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'''Cystic fibrosis''' (also known as '''CF''', '''mucovoidosis''', or '''mucoviscidosis''') is a [[genetic disorder]] known to be an inherited disease of the secretory glands, including the glands that make mucus and sweat.
'''Cystic fibrosis''' (also known as '''CF''', '''mucovoidosis''', or '''mucoviscidosis''') is a [[genetic disorder]] known to be an inherited disease of the secretory glands, including the glands that make mucus and sweat.


The hallmarks of cystic fibrosis are salty tasting skin, normal appetite but poor growth and poor weight gain, excess mucus production, frequent chest infections and coughing/shortness of breath. Males can be [[infertility|infertile]] due to the condition [[Congenital 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. As the child grows older it will have to exercise to release mucus stuck to the alveoli. Cilial epithilial cells in the patient have a mutated protein that instead of creating the right resin that is used to prevent the alveoli from collapsing, it makes a thicker resin, mucus. This makes the oxygen extraction in the alveoli harder as the molecules must travel through the mucus leading to breathlessness. Since the mucus stays there most of the time bacteria will thrive in it, causing multiple chest infections.
The hallmarks of cystic fibrosis are salty tasting skin, normal appetite but poor growth and poor weight gain, excess mucus production, frequent chest infections and coughing/shortness of breath. Males can be [[infertility|infertile]] due to [[congenital 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. As the child grows older it will have to exercise to release mucus stuck to the alveoli. Cilial epithilial cells in the patient have a mutated protein that instead of creating the right resin that is used to prevent the alveoli from collapsing, it makes a thicker resin, mucus. This makes the oxygen extraction in the alveoli harder as the molecules must travel through the mucus leading to breathlessness. Since the mucus stays there most of the time bacteria will thrive in it, causing multiple chest infections.


Although technically a [[rare disease]], cystic fibrosis is ranked as one of the most widespread life-shortening genetic diseases. It is most common among nations in the Western world; one in twenty-two people of Mediterranean descent is [[Genetic carrier|a carrier]] of one gene for CF, making it the most common genetic disease in these populations.{{Fact|date=May 2009}} An exception is [[Finland]], where one in 80 people carry a CF mutation.<ref name="pmid11813900">{{cite journal
Although technically a [[rare disease]], cystic fibrosis is ranked as one of the most widespread life-shortening genetic diseases. It is most common among nations in the Western world; one in twenty-two people of Mediterranean descent is [[Genetic carrier|a carrier]] of one gene for CF, making it the most common genetic disease in these populations.{{Fact|date=May 2009}} An exception is [[Finland]], where one in 80 people carry a CF mutation.<ref name="pmid11813900">{{cite journal

Revision as of 19:35, 5 October 2009

Cystic fibrosis
SpecialtyMedical genetics, pediatrics, pulmonology Edit this on Wikidata

Cystic fibrosis (also known as CF, mucovoidosis, or mucoviscidosis) is a genetic disorder known to be an inherited disease of the secretory glands, including the glands that make mucus and sweat.

The hallmarks of cystic fibrosis are salty tasting skin, normal appetite but poor growth and poor weight gain, excess mucus production, frequent chest infections and coughing/shortness of breath. Males can be infertile due to congenital 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. As the child grows older it will have to exercise to release mucus stuck to the alveoli. Cilial epithilial cells in the patient have a mutated protein that instead of creating the right resin that is used to prevent the alveoli from collapsing, it makes a thicker resin, mucus. This makes the oxygen extraction in the alveoli harder as the molecules must travel through the mucus leading to breathlessness. Since the mucus stays there most of the time bacteria will thrive in it, causing multiple chest infections.

Although technically a rare disease, cystic fibrosis is ranked as one of the most widespread life-shortening genetic diseases. It is most common among nations in the Western world; one in twenty-two people of Mediterranean descent is a carrier of one gene for CF, making it the most common genetic disease in these populations.[citation needed] An exception is Finland, where one in 80 people carry a CF mutation.[1] In the United States, 1 in 4,000 children are born with CF.[2] In 1997, about 1 in 3,300 caucasian children in the United States was born with cystic fibrosis. In contrast, only 1 in 15,000 African American children suffered from cystic fibrosis, and in Asian Americans the rate was even lower at 1 in 32,000.[3]

Signs and symptoms

Lung and sinus illness

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

Lung disease results from clogging the airways due to mucosa build-up and resulting inflammation. Inflammation and infection cause injury and structural changes to the lungs, leading 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. 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.[4] 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.[5][6]

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.[7] 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.[8]

The thick mucus seen in the lungs has a 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).[9] The lack of digestive enzymes leads to difficulty absorbing nutrients with their subsequent excretion in the feces, 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.[10] Older individuals with CF may also develop distal intestinal obstruction syndrome when thickened feces cause intestinal blockage.[11]

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.[12][13]

