June 25, 2020
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NORD gratefully acknowledges Ran D. Anbar, MD, President and Founder, Center Point Medicine, La Jolla, CA and Professor Emeritus of Pediatrics and Medicine, SUNY Upstate Medical University, for assistance in the preparation of this report.
Cystic fibrosis is a genetic disorder that often affects multiple organ systems of the body. Cystic fibrosis is characterized by abnormalities affecting certain glands (exocrine) of the body especially those that produce mucus. Saliva and sweat glands may also be affected. Exocrine glands secrete substances through ducts, either internally (e.g., glands in the lungs) or externally (e.g., sweat glands). In cystic fibrosis, these secretions become abnormally thick and can clog up vital areas of the body causing inflammation, obstruction and infection. The symptoms of cystic fibrosis can vary greatly in number and severity from one individual to another. Common symptoms include breathing (respiratory) abnormalities including a persistent cough, shortness of breath and lung infections; obstruction of the pancreas, which prevents digestive enzymes from reaching the intestines to help break down food and may result in poor growth and poor nutrition; and obstruction of the intestines. Cystic fibrosis is slowly progressive and often causes chronic lung damage, which eventually results in life-threatening complications. Because of improved treatments and new treatment options, the outlook and overall quality of life of individuals with cystic fibrosis has improved and over 50 percent of individuals with the disorder are adults. Cystic fibrosis is caused by mutations to the cystic fibrosis transmembrane conductance regulator (CFTR) gene and is inherited as an autosomal recessive trait.
The symptoms of cystic fibrosis result because mucus secretions are abnormally thick and sticky, whereas normally they are thin and slippery and serve as a protective lubricant. Other secreted material such as saliva, sweat and digestive juices may also be affected. These abnormal secretions can clog up vital tubes, ducts and passageways throughout the body.
Multiple organ systems may be affected by cystic fibrosis, especially the lungs and pancreas. The intestines, liver, sweat glands and reproductive organs also are frequently affected. The symptoms of cystic fibrosis can vary greatly from one individual to another. Some individuals may only have respiratory problems without other complications. Some individuals may only have a few mild symptoms; others may have serious complications. The severity of specific symptoms also varies. In early life, many individuals may have mild respiratory complications, while others may have serious, life-threatening respiratory complications. Affected individuals will not have all the symptoms discussed below.
Cystic fibrosis is often apparent shortly after birth, but before newborn screening, when symptoms were not severe, CF may not have been detected until years later and, in rare cases, even as late as during adulthood. Most cases diagnosed in adulthood have no associated symptoms (asymptomatic) or only very mild symptoms. At this time, newborn screening for CF is provided throughout the United States, and thus it has become much rarer for CF to be newly diagnosed later in life.
Affected individuals develop a variety of breathing (respiratory) complications due to the production of thick, sticky mucus that clogs various air passages in the body. Associated symptoms include a persistent cough that often produces mucus or phlegm (productive cough), wheezing, and shortness of breath. Because mucus clogs the airways, bacteria become trapped and accumulate within the lungs and air passages making individuals particularly prone to developing repeated (chronic) respiratory infections that lead to inflammation of the main air passages of the lungs (bronchitis), inflammation of the sinuses (sinusitis) and inflammation of the lungs. Clogging of the airways with mucus may also make it difficult to breath.
The immune system of individuals with cystic fibrosis responds to an infection by sending white blood cells to attack the infection. After attacking the infection, white blood cells break down and further clog the airways. Debris from the white blood cells can be very destructive to lung tissue, and is thought to be a major contributor to the lung damage that occurs in cystic fibrosis. Further, this debris tends to be very “sticky,” which adds to the difficulty of its clearance from the lungs. The repeated cycle of infection and immune system response progressively damages the lungs. Chronic mucus blockage and infection of the respiratory passageways may cause them to become abnormally widened (bronchiestasis), which permits more mucus to build up and further increase the risk of infection. Eventually, continued damage to the lungs can cause life-threatening respiratory failure or enlargement and improper function of the lower right chamber (ventricle) of the heart (cor pulmonale). Enlargement of the ventricle occurs because the heart must work harder to try and pump blood through the damaged lungs.
