A Disease For Hannibal Lector
I hate the term 'mad-cow' disease since it is more fear-inducing than helpful. But the other terms, such as bovine spongiform encephalopathy (BSE) or variant Creutzfeldt-Jakob disorder (vCJD), are not much more useful. It is a horribly fascinating disease, one that requires us to use our best tools to understand.
A BAD Protein
The etiology of this disease is very complex and is unlike any other disease. The causative agent is not a virus and actually has no DNA at all. It is unable to replicate in the normal sense. It is a protein, PnP, that causes other molecules of PnP in the brain to misfold, rendering them inactive and setting up a chain reaction where misfolded PnP proteins create more misfolded copies of themselves. This continues until the patient's mental process deteriorate totally.
Brains Are Bad
What very few of the articles really mention is that you have to come in contact with the nervous tissue of infected cattle, the brains, for example, in order to have any chance of being infected at all. I first ran across these illnesses while researching an undergraduate paper. I wrote about kuru, a disease that attacked cannibals in New Guinea, who ate the brains of their fellows. Muscle tissue, the normal steak we eat, is not a problem as it does not appear to contain the causative agent. The proteins that cause BSE or vCJD are located in the brain, do their damage in the brain and are transmitted by nervous system material.
Genes May Play A Part
But it may be more complex than that. In the outbreak in England, millions of people could have been exposed but only about 150 or so succumbed. There could be a genetic reason for this. The normal human protein, the one that is malfolded by the beef form, is found in two variants, differing by a single amino acid at position 129. It can be either a Valine or a Methionine. Since everyone carries two copies of the gene for this protein, the distributions of these forms in the population are 40% Met/Met, 50% Met/Val and 10% Val/Val, although this distribution can vary among populations. Interestingly, all 105 people from Great Britain who were tested, as well as one person in this country, were Met/Met, possessing only the Met form of the protein. If you want, you can find out which form of the gene you possess, although I would be very amazed to see this being the only determinant.
Memories, Light The Corners Of My Mind
We still do not know enough about the causes of vCJD, nor its progression in different populations. However, there are good animal models that are opening up whole areas of research, not only into vCJD but Alzheimer's and even memory itself. Carl discusses recent, very exciting work that may explain the particularly insidious nature of this illness, as well as elucidate how we remember things. (12/26/2003 7:52:13 PM)
Living Code - corante.com |
