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Updated 13 February 2013

Cystic fibrosis

Cystic fibrosis is an inherited disease characterised by abnormally thick, sticky mucus that prevents organs such as the lungs and pancreas from working correctly.

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Summary

  • Cystic fibrosis is an inherited disease characterised by abnormally thick, sticky mucus that prevents organs such as the lungs and pancreas from working correctly.
  • Cystic fibrosis is the most common genetic disease in the white population.
  • Common symptoms of cystic fibrosis include intestinal blockage in newborns, salty-tasting skin, and chronic respiratory problems.
  • The standard diagnostic test for cystic fibrosis is the sweat test.
  • Mainstays of treatment include antibiotics, replacement enzymes and bronchial airway drainage.
  • The median life expectancy is just under 30 years (compared to about eight years three decades ago), and is increasing steadily.
  • Cystic fibrosis cannot be cured or prevented, but with current medical advances the outlook for those with the disease is steadily improving.

Alternative names

CF; mucoviscidosis

Definition

Cystic fibrosis (CF) is an inherited disease, in which the glands that secrete mucus, tears, sweat, saliva and digestive juices secrete an abnormally thick, sticky mucus. Instead of acting as a lubricant, the secretions may plug up tubes, ducts and passageways in the body, particularly in the lungs and pancreas.

People with CF often require frequent hospitalisation and nearly always the continuous use of medication and other treatments.

Who gets it and who is at risk?

About one child in 2000 is born with cystic fibrosis, and about one in 20 people are carriers (they carry the defective gene for CF but do not have the disease).

Cystic fibrosis is most common among Caucasians (whites) of Northern or Central European descent, and is far less common in other ethnic groups.

The greatest risk factor for CF is a family history of the disease. If both parents come from families with CF, the chances are one in four that each of their children will have CF.

Causes

Cystic fibrosis is caused by a defective gene. This gene is recessive, meaning you need to inherit two copies of it (one from each parent) to have the disease. The CF gene prevents the body from normal production of a protein called CFTR, which controls the transport of salt (chloride) into and out of cells. This is one of the ways in which the correct consistency of mucous is maintained. The protein product of the CF gene is defective, and does not allow sufficient salt to exit the cells. This results in the thick, sticky secretions, and increased salt in sweat.

If you inherit only one copy of the CF gene, you will not develop CF, but you may be a carrier and possibly pass the gene on to your children. If two carriers conceive a child, there is a 25% chance the child will have CF; a 50% chance the child will be a CF carrier; and a 25% chance the child will be neither a carrier nor have the disease.

Symptoms and signs

The specific symptoms of cystic fibrosis can vary, depending on the severity of the disease, and the age of the person with CF. Symptoms and signs include the following:

  • A salty taste to the skin, and sometimes salt crystals on the skin. People with CF tend to have two to five times the normal amount of salt in their sweat.
  • Thick sputum (substance produced by coughing or clearing the throat)
  • Chronic coughing or wheezing
  • Frequent respiratory infections
  • Growths (polyps) in the nasal passages
  • Meconium ileus (intestinal blockage in newborns): occurs when meconium — tar-like, greenish-black stools normally passed by an infant in the first 24-48 hours of life — becomes too thick to pass through the intestines.
  • A blockage in the bowel in older children and adults
  • Foul-smelling, greasy, bulky stools
  • Excessive appetite but poor weight gain
  • Delayed growth
  • Clubbing (enlargement or rounding) of the fingertips and toes
  • Diarrhoea
  • Chronic liver disease
  • Becoming tired easily
  • Displacement of one part of the intestine into another part (intussusception)
  • Protrusion of part of the rectum through the anus (rectal prolapse), often caused by stools that are difficult to pass or by excessive coughing

Diagnosis

The sweat test, the standard diagnostic test for cystic fibrosis, is a simple, painless test that measures the amount of chloride, or salt, in the sweat. Your doctor applies a sweat-stimulating chemical to a small area on your arm or leg. An electrode attached to the area stimulates a weak electric current, causing a tingling or warm feeling. After 5-12 minutes your doctor collects sweat from the stimulated area and sends it to the laboratory for chloride analysis. The sweat test is performed twice. A consistently high level of chloride indicates CF. This test does not reveal the severity of the disease, nor can it predict the outcome for a particular individual. As newborns may not produce enough sweat for a reliable diagnosis, the sweat test may not be performed until an infant is several months old.