In many cases, cystic fibrosis causes pancreatic insufficiency. The pancreas is a small organ located behind the stomach that secretes enzymes that travel to the intestines and aid in digestion. The pancreas also secretes other hormones such as insulin, which helps break down sugar. When mucous builds up in the pancreatic ducts, it may block the enzymes from reaching the intestines and helping the breakdown and absorption of food and nutrients. Failure of the body to breakdown and absorb nutrients is called malabsorption and can result in a variety of nutritional deficiencies in affected individuals. In childhood, it may result in failure of an affected child to grow and gain weight at the expected rate for age and sex (failure to thrive). Affected individuals may also have large, loose, foul-smelling stools that contain and excess of fat (steatorrhea) and other nutrients due to malabsorption.
The first symptom in 10-20% of cases diagnosed during infancy is meconium ileus -obstruction of the intestines at birth with a thick, tarry substance called meconium. Meconium is the medical term for an infant’s first stool, which is passed shortly after birth.
CF causes an abnormality that prevents the absorption of salt from sweat, which results in higher than normal levels of salt in the sweat. Salt depletion may upset the balance of minerals in the body, causing abnormal heart rhythms or the body to overheat.
Mucus can also accumulated within the small tubes that carry bile from the liver to the intestines (bile ducts) causing obstruction and inflammation. In some cases, high blood pressure of the major vein that carries blood to the liver from the digestive organs may occur (portal hypertension). Obstruction of the bile ducts can damage the liver, eventually leading to scarring of the liver (cirrhosis). Damage to the liver can potentially become life-threatening.
Most boys with cystic fibrosis are born without the small tubes that carry sperm out from the testes (congenital absence of the vas deferens) resulting in infertility. In other cases, male infertility may be caused by underdevelopment (atrophy) or damage (fibrosis) of the vas deferens. In some girls, fertility may be reduced due to the accumulation of abnormal mucus in the cervix and irregular menstrual periods.
Additional respiratory symptoms may be associated with cystic fibrosis including the development of small growths in the nose (nasal polyps), coughing up of blood (hemoptysis), recurrent episodes of lung collapse (pneumothorax), and abnormally fast breathing (tachypnea).
Additional gastrointestinal symptoms associated with cystic fibrosis may occur including recurrent abdominal pain, bloating (distention) of the abdomen, backflow of the contents of the stomach into the tube (esophagus) that connects the back of the mouth to the stomach (gastroesophageal reflux) and protrusion of part of the rectum through the anus (rectal prolapse). In some cases, the gall bladder may be filled with thick, sticky mucus and fail to function properly. The gall bladder is a small, pear-shaped organ located under the liver that stores bile. Some individuals may develop gall stones.
Most individuals with cystic fibrosis develop rounding or flattening (clubbing) of the tips of the fingers or toes.
Individuals with cystic fibrosis may be at risk for developing cystic fibrosis-related diabetes mellitus (CFRD). CFRD may occur in some adolescents with cystic fibrosis, although the prevalence increases during adulthood, as the longer patients live with cystic fibrosis, the more likely they are to develop CFRD. The onset of CFRD is slow and individuals may not have symptoms (asymptomatic). CFRD develops due to damage to the pancreas (which limits insulin production) and increased resistance to insulin. CFRD can also worsen lung function in affected individuals.
Another specific condition that may develop in individuals with cystic fibrosis is known as distal intestinal obstruction syndrome (DIOS), in which food, mucus and stool clog the intestines. This condition can cause stomach aches, bloating, cramping, nausea and loss of appetite. In severe cases, it may cause pain, vomiting and watery stools. The incidence of DIOS appears to increase with age; most cases tend to occur in adolescents and adults.
Cystic fibrosis is caused by mutations of the cystic fibrosis transmembrane conductance regulator (CFTR) gene. This defective gene is inherited as an autosomal recessive trait. Genetic diseases are determined by the combination of genes for a particular trait that are on the chromosomes received from the father and the mother.
