Cystic Fibrosis

Causes and Effects of CF
Symptoms of CF Photo

In cystic fibrosis (SISS-tick fy-BROH-sis), or CF, an imbalance of salt causes the lungs to fill with a thick, sticky mucus. The mucus interferes with breathing and encourages growth of bacteria. CF may also affect other organs, including the digestive system and the reproductive system.

CF is a genetic disease caused by a mutation in the body's DNA -- and because children can inherit this mutation from their parents. CF affects about 1 in 3,500 births in the U.S. Many more people are symptomless carriers of the gene -- as many as 1 in 20 Americans. CF is far more prevalent in Caucasian-Americans, affecting 1 in 2,000 to 3,000 births. It is less common in African-Americans (1 in 15,000 to 17,000 births) and Asian-Americans (1 in 31,000 to 100,000 births).

If a carrier of CF has a child with a person without the mutation, that child may be a carrier, but will not have the disease. Children can only get the disease when both parents are carriers, or one has CF.

Treatment for CF has improved enormously. In the 1960s, life expectancy of children with CF was less than 8 years. Today 50 percent of CF sufferers are living into their late 30s or longer, some even into and past their 50s.

It's also important to understand that, while a faulty gene causes CF, other factors can make the disease better or worse. People with the same CF mutation may have very different symptoms and severity of symptoms. Even brothers and sisters born with the same faulty gene can have different symptoms1.

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Causes and Effects of CF

A mutation in the gene that produces the cystic fibrosis transmembrane conductance regulator, or CFTR, causes CF. One particular mutation, called delta F508, causes about 70 percent of CF cases. A number of other mutations in CFTR cause the remaining 30 percent. Many CF mutations have not yet been discovered.

The CFTR protein helps chloride ions -- half of the familiar sodium chloride, or table salt -- exit the body's cells. CF mutations cause too much chloride to build up in the cells. This, in turn, causes the cells to fill up with sodium. The result is too much salt inside the cells, which take up more water, just as a saltshaker will absorb water on a humid day.

By robbing the airway passages of water, lung cells affected by CFTR mutations make the mucus that normally protects those passages far too thick and sticky. This thick mucus can clog the airways, making it more difficult to breathe. It also encourages the growth of dangerous bacteria, particularly Pseudomonas aeruginosa (SUE-doh-moh-nus air-uh-jin-OH-sa), a type of pneumonia bacterium2.

To make matters worse, white blood cells that come to the lung to fight off the bacteria die there. Their DNA, which is sticky itself, tends to thicken the mucus even more.

While CF is best known for its devastating effects on the lungs, the disease may also affect other organs. Often mucus blocks the passageways of the pancreas, an organ in the abdomen that produces digestive enzymes. These blockages prevent the digestive enzymes getting from the pancreas to the stomach and intestines, leading to malnutrition and inability to gain weight.

Women with CF often have irregular menses (periods), and thick mucus can form in their reproductive tract, making it difficult for them to get pregnant. A woman with CF can become pregnant with reasonable safety if she has good lung function. But the risk of her partner being an unidentified CF carrier means that 1 in 50 children born to mothers with CF will have the disease. Men with CF are infertile 95 percent of the time, because of incomplete development of the vas deferens. These tubes normally carry sperm from the testicles to the penis.

More rarely, CF mucus may block the bile ducts in the liver, causing liver disease. Another possible effect of CF is meconium ileus (meh-KOH-nee-um ILL-ee-us), a condition in which a baby with CF has an obstruction of the intestines at birth3.

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Symptoms of CF

One of the earliest signs of CF is too much salt in the sweat. Centuries ago, midwives would taste a newborn baby's skin -- if it tasted salty, they knew its chances of surviving childhood would be slim. Interestingly enough, salt levels in the sweat form the basis of modern CF diagnosis as well.

More dangerous symptoms of CF are:

  • nagging cough producing thick yellow, green, or brown mucus, particularly in the morning
  • wheezing or "crackles" in the lungs - sounds like rice cereal being crushed
  • bulky stools
  • repeated, persistent infections, particularly pneumonia
  • weight loss, despite a big appetite and generous food intake
  • digestive and reproductive problems, including a delay of one to four years of puberty
  • respiratory failure - the biggest cause of death in CF

Later in the disease, other signs of CF include:

  • barrel-shaped chest
  • clubbing - enlargement and deformation of the fingers and toes
  • sinusitis - sinus inflammation
  • pneumothorax (new-moh-THOR-ax) - potentially deadly breaks in the lung tissue that allow the space around the lungs in the chest to fill with air
  • hemoptysis - spitting blood
  • cor pulmonale - enlargement of the right side of the heart
  • rectal prolapse - tissues in the rectum come partway out of the body
  • liver disease
  • pancreas inflammation
  • gallstones

If you experience any of the above symptoms, see your health care professional immediately for an accurate diagnosis and treatment to relieve your symptoms.

References

1. Statistics from the American Association for Respiratory Care and the Cystic Fibrosis Foundation.

2. Statistics from Kerem E et al. (1990) "The relation between genotype and phenotype in cystic fibrosis--analysis of the most common mutation (delta F508)," The New England Journal of Medicine 323(22):1517-1522.

3. Statistics from the Boomer Esiason Foundation and the American Association for Respiratory Care.

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