Endocrine disease and growth

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 a type of diabetes that is unique to those with the disease.[14] This Cystic Fibrosis Related Diabetes (CFRD) shares characteristics that can be found in Type 1 and Type 2 diabetics and is one of the principal non-pulmonary complications of CF.[15] Vitamin D is involved in calcium and phosphorus regulation. Poor uptake of vitamin D from the diet because of malabsorption can lead to the bone disease osteoporosis in which weakened bones are more susceptible to fractures.[16] In addition, people with CF often develop clubbing of their fingers and toes due to the effects of chronic illness and low oxygen in 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 infertile but are not sterile and can have children with assisted reproductive techniques.[17] These men make normal sperm but are missing the tube (vas deferens), which connects the testes to the ejaculatory ducts of the penis.[18] Many men found to have congenital absence of the vas deferens during evaluation for infertility have a mild, previously undiagnosed form of CF.[19] Some women have fertility difficulties due to thickened cervical mucus or malnutrition. In severe cases, malnutrition disrupts ovulation and causes amenorrhea.[20]

Cause

Cystic Fibrosis has an autosomal recessive pattern of inheritance.

CF is caused by a mutation in the gene 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 disease.

Pathophysiology

The protein created by this gene is anchored to the outer membrane of cells in the sweat glands, lungs, pancreas, and other affected organs. The protein spans this membrane and acts as a channel connecting the inner part of the cell (cytoplasm) to the surrounding fluid. This channel is primarily responsible for controlling the movement of chloride from inside to outside of the cell; however, in the sweat ducts it facilitates the movement of chloride from the sweat into the cytoplasm. When the CFTR protein does not work, chloride is trapped inside the cells in the airway and outside in the skin. Because chloride is negatively charged, positively charged cations cross into the cell because they are affected by the electrical attraction of the chloride ions. Sodium is the most common ion in the extracellular space and the combination of sodium and chloride creates the salt, which is lost in high amounts in the sweat of individuals with CF. This lost salt forms the basis for the sweat test.[4]

How this malfunction of cells in cystic fibrosis causes the clinical manifestations of CF is not well understood. One theory suggests that the lack of chloride exodus through the CFTR protein leads to the accumulation of more viscous, nutrient-rich mucus in the lungs that allows bacteria to hide from the body's immune system. Another theory proposes that the CFTR protein failure leads to a paradoxical increase in sodium and chloride uptake, which, by leading to increased water reabsorption, creates dehydrated and thick mucus. Yet another theory focuses on abnormal chloride movement out of the cell, which also leads to dehydration of mucus, pancreatic secretions, biliary secretions, etc. These theories all support the observation that the majority of the damage in CF is due to blockage of the narrow passages of affected organs with thickened secretions. These blockages lead to remodeling and infection in the lung, damage by accumulated digestive enzymes in the pancreas, blockage of the intestines by thick faeces, etc.[4]

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. As of 2006 in the United States, 10 percent of cases are diagnosed shortly after birth as part of newborn screening programs. The newborn screen initially measures for raised blood concentration of immunoreactive trypsinogen.[21] 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 mutated copy of the CFTR gene (carriers) or, in rare instances, even in individuals with two normal copies of the CFTR gene. Due to these false positives, CF screening in newborns is somewhat controversial.[citation needed] Most states and countries do not screen for CF routinely at birth. 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.[22]

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 abnormalities, vitamin deficiencies, and the onset of diabetes. DEXA scans can screen for osteoporosis and testing for fecal elastase can help diagnose insufficient digestive enzymes.

Prenatal diagnosis

Couples who are pregnant or who are planning a pregnancy can themselves be tested for CFTR gene mutations to determine the likelihood that their child will be born with cystic fibrosis. Testing is typically performed first on one or both parents and, if the risk of CF is found to be high, testing on the fetus can then be performed. Cystic fibrosis testing is offered to many couples in the US.[23] The American College of Obstetricians and Gynecologists (ACOG) recommends testing for couples who have a personal or close family history. Additionally, ACOG recommends that carrier testing be offered to all Caucasian couples and be made available to couples of other ethnic backgrounds.[24]

Because development of CF in the fetus requires each parent to pass on a mutated copy of the CFTR gene and because CF testing is expensive, testing is often performed on just one parent initially. If that parent is found to be a carrier of a CFTR gene mutation, the other parent is then tested to calculate the risk that their children will have CF. CF can result from more than a thousand different mutations and, as of 2006, it is not possible to test for each one. Testing analyzes the blood for the most common mutations such as ΔF508 — most commercially available tests look for 32 or fewer different mutations. If a family has a known uncommon mutation, specific screening for that mutation can be performed. Because not all known mutations are found on current tests, a negative screen does not guarantee that a child will not have CF.[25] In addition, because the mutations tested are necessarily those most common in the highest risk groups, testing in lower risk ethnicities is less successful because the mutations commonly seen in these groups are less common in the general population. These couples may therefore consider testing through labs that offer CF screens with a high number of mutations tested.

