Cystic fibrosis

Cystic fibrosis is a hereditary disease affecting the exocrine (mucus) glands of the lungs, liver, pancreas, and intestines, causing progressive disability due to multisystem failure.

Thick mucus production results in frequent lung infections. Diminished secretion of pancreatic enzymes is the main cause of poor growth, fatty diarrhea, and deficiency in fat-soluble vitamins. Males can be infertile due to the condition congenital bilateral absence of the vas deferens. Often, symptoms of CF appear in infancy and childhood. Meconium ileus is a typical finding in newborn babies with CF.

Individuals with cystic fibrosis can be diagnosed prior to birth by genetic testing. Newborn screening tests are increasingly common and effective (although false positives may occur, and children need to be brought in for a sweat test to distinguish disease vs carrier status). The diagnosis of CF may be confirmed if high levels of salt are found during a sweat test, although some false positives may occur.

There is no cure for CF, and most individuals with cystic fibrosis die young: many in their 20s and 30s from lung failure. However, with the continuous introduction of many new treatments, the life expectancy of a person with CF is increasing to ages as high as 40 or 50. Lung transplantation is often necessary as CF worsens.

Cystic fibrosis is one of the most common life-shortening, childhood-onset inherited diseases.

CF is caused by a mutation in a gene called the cystic fibrosis transmembrane conductance regulator (CFTR). The product of this gene is a chloride ion channel important in creating sweat, digestive juices, and mucus. Although most people without CF have two working copies (alleles) of the CFTR gene, only one is needed to prevent cystic fibrosis. CF develops when neither allele can produce a functional CFTR protein. Therefore, CF is considered an autosomal recessive

Symptomatic diseases

Lung and sinus disease

Lung disease results from clogging the airways due to mucus buildup and resulting inflammation. Inflammation and infection cause injury to the lungs and structural changes that lead to a variety of symptoms. In the early stages, incessant coughing, copious phlegm production, and decreased ability to exercise are common. Many of these symptoms occur when bacteria that normally inhabit the thick mucus grow out of control and cause pneumonia. In later stages of CF, changes in the architecture of the lung further exacerbate chronic difficulties in breathing.

(Aspergillus fumigatus - A common fungus which can lead to worsening lung disease in people with CF)

Other symptoms include coughing up blood (hemoptysis), changes in the major airways in the lungs (bronchiectasis), high blood pressure in the lung (pulmonary hypertension), heart failure, difficulties getting enough oxygen to the body (hypoxia), and respiratory failure requiring support with breathing masks such as bilevel positive airway pressure machines or ventilators. In addition to typical bacterial infections, people with CF more commonly develop other types of lung disease. Among these is allergic bronchopulmonary aspergillosis, in which the body's response to the common fungus Aspergillus fumigatus causes worsening of breathing problems. Another is infection with mycobacterium avium complex (MAC), a group of bacteria related to tuberculosis, which can cause further lung damage and does not respond to common antibiotics.

Mucus in the paranasal sinuses is equally thick and may also cause blockage of the sinus passages, leading to infection. This may cause facial pain, fever, nasal drainage, and headaches. Individuals with CF may develop overgrowth of the nasal tissue (nasal polyps) due to inflammation from chronic sinus infections. These polyps can block the nasal passages and increase breathing difficulties.

Gastrointestinal, liver and pancreatic disease

Prior to prenatal and newborn screening, cystic fibrosis was often diagnosed when a newborn infant failed to pass feces (meconium). Meconium may completely block the intestines and cause serious illness. This condition, called meconium ileus, occurs in 10% of newborns with CF. In addition, protrusion of internal rectal membranes (rectal prolapse) is more common in CF because of increased fecal volume, malnutrition, and increased intra–abdominal pressure due to coughing.

The thick mucus seen in the lungs and its counterpart in thickened secretions from the pancreas, an organ responsible for providing digestive juices which help break down food. These secretions block the movement of the digestive enzymes into the duodenum and result in irreversible damage to the pancreas, often with painful inflammation (pancreatitis). The lack of digestive enzymes leads to difficulty absorbing nutrients with their subsequent excretion in the faeces, a disorder known as malabsorption. Malabsorption leads to malnutrition and poor growth and development because of calorie loss. Individuals with CF also have difficulties absorbing the fat-soluble vitamins A, D, E, and K. In addition to the pancreas problems, people with cystic fibrosis experience more heartburn, intestinal blockage by intussusception, and constipation. Older individuals with CF may also develop distal intestinal obstruction syndrome when thickened faeces cause intestinal blockage.

