Cystic fibrosis (CF) is a genetic condition that affects a protein in the body. People who have cystic fibrosis have a faulty protein that affects the body’s cells, tissues, and the glands that make mucus and sweat.
Mucus is normally slippery and protects the linings of the airways, digestive tract, and other organs and tissues. People who have cystic fibrosis make thick, sticky mucus that can build up and lead to blockages, damage, or infections in the affected organs. Inflammation also causes damage to organs such as the lungs and pancreas.
Some people who have cystic fibrosis have few or no symptoms, while others experience severe symptoms or life-threatening complications. Symptoms of cystic fibrosis depend on which organs are affected and the severity of the condition. The most serious and common complications of cystic fibrosis are problems with the lungs, also known as pulmonary or respiratory problems, which may include serious lung infections. People who have cystic fibrosis often also have problems maintaining good nutrition, because they have a hard time absorbing the nutrients from food. This is a problem that can delay growth.
Symptoms of cystic fibrosis depend on which organs are affected and the severity of the condition. Most people who have cystic fibrosis have noticeable symptoms. Some people have few or no symptoms, while others experience severe symptoms or life-threatening complications. Symptoms may also change over time.
Cystic fibrosis most commonly affects the lungs. Some people who have cystic fibrosis may have wheezing and a cough that may produce mucus or blood.
Other symptoms depend on the organs affected and may include:
- Blockage of the intestine in a baby soon after birth
- Clubbing of fingers and toes due to less oxygen getting to the hands and feet
- Fever, which may include night sweats
- Gastrointestinal symptoms, such as severe abdominal pain, chronic diarrhea, or constipation
- jaundice, or yellow skin, for an abnormally long time after birth
- Low body mass index (BMI) or being underweight
- Muscle and joint pain
- Delayed growth or puberty
- Salty skin and saltier than normal sweat
- Sinus infections
What causes cystic fibrosis?
Cystic fibrosis is an inherited disease caused by mutations in a genes called the cystic fibrosis transmembrane conductance regulator (CFTR) gene. The CFTR gene provides instructions for the CFTR protein. The CFTR protein is located in every organ of the body that makes mucus, including the lungs, liver, pancreas, and intestines, as well as sweat glands. The CFTR protein has also been found in other cells in the body, such as cells of the heart and the immune system. The mutations in the CFTR gene cause the CFTR protein to not work properly. This causes thick, sticky mucus and blockages in the lungs and digestive system.
Normally, mucus coats tiny hair-like structures called cilia in the airways of your lungs, which sweep the mucus particles up to the nose and mouth where your body can get rid of them. In people who have cystic fibrosis, this process does not work properly.
What gene mutations cause cystic fibrosis?
There are almost 2,000 known disease-causing mutations of the CFTR gene. Different mutations have different effects on how the CFTR protein is made and how it works. In the most common gene mutation, part of the CFTR gene is missing, resulting in a protein that does not work properly.
Normally, the CFTR protein controls the movement of ions from inside the cell to outside the cell. In people who have cystic fibrosis, the mutated gene causes the protein to not work properly, which, in turn, affects the movement of sodium and water. When this happens, the sweat glands make sweat that is saltier than it is in people who do not have cystic fibrosis. To diagnose cystic fibrosis, your doctor will assess your symptoms and recommend some tests, including a sweat test for high sweat chloride. Also, there is less water in the mucus, which makes the mucus thick and sticky. The thick mucus creates blockages in the lungs and digestive system.
How is cystic fibrosis inherited?
Every person inherits two CFTR genes, one gene from each parent. Children who inherit a CFTR gene with a mutation from both parents will have cystic fibrosis. When a mutated CFTR gene is inherited from only one parent and a normal CFTR gene is inherited from the other, the person will be a cystic fibrosis carrier. CF carriers are generally healthy, but they can pass the mutated CFTR gene on to their children.
Screening for cystic fibrosis
Genetic testing may be performed to look for carriers, as well as to screen relatives of people who have cystic fibrosis. Genetic testing may also be used as prenatal screening tool to look for a mutated CFTR gene. All newborns in the United States are now screened for cystic fibrosis. Since universal screening for cystic fibrosis began relatively recently, there are still young people and adults who have not been screened.
Carrier screening to detect CFTR mutations : Genetic testing can tell you if you carry a mutation of the CFTR gene. This is called carrier testing. People who have inherited a mutation of the CFTR gene from one parent are cystic fibrosis carriers. People who have inherited a mutation of the CFTR gene from both parents will have cystic fibrosis.