Couples who are at high risk for having a child with CF will often opt to perform further testing before or during pregnancy. In vitro fertilization with preimplantation genetic diagnosis offers the possibility to examine the embryo prior to its placement into the uterus. The test, performed 3 days after fertilization, looks for the presence of abnormal CF genes. If two mutated CFTR genes are identified, the embryo is not used for embryo transfer and an embryo with at least one normal gene is implanted.

During pregnancy, testing can be performed on the placenta (chorionic villus sampling) or the fluid around the fetus (amniocentesis). However, chorionic villus sampling has a risk of fetal death of 1 in 100 and amniocentesis of 1 in 200,[26] although a recent study has indicated this may actually be much lower, perhaps 1 in 1,600,[1] so the benefits must be determined to outweigh these risks prior to going forward with testing. Alternatively, some couples choose to undergo third party reproduction with egg or sperm donors}.

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.[27]

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 (and sometimes Burkholderia cepacia) 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.[27]

One way in which infection has spread is by passage between different individuals with CF.[28] In the past, people with CF often participated in summer "CF Camps" and other recreational gatherings.[29][30] Hospitals grouped patients with CF into common areas and routine equipment (such as nebulizers)[31] was not sterilized between individual patients.[32] 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.[33] Often, patients with particularly damaging bacteria will attend clinics on different days and in different buildings than those without these infections.

Molecular biology

CFTR protein - Molecular structure of the CFTR protein

The CFTR gene is found at the q31.2 locus of chromosome 7, is 230,000 base pairs long, and creates a protein that is 1,480 amino acids long. The most common mutation, ΔF508, is a deletion (Δ) of three nucleotides that results in a loss of the amino acid phenylalanine (F) at the 508th (508) position on the protein. This mutation accounts for two-thirds of CF cases worldwide and 90 percent of cases in the United States; however, there are over 1,400 other mutations that can produce CF.[34] In Caucasian populations, the frequency of mutations is as follows:[35]

Mutation Frequency
worldwide
ΔF508 66.0%
G542X 2.4%
G551D 1.6%
N1303K 1.3%
W1282X 1.2%
All others 27.5%

The distribution of these alleles varies among populations. The frequency of ΔF508 carriers has been estimated to be 1:200 in northern Sweden, 1:143 in Lithuanians, and 1:38 in Denmark. No ΔF508 carriers were found among 171 Finns and 151 Saami people.[36] ΔF508 does occur in Finland, but it is a minority allele there. Cystic fibrosis is known to occur in only 20 families (pedigrees) in Finland, and within these families ΔF508 occurs in 45% of chromosomes carrying a cystic fibrosis mutation.[37]

The location of the CFTR gene on chromosome 7

There are several mechanisms by which these mutations cause problems with the CFTR protein. ΔF508, for instance, creates a protein that does not fold normally and is degraded by the cell. Several mutations, which are common in the Ashkenazi Jewish population, result in proteins that are too short because production is ended prematurely. Less common mutations produce proteins that do not use energy normally, do not allow chloride to cross the membrane appropriately, or are degraded at a faster rate than normal. Mutations may also lead to fewer copies of the CFTR protein being produced.[4]

Structurally, CFTR is a type of gene known as an ABC gene.[4] Its protein possesses two ATP-hydrolyzing domains which allows the protein to use energy in the form of ATP. It also contains two domains comprising 6 alpha helices apiece, which allow the protein to cross the cell membrane. A regulatory binding site on the protein allows activation by phosphorylation, mainly by cAMP-dependent protein kinase.[4] The carboxyl terminal of the protein is anchored to the cytoskeleton by a PDZ domain interaction.[38]

Management

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 and pancreatic enzyme supplements), the reproductive organs (including Assisted Reproductive Technology (ART)) and psychological support.[21] In addition, therapies such as transplantation and gene therapy aim to cure some of the effects of cystic fibrosis. Gene therapy aims to introduce normal CFTR to airway. Theoretically this process should be simple as the airway is easily accessible and there is only a single gene defect to correct. There are two CFTR gene introduction mechanisms involved, the first use of a viral vector (adenovirus, adeno-associated virus or retro virus) and secondly the use of Liposome. However there are some problems associated with these methods involving efficiency (liposomes insufficient protein) and delivery (virus provokes an immune response).

