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Cystic Fibrosis

Cystic Fibrosis

Definition

Cystic fibrosis (CF) is an inherited disease that affects the lungs, digestive system, sweat glands, and male fertility. Its name derives from the fibrous scar tissue that develops in the pancreas, one of the principal organs affected by the disease.

Description

Cystic fibrosis affects the body's ability to move salt and water in and out of cells. This defect causes the lungs and pancreas to secrete thick mucus, blocking passageways and preventing proper function.

CF affects approximately 30,000 children and young adults in the United States, and about 3,000 babies are born with CF every year. CF primarily affects people of white northern-European descent; rates are much lower in non-white populations.

Many of the symptoms of CF can be treated with drugs or nutritional supplements. Close attention to and prompt treatment of respiratory and digestive complications have dramatically increased the expected life span of a person with CF. While several decades ago most children with CF died by age two, today about half of all people with CF live past age 31. That median age is expected to grow as new treatments are developed, and it is estimated that a person born in 1998 with CF has a median expected life span of 40 years.

Causes and symptoms

Causes

Cystic fibrosis is a genetic disease, meaning it is caused by a defect in the person's genes. Genes, found in the nucleus of all the body's cells, control cell function by serving as the blueprint for the production of proteins. Proteins carry out a wide variety of functions within cells. The gene that, when defective, causes CF is called the CFTR gene, which stands for cystic fibrosis transmembrane conductance regulator. A simple defect in this gene leads to all the consequences of CF. There are over 500 known defects in the CFTR gene that can cause CF. However, 70% of all people with a defective CFTR gene have the same defect, known as delta-F508.

Much as sentences are composed of long strings of words, each made of letters, genes can be thought of as long strings of chemical words, each made of chemical letters, called nucleotides. Just as a sentence can be changed by rearranging its letters, genes can be mutated, or changed, by changes in the sequence of their nucleotide letters. The gene defects in CF are called point mutations, meaning that the gene is mutated only at one small spot along its length. In other words, the delta-F508 mutation is a loss of one "letter" out of thousands within the CFTR gene. As a result, the CFTR protein made from its blueprint is made incorrectly, and cannot perform its function properly.

The CFTR protein helps to produce mucus. Mucus is a complex mixture of salts, water, sugars, and proteins that cleanses, lubricates, and protects many passageways in the body, including those in the lungs and pancreas. The role of the CFTR protein is to allow chloride ions to exit the mucus-producing cells. When the chloride ions leave these cells, water follows, thinning the mucus. In this way, the CFTR protein helps to keep mucus from becoming thick and sluggish, thus allowing the mucus to be moved steadily along the passageways to aid in cleansing.

In CF, the CFTR protein cannot allow chloride ions out of the mucus-producing cells. With less chloride leaving, less water leaves, and the mucus becomes thick and sticky. It can no longer move freely through the passageways, so they become clogged. In the pancreas, clogged passageways prevent secretion of digestive enzymes into the intestine, causing serious impairment of digestionespecially of fatwhich may lead to malnutrition. Mucus in the lungs may plug the airways, preventing good air exchange and, ultimately, leading to emphysema. The mucus is also a rich source of nutrients for bacteria, leading to frequent infections.

INHERITANCE OF CYSTIC FIBROSIS. To understand the inheritance pattern of CF, it is important to realize that genes actually have two functions. First, as noted above, they serve as the blueprint for the production of proteins. Second, they are the material of inheritance: parents pass on characteristics to their children by combining the genes in egg and sperm to make a new individual.

Each person actually has two copies of each gene, including the CFTR gene, in each of their body cells. During sperm and egg production, however, these two copies separate, so that each sperm or egg contains only one copy of each gene. When sperm and egg unite, the newly created cell once again has two copies of each gene.

The two gene copies may be the same or they may be slightly different. For the CFTR gene, for instance, a person may have two normal copies, or one normal and one mutated copy, or two mutated copies. A person with two mutated copies will develop cystic fibrosis. A person with one mutated copy is said to be a carrier. A carrier will not have symptoms of CF, but can pass on the mutated CFTR gene to his/her children.

When two carriers have children, they have a one in four chance of having a child with CF each time they conceive. They have a two in four chance of having a child who is a carrier, and a one in four chance of having a child with two normal CFTR genes.

Approximately one in every 25 Americans of northern-European descent is a carrier of the mutated CF gene, while only one in 17,000 African Americans and one in 30,000 Asian Americans are carriers. Since carriers are symptom-free, very few people will know whether or not they are carriers unless there is a family history of the disease. Two white Americans with no family history of CF have a one in 2,500 chance of having a child with CF.

DOROTHY ANDERSEN (19011963)

Dorothy Andersen was born on May 15, 1901, in Asheville, North Carolina. She was the only child of Hans Peter Andersen and the former Mary Louise Mason. Orphaned as a young adult, Andersen put herself through Saint Johnsbury Academy and Mount Holyoke College before enrolling in the Johns Hopkins School of Medicine, from which she received her M.D. in 1926.

Andersen turned instead to medical research as a pathologist at Babies Hospital of the Columbia-Presbyterian Medical Center in New York City, where she stayed for more than 20 years, eventually becoming chief of pathology in 1952. Andersen is probably best known for her discovery of cystic fibrosis in 1935. That discovery came about during the postmortem examination of a child who had supposedly died of celiac disease, a nutritional disorder. She searched for similar cases in the autopsy files and in medical literature, eventually realizing that she had found a disease that had never been described and to which she gave the name cystic fibrosis.

It may seem puzzling that a mutated gene with such harmful consequences would remain so common; one might guess that the high mortality of CF would quickly lead to loss of the mutated gene from the population. Some researchers now believe the reason for the persistence of the CF gene is that carriers, those with only one copy of the gene, are protected from the full effects of cholera, a microorganism that infects the intestine, causing intense diarrhea and eventual death by dehydration. It is believed that having one copy of the CF gene is enough to prevent the full effects of cholera infection, while not enough to cause the symptoms of CF. This so-called "heterozygote advantage" is seen in some other genetic disorders, including sickle-cell anemia.

Symptoms

The most severe effects of cystic fibrosis are seen in two body systems: the gastrointestinal (digestive) system, and the respiratory tract, from the nose to the lungs. CF also affects the sweat glands and male fertility. Symptoms develop gradually, with gastrointestinal symptoms often the first to appear.

GASTROINTESTINAL SYSTEM. Ten to fifteen percent of babies who inherit CF have meconium ileus at birth. Meconium is the first dark stool that a baby passes after birth; ileus is an obstruction of the digestive tract. The meconium of a newborn with meconium ileus is thickened and sticky, due to the presence of thickened mucus from the intestinal glands. Meconium ileus causes abdominal swelling and vomiting, and often requires surgery immediately after birth. Presence of meconium ileus is considered highly indicative of CF. Borderline cases may be misdiagnosed, however, and attributed instead to "milk allergy."

Other abdominal symptoms are caused by the inability of the pancreas to supply digestive enzymes to the intestine. During normal digestion, as food passes from the stomach into the small intestine, it is mixed with pancreatic secretions which help to break down the nutrients for absorption. While the intestines themselves also provide some digestive enzymes, the pancreas is the major source of enzymes for the digestion of all types of foods, especially fats and proteins.