Thickened secretions also may cause liver problems in patients with CF. Bile secreted by the liver to aid in digestion may block the bile ducts, leading to liver damage. Over time, this can lead to cirrhosis, in which the liver fails to rid the blood of toxins and does not make important proteins such as those responsible for blood clotting.

Endocrine disease and growth

(Clubbing Patients with CF can often have enlargement of their fingers)

The pancreas contains the islets of Langerhans, which are responsible for making insulin, a hormone that helps regulate blood glucose. Damage of the pancreas can lead to loss of the islet cells, leading to diabetes that is unique to those with the disease. Cystic Fibrosis Related Diabetes (CFRD), as it is known as, shares characteristics that can be found in Type 1 and Type 2 diabetics and is one of the principal non-pulmonary complications of CF.Vitamin D is involved in calcium and phosphorus regulation. Poor uptake of vitamin D from the diet because of malabsorption leads to the bone disease osteoporosis in which weakened bones are more susceptible to fractures. In addition, people with CF often develop clubbing of their fingers and toes due to the effects of chronic illness and low oxygen on their tissues.

Poor growth is a hallmark of CF. Children with CF typically do not gain weight or height at the same rate as their peers, and occasionally are not diagnosed until investigation is initiated for poor growth. The causes of growth failure are multi–factorial and include chronic lung infection, poor absorption of nutrients through the gastrointestinal tract, and increased metabolic demand due to chronic illness.

Infertility

Infertility affects both men and women. At least 97 percent of men with cystic fibrosis are sterile. These men make normal sperm but are missing the tube (vas deferens), which connects the testes to the ejaculatory ducts of the penis. Many men found to have congenital absence of the vas deferens during evaluation for infertility have a mild, previously undiagnosed form of CF. Some women have fertility difficulties due to thickened cervical mucus or malnutrition. In severe cases, malnutrition disrupts ovulation and causes amenorrhea

Diagnosis and monitoring

Cystic fibrosis may be diagnosed by many different categories of testing including those such as, newborn screening, sweat testing, or genetic testing. The newborn screen initially measures for raised blood concentration of immunoreactive trypsinogen. Infants with an abnormal newborn screen need a sweat test in order to confirm the CF diagnosis. Trypsinogen levels can be increased in individuals who have a single CF gene (carriers) or, in rare instances, even in individuals without a CF gene. Due to these false positives, CF screening in newborns is somewhat controversial. Therefore, most individuals are diagnosed after symptoms prompt an evaluation for cystic fibrosis. The most commonly-used form of testing is the sweat test. Sweat-testing involves application of a medication that stimulates sweating (pilocarpine) to one electrode of an apparatus and running electric current to a separate electrode on the skin. This process, called iontophoresis, causes sweating; the sweat is then collected on filter paper or in a capillary tube and analyzed for abnormal amounts of sodium and chloride. People with CF have increased amounts of sodium and chloride in their sweat. CF can also be diagnosed by identification of mutations in the CFTR gene.

A multitude of tests are used to identify complications of CF and to monitor disease progression. X-rays and CAT scans are used to examine the lungs for signs of damage or infection. Examination of the sputum under a microscope is used to identify which bacteria are causing infection so that effective antibiotics can be given. Pulmonary function tests measure how well the lungs are functioning, and are used to measure the need for and response to antibiotic therapy. Blood tests can identify liver problems, vitamin deficiencies, and the onset of diabetes. DEXA scans can screen for osteoporosis and testing for fecal elastase can help diagnose insufficient digestive enzymes.

The role of chronic infection in lung disease

The lungs of individuals with cystic fibrosis are colonized and infected by bacteria from an early age. These bacteria, which often spread amongst individuals with CF, thrive in the altered mucus, which collects in the small airways of the lungs. This mucus encourages the development of bacterial microenvironments (biofilms) that are difficult for immune cells (and antibiotics) to penetrate. The lungs respond to repeated damage by thick secretions and chronic infections by gradually remodeling the lower airways (bronchiectasis), making infection even more difficult to eradicate.

