Cystic Fibrosis is carried through 250,000 base pairs of DNA. Within those pairs is the gene CFTR. A change in the gene, or mutation, is what causes Cystic Fibrosis.
This mutation causes the secretions in the body, like sweat, tears and mucus, to become thick, sticky and salty. They then coat the surfaces of tissues in the lungs, pancreas and reproductive tract.
Not only is Cystic Fibrosis the most common genetic disease in the Caucasian population, but it is one of the few diseases that natural selection has yet to eradicate.
The most common mutation is delta-F508 which appeared about 52,000 years ago. Xavier Estivill, a geneticist, says that because it has lasted so long there must be an advantage to having the disease. That advantage is protection against diarrhea-inducing bacteria like Salmonella, Cholera and E. coli.
Cystic Fibrosis, is dominant in people of a northern European background. A physiologist, Paul Quintin, thinks that it only survived in Europe because when epidemics of E. coli and other bacterias like it hit, everyone except the people with Cystic Fibrosis, and carriers of the disease died. Therefore only carriers of the disease were able to reproduce, thus spreading the gene throughout the northern European population.