In CF, thick mucus blocks the pancreatic duct, which is eventually closed off completely by scar tissue formation, leading to a condition known as pancreatic insufficiency. Without pancreatic enzymes, large amounts of undigested food pass into the large intestine. Bacterial action on this rich food source can cause gas and abdominal swelling. The large amount of fat remaining in the feces makes it bulky, oily, and foul-smelling.

Because nutrients are only poorly digested and absorbed, the person with CF is often ravenously hungry, underweight, and shorter than expected for his age. When CF is not treated for a longer period, a child may develop symptoms of malnutrition, including anemia, bloating, and, paradoxically, appetite loss.

Diabetes becomes increasingly likely as a person with CF ages. Scarring of the pancreas slowly destroys those pancreatic cells which produce insulin, producing type I, or insulin-dependent diabetes.

Gall stones affect approximately 10% of adults with CF. Liver problems are less common, but can be caused by the buildup of fat within the liver. Complications of liver enlargement may include internal hemorrhaging, abdominal fluid (ascites ), spleen enlargement, and liver failure.

Other gastrointestinal symptoms can include a prolapsed rectum, in which part of the rectal lining protrudes through the anus; intestinal obstruction; and rarely, intussusception, in which part of the intestinal tube slips over an adjoining part, cutting off blood supply.

Somewhat less than 10% of people with CF do not have gastrointestinal symptoms. Most of these people do not have the delta-F508 mutation, but rather a different one, which presumably allows at least some of their CFTR proteins to function normally in the pancreas.

RESPIRATORY TRACT. The respiratory tract includes the nose, the throat, the trachea (or windpipe), the bronchi (which branch off from the trachea within each lung), the smaller bronchioles, and the blind sacs called alveoli, in which gas exchange takes place between air and blood.

Swelling of the sinuses within the nose is common in people with CF. This usually shows up on x ray, and may aid the diagnosis of CF. However, this swelling, called pansinusitis, rarely causes problems, and does not usually require treatment.

Nasal polyps, or growths, affect about one in five people with CF. These growths are not cancerous, and do not require removal unless they become annoying. While nasal polyps appear in older people without CF, especially those with allergies, they are rare in children without CF.

The lungs are the site of the most life-threatening effects of CF. The production of a thick, sticky mucus increases the likelihood of infection, decreases the ability to protect against infection, causes inflammation and swelling, decreases the functional capacity of the lungs, and may lead to emphysema. People with CF will live with chronic populations of bacteria in their lungs, and lung infection is the major cause of death for those with CF.

The bronchioles and bronchi normally produce a thin, clear mucus that traps foreign particles including bacteria and viruses. Tiny hair-like projections on the surface of these passageways slowly sweep the mucus along, out of the lungs and up the trachea to the back of the throat, where it may be swallowed or coughed up. This "mucociliary escalator" is one of the principal defenses against lung infection.

The thickened mucus of CF prevents easy movement out of the lungs, and increases the irritation and inflammation of lung tissue. This inflammation swells the passageways, partially closing them down, further hampering the movement of mucus. A person with CF is likely to cough more frequently and more vigorously as the lungs attempt to clean themselves out.

At the same time, infection becomes more likely since the mucus is a rich source of nutrients. Bronchitis, bronchiolitis, and pneumonia are frequent in CF. The most common infecting organisms are the bacteria Staphylococcus aureus, Haemophilus influenzae, and Pseudomonas aeruginosa. A small percentage of people with CF have infections caused by Burkholderia cepacia, a bacterium which is resistant to most current antibiotics (Burkholderia cepacia was formerly known as Pseudomonas cepacia.) The fungus Aspergillus fumigatus may infect older children and adults.

The body's response to infection is to increase mucus production; white blood cells fighting the infection thicken the mucus even further as they break down and release their cell contents. These white blood cells also provoke more inflammation, continuing the downward spiral that marks untreated CF.

As mucus accumulates, it can plug up the smaller passageways in the lungs, decreasing functional lung volume. Getting enough air can become difficult; tiredness, shortness of breath, and intolerance of exercise become more common. Because air passes obstructions more easily during inhalation than during exhalation, over time, air becomes trapped in the smallest chambers of the lungs, the alveoli. As millions of alveoli gradually expand, the chest takes on the enlarged, barrel-shaped appearance typical of emphysema.

For unknown reasons, recurrent respiratory infections lead to "digital clubbing," in which the last joint of the fingers and toes becomes slightly enlarged.

SWEAT GLANDS. The CFTR protein helps to regulate the amount of salt in sweat. People with CF have sweat that is much saltier than normal, and measuring the saltiness of a person's sweat is the most important diagnostic test for CF. Parents may notice that their infants taste salty when they kiss them. Excess salt loss is not usually a problem except during prolonged exercise or heat. While most older children and adults with CF compensate for this extra salt loss by eating more salty foods, infants and young children are in danger of suffering its effects (such as heat prostration), especially during summer. Heat prostration is marked by lethargy, weakness, and loss of appetite, and should be treated as an emergency condition.

FERTILITY. Ninety-eight percent of men with CF are sterile, due to complete obstruction or absence of the vas deferens, the tube carrying sperm out of the testes. While boys and men with CF form normal sperm and have normal levels of sex hormones, sperm are unable to leave the testes, and fertilization is not possible. Most women with CF are fertile, though they often have more trouble getting pregnant than women without CF. In both boys and girls, puberty is often delayed, most likely due to the effects of poor nutrition or chronic lung infection. Women with good lung health usually have no problems with pregnancy, while those with ongoing lung infection often do poorly.

Diagnosis

The decision to test a child for cystic fibrosis may be triggered by concerns about recurring gastrointestinal or respiratory symptoms, or salty sweat. A child born with meconium ileus will be tested before leaving the hospital. Families with a history of CF may wish to have all children tested, especially if there is a child who already has the disease. Some hospitals now require routine screening of newborns for CF.

Sweat test

The sweat test is both the easiest and most accurate test for CF. In this test, a small amount of the drug pilocarpine is placed on the skin. A very small electrical current is then applied to the area, which drives the pilocarpine into the skin. The drug stimulates sweating in the treated area. The sweat is absorbed onto a piece of filter paper, and is then analyzed for its salt content. A person with CF will have salt concentrations that are one-and-one-half to two times greater than normal. The test can be done on persons of any age, including newborns, and its results can be determined within an hour. Virtually every person who has CF will test positively on it, and virtually everyone who does not will test negatively.

Genetic testing

The discovery of the CFTR gene in 1989 allowed the development of an accurate genetic test for CF. Genes from a small blood or tissue sample are analyzed for specific mutations; presence of two copies of the mutated gene confirms the diagnosis of CF in all but a very few cases. However, since there are so many different possible mutations, and since testing for all of them would be too expensive and time-consuming, a negative gene test cannot rule out the possibility of CF.

Couples planning a family may decide to have themselves tested if one or both have a family history of CF. Prenatal genetic testing is possible through amniocentesis. Many couples who already have one child with CF decide to undergo prenatal screening in subsequent pregnancies, and use the results to determine whether to terminate the pregnancy. Siblings in these families are also usually tested, both to determine if they will develop CF, and to determine if they are carriers, to aid in their own family planning. If the sibling has no symptoms, determining his carrier status is often delayed until his teen years or later, when he is closer to needing the information to make decisions.