The standard test to check for possible cystic fibrosis carriers looks for 23 of the most common disease-causing gene mutations. If you have a positive test, there is a 99% chance you are a carrier. However, if you have a negative test, there is still a small chance that you could carry a CFTR mutation that did not show up on the test.
Siblings of a person who has cystic fibrosis may want to be tested for cystic fibrosis whether or not they have symptoms. Other relatives, such as first cousins and half-siblings, may be tested if they have symptoms, or if the family is concerned that the individual may have cystic fibrosis.
After a positive screening test, the diagnosis should be confirmed with further testing.
Prenatal screening: Couples who are planning to have children may want to be tested to see if they are cystic fibrosis carriers. Genetic testing, such as the carrier screening described above, may be done before or during pregnancy. Often, the mother is tested first. However, if you are already pregnant, you and your partner may choose to be tested at the same time. If the father has a family history of cystic fibrosis, he may be tested first. Similar to standard genetic testing, prenatal screening uses a sample of blood, saliva, or cells from the inside of your cheek to check your DNA.
If one partner is a carrier for a cystic fibrosis gene mutation, then the next step is to test the partner if this has not been done. If both parents are cystic fibrosis carriers, then prenatal diagnostic testing may be performed to see whether your unborn baby has cystic fibrosis or is a carrier.
Newborn screening: When a child has cystic fibrosis, it is very important to diagnose it early to help prevent complications. Newborn screening for cystic fibrosis is performed during a baby’s first 2 to 3 days of life. A few drops of blood from a heel prick are placed on a special card and analyzed in labs.
The type of newborn screening that is performed varies from state to state. Every state and the District of Columbia begins with a blood test to check for levels of a chemical made by the pancreas called immunoreactive trypsinogen (IRT). In people who have cystic fibrosis, IRT tends to be high. However, most babies with high levels of IRT do not have cystic fibrosis. IRT may also be high if the baby is premature, had a stressful delivery, or is a carrier of cystic fibrosis.
Some states test only IRT for cystic fibrosis newborn screening. Other states test IRT and also perform DNA testing. In states that test both IRT and DNA, if IRT is high, then the hospital will test the baby’s DNA for some of the gene mutations that cause cystic fibrosis.
After a positive screening test, the diagnosis should be confirmed with further testing.
Sweat test: A sweat test checks for high levels of chloride in your sweat. The sweat test is the standard test for diagnosing cystic fibrosis. It may be used if you have symptoms that may indicate cystic fibrosis or to confirm a positive diagnosis from a screening of your newborn baby. A normal sweat chloride test alone does not mean you do not have cystic fibrosis. Lower levels of chloride may indicate the need for further testing to diagnose or rule out cystic fibrosis.
Airway clearance techniques: Airway clearance techniques help loosen lung mucus so it can be cleared, reducing infections and improving breathing. The techniques include special ways of breathing and coughing, devices used by mouth and therapy vests that use vibrations to loosen mucus, and chest physical therapy. These techniques are often used along with medicines such as bronchodilators and mucus thinners.
Medicines: Medicines to treat cystic fibrosis include those used to maintain and improve lung function, fight infections, clear mucus and help breathing, and work on the faulty CFTR protein.
- Antibiotics prevent or treat lung infections and improve lung function. Your doctor may prescribe oral, inhaled, or intravenous (IV) antibiotics.
- Anti-inflammatory medicines, such as ibuprofen or corticosteroids, reduce inflammation. Inflammation causes many of the changes in cystic fibrosis, such as lung disease. Ibuprofen is especially beneficial for children, but side effects can include kidney and stomach problems. Corticosteroids can cause bone thinning and increased blood sugar and blood pressure.
- Bronchodilators relax and open airways. These treatments are taken by inhaling them.
- CFTR modulators improve the function of the faulty CFTR protein. They improve lung function and help prevent lung problems and other complications. Examples include ivacaftor and lumacaftor and a triple combination medicine (elexacaftor–tezacaftor–ivacaftor). The combination medicine is the first approved treatment that may help up to 90% of people who have cystic fibrosis. It is currently approved to use in adults and children older than 12 years.
- Mucus thinners make it easier to clear the mucus from your airways. These treatments are taken by inhaling them.
Surgery: Surgery may be an option for people with advanced conditions.
- A lung transplant may help people with advanced lung disease and respiratory failure.
- A liver transplant may be an option for advanced liver disease such as cirrhosis.