Recessive genetic disorders occur when an individual inherits the same abnormal gene for the same trait from each parent. If an individual receives one normal gene and one gene for the disease, the person will be a carrier for the disease, but usually will not show symptoms. The risk for two carrier parents to both pass the defective gene and, therefore, have an affected child is 25 percent with each pregnancy. The risk to have a child who is a carrier like the parents is 50 percent with each pregnancy. The chance for a child to receive normal genes from both parents and be genetically normal for that particular trait is 25 percent. The risk is the same for males and females.
Investigators have determined that the CFTR gene is located on the long arm (q) of chromosome 7 (7q31.2). Chromosomes, which are present in the nucleus of human cells, carry the genetic information for each individual. Human body cells normally have 46 chromosomes. Pairs of human chromosomes are numbered from 1 through 22 and the sex chromosomes are designated X and Y. Males have one X and one Y chromosome and females have two X chromosomes. Each chromosome has a short arm designated “p” and a long arm designated “q”. Chromosomes are further sub-divided into many bands that are numbered. For example, “chromosome 7q31.2” refers to band 31.2 on the long arm of chromosome 7. The numbered bands specify the location of the thousands of genes that are present on each chromosome.
The CFTR gene primarily is expressed in cells lining the airways, gastrointestinal tract, pancreas, sweat glands, and genitourinary system. The gene controls the production of a protein that regulates the transfer of chloride and sodium across cell membranes. Accordingly, investigators speculate that inheritance of the defective CFTR gene results in disruption of chloride and sodium transfer, ultimately leading to low levels of certain bodily fluids (dehydration), abnormally thick mucus and other glandular secretions, salt loss, and impaired glandular functioning.
Cystic fibrosis is the most common, life-limiting recessive genetic disorder in Caucasians. Approximately 30,000 people have cystic fibrosis in the United States. One thousand new cases are diagnosed each year, with males and females affected in equal numbers. The disorder occurs predominately among Caucasians, occurring in approximately one of every 3,200 live Caucasian births compared to one in 3,900 live births of all Americans. Among African Americans, CF is manifest in about one in 15-17,000 live births. There is also a small but significant number of Americans of Asian descent who are affected by the disorder.
In many cases, CF is apparent soon after birth and most affected individuals are diagnosed by age 3. Approximately 10% of those affected were diagnosed after 18 years of age, but this figure is falling because of the institution of newborn screening.
A diagnosis of cystic fibrosis may be suspected based upon newborn screening, identification of characteristic symptoms (e.g., pulmonary disease, pancreatic insufficiency) or a positive family history. The standard diagnostic test for cystic fibrosis is the sweat test, a painless and simple procedure that measures the amount of salt in the sweat. Genetic testing can identify carriers of the defective gene. In May 2005, the U.S. Food and Drug Administration (FDA) approved the first DNA-based blood test to help detect cystic fibrosis. The Tag-It Cystic Fibrosis Kit directly analyzes human DNA to find genetic variations indicative of the disease. All 50 States have newborn screening for CF. In most states, immunoreactive trypsinogen (IRT) assays are performed on dried blood spots from newborns. Trypsinogen is synthesized in the pancreas and IRT levels are elevated in CF. Abnormal IRT results are followed up with sweat testing and/or molecular genetic (DNA-based) testing to confirm the diagnosis.
There is at present no cure for cystic fibrosis. Treatment depends upon the stage of the disease and the specific organs that are involved. Treatment is geared toward reducing the thickness and amount of mucus in the airways, preventing infections, preventing blockage of the intestines and ensuring the proper intake of vitamins and nutrients.
Various forms of chest physical therapy, such as applying cupped hands vigorously to the back and chest, helps to dislodge thick mucus from the lungs and maintain clear airways. Some physical therapy techniques require assistance from family members or friends; others can be performed by adults with cystic fibrosis without aid. In some cases, devices such as a mechanical vest may be used to help clear airways. This inflatable vest creates vibrations (high-frequency air waves) that loosen mucus in the chest. Other devices require affected individuals to blow into a tube, which helps loosen and dislodge mucus.
