Cystic fibrosis (CF) is a genetic disease that affects the body’s exocrine
glands, causing them to secrete an excess of mucus and other secretions.
Exocrine glands are responsible for secreting substances onto body surfaces both
internally (such as in the lungs) and externally (such as on the skin). Examples
of these secretions include sweat, tears, digestive juices and mucus.
Every year, 1,000 children with CF are born in the United States. CF affects
one in 3,000 Caucasian babies, making CF one of the most common genetic diseases
among Caucasians. Among African-Americans, the risk is much lower (one in
13,000) and among Asian Americans, the disease is very rare (one in 50,000). CF
affects males and females equally.
Overall, there are 30,000 Americans with CF, and an estimated 8 million
people carry one copy of the defective gene that causes the disease. These
carriers do not have symptoms of CF, because a person must inherit two defective
gene copies, one from each parent, to develop the disease. However, each child
of two CF carriers has a one in four chance of being born with CF. Genetic
testing is now available to identify couples at risk for having children with
CF.
Symptoms of CF
Normal mucus forms a gel-like barrier that plays an important role in
protecting the cells lining the inside surfaces of these tissues. In the lungs,
mucus also transports dust and other particles out of the airways and helps to
prevent infection. For patients with CF, the chemical properties of mucus become
altered; instead of protecting tissues from harm, the abnormal mucus obstructs
the ducts and airways, causing tissue damage.
The most characteristic symptom of CF is the excessive production of thick,
sticky mucus in the airways. Several factors may contribute to this mucus
abnormality. In CF, the cells lining the airways do not transport salt and water
normally, so mucus and other airway secretions may be depleted of water, thus
becoming abnormally thick.
There are also chemical changes in the mucus proteins. The mucus becomes so
thick that it clogs the airways and provides an environment in which bacteria
thrive. In response, white blood cells are recruited into the lungs to fight the
infection. These white blood cells die and release their genetic material,
sticky DNA, into the mucus. This DNA aggravates the already excessive stickiness
of the mucus, setting up a cycle of further airway obstruction, inflammation and
infection. To dislodge the mucus, CF patients cough frequently and require
time-consuming daily chest and back clapping and body positioning to drain lung
secretions.