Sunday, November 22, 2009

Mad cows and cannibals...

A new article in the New England Journal of Medicine (1) shows the recent evolution of a mutation in a population of people in Papua, New Guinea that is protective against the degenerative brain disorder known as kuru.  Kuru is a prion disease which is a disease (specifically a transmissable spongiform encephalopathy) that is caused by proteins that act like viruses.  That is, the proteins are transmissable (i.e. contageous) and though they don't replicate themselves like viruses or bacteria would, they somehow seem to be able to cause all the other similar proteins in their host/victim to misfold in a way that then causes the build up of neurodegenerative plaques which are often fatal.  Mostly, these diseases are transmitted through the eating of meat, as in Mad cow disease (which is known as Bovine spongiform encephalopathy, or BSE, in animals, the mutated form of which, in humans, is called Creutzfeld-Jakob Disease, or CJD).  Kuru is a lot like CJD or BSE, and was passed on in the tribes of Papua New Guinea by the practice of the eating of dead relatives in memorial services.  Though this practice was ended in the 1950s, the populations of people in this area experienced kuru epidemics that shaped the evolution of their tribes.  One tribe in particular seems to have a high prevalence of a mutation (G127V) that protects them against kuru.  Since kuru is fatal (killing many women and children in these populations), it makes sense that this mutation would be selected for, and its prevalence would increase in the population.  This is particularly exciting because, not only is this a great example of evolution in action (in humans no less!), but as of yet, there are no treatments for CJD or kuru, and these diseases are often, almost always, fatal.  The discovery of this mutation in a population that has evolved a resistance to a prion disease will offer insights into how we might go about protecting the brains of those who haven't evolved a resistance to prion diseases, and hopefully save some lives.

1. Mead, Simon, Whitfield, Jerome, Poulter, Mark, Shah, Paresh, Uphill, James, Campbell, Tracy, Al-Dujaily, Huda, Hummerich, Holger, Beck, Jon, Mein, Charles A., Verzilli, Claudio, Whittaker, John, Alpers, Michael P., Collinge, John. A Novel Protective Prion Protein Variant that Colocalizes with Kuru Exposure. New England Journal of Medicine, 2009; 361 (21): 2056 DOI: 10.1056/NEJMoa0809716

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