Newborn screening

Some states now require screening of newborns for CF, using a test known as the IRT test. This is a blood test which measures the level of immunoreactive trypsinogen, which is generally higher in babies with CF than those without it. This test gives many false positive results immediately after birth, and so requires a second test several weeks later. A second positive result is usually followed by a sweat test.

Treatment

There is no cure for CF. Treatment has advanced considerably in the past several decades, increasing both the life span and the quality of life for most people affected by CF. Early diagnosis is important to prevent malnutrition and infection from weakening the young child. With proper management, many people with CF engage in the full range of school and sports activities.

Nutrition

People with CF usually require high-calorie diets and vitamin supplements. Height, weight, and growth of a person with CF are monitored regularly. Most people with CF need to take pancreatic enzymes to supplement or replace the inadequate secretions of the pancreas. Tablets containing pancreatic enzymes are taken with every meal; depending on the size of the tablet and the meal, as many as 20 tablets may be needed. Because of incomplete absorption even with pancreatic enzymes, a person with CF needs to take in about 30% more food than a person without CF. Low-fat diets are not recommended except in special circumstances, since fat is a source of both essential fatty acids and abundant calories.

Some people with CF cannot absorb enough nutrients from the foods they eat, even with specialized diets and enzymes. For these people, tube feeding is an option. Nutrients can be introduced directly into the stomach through a tube inserted either through the nose (a nasogastric tube) or through the abdominal wall (a gastrostomy tube). A jejunostomy tube, inserted into the small intestine, is also an option. Tube feeding can provide nutrition at any time, including at night while the person is sleeping, allowing constant intake of high-quality nutrients. The feeding tube may be removed during the day, allowing normal meals to be taken.

Respiratory health

The key to maintaining respiratory health in a person with CF is regular monitoring and early treatment. Lung function tests are done frequently to track changes in functional lung volume and respiratory effort. Sputum samples are analyzed to determine the types of bacteria present in the lungs. Chest x rays are usually taken at least once a year. Lung scans, using a radioactive gas, can show closed off areas not seen on the x ray. Circulation in the lungs may be monitored by injection of a radioactive substance into the bloodstream.

People with CF live with chronic bacterial colonization; that is, their lungs are constantly host to several species of bacteria. Good general health, especially good nutrition, can keep the immune system healthy, which decreases the frequency with which these colonies begin an infection, or attack on the lung tissue. Exercise is another important way to maintain health, and people with CF are encouraged to maintain a program of regular exercise.

In addition, clearing mucus from the lungs helps to prevent infection; and mucus control is an important aspect of CF management. Postural drainage is used to allow gravity to aid the mucociliary escalator. For this technique, the person with CF lies on a tilted surface with head downward, alternately on the stomach, back, or side, depending on the section of lung to be drained. An assistant thumps the rib cage to help loosen the secretions. A device called a "flutter" offers another way to loosen secretions: it consists of a stainless steel ball in a tube. When a person exhales through it, the ball vibrates, sending vibrations back through the air in the lungs. Some special breathing techniques may also help clear the lungs.

Several drugs are available to prevent the airways from becoming clogged with mucus. Bronchodilators and theophyllines open up the airways; steroids reduce inflammation; and mucolytics loosen secretions. Acetylcysteine (Mucomyst) has been used as a mucolytic for many years but is not prescribe frequently now, while DNase (Pulmozyme) is a newer product gaining in popularity. DNase breaks down the DNA from dead white blood cells and bacteria found in thick mucus.

People with CF may pick up bacteria from other CF patients. This is especially true of Burkholderia cepacia, which is not usually found in people without CF. While the ideal recommendation from a health standpoint might be to avoid contact with others who have CF, this is not usually practical (since CF clinics are a major site of care), nor does it meet the psychological and social needs of many people with CF. At a minimum, CF centers recommend avoiding prolonged close contact between people with CF, and scrupulous hygiene, including frequent hand washing. Some CF clinics schedule appointments on different days for those with and without B. cepacia colonies.

Some doctors choose to prescribe antibiotics only during infection, while others prefer long-term antibiotic treatment against S. aureus. The choice of antibiotic depends on the particular organism or organisms found. Some antibiotics are given as aerosols directly into the lungs. Antibiotic treatment may be prolonged and aggressive.

Supplemental oxygen may be needed as lung disease progresses. Respiratory failure may develop, requiring temporary use of a ventilator to perform the work of breathing.

Lung transplantation has become increasingly common for people with CF, although the number of people who receive them is still much lower than those who want them. Transplantation is not a cure, however, and has been likened to trading one disease for another. Long-term immunosuppression is required, increasing the likelihood of other types of infection. About 50% of adults and more than 80% of children who receive lung transplants live longer than two years. Liver transplants are also done for CF patients whose livers have been damaged by fibrosis.

Long-term use of ibuprofen has been shown to help some people with CF, presumably by reducing inflammation in the lungs. Close medical supervision is necessary, however, since the effective dose is high and not everyone benefits. Ibuprofen at the required doses interferes with kidney function, and together with aminoglycoside antibiotics, may cause kidney failure.

A number of experimental treatments are currently the subject of much research. Some evidence indicates that aminoglycoside antibiotics may help overcome the genetic defect in some CF mutations, allowing the protein to be made normally. While promising, these results would apply to only about 5% of those with CF.

Gene therapy is currently the most ambitious approach to curing CF. In this set of techniques, non-defective copies of the CFTR gene are delivered to affected cells, where they are taken up and used to create the CFTR protein. While elegant and simple in theory, gene therapy has met with a large number of difficulties in trials so far, including immune resistance, very short duration of the introduced gene, and inadequately widespread delivery.

KEY TERMS

Carrier A person with one copy of a defective gene, who does not have the disease it causes, but can pass along the defective gene to offspring.

CFTR Cystic fibrosis transmembrane conductance regulator, the protein responsible for regulating chloride movement across cells in some tissues. When a person has two defective copies of the CFTR gene, cystic fibrosis is the result.

Emphysema A pathological accumulation of air in organs or tissues; term especially applied to the condition when in the lungs.

Mucociliary escalator The coordinated action of tiny projections on the surfaces of cells lining the respiratory tract, which moves mucus up and out of the lungs.

Mucolytic An agent that dissolves or destroys mucin, the chief component of mucus.

Pancreatic insufficiency Reduction or absence of pancreatic secretions into the digestive system due to scarring and blockage of the pancreatic duct.

Alternative treatment

In homeopathic medicine, the symptoms of the disease would be addressed to enhance the quality of life for the person with cystic fibrosis. Treating the cause of CF, because of the genetic basis for the disease, is not possible. Naturopathic medicine seeks to treat the whole person, however, and in this approach might include:

  • mucolytics to help thin mucus
  • supplementation of pancreatic enzymes to assist in digestion
  • respiratory symptoms can be addressed to open lung passages
  • hydrotherapy techniques to help ease the respiratory symptoms and help the body eliminate
  • immune enhancements can help revent the development of secondary infections
  • dietary enhancements and adjustments are used to treat digestive and nutritional problems

Prognosis

People with CF may lead relatively normal lives, with the control of symptoms. The possible effect of pregnancy on the health of a woman with CF requires careful consideration before beginning a family; as do issues of longevity, and their children's status as carriers. Although most men with CF are functionally sterile, new procedures for removing sperm from the testes are being tried, and may offer more men the chance to become fathers.