File:CFtreatmentvest2.JPG
A typical breathing treatment for cystic fibrosis, using a mask nebuliser and the ThAIRapy Vest

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 patient's 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. This prolonged therapy often necessitates hospitalization and insertion of a more permanent IV such as a PICC line or Port-a-Cath. 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.[39][40] Inhaled therapy with the antibiotic aztreonam is also being developed and clinical trials have shown great promise.[41] Oral antibiotics such as ciprofloxacin or azithromycin are given to help prevent infection or to control ongoing infection.[42] 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, chest physiotherapy (CPT) is utilized; a respiratory therapist percusses an individual's chest with his or her hands several times a day, to loosen up secretions. Devices that recreate this percussive therapy include the ThAIRapy Vest (pioneered under Dr. Warren J Warwick at the University of Minnesota) 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.[citation needed] These are portable and adapted for home use.[43] Physiotherapy is essential to help manage an individuals chest on a long term basis, and can also teach techniques for the older child and teenager to manage themselves at home. 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.[44] Dornase is a recombinant human deoxyribonuclease, which breaks down DNA in the sputum, thus decreasing its viscosity.[45] 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.[46] During severe illness, people with CF may need to have a tube placed in their throats (a procedure known as a tracheostomy) 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.[47] Development of osteoporosis can be prevented by increased intake of vitamin D and calcium, and can be treated by bisphosphonates.[48] Poor growth may be avoided by insertion of a feeding tube for increasing calories through supplemental feeds or by administration of injected growth hormone.[49]

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, and over time reduce the patient's sense of smell. 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.[50] Female infertility may be overcome by assisted reproduction technology, particularly embryo transfer techniques. Male infertility may be overcome with intracytoplasmic sperm injection.[51] 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/or diabetes.[52] Lung transplantation is considered when lung function approaches a point where it threatens survival or requires assistance from mechanical devices.[53] This point is typically when lung function declines to approximately 20 to 30 percent, however there is a small time frame when transplantation is feasible as the patient must be healthy enough to endure the procedure.

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.[54] Multiple approaches have been tested for gene transfer, such as liposomes and viral vectors in animal models and clinical trials. However, at this time gene therapy is still a relatively inefficient treatment option.[55] Ideally, transferring the normal CFTR gene into the affected epithelium cells would result in the production of functional CFTR in all target cells, without adverse reactions or an inflammation response. But if too few cells take up the vector and express the gene, the treatment has little effect. Additionally, problems have been noted in cDNA recombination, such that the gene introduced by the treatment is rendered unusable.[56]

Research

Since cystic fibrosis is a genetic disease, the only way to prevent or cure it would be with gene therapy at an early age. Ideally, gene therapy could repair or replace the defective gene. Another option for treatment would be to give a person with cystic fibrosis the active form of the protein product that is scarce or missing. Lung transplantation is often necessary as CF worsens.[citation needed]

Foundations, trusts and organizations

There are many foundations and trusts dedicated to researching cures and treatments for cystic fibrosis, and assisting people suffering from the disease. A list of cystic fibrosis organizations is available and more information can be found on the disease and living with cystic fibrosis from these organizations.

Prognosis

Average life expectancy is around 36.8 years according to the Cystic Fibrosis Foundation, although improvements in treatments mean persons born in recent years may expect to live longer.[57]

Epidemiology

Cystic fibrosis is the most common life-limiting autosomal recessive disease among people of European heritage.[58] In the United States, approximately 30,000 individuals have CF; most are diagnosed by six months of age. Canada has approximately 3,000 citizens with CF. Approximately 1 in 25 people of European descent is a carrier of a cystic fibrosis mutation. Although CF is less common in these groups, approximately 1 in 46 Hispanics, 1 in 65 Africans and 1 in 90 Asians carry at least one abnormal CFTR gene.[59][60]

Cystic fibrosis is diagnosed in males and females equally. For unclear reasons, males tend to have a longer life expectancy than females [61][62][63], although recent studies suggest this gender gap may no longer exist in younger patients with access to excellent health care facilities [64][65]. Similarly, life expectancy for people with CF depends largely upon access to health care. In 1959, the median age of survival of children with cystic fibrosis was six months. In the United States, the life expectancy for infants born in 2006 with CF is 36.8 years, based upon data compiled by the Cystic Fibrosis Foundation.[57]

The Cystic Fibrosis Foundation also compiles lifestyle information about American adults with CF. In 2004, the foundation reported that 91% had graduated high school and 54% had at least some college education. Employment data revealed 12.6% of adults were disabled and 9.9% were unemployed. Marital information showed that 59% of adults were single and 36% were married or living with a partner. In 2004, 191 American women with CF were pregnant.

History

National Library of Medicine photo of Dorothy Hansine Andersen. Andersen first described cystic fibrosis of the pancreas.

Cystic fibrosis (CF) was recognized as specific entity during the 1930s. There is nothing resembling CF described in the 1032 pages of Sir Frederick Still's 1927 Edition of Common Disorders and Diseases of Childhood. [66] Formerly known as "cystic fibrosis of the pancreas," this entity has increasingly been labeled simply "cystic fibrosis."[67]

Indeed, literature from Germany and Switzerland in the 18th century warned, "Wehe dem Kind, das beim Kuß auf die Stirn salzig schmekt, es ist verhext und muss bald sterben" — "Woe is the child who tastes salty when kissed on the forehead, for it is cursed and soon must die," recognizing the association between the salt loss in CF and illness.

