WASHINGTON, Oct. 6 -- The most common fatal genetic disease of Caucasians may be around today because the carriers of the defective gene are resistant to the ravages of cholera. Using a mouse model, researchers from the University of North Carolina in Chapel Hill report in this week's issue of the journal Science that mice who were carriers of the cystic fibrosis gene were not as severely affected by cholera as normal mice. The finding could eventually lead to a treatment for cholera in humans. 'Cystic fibrosis is the most common fatal genetic disorder of the Caucasian population -- affecting one out of every 25 Caucasians. There must be some reason why the number of carriers is so high,' said Sherif Gabriel, membrane physiologist at the University of North Carolina. 'This study gives us a direct correlation between the presence of cystic fibrosis carriers and cholera resistance.' Cystic fibrosis is a genetic disease affecting predominantly Caucasians that causes abnormally sticky mucus secretions which lead to intestinal obstructions, lung disease and early death. Scientists first began suspecting the cholera link when they found that cystic fibrosis patients lack a channel that allows fluids exit cells in the airways and the intestine. Cholera kills patients by creating a toxin that permanently opening these channels in the intestine causing death by diarrhea. 'The situation with cystic fibrosis is most similar to sickle cell anemia where the carriers of the defect are resistant to malaria,' said Gabriel. Like sickle cell anemia, a person who suffers from cystic fibrosis must have inherited a defective copy from each parent.
People who inherit only one copy of the defective gene -- carriers -- do not have symptoms of cystic fibrosis. The North Carolina scientists created cystic fibrosis mice, who had both copies of the gene for the disease -- CFTR, and carrier mice, that had one copy. The mice with both copies did not create any of the channels. The carrier mice made half as many channels as normal mice. When the scientists exposed the mice to six hours of cholera toxin, the carrier mice lost half as much fluid and had half as much diarrhea as the normal mice. 'We can only extrapolate to human population,' said Gabriel. 'But, the supposition is that humans would have a similar 50 percent response. ' People who get less diarrhea would have a much greater chance of surviving an infection with cholera, Gabriel said. 'I believe that effect -- we see it ourselves, although it's not so pronounced,' said transport physiologist Lane Clark of the University of Missouri. 'It promotes the idea that CFTR would make a logical target for cholera therapies.' Currently, the only treatment for cholera is massive amounts of intravenous fluids which are hard to obtain in the countries are most often affected by cholera. However, Clark cautions that cholera causes diarrhea by more than a single mechanism and those routes need further investigation.