to the conversion of various soluble proteins to insoluble macromolecular structures, such as intermediate filaments, keratin, collagen, etc. The solubility of proteins is influenced by their overall shape, with globular proteins being more soluble than proteins with large beta-pleated sheets. In this latter configuration, proteins become amyloid in nature, a term referring to their staining characteristic. One such amyloid protein has been termed "prion" for "proteinaceous infectious particles". It was suggested that the abnormal (amyloid) protein was itself infectious and able to induce progressive disease when transferred between individuals. This "prion" hypothesis was supported by the observation of disease occurring in humans and animals that inherited an altered prion protein that had an enhanced tendency to "spontaneously" generate or transform into the amyloid configured prion protein (PrP), thereby begining the process. Subsequently, even if genetically normal individuals became exposed to the prion proteins, e.g. by ingestion with food, disease can develop, along with the potential for further transmission. The role of stealth viruses as the true underlying cause of prion diseases is under investigation at CCID.
Prion diseases include scrapie in sheep and in goats, bovine spongiform encephalopathy or mad cow disease in cattle, feline spongiform encephalopathy in cats and Creutzfeldt-Jakob disease, kuru, Gerstmann-Straussler-Scheinker syndrome and fatal familial insomnia in humans.
Prion diseases have also been identified in mink, mule, deer and elk. Of major concern is that disease can be spread accross species. For example, the emergence of mad cow disease has been traced to the use of sheep-derived tissue as a food supplement to feed cows. The cow disease appears to have been further transmitted to humans. Human transmission has also occurred due to contaminated growth hormone prepared from human pituitary glands and from contaminated corneal transplants and surgical instruments.
An assay based on the detection of a neuronal protein 14-3-3 in cerebrospinal fluid of patients with Creutzfeldt-Jakob disease was recently described by Dr. Michael Harrington and his colleagues in the New England Journal of Medicine. CCID has been licensed by the California Institute of Technology to perform the 14-3-3 assay.(see Clinical Laboratory).