In the 19th century, Carl von Rokitansky described a case of fetal death with meconium peritonitis, a complication of meconium ileus associated with cystic fibrosis. Meconium ileus was first described in 1905 by Karl Landsteiner.[68] In 1936, Guido Fanconi published a paper describing a connection between celiac disease, cystic fibrosis of the pancreas, and bronchiectasis.[69]

In 1938 Dorothy Hansine Andersen published an article, "Cystic Fibrosis of the Pancreas and Its Relation to Celiac Disease: a Clinical and Pathological Study," in the American Journal of Diseases of Children. She described the characteristic cystic fibrosis of the pancreas and correlated it with the lung and intestinal disease prominent in CF.[66] She also first hypothesized that CF is a recessive disease and first used pancreatic enzyme replacement to treat affected children. In 1952 Paul di Sant' Agnese discovered abnormalities in sweat electrolytes; a sweat test was developed and improved over the next decade.[70]

In 1988 the first mutation for CF, ΔF508 on the seventh chromosome, was discovered by Francis Collins, Lap-Chee Tsui and John R. Riordan. Research has subsequently found over 1,000 different mutations that cause CF. Lap-Chee Tsui led a team of researchers at the Hospital for Sick Children in Toronto that discovered the gene responsible for CF in 1989. Cystic fibrosis represents the first genetic disorder elucidated strictly by the process of reverse genetics.

Because mutations in the CFTR gene are typically small, classical genetics techniques had been unable to accurately pinpoint the mutated gene.[71] Using protein markers, gene-linkage studies were able to map the mutation to chromosome 7. Chromosome-walking and -jumping techniques were then used to identify and sequence the gene.[72]

Theories about the prevalence of CF

The ΔF508 mutation is estimated to be up to 52,000 years old.[73] Numerous hypotheses have been advanced as to why such a lethal mutation has persisted and spread in the human population. Other common autosomal recessive diseases such as sickle-cell anemia have been found to protect carriers from other diseases, a concept known as heterozygote advantage. Resistance to the following have all been proposed as possible sources of heterozygote advantage:

  • Cholera: With the discovery that cholera toxin requires normal host CFTR proteins to function properly, it was hypothesized that carriers of mutant CFTR genes benefited from resistance to cholera and other causes of diarrhea.[74] Further studies have not confirmed this hypothesis.[75][76]
  • Typhoid: Normal CFTR proteins are also essential for the entry of Salmonella typhi into cells,[77] suggesting that carriers of mutant CFTR genes might be resistant to typhoid fever. No in vivo study has yet confirmed this. In both cases, the low level of cystic fibrosis outside of Europe, in places where both cholera and typhoid fever are endemic, is not immediately explicable.
  • Diarrhea: It has also been hypothesized that the prevalence of CF in Europe might be connected with the development of cattle domestication. In this hypothesis, carriers of a single mutant CFTR chromosome had some protection from diarrhoea caused by lactose intolerance, prior to the appearance of the mutations that created lactose tolerance.[78]
  • Tuberculosis: Poolman and Galvani from Yale University have added another possible explanation - that carriers of the gene have some resistance to TB.[79][80]

