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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).

In relation to the text above, judge the items from 11 through 20.

Some accounts of the pathogenic prion disease seem to bear out a basic tenet that any agent that increases in titer must involve replication of nucleic acid.