Your doctor may perform genetic analysis of a blood sample to confirm a diagnosis of CF. In about 90% of cases, CF can be detected through genetic analysis.

You may also undergo tests to help determine the extent and severity of your CF. Among these are tests to measure lung, pancreas and liver function.

Because CF is an inherited disease, siblings of a child with the disease should be tested, even if they show no symptoms. Other family members, especially first cousins, may also want to be tested. In most cases family members can be screened with a sweat test, although sometimes gene testing may also be done. Screening of family members may detect the CF gene in 60-90% of carriers, depending on the test used.

Treatment

Treatment of cystic fibrosis depends on the severity of the disease and which organs are affected. Early diagnosis and comprehensive, intensive therapy can lengthen survival time and improve overall quality of life. Treatment may include the following:

Medication and nutrition

Antibiotics used to treat bacterial lung infections may be received orally, intravenously or inhaled directly into airways - such as the antibiotic tobramycin (TOBI).

Mucus-thinning drugs. The inhaled drug dornase alfa (Pulmozyme) makes mucus thinner and easier to cough up. Possible side effects include sore throat and chest irritation.

Bronchodilators. These inhaled medications, such as albuterol, are used to help clear bronchial secretions and keep the respiratory airways open.

Oral enzymes and better nutrition. Because of mucus blocking the digestive process, people with CF may need replacement oral pancreatic enzymes and other dietary supplements.

Physical Therapy

Chest physiotherapy, or bronchial airway drainage, includes postural drainage and chest percussion. Postural drainage involves positioning the body so that gravity encourages mucus drainage from a particular part of the lung. Sputum is then coughed up.

Percussion requires vigorously striking the back and chest with cupped hands to dislodge mucus in the lungs. Mechanical aids can also be used, such as a mechanical percussor (an electric chest "clapper"), or an inflatable vest with a machine attached that vibrates at high frequency. People with CF need bronchial airway drainage at least twice a day for 20 to 30 minutes. Your doctor or respiratory therapist will show you how to perform this procedure at home.

Surgery

Lung transplant may be considered in some cases.

Psychological support

Joining a support group where members share common experiences and problems can often alleviate the stress of living with CF.

Home treatment

If you or your child has CF, you need to be conscientious about prescribed medication and diet, early recognition of infection, and performing regular chest percussion. In addition, the following can help towards controlling the disease:

  • Ensure your child's immunizations are up to date. CF doesn't affect the immune system itself, but people with CF are more likely to develop complications when they fall ill.
  • Lead as normal and active a life as possible. Regular exercise is very important for people with CF, because it helps loosen mucus in the airways and strengthens the lungs and heart.
  • Eat a healthy diet.
  • Drink plenty of liquids to help loosen the mucus and avoid dehydration.
  • Ban smoking in your home, and avoid smoke as much as possible elsewhere. Passive smoking increases the risk of lung infection and makes it harder to breathe.
  • To protect against infection, ensure that family members wash their hands before eating, after using the bathroom, when coming home from work or school and after being in contact with anyone who has a transmissible illness.

Future treatments

There are several promising research directions towards finding a cure for cystic fibrosis. One area of genetic research aims to artificially insert copies of the normal gene into cells of the respiratory tract. The challenge is to find a way to deliver the normal genetic material to the affected cells. Different methods have been developed as delivery systems, and clinical trials are underway to test their effectiveness.