See also

References

  1. ^ Hytönen M, Patjas M, Vento SI, Kauppi P, Malmberg H, Ylikoski J, Kere J (2001). "Cystic fibrosis gene mutations deltaF508 and 394delTT in patients with chronic sinusitis in Finland". Acta Oto-laryngologica. 121 (8): 945–7. PMID 11813900. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
  2. ^ About Cystic Fibrosis
  3. ^ Genetic testing for cystic fibrosis
  4. ^ a b c d e f Rowe SM, Miller S, Sorscher EJ. Cystic fibrosis. N Engl J Med. 2005 May 12;352(19):1992–2001. PMID 15888700
  5. ^ Maldonado M, Martinez A, Alobid I, Mullol J. The antrochoanal polyp. Rhinology. 2004 Dec;42(4):178-82. Review. PMID 15626248
  6. ^ Ramsey B, Richardson MA. Impact of sinusitis in cystic fibrosis. Allergy Clin Immunol. 1992 Sep;90(3 Pt 2):547-52. PMID 1527348
  7. ^ Eggermont E, De Boeck K. Small-intestinal abnormalities in cystic fibrosis patients. Eur J Pediatr. 1991 Oct;150(12):824-8. Review. PMID 1743211
  8. ^ Kulczycki LL, Shwachman H. Studies in cystic fibrosis of the pancreas; occurrence of rectal prolapse. N Engl J Med. 1958 Aug 28;259(9):409-12. PMID 13578072
  9. ^ Cohn JA, Friedman KJ, Noone PG, Knowles MR, Silverman LM, Jowell PS. Relation between mutations of the cystic fibrosis gene and idiopathic pancreatitis. N Engl J Med. 1998 Sep 3;339(10):653-8. PMID 9725922
  10. ^ Malfroot A, Dab I. New insights on gastro-oesophageal reflux in cystic fibrosis by longitudinal follow up. Arch Dis Child. 1991 Nov;66(11):1339–45. PMID 175564
  11. ^ Khoshoo V, Udall JN Jr. Meconium ileus equivalent in children and adults. Am J Gastroenterol. 1994 Feb;89(2):153-7. PMID 8304294
  12. ^ Williams SG, Westaby D, Tanner MS, Mowat AP. Liver and biliary problems in cystic fibrosis. Br Med Bull. 1992 Oct;48(4):877-92. PMID 1458306
  13. ^ Colombo C, Russo MC, Zazzeron L, Romano G. Liver disease in cystic fibrosis. J Pediatr Gastroenterol Nutr. 2006 Jul;43 Suppl 1:S49-55. PMID 16819402
  14. ^ Moran A, Pyzdrowski KL, Weinreb J, Kahn BB, Smith SA, Adams KS, Seaquist ER.Insulin sensitivity in cystic fibrosis. Diabetes. 1994 Aug;43(8):1020–6. PMID 8039595
  15. ^ Alves Cde A, Aguiar RA, Alves AC, Santana MA. Diabetes mellitus in patients with cystic fibrosis. J Bras Pneumol. 2007 Apr;33(2):213-21. PMID 17724542
  16. ^ Haworth CS, Selby PL, Webb AK, Dodd ME, Musson H, McL Niven R, Economou G, Horrocks AW, Freemont AJ, Mawer EB, Adams JE. Low bone mineral density in adults with cystic fibrosis. Thorax. 1999 Nov;54(11):961-7. PMID 10525552
  17. ^ McCallum TJ, Milunsky JM, Cunningham DL, Harris DH, Maher TA, Oates RD. Fertility in men with cystic fibrosis: an update on current surgical practices and outcomes. Chest. 2000 Oct;118(4):1059–62. PMID 11035677
  18. ^ Dodge JA. Male fertility in cystic fibrosis. Lancet. 1995 Sep 2;346(8975):587-8. PMID 7650999
  19. ^ Augarten A, Yahav Y, Kerem B, Halle D, Laufer J, Szeinberg A, Dor J, Mashiach S, Gazit E, Madgar I. Congenital bilateral absence of vas deferens in the absence of cystic fibrosis. Lancet 344: 1473–1474, 1994. PMID 7968122
  20. ^ Gilljam M, Antoniou M, Shin J, Dupuis A, Corey M, Tullis DE. Pregnancy in cystic fibrosis. Fetal and maternal outcome. Chest. 2000 Jul;118(1):85–91. PMID 10893364
  21. ^ a b Davies J et al. Cystic Fibrosis. BMJ. 2007 Dec 15;335(7632):1255–59.
  22. ^ Stern, RC. The diagnosis of cystic fibrosis. N Engl J Med 1997; 336:487. PMID 9017943
  23. ^ ACOG Committee Opinion #325: Update on Carrier Screening for Cystic Fibrosis. Obstet Gynecol 2005; 106:1465.
  24. ^ American College of Obstetricians and Gynecologists and American College of Medical Genetics. Preconception and prenatal carrier screening for cystic fibrosis. Clinical and laboratory guidelines. American College of Obstetricians and Gynecologists, Washington, DC, October 2001.
  25. ^ Elias, S, Annas, GJ, Simpson, JL. Carrier screening for cystic fibrosis: Implications for obstetric and gynecologic practice. Am J Obstet Gynecol 1991; 164:1077. PMID 2014829
  26. ^ Tabor A, Philip J, Madsen M, Bang J, Obel EB, Norgaard-Pedersen B. Randomised controlled trial of genetic amniocentesis in 4606 low-risk women. Lancet. 1986 Jun 7;1(8493):1287–93. PMID 2423826