Approximately half of people with CF live past the age of 30. Because of better and earlier treatment, a person born today with CF is expected, on average, to live to age 40.

Prevention

Adults with a family history of cystic fibrosis may obtain a genetic test of their carrier status for purposes of family planning. Prenatal testing is also available. There is currently no known way to prevent development of CF in a person with two defective gene copies.

Resources

ORGANIZATIONS

Cystic Fibrosis Foundation. 6931 Arlington Road, Bethesda, MD 20814. (800) 344-4823. http://www.cff.org.

OTHER

CysticFibrosis.com. http://www.cysticfibrosis.com.

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Cystic Fibrosis

Cystic fibrosis

Definition

Cystic fibrosis (CF) is an inherited disease that affects the lungs, digestive system, sweat glands, and male fertility. Its name derives from the fibrous scar tissue that develops in the pancreas, one of the principal organs affected by the disease.

Description

Cystic fibrosis affects the body's ability to move salt and water in and out of cells. This defect causes the lungs and pancreas to secrete thick mucus, blocking passageways and preventing proper function.

Many of the symptoms of CF can be treated with drugs or nutritional supplements. Close attention to and prompt treatment of respiratory and digestive complications have dramatically increased the expected life span of a person with CF. While in the 1970s, most children with CF died by age two, in the early 2000s about half of all people with CF live past age 31. That median age is expected to grow as new treatments are developed, and it is estimated that a person born in 1998 with CF has a median expected life span of 40 years.

Demographics

CF affects approximately 30,000 children and young adults in the United States, and about 3,000 babies are born with CF every year. CF primarily affects people of white northern-European descent; rates are much lower in non-white populations.

Causes and symptoms

Causes

Cystic fibrosis is a genetic disease, meaning it is caused by a defect in the person's genes. Genes, found in the nucleus of all the body's cells, control cell function by serving as the blueprint for the production of proteins. Proteins carry out a wide variety of functions within cells. The gene that, when defective, causes CF is called the CFTR gene, which stands for cystic fibrosis transmembrane conductance regulator. A simple defect in this gene leads to all the consequences of CF. There are over 500 known defects in the CFTR gene that can cause CF. However, 70 percent of all people with a defective CFTR gene have the same defect, known as delta-F508.

Much as sentences are composed of long strings of words, each made of letters; genes can be thought of as long strings of chemical words, each made of chemical letters, called nucleotides. Just as a sentence can be changed by rearranging its letters, genes can be mutated, or changed, by changes in the sequence of their nucleotide letters. The gene defects in CF are called point mutations, meaning that the gene is mutated only at one small spot along its length. In other words, the delta-F508 mutation is a loss of one "letter" out of thousands within the CFTR gene. As a result, the CFTR protein made from its blueprint is made incorrectly and cannot perform its function properly.

The CFTR protein helps to produce mucus. Mucus is a complex mixture of salts, water, sugars, and proteins that cleanses, lubricates, and protects many passageways in the body, including those in the lungs and pancreas. The role of the CFTR protein is to allow chloride ions to exit the mucus-producing cells. When the chloride ions leave these cells, water follows, thinning the mucus. In this way, the CFTR protein helps to keep mucus from becoming thick and sluggish, thus allowing the mucus to be moved steadily along the passageways to aid in cleansing.

In CF, the CFTR protein cannot allow chloride ions out of the mucus-producing cells. With less chloride leaving, less water leaves, and the mucus becomes thick and sticky. It can no longer move freely through the passageways, so they become clogged. In the pancreas, clogged passageways prevent secretion of digestive enzymes into the intestine, causing serious impairment of digestionespecially of fatwhich may lead to malnutrition . Mucus in the lungs may plug the airways, preventing good air exchange and, ultimately, leading to emphysema. The mucus is also a rich source of nutrients for bacteria, leading to frequent infections.

inheritance of cystic fibrosis Each person actually has two copies of each gene, including the CFTR gene, in each of their body cells. During sperm and egg production, however, these two copies separate, so that each sperm or egg contains only one copy of each gene. When sperm and egg unite, the newly created cell once again has two copies of each gene.

The two gene copies may be the same or they may be slightly different. For the CFTR gene, for instance, a person may have two normal copies, or one normal and one mutated copy, or two mutated copies. A person with two mutated copies will develop cystic fibrosis. A person with one mutated copy is said to be a carrier. A carrier will not have symptoms of CF but can pass on the mutated CFTR gene to his/her children.

When two carriers have children, they have a one-in-four chance of having a child with CF each time they conceive. They have a two-in-four chance of having a child who is a carrier, and a one-in-four chance of having a child with two normal CFTR genes.

Approximately one in every 25 Americans of northern-European descent is a carrier of the mutated CF gene, while only one in 17,000 African Americans and one in 30,000 Asian Americans are carriers. Since carriers are symptom-free, very few people know if they are carriers unless there is a family history of the disease. Two white Americans with no family history of CF have a one in 2,500 chance of having a child with CF.

It may seem puzzling that a mutated gene with such harmful consequences would remain so common; one might guess that the high mortality of CF would quickly lead to loss of the mutated gene from the population. Some researchers in the early 2000s believe the reason for the persistence of the CF gene is that carriers, those with only one copy of the gene, are protected from the full effects of cholera, a microorganism that infects the intestine, causing intense diarrhea and eventual death by dehydration . It is believed that having one copy of the CF gene is enough to prevent the full effects of cholera infection, while not enough to cause the symptoms of CF. This so-called "heterozygote advantage" is seen in some other genetic disorders, including sickle-cell anemia.

Symptoms

The most severe effects of cystic fibrosis are seen in two body systems: the gastrointestinal (digestive) system and the respiratory tract from the nose to the lungs. CF also affects the sweat glands and male fertility. Symptoms develop gradually, with gastrointestinal symptoms often the first to appear.

gastrointestinal system Approximately 10 to 15 percent of babies who inherit CF have meconium ileus at birth. Meconium is the first dark stool that a baby passes after birth; ileus is an obstruction of the digestive tract. The meconium of a newborn with meconium ileus is thickened and sticky, due to the presence of thickened mucus from the intestinal glands. Meconium ileus causes abdominal swelling and vomiting and often requires surgery immediately after birth. Presence of meconium ileus is considered highly indicative of CF. Borderline cases may be misdiagnosed, however, and attributed instead to milk allergy.

Other abdominal symptoms are caused by the inability of the pancreas to supply digestive enzymes to the intestine. During normal digestion, as food passes from the stomach into the small intestine, it is mixed with pancreatic secretions that help to break down the nutrients for absorption. While the intestines themselves also provide some digestive enzymes, the pancreas is the major source of enzymes for the digestion of all types of foods, especially fats and proteins.

In CF, thick mucus blocks the pancreatic duct, which is eventually closed off completely by scar tissue formation, leading to a condition known as pancreatic insufficiency. Without pancreatic enzymes, large amounts of undigested food pass into the large intestine. Bacterial action on this rich food source can cause gas and abdominal swelling. The large amount of fat remaining in the feces makes it bulky, oily, and foul-smelling.

Because nutrients are only poorly digested and absorbed, the person with CF is often ravenously hungry, underweight, and shorter than expected for his age. When CF is not treated for a longer period, a child may develop symptoms of malnutrition, including anemia, bloating, and, paradoxically, appetite loss.