Over time, both the types of bacteria and their individual characteristics change in individuals with CF. In the initial stage, common bacteria such as Staphylococcus aureus and Hemophilus influenzae colonize and infect the lungs. Eventually, however, Pseudomonas aeruginosa dominates. Once within the lungs, these bacteria adapt to the environment and develop resistance to commonly used antibiotics. Pseudomonas can develop special characteristics that allow the formation of large colonies, known as "mucoid" Pseudomonas, which are rarely seen in people that do not have CF.

One way in which infection has spread is by passage between different individuals with CF. In the past, people with CF often participated in summer "CF Camps" and other recreational gatherings. Hospitals grouped patients with CF into common areas and routine equipment (such as nebulizers) was not sterilized between individual patients. This led to transmission of more dangerous strains of bacteria among groups of patients. As a result, individuals with CF are routinely isolated from one another in the healthcare setting and healthcare providers are encouraged to wear gowns and gloves when examining patients with CF in order to limit the spread of virulent bacterial strains. Often, patients with particularly damaging bacteria will attend clinics on different days and in different buildings than those without these infections.

Treatment

(A typical breathing treatment for cystic fibrosis, using a mask nebuliser and the ThAIRapy Vest)

The cornerstones of management are proactive treatment of airway infection, and encouragement of good nutrition and an active lifestyle. The treatment for cystic fibrosis continues throughout a patient's life, and is aimed at maximizing organ function, and therefore quality of life. At best, current treatments delay the decline in organ function. Treatment typically occurs at specialist multidisciplinary centres, and is tailored to the individual, because of the wide variation in disease symptoms. Targets for therapy are the lungs, gastrointestinal tract (including insulin treatment), the reproductive organs (including Assisted Reproductive Technology (ART)) and psychological support. In addition, therapies such as transplantation and gene therapy aim to cure some of the effects of cystic fibrosis.

The most consistent aspect of therapy in cystic fibrosis is limiting and treating the lung damage caused by thick mucus and infection with the goal of maintaining quality of life. Intravenous, inhaled, and oral antibiotics are used to treat chronic and acute infections. Mechanical devices and inhalation medications are used to alter and clear the thickened mucus. These therapies, while effective, can be extremely time consuming to the patient. One of the most important battles that CF patients face is finding the time to comply with all the prescribed treatments while balancing a normal life.

Antibiotics to treat lung disease

Many CF patients are on one or more antibiotics at all times, even when they are considered healthy, to suppress the infection as much as possible. Antibiotics are absolutely necessary whenever pneumonia is suspected or there has been a noticeable decline in lung function. Antibiotics are usually chosen based on the results of a sputum analysis and the patients past response. Many bacteria common in cystic fibrosis are resistant to multiple antibiotics and require weeks of treatment with intravenous antibiotics such as vancomycin, tobramycin, meropenem, ciprofloxacin, and piperacillin. Inhaled therapy with antibiotics such as tobramycin and colistin is often given for months at a time in order to improve lung function by impeding the growth of colonized bacteria. Inhaled therapy with the antibiotic aztreonam is also being developed and clinical trials have shown great promise. Oral antibiotics such as ciprofloxacin or azithromycin are given to help prevent infection or to control ongoing infection. Some individuals spend years between hospitalizations for antibiotics, whereas others require several antibiotic treatments each year.

Several common antibiotics such as tobramycin and vancomycin can cause hearing loss, damage to the balance system in the inner ear or kidney problems with long-term use. In order to prevent these side-effects, the amount of antibiotics in the blood are routinely measured and adjusted accordingly.

Other methods to treat lung disease

Several mechanical techniques are used to dislodge sputum and encourage its expectoration. In the hospital setting, physical therapy is utilized; a therapist pounds an individual's chest with his or her hands several times a day. Devices that recreate this percussive therapy include the ThAIRapy Vest and the intrapulmonary percussive ventilator (IPV). Newer methods such as Biphasic Cuirass Ventilation, and associated clearance mode available in such devices, now integrate a cough assistance phase, as well as a vibration phase for dislodging secretions. Biphasic Cuirass Ventilation is also shown to provide a bridge to transplantation. These are portable and adapted for home use. Aerobic exercise is of great benefit to people with cystic fibrosis. Not only does exercise increase sputum clearance but it also improves cardiovascular and overall health.

