The Molecular Biology Of Cystic Fibrosis Introduction to Cystic Fibrosis Cystic Fibrosis (CF) is the most common lethal genetic disease of Caucasians, which causes certain glands to malfunction. In CF, mucous glands produce a thick, sticky mucus which interferes with breathing and digestion. Mucus clogs passages in lungs and airways, causing breathing difficulty, chronic coughing, and sometimes heart failure. Mucus also blocks ducts in the pancreas, preventing digestive enzymes from reaching the intestines, and it may also clog the liver and digestive tract (CF Foundation 2). Today, about 30,000 people