Diabetes becomes increasingly likely as a person with CF ages. Scarring of the pancreas slowly destroys those pancreatic cells which produce insulin, producing type I, or insulin-dependent diabetes.

Gallstones affect approximately 10 percent of adults with CF. Liver problems are less common but can be caused by the buildup of fat within the liver. Complications of liver enlargement may include internal hemorrhaging, accumulation of abdominal fluid (ascites), spleen enlargement, and liver failure.

Other gastrointestinal symptoms can include a prolapsed rectum, in which part of the rectal lining protrudes through the anus; intestinal obstruction; and rarely, intussusception, in which part of the intestinal tube slips over an adjoining part, cutting off blood supply.

Somewhat less than 10 percent of people with CF do not have gastrointestinal symptoms. Most of these people do not have the delta-F508 mutation but a different one, which presumably allows at least some of their CFTR proteins to function normally in the pancreas.

respiratory tract The respiratory tract includes the nose, the throat, the trachea (or windpipe), the bronchi (which branch off from the trachea within each lung), the smaller bronchioles, and the blind sacs called alveoli, in which gas exchange takes place between air and blood.

Swelling of the sinuses within the nose is common in people with CF. This usually shows up on an x ray and may aid the diagnosis of CF. However, this swelling, called pansinusitis, rarely causes problems and does not usually require treatment.

Nasal polyps, or growths, affect about one in five people with CF. These growths are not cancerous and do not require removal unless they become annoying. While nasal polyps appear in older people without CF, especially those with allergies , they are rare in children without CF.

The lungs are the site of the most life-threatening effects of CF. The production of a thick, sticky mucus increases the likelihood of infection, decreases the ability to protect against infection, causes inflammation and swelling, decreases the functional capacity of the lungs, and may lead to emphysema. People with CF live with chronic populations of bacteria in their lungs, and lung infection is the major cause of death for those with CF.

The bronchioles and bronchi normally produce a thin, clear mucus that traps foreign particles including bacteria and viruses. Tiny hair-like projections on the surface of these passageways slowly sweep the mucus along, out of the lungs and up the trachea to the back of the throat, where it may be swallowed or coughed up. This "mucociliary escalator" is one of the principal defenses against lung infection.

The thickened mucus of CF prevents easy movement out of the lungs and increases the irritation and inflammation of lung tissue. This inflammation swells the passageways, partially closing them down, further hampering the movement of mucus. A person with CF is likely to cough more frequently and more vigorously as the lungs attempt to clean themselves out.

At the same time, infection becomes more likely since the mucus is a rich source of nutrients. Bronchitis, bronchiolitis , and pneumonia are frequent in CF. The most common infecting organisms are the bacteria Staphylococcus aureus, Haemophilus influenzae, and Pseudomonas aeruginosa. A small percentage of people with CF have infections caused by Burkholderia cepacia, a bacterium which was resistant to most antibiotics as of 2004. (Burkholderia cepacia was formerly known as Pseudomonas cepacia.) The fungus Aspergillus fumigatus may infect older children and adults.

The body's response to infection is to increase mucus production; white blood cells fighting the infection thicken the mucus even further as they break down and release their cell contents. These white blood cells also provoke more inflammation, continuing the downward spiral that marks untreated CF.

As mucus accumulates, it can plug up the smaller passageways in the lungs, decreasing functional lung volume. Getting enough air can become difficult; tiredness, shortness of breath, and intolerance of exercise become more common. Because air passes obstructions more easily during inhalation than during exhalation, over time, air becomes trapped in the smallest chambers of the lungs, the alveoli. As millions of alveoli gradually expand, the chest takes on the enlarged, barrel-shaped appearance typical of emphysema.

For unknown reasons, recurrent respiratory infections lead to digital clubbing, in which the last joint of the fingers and toes becomes slightly enlarged.

sweat glands The CFTR protein helps to regulate the amount of salt in sweat. People with CF have sweat that is much saltier than normal, and measuring the saltiness of a person's sweat is the most important diagnostic test for CF. Parents may notice that their infants taste salty when they kiss them. Excess salt loss is not usually a problem except during prolonged exercise or heat. While most older children and adults with CF compensate for this extra salt loss by eating more salty foods, infants and young children are in danger of suffering its effects (such as heat prostration), especially during summer. Heat prostration is marked by lethargy, weakness, and loss of appetite and should be treated as an emergency condition.

fertility Some 98 percent of men with CF are sterile, due to complete obstruction or absence of the vas deferens (the tube carrying sperm out of the testes). While boys and men with CF form normal sperm and have normal levels of sex hormones, sperm are unable to leave the testes, and fertilization is not possible. Most women with CF are fertile, though they often have more trouble getting pregnant than women without CF. In both boys and girls, puberty is often delayed, most likely due to the effects of poor nutrition or chronic lung infection. Women with good lung health usually have no problems with pregnancy, while those with ongoing lung infection often do poorly.

Diagnosis

The decision to test a child for cystic fibrosis may be triggered by concerns about recurring gastrointestinal or respiratory symptoms or salty sweat. A child born with meconium ileus will be tested before leaving the hospital. Families with a history of CF may wish to have all children tested, especially if there is a child who already has the disease. Some hospitals require routine screening of newborns for CF.

Sweat test

The sweat test is both the easiest and most accurate test for CF. In this test, a small amount of the drug pilocarpine is placed on the skin. A very small electrical current is then applied to the area, which drives the pilocarpine into the skin. The drug stimulates sweating in the treated area. The sweat is absorbed onto a piece of filter paper and is then analyzed for its salt content. A person with CF will have salt concentrations that are 1.5 to 2 times greater than normal. The test can be done on persons of any age, including newborns, and its results can be determined within an hour. Virtually every person who has CF will test positively on it, and virtually everyone who does not will test negatively.

Genetic testing

The discovery of the CFTR gene in 1989 allowed the development of an accurate genetic test for CF. Genes from a small blood or tissue sample are analyzed for specific mutations; presence of two copies of the mutated gene confirms the diagnosis of CF in all but a very few cases. However, since there are so many different possible mutations and since testing for all of them would be too expensive and time-consuming, a negative gene test cannot rule out the possibility of CF.

Couples planning a family may decide to have themselves tested if one or both have a family history of CF. Prenatal genetic testing is possible through amniocentesis . Many couples who already have one child with CF decide to undergo prenatal screening in subsequent pregnancies and use the results to determine whether to terminate the pregnancy. Siblings in these families are also usually tested, to determine if they will develop CF and to determine if they are carriers, to aid in their own family planning. If the sibling has no symptoms, determining his carrier status is often delayed until his teen years or later, when he is closer to needing the information to make decisions.

Newborn screening

Some states in the early 2000s require screening of newborns for CF, using a test known as the IRT test. This blood test measures the level of immunoreactive trypsinogen, which is generally higher in babies with CF than those without it. This test gives many false positive results immediately after birth and so requires a second test several weeks later. A second positive result is usually followed by a sweat test.

Treatment

As of 2004 there was no cure for CF. However, treatment advanced during the last quarter of the twentieth century, increasing both the life span and the quality of life for most people affected by CF. Early diagnosis is important to prevent malnutrition and infection from weakening the young child. With proper management, many people with CF engage in the full range of school and sports activities.