Antibiotics may be used to treat lung infections. The antibiotic drugs TOBI (tobramycin) and Cayston (aztreonam) have been approved by the Food and Drug Administration (FDA) for the treatment of bronchopulmonary infections of Pseudomonas aeruginosa (the most common source of chronic lung infection) in individuals with cystic fibrosis.
When the gastrointestinal system is involved, affected individuals may need to eat an enriched diet and/or take replacement vitamins, especially vitamins A, D, E and K, which are absorbed when mixed with fatty foods. Also, studies have shown that neonatal screening may provide an opportunity to prevent malnutrition in infants with cystic fibrosis. Pancreatic insufficiency may be treated by enzyme replacement therapy and diet.
The drug Pulmozyme (dornase alfa) was approved by the FDA for the treatment of CF in 1993. In clinical trials, this mucus-thinning drug reduced the rate of respiratory infection and improved pulmonary function. FDA approval is limited to those over the age of five years. Pulmozyme is a mucolytic, a drug designed to help thin, loosen and clear mucus.
Kalydeco (ivacaftor) was approved by the FDA in 2012 as a treatment for cystic fibrosis arising from the G551D mutation, as it is proven to be effective in patients with this mutation. Kalydeco also has been shown to be effective for adults with cystic fibrosis arising from the R117H-CFTR mutation. The drug targets abnormal chloride trafficking in cystic fibrosis, which is the condition’s underlying cause. It works by increasing the time that activated CFTR channels at the cell surface remain open, allowing for more normal chloride flux in lung tissue.
In 2014, Kalydeco was approved for expanded use to treat individuals age six and older who have eight additional cystic fibrosis mutations, which are similar in function to that of the G551D mutation. In 2017, Kalydeco was approved for expanded use to treat a total of 33 CFTR gene mutations.
In 2015, Orkambi (a combination of ivacaftor and lumacaftor) was approved to treat patients 12 years and older who have the F508del mutation. Having two copies of this mutation is the leading cause of CF, and this is the first drug approved for the specific mutation. In 2016, Orkambi was approved for CF patients with the F508del mutation aged 6-11 years.
In 2018, Symdeko (tezacaftor/ivacaftor) was approved to treat people with CF ages 12 and older who have two copies of the most common mutation in the CFTR gene, F508del, and for people who have one of 26 other specific CF mutations.
In 2019, the FDA approved Trikafta (elexacaftor/ivacaftor/tezacaftor) as the first triple combination therapy to treat patients 12 years and older with CF who have at least one F508del mutation in the CFTR gene, which is estimated to be ~90% of the CF population.
Medications that widen the bronchial tubes and aid in the clearing of mucus (bronchodilators) may be used in some cases. Albuterol is an example of a bronchodilator. Ibuprofen in high doses has been show to slow the rate of lung function decline in individuals with cystic fibrosis. Treatment of individuals with cystic fibrosis with hypertonic saline (sterilized, extra-salty water) has shown better mucus clearance and improved lung function in patients 6 years of age or older.
In severe cases of cystic fibrosis, a lung transplant may be necessary. A decision concerning lung transplant is made by physicians and other members of the health care team in careful consultation with the patient, based upon the specifics of his or her case; a thorough discussion of the potential benefits and risks; patient preference; and other appropriate factors. It is essential for patients to demonstrate their ability to be adherent to their prescribed cystic fibrosis therapies before transplant, because lack of adherence to anti-rejection therapy following transplantation can lead to a rapid death.
Genetic counseling is recommended for affected individuals and their families. Other treatment is symptomatic and supportive.
Information on current clinical trials is posted on the Internet at www.clinicaltrials.gov. All studies receiving U.S. Government funding, and some supported by private industry, are posted on this government web site.
For information about clinical trials being conducted at the NIH Clinical Center in Bethesda, MD, contact the NIH Patient Recruitment Office:
Tollfree: (800) 411-1222
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Some current clinical trials also are posted on the following page on the NORD website:
For information about clinical trials sponsored by private sources, contact:
For information about clinical trials conducted in Europe, contact:
Please note that some of these organizations may provide information concerning certain conditions potentially associated with this disorder.
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