Cystic fibrosis (CF), also called mucoviscidosis, is an autosomal recessive hereditary disease that affects the lungs, sweat glands and the digestive system.
Symptoms
The symptoms of CF usually develop during early childhood. Both lungs and pancreas produce abnormally viscous mucus. This mucus begins to build up and starts to clog the opening to the pancreas and the lungs. The mucus in the lungs can become a growth medium for bacteria, resulting in chronic respiratory infections and eventual permanent damage to the lung tissue. As lung function deteriorates, CF patients develop pulmonary hypertension and eventually cor pulmonale. Death usually occurs from severe infection or heart failure. These thick secretions also obstruct the pancreas, preventing digestive enzymes from reaching the intestines to help break down and absorb food.
The disease can be diagnosed by a high salt concentration in a baby's sweat or by genetic testing.
History and statistics
Cystic fibrosis (CF) was first described as a disease in the late 1930s. It is the most common genetic disease among people with European ancestry. Approximately one in every 25 people of European descent is a carrier for the cystic fibrosis gene, having one normal gene and one CF gene. Since cystic fibrosis is recessive, both copies of the gene have to be CF genes to cause the symptoms that occur in about 1 in every 2500 children. The high incidence of this lethal gene can be explained by the fact that CF carriers, who don't show any symptoms, enjoy some protection against cholera, since the extreme water loss in the intestines is prevented. People from areas where cholera is not a problem show a much lower incidence of CF. Genetic counseling and genetic testing is recommended for families who may be carriers of cystic fibrosis.
In 1988, the gene for CF was discovered by Francis Collins and Lap Tsu Chui on the seventh chromosome of the human genome.
Biological causes
At the genetic level, cystic fibrosis is the result of an in-frame deletion of three base pairs in the DNA. Cystic fibrosis results from the production of an abnormal CFTR protein (cystic fibrosis transmembrane conductance regulator). CFTR functions in transporting chloride ions across epithelial cells found in the lung and intestinal tract. Since water follows ions by osmosis, this results in water depletion and viscous mucus. The most common CFTR protein abnormality is a mutation termed ΔF508, which is characterized by the deletion of the DNA basepair sequence at chromosome location 7q that codes for a single amino acid, phenylalanine.
Recent medical research is beginning to show that an imbalance of essential fatty acids may play a role in cystic fibrosis. Tissue samples from both mice, and more recently humans, with CF show an excess of arachidonic acid (AA) and a deficiency of docosahexaenoic acid (DHA). Research has also indicated that healthy individuals with one copy of the CF gene and one copy of the normal gene have fatty acid levels in between those of CF patients and people with no CFTR gene mutations. Further research is needed to show how this is linked to the CFTR gene defect and what implications this may have on treatment of cystic fibrosis.
Complications
Cross-infection
CF patients often cannot interact with each other socially due to worries of cross-infection of Pseudomonas, MRSA, Burkholderia cepacia, and other bacteria. These infections thrive in the thick mucus of CF patients' lungs and cause complications and possibly death. Therefore CF patients who do not have a certain bacteria type cannot meet with those who do. Because of this risk CF patients must remain in isolation during hospital stays, and special precautions must be taken. This risk previously caused many CF clinics to recommend that CF patients live in isolation and never meet. However recently these views have been changed because of the possible psychological problems this may cause; instead CF patients are encouraged to exercise caution, avoid direct physical contact, and possibly wear surgical masks.
Digestion
In addition to pulmonary infections, most people with CF also have problems with digestion, particularly the digestion of fats. This leads to malabsorption and difficulty gaining and maintaining weight, which in turn affects overall health. This is due to the abnormally sticky mucus that blocks the release of digestive enzymes from the pancreas. Pancreatic insufficiency is treated with supplemental enzymes. Usually water-miscible forms of the fat-soluble vitamins A, D, E, and K are required as the decreased fat absorption can lead to deficiencies of these vitamins.
Diabetes
CF patients also have an increased incidence of diabetes mellitus because of the pancreatic blockage. The chronic blocking causes the Islets of Langerhans to degrade over time and decrease insulin production, causing hyperglycemia.
Other complications
Cystic fibrosis also causes a defect in the vas deferens causing sterility in approximately 98% of males with the disease. Also, men who were born with congenital absence of the vas deferens have an increased risk to be carriers of CF.
Many CF patients, to some degree, experience the widening of the tips of their fingers, known as "clubbing". The condition affects fingers and toes, and results in the tip of the digit being round and enlarged.
Treatment
Daily chest physiotherapy and aerosol breathing treatments are very commonly prescribed for CF treatment. Typical physical therapy involves manual chest percussion (pounding), or possibly using a device such as the ThAIRapy Vest or the Intrapulmonary Percussive Ventilator (IPV) to achieve the same effect: loosening of the thick mucus. Aerosolized medicines commonly given include albuterol, ipratropium bromide , and Pulmozyme to loosen secretions and decrease inflammation. Inhaled aminoglycoside antibiotics are sometimes given to fight infections.
CF patients are typically hospitalized somewhat regularly, often every 6 months depending on the severity of the case. Patients often have intravenous antibiotics through a PICC line or chest port .
Earlier approaches to diabetes treatment among CF patients generally did not address long-term effects because of the short CF life expectancy. However due to improving treatment of CF patients and their resulting longer lifespan, it is increasingly common to address diabetes symptoms that are not immediately harmful. As maintaining body weight is important for CF patients, a typical diabetic diet is not feasible and therefore insulin doses are instead adjusted to fit the typical high-calorie/high-fat CF diet.
Due to advances in medical treatment, the median life expectancy of a newborn with cystic fibrosis increased from 4 years (in the 1960s) to 32 years today. These procedures include the intake of digestion enzymes, nutritional supplements, percussion and postural drainage of the lungs, improved antibiotics and inhalation of aerosols containing medication. A few attempts at gene therapy were initially successful, but failed to produce acceptable long-term results.
Some cystic fibrosis patients go on to have a lung transplant.
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Last updated: 08-16-2005 22:25:53
