CYSTIC FIBROSIS
DEFINITION
Cystic fibrosis (CF) is a hereditary disease that affects the lungs, digestive system, sweat glands, and male reproductive organs.
DESCRIPTION
Cystic fibrosis affects the body's ability to move salts and water in and out of cells. This defect causes the lungs and pancreas to secrete (release) thick mucus. The mucus blocks various passageways in the body, preventing them from functioning normally.
CF affects about thirty thousand children and young adults in the United States. About three thousand babies are born with the condition each year in this country. The disorder primarily affects people of white, northern European ancestry. Nonwhite populations have a much lower rate of cystic fibrosis.
There is no cure for CF. However, symptoms of the disease can be treated. Proper care and treatment can greatly improve the lifestyle of a person with the condition. For example, prompt attention to digestive and respiratory (breathing) problems has extended the lives of many patients. At one time, children with CF usually died by the age of two years. Today, many people with CF live beyond the age of thirty.
CAUSES
Cystic fibrosis is a genetic disorder. Genes are the chemical units in every cell that tell cells what functions they should perform and what substances they should manufacture in order to operate normally. Genes can be damaged in a variety of ways. For example, certain chemicals contained in the foods we eat can damage a gene. When that happens, the gene is no longer able to give correct instructions to a cell and the cell does not have the information it needs to produce all the substances it requires to stay healthy. When this happens, a medical problem develops in some part of the body.
Genes are passed down from one generation to the next. A person whose body contains a damaged gene may pass that gene to his or her children. The children may develop the same genetic disorder that the parent had.
Cystic fibrosis is caused by a defect in the gene known as the CFTR gene. The abbreviation CFTR stands for cystic fibrosis transmembrane conductance regulator. The CFTR gene carries instructions for the production of mucus in cells. Mucus is a mixture of water, salts, sugars, and proteins. Its job is to cleanse, lubricate, and protect passageways in the body.
Cells that contain a defective CFTR gene have lost the ability to make mucus properly. The mucus they produce has too little water in it and is thick and syrupy. This mucus does not improve the functioning of passageways in the body. Instead, it causes them to become clogged. Substances that are supposed to pass through passageways, such as air and blood, are unable to flow normally and the symptoms of CF begin to appear.
Cystic Fibrosis: Words to Know
- CFTR:
- An abbreviation for cystic fibrosis transmembrane conductance regulator, a chemical that controls the amount of water in mucus.
- Genes:
- Chemical units that carry the information that tells cells what functions to perform.
- Genetic disorder:
- A medical condition caused when a person has one or more defective genes.
- Meconium ileus:
- A condition that appears in newborn babies with cystic fibrosis, in which the baby's first bowel movement is abnormally dark, thick, and sticky.
- Mucolytic:
- Any type of medication that breaks up mucus and makes it flow more easily.
- Mucus:
- A mixture of water, salts, sugars, and proteins, which has the job of cleansing, lubricating, and protecting passageways in the body.
- Pancreas:
- An organ near the stomach that secretes enzymes needed to digest food.
- Screening:
- Using a test or group of tests to look for some specific medical disorder.
SYMPTOMS
The most severe symptoms of CF occur in two body systems: the gastrointestinal (digestive) system and the respiratory tract. CF also affects the sweat glands and the male reproductive organs.
Gastrointestinal System
One of the first symptoms of CF in young babies is meconium ileus (pronounced muh-KO-nee-um ILL-ee-us). Meconium ileus is characterized by a thick, sticky, dark stool. The stool has these features because the mucus it contains is thicker than normal. Meconium ileus is also marked by abdominal swelling and vomiting. The presence of meconium ileus is a strong indication of cystic fibrosis.
A defective CFTR gene also causes damage to the pancreas. The pancreas provides enzymes needed in the digestion of food. Enzymes are chemicals present in all cells that make possible hundreds of different chemical reactions. If these enzymes are not present, necessary chemical reactions may not occur. In the case of CF, the pancreas makes a very thick type of mucus. The mucus blocks openings in the pancreas and enzymes produced by the pancreas cannot get out of the organ. Food passes through the stomach without being digested.