Other research is aimed at modifying the protein produced by the CF gene, to help normalise the movement of salt and water into and out of the cells, or to find other ways to stimulate cells to secrete chloride. This should produce thinner, less sticky mucus.

Another study suggests that the pain reliever ibuprofen may slow lung deterioration in some children with CF; further testing needs to be done to confirm this.

Prevention

The genetic cause of cystic fibrosis cannot be removed at present, although to a steadily increasing extent its negative effects are being alleviated. The only way to prevent people being born with CF is for two CF carriers not to have children. If you have a family history of CF, consider genetic counselling before starting a family.

You can go some way towards preventing the complications of CF, such as infections, by being vigilant about your or your child's health (see "Home Treatment").

Outcome

Progress in genetic research has lead to earlier detection of the disease. Because of this and improved treatment methods, many people with CF now live into their 30s and can lead fuller, healthier lives. The median life expectancy is just under 30 years (compared to about eight years three decades ago), and is increasing steadily.

The course of CF, which is largely determined by the degree of lung damage, varies greatly. Deterioration is inevitable, however. Death usually results from respiratory complications.

Complications of CF include the following:

  • Chronic respiratory infections. Respiratory infections are common because the thick mucus blocks the airways and provides a favourable environment for bacteria. The mucus also physically blocks the airways, making breathing difficult. Although antibiotics can reduce the frequency and severity of attacks, the bacteria are never completely eradicated, and may become resistant to long-term antibiotic use. Respiratory conditions may include:
    • Pneumonia: inflammation of the lungs.
    • Bronchitis: inflammation of the bronchial tubes - the airways leading to the lungs.
    • Bronchiectasis: abnormal dilation of the bronchial tubes that makes it more difficult to clear the airways.
    • Pneumothorax: collection of air between the membranes surrounding the lung, which can cause lung collapse.
    • Hemoptysis: coughing up blood from bleeding of the lung.
    • Chronic respiratory failure: chronic poor ventilation by the lungs.
    • Cor pulmonale: failure of one of the heart chambers, as a result of chronic respiratory problems.
  • Nutritional deficiencies and chronic diarrhoea. The thick mucus can obstruct the pancreas, where important digestive enzymes are made, preventing these from reaching the intestines and helping to digest food. The result is malabsorption (inadequate absorption of nutrients from the intestine) and malnutrition (lack of sufficient nutrition). Children with CF therefore often have delayed growth as a result of poor nutrition.
  • Liver disease. The bile duct, which carries secretions (bile) from the liver to the small intestine, may become blocked and inflamed, leading to liver problems.
  • Diabetes mellitus. Because CF often affects the pancreas, which is crucial in controlling blood sugar levels, about 7% of people with CF develop type 1 (insulin-dependent) diabetes.
  • Reproductive problems. Because thick secretions often block the vas deferens (the tube that transports sperm from the testes), about 98% of men with CF are sterile. Fertility methods and surgical procedures may sometimes allow men with CF to father children. Women with CF are less likely to conceive than healthy women, because thickened mucus in the reproductive system may retard the movement of sperm to the egg. However, conception and successful pregnancy are usually possible. Women should discuss and carefully consider all the possible risks with their doctor. Oral contraceptives can sometimes aggravate certain symptoms of CF, so different birth control options should be considered.
  • Osteoporosis and arthritis.

When to call the doctor

Consult your doctor if symptoms develop that suggest an infant or child may have cystic fibrosis (see Symptoms and Signs).

Call your doctor if a person diagnosed with CF develops new symptoms, particularly breathing difficulties, fever, a worsening cough, coughing up blood, increased fatigue or decreased appetite.

If you or your child has been diagnosed with CF, arrange for regular CF examinations, and see your local doctor for monitoring of medications and any lung or digestive problems.

Reviewed by Prof. Don du Toit, Faculty of Health Sciences, University of Stellenbosch

 
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