  27. ^ a b Saiman L. Microbiology of early CF lung disease. Paediatr Respir Rev. 2004;5 Suppl A:S367-9. PMID 14980298
  28. ^ Tummler B, Koopmann U, Grothues D, Weissbrodt H, Steinkamp G, von der Hardt H. Nosocomial acquisition of Pseudomonas aeruginosa by cystic fibrosis patients. J Clin Microbiol. 1991 Jun;29(6):1265–7. PMID 1907611
  29. ^ Centers for Disease Control and Prevention (CDC). Pseudomonas cepacia at summer camps for persons with cystic fibrosis. MMWR Morb Mortal Wkly Rep. 1993 Jun 18;42(23):456-9. PMID 7684813
  30. ^ Pegues DA, Carson LA, Tablan OC, FitzSimmons SC, Roman SB, Miller JM, Jarvis WR.Acquisition of Pseudomonas cepacia at summer camps for patients with cystic fibrosis. Summer Camp Study Group. J Pediatr. 1994 May;124(5 Pt 1):694–702. PMID 7513755
  31. ^ Pankhurst CL, Philpott-Howard J. The environmental risk factors associated with medical and dental equipment in the transmission of Burkholderia (Pseudomonas) cepacia in cystic fibrosis patients. J Hosp Infect. 1996 Apr;32(4):249-55. PMID 8744509
  32. ^ Jones AM, Govan JR, Doherty CJ, Dodd ME, Isalska BJ, Stanbridge TN, Webb AK. Identification of airborne dissemination of epidemic multiresistant strains of Pseudomonas aeruginosa at a CF centre during a cross infection outbreak. Thorax. 2003 Jun;58(6):525-7. PMID 12775867
  33. ^ Hoiby N. Isolation and treatment of cystic fibrosis patients with lung infections caused by Pseudomonas (Burkholderia) cepacia and multiresistant Pseudomonas aeruginosa. Neth J Med. 1995 Jun;46(6):280-7. PMID 7643943
  34. ^ Bobadilla JL, Macek M Jr, Fine JP, Farrell PM. Cystic fibrosis: a worldwide analysis of CFTR mutations--correlation with incidence data and application to screening. Human Mutation 2002 Jun; 19(6):575-606. PMID 12007216
  35. ^ Araújo FG, Novaes FC, Santos NP, Martins VC, Souza SM, Santos SE, Ribeiro-dos-Santos AK. Prevalence of ΔF508, G551D, G542X, R553X mutations among cystic fibrosis patients in the North of Brazil. Brazilian Journal of Medical and Biological Research 2005; 38:11–15. PMID 15665983
  36. ^ Wennberg C, Kucinskas V (1994). "Low frequency of the delta F508 mutation in Finno-Ugrian and Baltic populations". Human Heredity. 44 (3): 169–71. PMID 8039801.
  37. ^ Kere J, Savilahti E, Norio R, Estivill X, de la Chapelle A (1990). "Cystic fibrosis mutation delta F508 in Finland: other mutations predominate". Human Genetics. 85 (4): 413–5. PMID 2210753. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
  38. ^ Short DB, Trotter KW, Reczek D, Kreda SM, Bretscher A, Boucher RC, Stutts MJ, Milgram SL. An apical PDZ protein anchors the cystic fibrosis transmembrane conductance regulator to the cytoskeleton. J Biol Chem. 1998 Jul 31;273(31):19797-801. PMID 9677412
  39. ^ Pai VB, Nahata MC. Efficacy and safety of aerosolized tobramycin in cystic fibrosis. Pediatr Pulmonol. 2001 Oct;32(4):314-27. Review. PMID 11568993
  40. ^ Westerman EM, Le Brun PP, Touw DJ, Frijlink HW, Heijerman HG. Effect of nebulized colistin sulphate and colistin sulphomethate on lung function in patients with cystic fibrosis: a pilot study. J Cyst Fibros. 2004 Mar;3(1):23-8. PMID 15463883
  41. ^ Inhaled aztreonam lysine for chronic airway Pseudo...[Am J Respir Crit Care Med. 2008 - PubMed Result]
  42. ^ Hansen CR, Pressler T, Koch C, Hoiby N.Long-term azithromycin treatment of cystic fibrosis patients with chronic Pseudomonas aeruginosa infection; an observational cohort study. J Cyst Fibros. 2005 Mar;4(1):35–40. PMID 15752679
  43. ^ van der Schans C, Prasad A, Main E. Chest physiotherapy compared to no chest physiotherapy for cystic fibrosis. Cochrane Database Syst Rev. 2000;(2):CD001401. Review. PMID 10796781
  44. ^ Kuver R, Lee SP. Hypertonic saline for cystic fibrosis. N Engl J Med. 2006 Apr 27;354(17):1848–51; author reply 1848–51. PMID 16642591
  45. ^ Lieberman J. Dornase aerosol effect on sputum viscosity in cases of cystic fibrosis. JAMA. 1968 Jul 29;205(5):312-3. PMID 5694947
