An inherited condition that causes body secretions to be thick and abnormal
- Present at birth
- Due to an abnormal gene inherited from both parents
- Gender and lifestyle are not significant factors
Cystic fibrosis is the most common severe inherited disease among white people of European and North American origin. In the UK, about 1 in 2,500 babies is born with the disorder. Cystic fibrosis is much less common in people of African or Asian descent. The disorder affects all the fluid-and mucus-secreting glands in the body, leading to production of abnormally thick secretions, especially in the lungs and pancreas. As a result, children with cystic fibrosis experience recurrent chest infections and may have difficulty absorbing nutrients from food.
In the past, severe chest infections were a major cause of death in children with cystic fibrosis. Today, with better understanding of the disease and recent advances in treatment, most affected children survive into adulthood.
What are the causes?
Cystic fibrosis is caused by an abnormal gene, which is carried by about 1 in 25 people and inherited in an autosomal recessive manner (see Gene disorders). The abnormal gene occurs on chromosome number 7. Over 1,500 different mutations (abnormalities) in the gene have now been identified. Of these, the most common is called delta F508, and this is the cause of more than 7 in 10 cases of cystic fibrosis.
What are the symptoms?
A newborn baby with cystic fibrosis may have a swollen abdomen and may not pass meconium (thick, sticky faeces passed by newborn infants) for the first few days following birth. Other symptoms of cystic fibrosis usually develop later in infancy and may include:
Failure to put on weight or grow at the normal rate.
Pale, greasy faeces that float and have a particularly offensive smell.
Recurrent chest infections.
In many cases of cystic fibrosis, a constant cough develops, producing large amounts of sticky mucus.
Are there complications?
As cystic fibrosis progresses, the lung disorder bronchiectasis may occur, in which the main airways are abnormally widened. Abscesses may also form in the lungs. Further complications may include liver damage (see Cirrhosis) and persistent inflammation of the sinuses (see Sinusitis). About 1 in 20 children who have cystic fibrosis develop diabetes mellitus. In all affected children, abnormally high levels of salt are excreted in the sweat, which may lead to dehydration in hot weather.
Children with cystic fibrosis sometimes develop psychological problems as a result of the many difficulties that are associated with lifelong illness. Affected children may be unable to participate in normal childhood and school activities due to continual bad health and may therefore feel isolated.
In later life, almost all males with cystic fibrosis are infertile as a result of a birth defect in which the two vasa deferentia (the tubes through which sperm are propelled) are absent. About 1 in 5 affected females are infertile because the mucus secretions produced by the reproductive organs are abnormally thick.
How is it diagnosed?
All newborn babies are routinely screened for cystic fibrosis as part of the blood spot screening tests. An early diagnosis improves the long-term outlook by helping to prevent damage to the lungs in infancy. If the doctor suspects that a child has the condition later in infancy, a sweat test may be carried out to look for abnormally high levels of salt in the baby’s sweat. A sample of blood may also be tested to look for the abnormal gene. If the test result is found to be positive, siblings of the affected child can also be tested.
What is the treatment?
Treatment for cystic fibrosis is aimed at slowing the progression of lung disease and maintaining adequate nutrition.
Chest physiotherapy is usually performed twice a day to remove secretions from the lungs. Parents and older affected children are often taught how to carry out this procedure at home. If an affected child develops a chest infection, he or she will require immediate treatment with antibiotics. In addition, long-term use of antibiotics may be necessary to prevent other chest infections from developing. Older children sometimes require regular courses of intravenous antibiotics to eliminate bacteria that become established in the lung secretions. In this case, a permanent catheter may be inserted under general anaesthesia just below the chest wall so that antibiotics can be administered more easily (see Antibiotic delivery system). Some children with cystic fibrosis can be helped by inhaled drugs that reduce the stickiness of the secretions in the lungs. If the lungs are very severely damaged, it may be possible to carry out a heart–lung transplant.
A high-calorie diet helps to ensure that a child with cystic fibrosis grows normally. Most children also need to take pancreatic enzymes and vitamin supplements with every meal.
An affected child and his or her family will be offered psychological support, particularly during adolescence, when long-term illness is especially difficult to cope with. Family members may also find it helpful to join a support group.
Can it be prevented?
Genetic testing means that carriers can be identified and the condition can be detected antenatally. This form of testing may be offered to adults with a family history of cystic fibrosis and to partners of people who have the disease. If these test results are positive, the couple will be offered genetic counselling. A couple who are at risk may opt to use assisted conception, which enables the embryo to be tested for the abnormal gene before it is implanted by in-vitro fertilization. Pregnant women may be offered antenatal genetic tests.
In the future, cystic fibrosis may be treated with gene therapy, in which a normal gene is introduced into relevant tissues to prevent cystic fibrosis from developing.
What is the prognosis?
The average life expectancy of a person with cystic fibrosis has increased over the past 35 years. Due to advances in the specialized treatment of cystic fibrosis, most people with the disorder now survive into their third decade.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.
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