Nutrition

People with CF usually require high-calorie diets and vitamin supplements. Height, weight, and growth of a person with CF are monitored regularly. Most people with CF need to take pancreatic enzymes to supplement or replace the inadequate secretions of the pancreas. Tablets containing pancreatic enzymes are taken with every meal; depending on the size of the tablet and the meal, as many as 20 tablets may be needed. Because of incomplete absorption even with pancreatic enzymes, a person with CF needs to take in about 30 percent more food than a person without CF. Low-fat diets are not recommended except in special circumstances, since fat is a source of both essential fatty acids and abundant calories.

Some people with CF cannot absorb enough nutrients from the foods they eat, even with specialized diets and enzymes. For these people, tube feeding is an option. Nutrients can be introduced directly into the stomach through a tube inserted either through the nose (a nasogastric tube) or through the abdominal wall (a gastrostomy tube). A jejunostomy tube, inserted into the small intestine, is also an option. Tube feeding can provide nutrition at any time, including at night while the person is sleeping, allowing constant intake of high-quality nutrients. The feeding tube may be removed during the day, allowing normal meals to be taken.

Respiratory health

The key to maintaining respiratory health in a person with CF is regular monitoring and early treatment. Lung function tests are done frequently to track changes in functional lung volume and respiratory effort. Sputum samples are analyzed to determine the types of bacteria present in the lungs. Chest x-rays are usually taken at least once a year. Lung scans, using a radioactive gas, can show closed off areas not seen on the x ray. Circulation in the lungs may be monitored by injection of a radioactive substance into the bloodstream.

People with CF live with chronic bacterial colonization; that is, their lungs are constantly host to several species of bacteria. Good general health, especially good nutrition, can keep the immune system healthy, which decreases the frequency with which these colonies begin an infection or attack on the lung tissue. Exercise is another important way to maintain health, and people with CF are encouraged to maintain a program of regular exercise.

In addition, clearing mucus from the lungs helps to prevent infection, and mucus control is an important aspect of CF management. Postural drainage is used to allow gravity to aid the mucociliary escalator. For this technique, the person with CF lies on a tilted surface with head downward, alternately on the stomach, back, or side, depending on the section of lung to be drained. An assistant thumps the rib cage to help loosen the secretions. A device called a flutter offers another way to loosen secretions: it consists of a stainless steel ball in a tube. When a person exhales through it, the ball vibrates, sending vibrations back through the air in the lungs. Some special breathing techniques may also help clear the lungs.

Several drugs are available to prevent the airways from becoming clogged with mucus. Bronchodilators and theophyllines open up the airways; steroids reduce inflammation; and mucolytics loosen secretions. Acetylcysteine (Mucomyst) has been used as a mucolytic during the 1980s and 1990s but is not prescribe frequently in the early 2000s, while DNase (Pulmozyme) is a newer product gaining in popularity. DNase breaks down the DNA from dead white blood cells and bacteria found in thick mucus.

People with CF may pick up bacteria from other CF patients. This is especially true of Burkholderia cepacia, which is not usually found in people without CF. While the ideal recommendation from a health standpoint might be to avoid contact with others who have CF, this is not usually practical (since CF clinics are a major site of care), nor does it meet the psychological and social needs of many people with CF. At a minimum, CF centers recommend avoiding prolonged close contact between people with CF and scrupulous hygiene, including frequent hand washing. Some CF clinics schedule appointments on different days for those with and without B. cepacia colonies.

Some doctors choose to prescribe antibiotics only during infection, while others prefer long-term antibiotic treatment against S. aureus. The choice of antibiotic depends on the particular organism or organisms found. Some antibiotics are given as aerosols directly into the lungs. Antibiotic treatment may be prolonged and aggressive.

Supplemental oxygen may be needed as lung disease progresses. Respiratory failure may develop, requiring temporary use of a ventilator to perform the work of breathing.

Lung transplantation has become increasingly common for people with CF, although the number of people who receive lungs was as of 2004 much lower than those who want them. Transplantation is not a cure, however, and has been likened to trading one disease for another. Long-term immunosuppression is required, increasing the likelihood of other types of infection. About 50 percent of adults and more than 80 percent of children who receive lung transplants live longer than two years. Liver transplants are also done for CF patients whose livers have been damaged by fibrosis.

Long-term use of ibuprofen has been shown to help some people with CF, presumably by reducing inflammation in the lungs. Close medical supervision is necessary, however, since the effective dose is high and not everyone benefits. Ibuprofen at the required doses interferes with kidney function and, together with aminoglycoside antibiotics, may cause kidney failure.

A number of experimental treatments were as of 2004 the subject of much research. Some evidence indicates that aminoglycoside antibiotics may help overcome the genetic defect in some CF mutations, allowing the protein to be made normally. While promising, these results would apply to only about 5 percent of those with CF.

Gene therapy is the most ambitious approach to curing CF. In this set of techniques, non-defective copies of the CFTR gene are delivered to affected cells, where they are taken up and used to create the CFTR protein. While elegant and simple in theory, gene therapy has met with a large number of difficulties in trials, including immune resistance, very short duration of the introduced gene, and inadequately widespread delivery.

Prognosis

People with CF may lead relatively normal lives, with the control of symptoms. The possible effect of pregnancy on the health of a woman with CF requires careful consideration before she and her partner begin a family; as do issues of longevity, and the children's status as carriers. Although most men with CF are functionally sterile, new procedures for removing sperm from the testes are being tried and may offer more men the chance to become fathers.

Approximately half of people with CF live past the age of 30. Because of better and earlier treatment, a person born in 2004 with CF is expected, on average, to live to age 40.

Prevention

Adults with a family history of cystic fibrosis may obtain a genetic test of their carrier status for purposes of family planning. Prenatal testing is also available. There is no known way to prevent development of CF in a person with two defective gene copies.

KEY TERMS

Carrier A person who possesses a gene for an abnormal trait without showing signs of the disorder. The person may pass the abnormal gene on to offspring. Also refers to a person who has a particular disease agent present within his/her body, and can pass this agent on to others, but who displays no symptoms of infection.

Cystic fibrosis transmembrane conductance regulator (CFTR) The protein responsible for regulating chloride movement across cells in some tissues. Cystic fibrosis results when a person has two defective copies of the CFTR gene.

Emphysema A chronic respiratory disease that involves the destruction of air sac walls to form abnormally large air sacs that have reduced gas exchange ability and that tend to retain air within the lungs. Symptoms include labored breathing, the inability to forcefully blow air out of the lungs, and an increased susceptibility to respiratory tract infections. Emphysema is usually caused by smoking.

Mucociliary escalator The coordinated action of tiny projections on the surfaces of cells lining the respiratory tract, which moves mucus up and out of the lungs.

Mucolytic An agent that dissolves or destroys mucin, the chief component of mucus.

Pancreatic insufficiency Reduction or absence of pancreatic secretions into the digestive system due to scarring and blockage of the pancreatic duct.

Resources

BOOKS

Boat, Thomas F. "Cystic Fibrosis." In Nelson Textbook of Pediatrics. Edited by Richard E. Behrman et al. Philadelphia: Saunders, 2004.

Boucher, R. C., et al "Cystic Fibrosis." In Textbook of Respiratory Medicine, 3rd ed. Edited by John F. Murray and Jay A. Nadel. Philadelphia: Saunders, 2000.

