Typhoid Fever Protection Linked to Cystic Fibrosis Gene

Scientists say they may have discovered the reason cystic fibrosis is so common: typhoid fever.

Cystic fibrosis affects about 30,000 children and young adults in the United States. It occurs when a person inherits two defective copies of a gene called CFTR. A person who inherits only one bad copy isn’t affected.

About 12 million Americans carry a single defective copy of the gene. To remain that common, a potentially lethal gene must provide some kind of advantage to such carriers.

In 1994, researchers published evidence that a single bad copy of CFTR might give protection against cholera. In the May 7 issue of the journal Nature, scientists from Brigham and Women’s Hospital in Boston and elsewhere make a case for protection against typhoid fever.

They found that the typhoid fever germ uses the protein made by normal CFTR to infect gastrointestinal cells. Since fewer copies of that protein are made when one of the CFTR gene copies is defective, people with one bad gene copy may be less susceptible to typhoid fever.