Failure to digest food can produce a number of symptoms. The feces may become bulky, oily, and foul-smelling. The patient may constantly be hungry because food that is eaten is not digested. The patient may not grow to normal size without the nutrients provided by food. Over time, other symptoms that may develop include malnutrition, anemia (see anemias entry), bloating, and loss of appetite.
Respiratory Tract
The most life-threatening symptoms of CF occur in the lungs. The job of the lungs is to take oxygen from the air and deliver it to blood. Blood then takes oxygen to the cells of the body, where it is used to make energy.
The mucus that lines the lungs has a number of functions. One function is to prevent infection of the lungs. The mucus captures bacteria, viruses, fungi, and other agents that might cause disease. It then passes these materials back out of the lungs and into the throat. From there, they can be coughed up or swallowed.
In patients with CF, the mucus in the lungs becomes much thicker. Disease-causing agents are still captured, but they cannot be passed back into the throat very easily. Instead, the thick mucus holds bacteria, viruses, and other organisms in the lining of the lungs. The longer these organisms remain there, the greater the chance they will cause an infection of the lungs.
The presence of organisms in the lungs causes the immune system to become active. The immune system is a network of organs, tissues, cells, and chemicals designed to protect the body against infection by foreign agents. The immune system sends specialized cells to fight the disease-causing organisms trapped in the patient's lungs. These cells cause the lungs to become inflamed and swollen. The inflammation and swelling may close down passageways in the lungs, making it difficult for air to pass in and out of the lungs.
The thick mucus that lines the lungs also makes it more difficult for air to pass through the lungs. Patients may find themselves gasping for breath in order to get enough air. They may also begin to develop the symptoms of emphysema (see emphysema entry).
Sweat Glands
A defective CFTR gene can also affect the formation of sweat. A person with cystic fibrosis has sweat that is much saltier than normal. This problem is usually not serious except during heavy exercise or hot weather. In such cases, patients with CF usually eat more salty foods to make up for the salt lost in their sweat.
Male Reproductive System
Abnormally thick mucus can block the vas deferens in males. The vas deferens are tubes through which sperm passes. If these tubes are blocked, males are not able to produce sperm and are, therefore, infertile (incapable of producing children).
DIAGNOSIS
A number of factors may suggest that a child be tested for cystic fibrosis. The presence of any of the described symptoms may lead to such tests. These symptoms include gastrointestinal or respiratory problems that do not disappear, and the presence of salty sweat. A baby born with meconium ileus will be tested before leaving the hospital. Some hospitals now require routine CF screening for newborn babies.
The easiest and most accurate test for CF is a sweat test. A sample of an individual's sweat is collected. The sample is then tested for salt content. If the salt content is 1.5 to 2 times greater than normal, the individual probably has CF.
Genetic testing can also be used to diagnose CF. A small blood or tissue sample is taken from the patient. The sample can then be analyzed to determine whether the individual's CFTR gene is normal or defective. The presence of a defective gene means that the person has cystic fibrosis.
Screening of newborn babies is done with a test known as the IRT test. This test measures the amount of a particular chemical in the blood known as immunoreactive trypsinogen (pronounced trip-SIN-uh-juhn). Babies with CF have a high level of this chemical.
TREATMENT
There is no cure for cystic fibrosis, but there are many types of treatment that can help patients live longer and more comfortable lives. Early diagnosis is an important element of treatment. With proper management, many people with CF engage in the full range of normal activities.
Nutrition
People with CF often do not receive full benefit from the foods they eat. They may need a high calorie diet with vitamin supplements. In addition, pancreatic enzyme pills are often recommended. The pills provide enzymes to the patient's digestive system that would normally come from a healthy pancreas.
Some people cannot absorb enough nutrients from foods even with special diets and enzyme pills. For these people, tube feeding is an option. A tube is inserted through the nose or through a hole made in the abdominal wall. Food can be supplied through the tube at any time of the day or night, allowing constant intake of high-quality nutrients. The feeding tube may be removed during the day, allowing the patient to eat meals normally.
Respiratory Health
The key to survival for many patients with CF is careful monitoring of the respiratory system. Lung function tests are done frequently. These tests measure the amount of air the person's lungs are able to take in. Sputum (spit) tests are done to find out what kinds of bacteria are present in the lung and how many there are. Chest X rays monitor any changes in the size and shape of the lungs.
