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A new twist on prion disease

In 1997 Stanley Pruisner was awarded the Nobel Prize for physiology or medicine for his theory that a deviant form of a harmless protein could be an infectious agent, a transmitter of disease. Named prions (short for proteinaceous infectious particle) these misshapen proteins cause healthy proteins to misfold, fatally clumping together in the brain. Unlike other disease-causing agents where replicating molecule is presumed to be composed of nucleic acid, prions lack genetic material (DNA and RNA). Neurodegenerative prion diseases are often called spongiform encephalopathies because they leave the brain riddled with holes like a sponge. In animals, prion diseases include scrapie in sheep and bovine spongiform encephalopathy, commonly known as mad cow disease in cattle. In humans, diseases such as kuru and Creutzfeldt-Jakob disease (CJD) are also thought to be caused by prions. All the diseases are characterized by loss of motor control, dementia, paralysis, and ensuing death due to massive destruction of brain tissue.

Humans are thought to contract prion disease most commonly by eating prion-contaminated flesh. Kuru, a rare and fatal brain disorder, brought prion disease to the forefront. First described in the 1950s, kuru was most common among the Fore people of Papua New Guinea, who had a custom of eating the brains of their dead during funeral feasts. It is speculated that a tribe member developed CJD, his or her contaminated brain tissue was ingested, and the disease spread. Kuru reached epidemic levels in the 1960s, but the disease declined after the government discouraged the practice of cannibalism and now it has almost completely disappeared.

Inherited prion diseases are rare and passed through families. But it’s long been a puzzle why prions attack neurons more than other types of cells, and how they do their damage. In a new study, researchers propose that prions deplete a poorly understood protein that normally keeps nerve cells healthy. The theory still has a ways to go before it’s proven, but researchers are intrigued by this potential new twist on a mysterious disease.

The normal prion protein gene (PRNP) provides instructions for making a protein called the prion protein (PrP), which is active in the brain and several other tissues. Yet researchers don’t know exactly why but when prion misfolds, the results are disastrous.

Jennifer Couzin-Frankel. Science NOW. In: Daily News (adapted).

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Transmissible spongiform encephalopathies are a family of uncommon progressive neurodegenerative disorders that affect humans and are caused by a prion which typically infects cattle and is transmitted through infected meat.