IV. HOW PRIONS CAUSE DISEASES

Acquiring the disease

How are prion diseases acquired? Come cases of CJD and scrapie may be completely spontaneous. Prusiner speculates that wear and tear on a protein may cause it to transform into the rogue shape. ^{(Prusiner Prion 57)} This would be a rare occurrence.

In humans, some cases of CJD have been acquired through surgical instruments. When an instrument has been used on the brain of a person with CJD, it can be cleaned with ethanol and formaldehyde, left unused for a week, and still CJD may be transmitted to another person. ^{(Ricketts 3)} The chemicals normally disable bacteria and viruses, but seemed to have no effect on prions, the scrapie agent.

Is the scrapie agent DNA or protein? A series of experiments by Dr. Prusiner indicates that prions are protein.

There have also been those who acquired CJD through infected growth hormone. This hormone is extracted from the pituitary gland. In 1992, there had been 19 people who died from CJD infection acquired by this method.^{(Anderson 4)}

In all cases of TSE infection, enough scrapie protein must accumulate in the brain to start causing problems.^{(Prusiner Prion 55)} Once in the brain, the scrapie protein begins to multiply.

Replication Through Conformation

Several hypotheses have been presented regarding prion reproduction. The first proposition is that the protein is really a viral coat with DNA or RNA inside. Although this hypothesis is most conservative, it seems unlikely. All of the methods for disabling viruses are ineffective against prion diseases. The second idea is that the protein can rewrite the DNA of a cell. This seems outlandish, as "reverse translation" has never been seen. The third method, most plausible to Prusiner and a growing number of others, is that the shape of the protein may alter the genes or protein of the host cell, causing it to conform to the altered shape.^{(Prusiner Prions 58)}

From the information I've gathered, I lean toward the third explanation. It seems reasonable that a protein can cause another to alter its shape. For example, it's possible to get a solute concentrated in a supersaturated solution. It only takes a single seed crystal to change the whole mixture into a crystallized solid.^{(Ponte 130)} Is it impossible for a protein to "bend" others into a new shape? No. Usually the sheet is the more stable shape for proteins, so given enough prompting, the transformation can occur.

Distortion and death

Once significant amounts of malformed prions are in the brain, these PrP^Sc pieces tend to aggregate. In doing so, they stack on top of each other, forming rods. Scientist H. K. Narang found these rods in the brains of scrapie infected animals.^{(Prusiner Prions 59)} These rods distupt normal brain activity, and as more brain proteins are added, gaping holes are seen in the brain tissue. At this stage, the patient may experience loss of memory, paralysis and irrational behavior. The transformed tissue is no longer functional brain material. Eventually, the victim loses more and more ability until the brain ceases functioning and death results.

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