It’s PREE-on, Not PRI-on
Dr. Stanley Prusiner, a Nobel laureate, is also director of the Institute for Neuro-degenerative Diseases, and professor of neurology and biochemistry at UCSF. He focused on prion biology and variant CJD (Creutzfeldt-Jakob Disease), as well as therapeutic approaches to these diseases. For many years, people thought that diseases such as CJD, and fatal insomnia, scrapie of sheep, BSE of cows and chronic wasting disease were caused by slow viruses, or delayed-acting viruses. The reason? Scrapie, the prototypic disease, is a transmissible disease. The agent is small and filterable. There’s a rise in the scrapie agent that precedes disease, and there are many strains of scrapie agent that produce different patterns of disease.
Dr. Prusiner proceeded to do intense research over the years to uncover information about this enigma. The result of those studies was that every procedure that was used, after about a hundred-fold purification, destroyed proteins and infectivity. Every procedure that modified nucleic acids did nothing to the infectivity. Dr. Prusiner felt that labeling this an unconventional virus — or slow, or delayed-acting virus — was not a good idea, and a new term was needed to distinguish this unprecedented pathogen-causing scrapie from both viruses and viroids. So Dr. Prusiner invented the term “prions.” A composite word, derived from “protein” and
“infection,” it’s pronounced PREE-on, not PRI-on. Thanks to Dr. Prusiner’s research, we now know that prions are totally different from all other infectious pathogens. All pathogens — viruses, viroids, bacteria, fungi and parasites — replicate with an RNA or DNA genome directing the synthesis of progeny. Prions contain no nucleic acid, and the protein of the prion, PRP scrapie, directs the synthesis
of progeny.
A Variant on CJD
After an extensive discussion about the investigations and studies on the subject of prions and diseases, Dr. Prusiner shared valuable information on CJD and BSE. He said, “Turning to the human diseases, the sporadic form of Creutzfeldt-Jakob Disease is found at 1 per million across the earth. Sporadic, of course, means that there’s no relationship – in terms of geography, of family members, of people nearby, or of any particular part of the world. That’s the sporadic form – and it represents the majority of cases. And there’s somewhere between 3,000 and 6,000 cases of CJD on the planet in any year. About 10 to 15% of all cases are familial — Shanker disease, familial CJD, and fatal familial insomnia. These are autosomal-dominant diseases. And less than 1% are infectious — but these are the ones that make the newspaper all the time. Sporadic CJD is age dependent and seen mostly in older people. Now, over 100 cases of new-variant CJD — primarily in teenagers and young adults — have been recorded.
"New-variant CJD was first reported in 1996 by Bob Will and his colleagues in Edinburgh and it has been restricted to the U.K., except for three cases in France and one in Ireland. Data, using transgenic mice, argue that new-variant CJD is due to the ingestion of prions from cattle.”
BSE: Truly a World Threat
Dr. Prusiner went on to talk about BSE. “There’s a 3,200-page report, commissioned by Tony Blair, when he came into office. In this report, they come to the conclusion that BSE started with a mutation in the PRP gene of a single cow in southern England. But I think most scientists favor the idea that it began with scrapie in sheep, and then went into cows. These prions have spread into the food chain for humans, and we now have the disease. The transmission of prions from mad cows to people in Europe has really created a public health crisis and it threatens the food supply and blood supplies worldwide. And, in this case, it causes death, and we have no antibiotics.”
The studies by Dr. Prusiner and others made significant discoveries. According to Dr. Prusiner, “We now know that PRP scrapie is not granite, but it’s more like limestone, and it turns over. It can be washed away with a halftime of 30 hours. So these diseases (CJD, BSE, etc.) are kinetic races between the clearance of PRP scrapie and the formation of PRP scrapie. And that changes how we think about this therapeutically. I used to think that the molecule just accumulated as a rock, and there was no way to clear it out. But these studies show you that’s not true.”
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