h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

The New Scientist reports that a blood test for BSE may be within reach, because there is a marker for the disease that is detectable in blood cells or bone marrow well before any symptoms appear.

The article asserts that abnormal prion proteins are chemically identical to their healthy counterparts. Surely if two things are chemically identical but take up different shapes it must be due to an external factor. Further, it is said that there are differences in the genes switched on in the brains of infected animals, but these are detectable only in the final stages of the disease. If different genes are switched on, that must be due to an external factor in the cell environment, whether it's another gene's operation (triggered by...?) or some other change in the chemistry.

Researchers from the Roslin Institute near Edinburgh know that prions multiply in organs such as the spleen and tonsils long before they reach the brain. Are spleen and tonsils "specified offal", to be removed before meat can enter the commercial food chain?

And how do prions reach the brain? Via the blood supply, obviously? Which means they could be present in any tissue of the body.

This research has discovered a single gene, which was "turned down" in scrapie-infected mice. It makes a protein called erythroid differentiation-related factor (EDRF), and the same pattern shows up in sheep and cows. The function of EDRF is not yet known, but the Roslin researchers feel its detection will help scientists understand BSE.

I smell a cause and effect question here. The marker for BSE might be a gene which is switched off or turned down in the spleen of an infected animal. But what turns it down? A protein which is chemically identical to its healthy form? The environment which switches the shape of the protein? Or is the non-operation of the EDRF gene part of the causal chain which switches the protein shape?