Aerosolized medications that help loosen secretions include dornase alfa and hypertonic saline. Dornase is a recombinant human deoxyribonuclease, which breaks down DNA in the sputum, thus decreasing its viscosity. N-Acetylcysteine may also decrease sputum viscosity, but research and experience have shown its benefits to be minimal. Albuterol and ipratropium bromide are inhaled to increase the size of the small airways by relaxing the surrounding muscles.

As lung disease worsens, breathing support from machines may become necessary. Individuals with CF may need to wear special masks at night that help push air into their lungs. These machines, known as bilevel positive airway pressure (BiPAP) ventilators, help prevent low blood oxygen levels during sleep. BiPAP may also be used during physical therapy to improve sputum clearance. During severe illness, people with CF may need to have a tube placed in their throats and their breathing supported by a ventilator.

Treatment of other aspects of CF

(Intracytoplasmic sperm injection is used to provide fertility for men with cystic fibrosis)

Newborns with meconium ileus typically require surgery, whereas adults with distal intestinal obstruction syndrome typically do not. Treatment of pancreatic insufficiency by replacement of missing digestive enzymes allows the duodenum to properly absorb nutrients and vitamins that would otherwise be lost in the faeces. Even so, most individuals with CF take additional amounts of vitamins A, D, E, and K and eat high-calorie meals. It should be noted, however, that nutritional advice given to patients is, at best, mixed: Often, literature encourages the eating of high-fat foods without differentiating between saturated, unsaturated fat, and trans-fats; this lack of clear information runs counter to health advice given to the general population, and creates the risk of further serious health problems for people with cystic fibrosis as they grow older. So far, no large-scale research involving the incidence of atherosclerosis and coronary heart disease in adults with cystic fibrosis has been conducted. This is likely due to the fact that the vast majority of people with cystic fibrosis do not live long enough to develop clinically significant atherosclerosis or coronary heart disease.

The diabetes common to many CF patients is typically treated with insulin injections or an insulin pump. Development of osteoporosis can be prevented by increased intake of vitamin D and calcium, and can be treated by bisphosphonates. Poor growth may be avoided by insertion of a feeding tube for increasing calories through supplemental feeds or by administration of injected growth hormone.

Sinus infections are treated by prolonged courses of antibiotics. The development of nasal polyps or other chronic changes within the nasal passages may severely limit airflow through the nose. Sinus surgery is often used to alleviate nasal obstruction and to limit further infections. Nasal steroids such as fluticasone are used to decrease nasal inflammation. Female infertility may be overcome by assisted reproduction technology, particularly embryo transfer techniques. Male infertility may be overcome with intracytoplasmic sperm injection. Third party reproduction is also a possibility for women with CF.

Transplantation and gene therapy

Lung transplantation often becomes necessary for individuals with cystic fibrosis as lung function and exercise tolerance declines. Although single lung transplantation is possible in other diseases, individuals with CF must have both lungs replaced because the remaining lung would contain bacteria that could infect the transplanted lung. A pancreatic or liver transplant may be performed at the same time in order to alleviate liver disease and diabetes. Lung transplantation is considered when lung function approaches a point where it threatens survival or requires assistance from mechanical devices.

Gene therapy holds promise as a potential avenue to cure cystic fibrosis. Gene therapy attempts to place a normal copy of the CFTR gene into affected cells. Studies have shown that to prevent the lung manifestations of cystic fibrosis, only 5–10% the normal amount of CFTR gene expression is needed. Many approaches have been theorized and several clinical trials have been initiated but, as of 2006, many hurdles still exist before gene therapy can be successful. In theory placing the normal CFTR gene into the affected epithelium cells using a viral component works perfectly. However the clinical theories have shown the practical faults in the gene therapy. It is extremly difficult to inject the right cells with the virus. Another problem is that even if the virus actually managed to intervene with the normal RNA translation and managed to implant its own RNA into the translation system the scientist were not able to influence which part of the viral information was translated. So the gene therapy could have even negative impact on the patient instead of a positive one.