Thursday, September 07, 2006

Cystic fibrosis vs tuberculosis?

And for my sixth post of the day, since I'm in prolific form: another New Scientist article.

This time, I'm posting about a possible explanation for the persistence of Cystic fibrosis. (This is obviously a condition on my mind at the moment, although I don't think T has it).

Logically you might expect CF to die out or already to have died out, since in the past, commonly, sufferers would have shuffled off before reaching an age at which they would be likely to become parents. Therefore it might be anticipated that such a gene would disappear. However, CF has been recorded a very long way back in human history, so it may be that it gives some advantage when a person carries one copy of the gene.

The genetic condition, Sickle Cell anaemia provides a model for this: carrying one copy of the Sickle Cell gene protects against malaria and therefore gives an advantage to carriers, (presumably outweighing the disadvantage of losing people with two copies of the gene).

There is some research to suggest that CF confers some protection against Tuberculosis, which would explain why carrying one CF gene would be an advantage and hence why the mutation persists.

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