ORGANIZATIONS

Cystic Fibrosis Foundation. 6931 Arlington Road, Bethesda, MD 20814. Web site: <www.cff.org>.

WEB SITES

CysticFibrosis.com. Available online at <http://www.cysticfibrosis.com> (accessed December 26, 2004).

Richard Robinson Rosalyn Carson-DeWitt, MD

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cystic fibrosis

cystic fibrosis (sĬs´tĬk fībrō´sĬs), inherited disorder of the exocrine glands (see gland), affecting children and young people; median survival is 25 years in females and 30 years in males. It is caused by a genetic abnormality in the CF transmembrane conductance regulator (CFTR) gene that results in a misshapen CFTR protein and the consequent disruption of chloride transfer across cell membranes. As a result, chloride ions build up in the cells of the lungs and other organs. Water stays inside the cells to dilute the chloride rather than being drawn out of the cells by normal chloride movement and the normal secretions of the organs thicken. Mucus in the exocrine glands becomes thick and sticky and eventually blocks the ducts of these glands (especially in the pancreas, lungs, and liver), forming cysts. The disease also causes the sweat glands to secrete excessive salt, causing heat prostration in hot weather. Symptoms, which vary according to the severity of the condition and the glands involved, include a distended abdomen; diarrhea; bulky, foul-smelling stools; and malnutrition. Medical problems include nasal polyps and sinus disease, repeated respiratory infections, infertility, liver disease, and diabetes. Diagnosis is confirmed by a sweat test or measurement of transmembrane potential.

Treatment consists of dietary adjustment (low fat–high calorie) and the administration of vitamins, pancreatin, and antibiotics to ward off secondary infections. Special measures are necessary to decrease the viscosity of pulmonary secretions; aerosol application of recombinant human DNase, an enzyme that digests the sticky extracellular DNA that helps form these viscous secretions, was approved in 1993. In some cases lung transplantation (see transplantation, medical) is helpful. The identification of the abnormal gene (1989) paved the way for gene therapy aimed at altering the genetic structure by transferring to the patient cells with normal CFTR genes.

Identification of the genes has also made genetic testing and diagnosis possible. Evolutionary biologists have suggested that the gene, which must be inherited from both parents to cause the disorder, affords carriers some protection against cholera, a disease that kills through profound loss of fluids.

See P. Davis, Cystic Fibrosis (1993); M. E. Hodson and D. M. Geddes, Cystic Fibrosis (1994).

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cystic fibrosis

cystic fibrosis (CF, fibrocystic disease of the pancreas, mucoviscidosis) n. a hereditary disease affecting cells of the exocrine glands; the faulty gene responsible for the most common form of CF has been identified as lying on chromosome no. 7 and is recessive, i.e. both parents of the patient can be carriers without being affected by the disease. The abnormality results in the production of thick mucus, which obstructs the intestinal glands (causing meconium ileus in newborn babies), pancreas (causing deficiency of pancreatic enzymes resulting in malabsorption and failure to thrive), and bronchi (causing bronchiectasis). Respiratory infections, which may be severe, are a common complication.
www.cftrust.org.uk Website of the Cystic Fibrosis Trust

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Cystic Fibrosis

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) 9514422. http://www.cff.org.

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Cystic Fibrosis

Cystic Fibrosis

Rachels Story

What Is Cystic Fibrosis?

What Causes Cystic Fibrosis?

How Do Doctors Know Someone Has CF?

A Morning Ritual for Rachel

Living with CF

Resources

Cystic fibrosis is an inherited condition in which glands produce excessively sticky mucus. The sticky material clogs the lungs, liver pancreas, and intestines and makes it difficult to breathe and to digest food properly.

KEYWORDS

for searching the Internet and other reference sources

Chest physical therapy

Gene therapy

Mucoviscidosis

Phenylalanine

Pulmonary system

Rachels Story

Rachels parents were worried. They believed they provided all the proper care Rachel needed, just as they had for their older daughter when she was a baby. But Rachel failed to gain as much weight as other children her age, even though she seemed to have the typical appetite of an infant. Rachel also seemed to have more colds than other children had and a lot more colds than her older sister ever had. She coughed often and breathed with a wheezing sound. Then, around the time of her second birthday, Rachel developed pneumonia*.

* pneumonia
is an inflammation of the lungs, usually caused by bacteria, viruses, or chemical irritants.

Rachels failure to gain weight and her frequent respiratory infections led her doctor to suspect that Rachel had cystic fibrosis (SIS-tik fy-BRO-sis), which is usually known by its initials, CF. Tests confirmed the diagnosis.

CF is a hereditary disease that affects about 30,000 children and adults in the United States. It is the most common hereditary condition that affects people of European ancestry, occurring in 1 of every 2,000

live births. About 1,000 new cases of CF are diagnosed each year in the United States, usually by the time children reach their third birthday.

What Is Cystic Fibrosis?

Cystic fibrosis is a chronic, hereditary disease that affects many of the bodys organ systems. In CF, some of the thin, easy-flowing mucus* in the bodys respiratory and digestive systems become thicker. Glands* in the body produce mucus to do such things as lubricate the lungs, trap dust and bacteria that is inhaled through the nose, and protect the lining of the intestines from the acidic fluids that help digest food.

* mucus
is a combination of water, salt, cells, and other material that forms a coating that lines the respiratory and digestive systems.
* glands
are groups of cells that act on substances in the bloodstream to change them for use in other parts of the body or to remove them from the body.

The glands in people with CF, however, produce sticky mucus that clogs the passageways in the lungs, which makes it difficult to breathe and leads to infections. The sticky mucus also blocks the easy flow of digestive acids and enzymes from the pancreas* and liver* to the intestines. Without adequate amounts of these digestive fluids in the intestines, people with CF cannot break down their food into the substances the body needs for nourishment.

* pancreas
is an organ in the upper abdomen that secretes enzymes to help with digestion.
* liver
is a large organ with many functions, including secreting the digestive fluid bile.

What Causes Cystic Fibrosis?

CF is caused by a mutation in a gene* on chromosome 7. Chromosome 7 is one of 23 pairs of chromosomes that are part of each persons genetic makeup. The CF gene causes the production of a protein that lacks an important amino acid*, phenylalanine (fen-il-AL-a-neen). Without that amino acid, the protein hinders the ability of mucus to obtain the proper amounts of water and salt from the body, which the mucus needs to maintain its thin and easy-flowing texture. This turns the mucus into a dense, sticky substance that clogs the respiratory and digestive systems.

* genes
are chemicals in the body that help determine a persons characteristics, such as hair or eye color. They are inherited from a persons parents and are contained in the chromosomes found in the cells of the body.
* amino acids
are the chief components of proteins.

The obstructions in the lungs make it hard to breathe and can increase the risk of infections. The problems in the digestive system prevent the body from getting all the nutrients it needs from food. It also means people

with CF often have thicker, foul-smelling bowel movements, because fat in food cannot be broken down by digestive fluids and absorbed.

A person may carry the CF gene on one of the two copies of chromosome 7 and not have any signs of CF. This person is called a carrier*. Parents can pass the CF gene to many generations of offspring. When a person has the CF gene on both copies of chromosome 7, then that person will have CF. When parents are both carriers, such as Rachels parents, their children have a one in four chance of having CF. Estimates are that 10 million Americans, or 1 out of 29, carry the CF gene.

