Prion

Prion is short for "proteinaceous infectious particle." Dr. Stanley B. Prusiner gave the name "prion" to the substance he and his colleagues isolated in 1982 from diseased hamster brains, which by itself could transmit the neurological disease scrapie (first identified in sheep) to other animals. In the 1960s, two British scientists, radiation biologist Tikvah Alper and physicist J. S. Griffith, had laid the groundwork for the prion theory by suggesting that "an infectious agent that lacked nucleic acid could cause disease" and that "a protein ... could somehow misfold and then catalyze other proteins to do so."

The prion theory was controversial at first, since other known infectious agents - bacteria, viruses, parasites and fungi - contain their own genetic information (DNA or RNA). Prions, by contrast, are just proteins, with no genetic material. Without the genetic information that allows everything from viruses to human cells to replicate, scientists wondered, how could prions multiply and cause disease?

Prusiner showed that the gene for the prion protein was present in the genome of a wide range of mammals. Then why didn't all mammals have prion-related diseases? The prion protein could exist in one of two different forms. "In analogy to a well known literary work, the normal [prion protein] can be compared to the friendly Dr. Jekyll and the disease causing [altered prion protein] to the dangerous Mr. Hyde, the same entity but in two different manifestations."

Since the switch from normal to infectious protein form is belived to cause prion-related neurological wasting diseases in several different species, prions have "been defined as 'small proteinaceous infectious particles which resist inactivation by procedures that modify nucleic acids.' Prion diseases are often called spongiform encephalopathies because of the post mortem appearance of the brain with large vacuoles in the cortex and cerebellum. Probably most mammalian species develop these diseases."

Examples of animal prion diseases include:
 * Scrapie: Infection in genetically susceptible sheep
 * TME (transmissible mink encephalopathy): Infection with prions from sheep or cattle
 * CWD (chronic wasting disease) found in muledeer and elk
 * BSE (bovine spongiform encephalopathy): Infection with prion-contaminated MBM found in cows
 * Feline spongiform encephalopathy: Infection with prion-contaminated MBM found in cats

Examples of human prion diseases include:
 * CJD (Creutzfeld-Jacob Disease)
 * GSS (Gerstmann-Straussler-Scheinker syndrome): Germline mutations in PrP gene
 * FFI (Fatal familial Insomnia)
 * Kuru: Infection through ritualistic cannibalism
 * Alpers Syndrome

"The diseases are characterised by loss of motor control, dementia, paralysis, wasting and eventually death, typically following pneumonia. Fatal Familial Insomnia presents with an untreatable insomnia and dysautonomia. Details of pathogenesis are largely unknown.

"Visible end results at post-mortem are non-inflammatory lesions, vacuoles, amyloid protein deposits and astrogliosis."

In 1997, the Nobel Prize in Physiology or Medicine was awarded to Dr. Stanley B. Prusiner "for his pioneering discovery of an entirely new genre of disease-causing agents and the elucidation of the underlying priciples of their mode of action." As the Nobel Assembly explained: "Prions exist normally as innocuous cellular proteins, however, prions possess an innate capacity to convert their structures into highly stabile conformations that ultimately result in the formation of harmful particles, the causative agents of several deadly brain diseases of the dementia type in humans and animals. Prion diseases may be inherited, laterally transmitted, or occur spontaneously."

Other SourceWatch Resources

 * Mad cow disease - contains an extensive list of prion/ mad cow-related SourceWatch articles
 * Transmissible Spongiform Encephalopathies
 * Mad Cow Canada
 * Mad Cow USA