Cystic fibrosis (CF) is caused by a defective gene which causes the body to produce abnormally thick and sticky fluid, called mucus. This mucus builds up in the breathing passages of the lungs and in the pancreas, the organ that helps to break down and absorb food.

Millions of Americans carry the defective CF gene, but do not have any symptoms. That's because a person with CF must inherit two defective CF genes -- one from each parent. An estimated 1 in 29 Caucasian Americans have the CF gene. The disease is the most common, deadly, inherited disorder affecting Caucasians in the United States. It's more common among those of Northern or Central European descent.

Causes