What is it?
Cystic fibrosis (CF) is an inherited condition that mainly affects the lungs, pancreas and sweat glands. It causes the production of thick, sticky mucous that leads to recurrent respiratory infections and blocks the release of pancreatic enzymes, inhibiting the digestion or protein and fat. CF is one of the most common recessive genetic disorders in people of European origin.
From infancy affected children experience recurrent chest infections causing lung damage, and intestinal malabsorption leading to severe malnutrition and growth failure. There is an excess of salt in the sweat. Untreated, the condition is usually fatal in infancy or early childhood. With treatment, the average life expectancy of people who live to adulthood is about 37 years and this is increasing.
The disease is caused by mutations in a pair of genes located on chromosome 7. Every cell in the body (except the sex cells) has 46 chromosomes (23 pairs - one of each pair inherited from the mother and the other from the father). Genes on these chromosomes form the body’s blueprint for producing proteins that control body functions. There is a gene on each number 7 chromosome that is responsible for the production of a protein called cystic fibrosis transmembrane regulator (CFTR). Mutations in this gene lead to absent or defective CFTR production, causing CF. More than 2,000 different CF mutations have been identified, although some are much more common than others, F508del (previously known as deltaF508) being the most common in Australia.
Since CF is recessive, an affected individual must have a mutation in each CFTR gene on each chromosome 7 in order to have the disease (one abnormal copy from each parent.) Someone with only one mutation (inherited from one parent) and one working copy of the gene will be a CF carrier. Carriers do not have symptoms of the disease but they may pass on the non-working copy of the gene to their children. Both parents must be carriers or one parent be a carrier and the other have CF in order for their child to have CF. Approximately 1 in 25 Australians are carriers of a genetic mutation responsible for CF.
Having CF means the absence of, or defective production and function of CFTR. This leads to abnormal electrolyte and water movement in and out of the epithelial cells (the cells that line most body cavities). It results in thick, sticky mucus in the lungs and pancreas leading to respiratory infections and/or obstructed pancreatic and liver ducts leading to impaired fat and protein digestion. The majority of males with CF are also infertile due to missing or underdeveloped vas deferens (the tubules that transport sperm from the testes). Most people with CF will develop respiratory and pancreatic symptoms very early in life, although symptom severity will vary from person to person, even in those with the same mutations.
CF is one of the most common recessive genetic disorders in people of European origin. Currently, there is no prevention or cure, only treatment of the symptoms. However, research is being conducted to develop a cure and to enhance treatments. In fact, great strides in this effort have been made over the past 30 years with improvements in diagnosis, delivery of care, and treatment modalities, such that the median life expectancy is now 37 years.
Symptoms
Signs and symptoms associated with CF include:
CF interferes with electrolyte and fluid balances in the body. In most individuals affected by CF, sweat is up to five times saltier than normal and severe salt depletion can occur in very hot weather.
Much of the illness associated with CF is due to respiratory infections and lung complications. From early childhood the abnormal composition of the fluid lining the airways makes affected individuals prone to infection. The lubricating mucus in the lungs becomes thick and sticky, leading to chronic infections, severe inflammation and eventual lung damage. However, with early diagnosis through neonatal screening, early recognition of infection and aggressive treatment of the infections using oral, inhaled and intravenous antibiotics, chronic infection can be delayed or even prevented in many of those affected.
The excessively thick and sticky secretion lining the pancreatic ducts leads to obstruction and extensive destruction of pancreatic tissue. The resulting deficiency of pancreatic enzymes and bicarbonate causes severe intestinal malabsorption of fat and protein and fat-soluble vitamins with foul-smelling, greasy stools. Nutritional support with oral high energy supplements, pancreatic enzyme replacement therapy and supplements of fat-soluble vitamins A, D, E and K can, in many people, achieve improved absorption, nutritional state and growth. So most patients now survive into adult life, but some patients develop CF-related diabetes due to pancreatic damage, and some patients develop osteoporosis.
