Prions–the name comes from “proteinaceous infectious particle”–were big news in the 1980s, when it became clear that these proteins caused disease. But more than 30 years after they were discovered, we’re still figuring them out.

On this day in 1997, American biologist Stanley B. Prusiner received the Nobel Prize in medicine for his discovery of prions, “an entirely new genre of disease-causing agents,” in the words of the Nobel committee. But even though Prusiner’s work started in 1972, by 2017 we still only sort of understand prions.
You’ve probably heard of these infectious proteins in the context of brain diseases like mad cow disease (technical name: bovine spongiform encephalopathy). Humans can also get prion diseases, such as Creutzfeldt-Jacob disease and the rare Kuru, which was transmitted by the Fore people’s custom of eating their deceased as part of funerary rituals. These diseases, which are collectively known as transmissible spongiform encephalopathies, are only the best-understood part of the prion picture.
“Prions are distorted versions of normal proteins found in human and animal brain and other tissues,” explains Colorado State University’s Prion Research Center. “These distorted (‘misfolded’) proteins damage brain cells, leading to fatal dementias akin to human Alzheimer’s and Parkinson’s diseases.”
When normal proteins in your brain–for some reason that’s not fully understood–misfold, “they turn into contagious pathogens that recruit any other prions they come into contact with, grouping together in clumps that damage other cells and eventually cause the brain itself to break down,” writes Fiona MacDonald for ScienceAlert.
“...Technically speaking, proteins shouldn't be able to infect other proteins–they're not alive, after all–and scientists have never really been able to explain the behaviour of prions–hence their reputation as the weirdest molecules ever,”  she writes.
We’re still trying to figure out how normal proteins fold into prions and what causes them to do so, although there have been a number of advances in recent years. Among them, Alzheimer’s and Parkinson’s have recently been linked to prions. Scientists have suggested that these brain diseases are caused by similar protein folding and it has been suggested that they should be called “prionoid” diseases–similiar to TSEs, but not transmissible (that we know of.)
Today the study of prions is a fascinating branch of medicine, but the fact that someone found prions at all is pretty amazing. When Prusiner started work on them, it had been established that Creutzfeldt-Jakob, kuru and a sheep disease called scrapie could be transmitted by infected brains, but nobody knew what caused it. It took ten years for him to isolate a single protein that seemed to be the culprit; then it took even longer to achieve any kind of scientific consensus. Prusiner is now the director of the Institute for Neurogenerative Diseases at the University of California, San Francisco. He has continued to work on prion diseases.