An important element of good respiratory health is exercise. Exercise keeps the lungs healthy, active, and free of bacteria.
Clearing mucus from the lungs also helps protect against infection. Physical therapists have developed a number of techniques to help CF patients prevent mucus from collecting in the lungs. For example, a patient may lie on his or her stomach on a tilted surface with the head downward. An assistant then thumps on the patient's rib cage to help loosen mucus.
Drugs also can help maintain healthy lungs. For example, bronchodilators (pronounced brong-ko-die-LATE-urs) are substances that cause small air passages in the lungs to expand, allowing air to flow more freely. A group of drugs known as mucolytics (pronounced myu-kuh-LIH-tiks) also may be used. Mucolytics help loosen mucus and allow it to be expelled from the lungs more easily.
The use of antibiotics also may be necessary. Some doctors have their patients take antibiotics continuously to protect against lung infections. Other doctors use antibiotics only when an infection has actually developed.
In extreme cases, patients with CF may need oxygen therapy. Oxygen therapy is a procedure in which patients breathe air that is rich in oxygen. The higher oxygen content makes it easier for the body to get the oxygen it needs without working too hard.
Lung transplantation is a treatment of last resort. However, this form of treatment has its own set of problems. The drugs used during and after a
transplant operation cause severe problems of their own. One such problem is the weakening of the immune system.
On a long-term basis, the best hope for treating CF may be genetic therapy. Genetic therapy is a procedure by which correct copies of the CFTR gene are injected into a patient. The hope is that the correct genes will take over the task that the defective CFTR genes are unable to perform. Although much research is being done in this area, gene therapy is still in the experimental phase.
Alternative Treatment
Alternative practitioners recommend many of the same treatments used in traditional medicine. For example, they suggest the use of mucolytics to thin mucus and pancreatic enzymes to aid in digestion.
Efforts are also made to improve the patient's overall health and immune system. A variety of herbs is available to achieve these goals. In addition, hydrotherapy (water therapy) techniques may be helpful in relaxing the body and helping the patient breathe better.
EXPERIMENTING WITH GENE THERAPY
It may be possible to cure cystic fibrosis with gene therapy. The problem is to find ways to get good copies of the CFTR gene into a patient's body. Scientists are now working on techniques for accomplishing this goal.
One approach is to make good copies of the CFTR gene in the laboratory. These copies are then combined with viruses. Viruses are very good at infecting cells. This property is usually not beneficial for humans because it is the reason people become ill with viral diseases.
The combination of CFTR gene and virus is made into a nasal spray. Some fat droplets are also added to the spray. The fat serves as a carrier that takes the virus and gene to cells in the patient's body. If all works well, the virus enters cells in the patient's body, bringing the good copy of the CFTR gene with it. The gene begins to function properly, and the patient is cured.
Trials of the new nasal spray have been going on since the mid-1990s. The first step in the trials is to make sure that the spray does not harm people. The second step is to find out if the spray really works. That is, does it actually deliver good genes to the patient's body?
PROGNOSIS
The key to a good prognosis for cystic fibrosis is early detection and treatment. The effectiveness and variety of treatment methods greatly increased during the 1980s and 1990s. About half of all patients living with CF during this time could expect to live past the age of thirty. Researchers predict that a person born in the late 1990s with the disorder can expect to live to the age of forty.
PREVENTION
Since CF is a genetic disorder, there is no way to prevent the condition. However, couples who wish to have children may want to be tested for the presence of a defective CFTR gene. If that gene is present, it may be passed to any future children, placing those children at risk for cystic fibrosis.
FOR MORE INFORMATION
Books
Harris, Ann, and Maurice Super. Cystic Fibrosis: The Facts. New York: Oxford University Press, 1995.
Hopkins, Karen. Understanding Cystic Fibrosis. Jackson: University Press of Mississippi, 1998.
Orenstein, David. Cystic Fibrosis: A Guide for Patients and Family. Philadelphia: Lippincott-Raven, 1997.
Silverstein, Alvin, Robert Silverstein, and Virginia B. Silverstein. Cystic Fibrosis. New York: Franklin Watts, 1994.
Organizations
Cystic Fibrosis Foundation. 6931 Arlington Road, Bethesda, MD 20814. (301) 951–4422. http://www.cff.org.