Other problems and symptoms associated with CF include:
Tests
Laboratory tests may be used to screen for and help diagnose cystic fibrosis (CF), to determine whether someone is a genetic carrier of CF, and/or to evaluate a person with CF to help manage the condition.
Tests for screening and diagnosis:
Even when there is no family history of the disorder, the Royal Australian and New Zealand College of Obstetricians and Gynaecologists (RANZCOG) recommends that all couples planning a pregnancy or in their first trimester be offered information on carrier screening test for the more common genetic conditions that affect children, including cystic fibrosis.
All Australian newborn screen programs screen babies for cystic fibrosis. The following can be used in the testing for CF. Positive screening results may be followed by sweat chloride testing for confirmation.
Immunoreactive trypsin (IRT)
This newborn screening test for CF is performed on the blood spots collected on dried blood spot screening cards. Trypsinogen is produced in the pancreas and transported to the intestine, where it is activated to form the enzyme trypsin. In CF, thick mucus can obstruct pancreatic ducts and prevent trypsinogen from reaching the intestine. Blood IRT are elevated in people with CF, but positive results must be followed by confirmatory sweat chloride testing.
Elevated IRT in the first few days of life can also be caused by perinatal stress, renal failure, congenital infection, bowel atresia and some aneuploidies. An elevated IRT is usually followed with testing for the most common CFTR mutations including the F508del. Early diagnosis is essential so that treatment can be started before damage to the lungs with chronic infection occurs and malnutrition becomes established.
CF gene mutation
The most common CFTR mutation is F508del, which accounts for most of the mutations in those of Northern European descent. Testing of F508del in isolation or a panel of around 50 common mutations of the CF gene has been developed to screen general or targeted populations for CF and CF carrier status (the number of mutations screened within the panel varies between laboratories). Some laboratories offer expanded panels of up to 100 or more mutations. Less common mutations may not be detected. People who undergo CF gene mutation testing should receive genetic counselling to understand the implications of the results.
Sweat Chloride Test
This test involves measuring sodium and chloride from a sweat sample collected in a procedure in which local sweating is stimulated by using the drug, pilocarpine. Since the CFTR protein is altered or missing and chloride travel is restricted, the sweat in somone with CF may be up to five times saltier than normal. This test is considered the "gold standard" and is used to confirm positive newborn screening tests as well as to diagnose older children and adults.
Other laboratory tests used to check lung infection, organ function and fertility include:
Non-laboratory tests that may be performed include respiratory function tests, chest X-rays, lung scans including low-dose CT scan to look for air trapping and early bronchiectasis, bronchoscopies, bone scans, upper GI and small bowel X-rays and other gastrointestinal pancreatic and liver investigations such as ultrasound scans.
Treatment
Currently, there is no cure for cystic fibrosis and prevention is not possible at the present time. If a couple is known to be at high risk of having a child with CF, early detection can be accomplished with prenatal CF gene mutation testing, using amniocentesis or chorionic villi collection.
Newborn screening programs based on IRT testing and CF gene mutation testing are widely available in Australia. Early identification of a baby with CF enables parents to seek information, be referred to a specialist CF centre for expert help and to start early treatments of their infants to prevent or minimize lung damage and nutritional problems.
Treatments are tailored for the individual and goals usually involve activities to loosen and remove excess mucus from the lungs, prevent lung infections and blockages in the digestive tract and to provide adequate nutrition with specialised diets.
Some therapies may include exercise regimens and physical therapy as well as drugs such as antibiotics, anti-inflammatory medications, and bronco-dilators in addition to oral pancreatic enzymes and vitamin supplements.
Newer therapies called CTFR modulators have been developed. They may be used to correct the function of defective CTFR proteins. These modulators are effective only for CF patients with specific CF gene mutations.
Some people with CF may undergo a lung transplant, which can allow them to live longer and improves their quality of life. Research is being conducted to develop a cure and to enhance treatments. Great strides have been made over the past ten years, which are allowing many people with CF to live longer with improvement in quality of life.
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