* carriers
are people who have the genes for a disease without having the disease itself.

How Do Doctors Know Someone Has CF?

As far back as the 1600s, there were descriptions of children with symptoms of cystic fibrosis. It was not until 1938 that it was recognized as a separate disease, because lung infections are common to many conditions. Even today, the symptoms of CF sometimes can be confused with pneumonia or asthma.

Symptoms

Cystic fibrosis affects each person differently. Many people with CF do not appear to be severely ill. In general, people with CF have some or all of these symptoms:

  • Salty-tasting skin and sweat
  • Persistent cough or wheezing
  • Many respiratory infections
  • Bulky, smelly stools or bowel movements
  • Nasal polyps (small growths in the nose)
  • Enlargement of the fingertips and toes (clubbing)

Also, people with CF may eat large amounts of food but still be hungry. The food is not being digested properly, because the mucus is blocking the ability of digestive enzymes* and acids to break down food and absorb nutrients. Large portions of the poorly digested food are passed out during bowel movements. The individual may lose weight.

* enzymes
are natural substances that speed up specific chemical reactions in the body.

Later the pancreas may clog up and fail to secrete the enzymes essential to normal digestion. The liver becomes clogged, which may lead to cirrhosis (si-RO-sis), a condition in which the liver becomes hardened and fails. Diabetes also develops frequently in people with CF as they get older.

Diagnosis Doctors may begin to suspect CF soon after birth when the baby becomes ill with repeated respiratory infections, fails to gain weight despite a healthy appetite, and shows other symptoms of CF. In addition, about 10 percent of infants with CF have intestinal blockage due to thick mucus that is apparent at birth. Many of the symptoms of CF are common in people who do not have the disease, but there are tests to confirm a person has CF.

A sweat test is considered the best method to diagnose cystic fibrosis because it is relatively easy to perform and is accurate. The test determines the salt content of perspiration. Although sweat can seem salty in people without CF, the level of salt in the perspiration of people with CF is higher. A more complicated test looks for the CF gene on both copies of chromosome 7.

A Morning Ritual for Rachel

After her doctor determined that Rachel had cystic fibrosis, her parents worried she would not have a chance to do many of the same things as her older sister or other children. But as she grew, Rachel went to school, participated in sports, and did many other everyday activities.

Most people with CF get treatment that involves helping them breathe more easily and digest food better, which makes day-to-day activities less difficult. Although their symptoms can range from mild to severe, many people with CF receive treatments similar to Rachels.

For example, Rachel receives chest physical therapy. Each morning, her parents vigorously thump Rachels back and chest to help loosen the thick mucus in her lungs so she can cough it out. They learned the technique from a physical therapist after Rachel was diagnosed with CF.

Coughing is one of the main ways that people with CF can clear the mucus from their lungs. In school, Rachels teachers were told to expect her to cough often. Although the teacher and the students knew Rachel had CF, they did not make a big deal about her coughing. Rachel kept her own box of tissues on her desk, so she could cough the mucus into it and toss it into a nearby garbage can.

Turning on the CF Gene

In 1989, scientists discovered the location of the CF gene. If they could replace the defective gene with a normal gene, then they would be able to cure the cells that produce the defective CF protein. This would mean the mucus in the respiratory and digestive systems would be thin and easy flowing as opposed to thick and sticky.

In 1990, two teams of researchers were able to correct CF cells in lab dishes, by adding normal copies of the gene. In the spring of 1993 the first experimental dose was given to a person with CF. In October 1993, scientists determined that gene treatment had repaired a damaged gene in a human patient.

Gene therapy is a complicated experimental process. Scientists are beginning to understand what methods can be used to deliver the gene to the parts of the body where it can do its work. And they are studying how often the treatment would need to be repeated to assure the best results.

It could be that the gene therapy never would be able fix all of the defective genes, but it might cause enough of them to work properly to improve the quality of life for people with CF.

Rachel also participated in physical education classes. Exercise is another way that people with CF loosen the mucus in their lungs. Sometimes Rachel got tired more quickly than the other children, because she could not breathe as easily. But she joined in many of the exercises and games on most days.

At lunch and other times she ate a meal or snacks, Rachel took pills. The pills contained enzymes to help her digest food. Without them, the mucus in her digestive system would prevent her from getting the nutrients she needs from food. Even with the enzyme pills, Rachel and others with CF often need to take vitamin supplements and eat a diet rich in nutrients to assure they get the proper nourishment.

Rachel and others with CF also take antibiotics to prevent or treat lung infections. Sometimes, the antibiotics are taken as pills or inhaled into the lungs using a device called a nebulizer. People with CF also sometimes take prescription medications that thin the mucus and help reduce lung inflammation, which makes breathing easier and helps reduce the number of lung infections.

Perhaps the most exciting news for people with CF like Rachel was the discovery of the CF gene in 1989. It has led to research into gene therapy.

Living with CF

Once, CF almost always caused death in childhood. But treatments in recent decades have allowed many people with cystic fibrosis to live into adulthood. As with children, the symptoms for an adult can range from mild to severe, but eventually the recurring infections in the lungs begin to damage the lungs ability to function. This is the usual reason people with CF eventually die.

The Cystic Fibrosis Foundation says that now the average life expectancy of people with CF is 31 years. That is many years longer than in the past, but it still means only half of the people with CF will live that long. About half will live longer. With treatment, people with CF are able to do many of the things that other people do. And with work continuing in gene therapy, there is optimism that CF research is advancing toward a cure.

Boomer Fights Back

When Gunnar Esaison was diagnosed in 1993 with cystic fibrosis, his father, Boomer Esaison, decided to fight back. The Cincinnati Bengals quarterback, National Football League star, and television sports reporter had been a fierce competitor for many years. Now, his greatest battle became the fight against CF.

The NFL star started the Boomer Esaison Foundation, with the main goal being to find a cure for CF. The Foundation supports basic research and clinical trials for new CF treatments.

See also

Asthma

Genetic Diseases

Pneumonia

Resources

Books

Grinshaw, Joshua. My Heart Is Full of Wishes. Austin, TX: Raintree-Steck-Vaughn, 1995. A young boy with CF describes his dreams.

Harris, Ann. Cystic Fibrosis: The Facts. New York: Oxford University Press, 1995.

Silverstein, Alvin. Cystic Fibrosis. New York: Venture Books, 1994.

Organization

Cystic Fibrosis Foundation, 6931 Arlington Rd., Bethesda, MD 20814 http://www.cff.org

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cystic fibrosis

cystic fibrosis Hereditary glandular disease in which the body produces abnormally thick mucus that obstructs the breathing passages, causing chronic lung disease. There is a deficiency of pancreatic enzymes, an abnormally high salt concentration in the sweat and a general failure to gain weight. The disease is treated with antibiotics, pancreatic enzymes and a high-protein diet; sufferers must undergo vigorous physiotherapy to keep the chest as clear as possible.

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cystic fibrosis

cystic fibrosis A genetic disease due to a failure of the normal transport of chloride ions across cell membranes. This results in abnormally viscous mucus, affecting especially the lungs and secretion of pancreatic juice, hence impairing digestion.

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cystic fibrosis

cys·tic fi·bro·sis • n. a hereditary disorder affecting the exocrine glands. It causes the production of abnormally thick mucus, leading to the blockage of the pancreatic ducts, intestines, and bronchi.

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