  46. ^ Moran F, Bradley J. Non-invasive ventilation for cystic fibrosis. Cochrane Database Syst Rev. 2003;(2):CD002769. Review. PMID 12804435
  47. ^ Onady GM, Stolfi A. Insulin and oral agents for managing cystic fibrosis-related diabetes. Cochrane Database Syst Rev. 2005 Jul 20;(3):CD004730. Review. PMID 16034943
  48. ^ Conway SP, Oldroyd B, Morton A, Truscott JG, Peckham DG. Effect of oral bisphosphonates on bone mineral density and body composition in adult patients with cystic fibrosis: a pilot study. Thorax. 2004 Aug;59(8):699–703. PMID 15282392
  49. ^ Hardin DS, Rice J, Ahn C, Ferkol T, Howenstine M, Spears S, Prestidge C, Seilheimer DK, Shepherd R. Growth hormone treatment enhances nutrition and growth in children with cystic fibrosis receiving enteral nutrition.J Pediatr. 2005 Mar;146(3):324-8. PMID 15756212
  50. ^ Marks SC, Kissner DG. Management of sinusitis in adult cystic fibrosis. Am J Rhinol. 1997 Jan-Feb;11(1):11-4. PMID 9065342
  51. ^ Phillipson GT, Petrucco OM, Matthews CD. Congenital bilateral absence of the vas deferens, cystic fibrosis mutation analysis and intracytoplasmic sperm injection. Hum Reprod. 2000 Feb;15(2):431-5. PMID 10655317
  52. ^ Simultaneous liver and pancreas transplantation in patients with cystic fibrosis. Transplant Proc. 2005 Oct;37(8):3567–9. PMID 16298663
  53. ^ Belkin RA, Henig NR, Singer LG, Chaparro C, Rubenstein RC, Xie SX, Yee JY, Kotloff RM, Lipson DA, Bunin GR. Risk factors for death of patients with cystic fibrosis awaiting lung transplantation. Am J Respir Crit Care Med. 2006 Mar 15;173(6):659-66. Epub 2005 Dec 30. PMID 16387803
  54. ^ Ramalho AS, Beck S, Meyer M, Penque D, Cutting GR, Amaral MD. Five percent of normal cystic fibrosis transmembrane conductance regulator mRNA ameliorates the severity of pulmonary disease in cystic fibrosis. Am J Respir Cell Mol Biol. 2002 27(5):619-27. PMID 12397022
  55. ^ Tate S, Elborn S. Progress towards gene therapy for cystic fibrosis.Expert Opin Drug Deliv. 2005 Mar;2(2):269-80. Review. PMID 16296753
  56. ^ http://www.ncbi.nlm.nih.gov/entrez/dispomim.cgi?id=219700
  57. ^ a b "New Statistics Show CF Patients Living Longer". Cystic Fibrosis Foundation. April 26, 2006. Retrieved 2007-12-09. {{cite web}}: Check date values in: |date= (help)
  58. ^ Ottawa university boots cystic fibrosis from charity drive, National Post, November 25, 2008
  59. ^ Rosenstein BJ and Cutting GR. The diagnosis of cystic fibrosis: a consensus statement. Cystic Fibrosis Foundation Consensus Panel. J Pediatr. 1998 Apr;132(4):589-95. Review. PMID 9580754
  60. ^ Hamosh A, Fitz-Simmons SC, Macek M Jr, Knowles MR, Rosenstein BJ, Cutting GR. Comparison of the clinical manifestations of cystic fibrosis in black and white patients. J Pediatr. 1998 Feb;132(2):255-9. PMID 9506637
  61. ^ Rosenfeld, M, Davis, R, FitzSimmons, S, et al. Gender gap in cystic fibrosis mortality. Am J Epidemiol 1997 145,794–803
  62. ^ Zeitlin PL. Cystic fibrosis and estrogens: a perfect storm J Clin Invest 2008 118(12):3841-4
  63. ^ Coakley RD, Sun H, Clunes LA, Rasmussen JE, Stackhouse JR, Okada SF, Fricks I, Young SL, Tarran R. 17beta-Estradiol inhibits Ca2+-dependent homeostasis of airway surface liquid volume in human cystic fibrosis airway epithelia. J Clin Invest 2008 118(12):4025-35
  64. ^ Verma N, Bush A, Buchdahl R. Is there still a gender gap in cystic fibrosis? Chest 2007 128,2824-2834
  65. ^ Moran A, Dunitz J, Nathan B, Saeed A, Holme B, Thomas W. Cystic Fibrosis Related Diabetes: Current Trends in Prevalence, Incidence and Mortality Diabetes Care 2009 Epub,ahead of print
  66. ^ a b D.H. Andersen, "Cystic Fibrosis of the Pancreas and Its Relation to Celiac Disease: a Clinical and Pathological Study," Am. J. Dis. Child., 1938, 56:344–399.
  67. ^ "Cystic Fibrosis; CF - Mucoviscidosis". Entrez. April 26, 2006. Retrieved 2007-02-28. {{cite web}}: Check date values in: |date= (help)
  68. ^ R. Busch, "On the History of Cystic Fibrosis," Acta Univ Carol [Med] (Praha), 1990, 36(1-4):13-5. PMID 2130674
  69. ^ G. Fanconi, E. Uehlinger, C. Knauer, "Das coeliakiesyndrom bei angeborener zysticher pankreasfibromatose und bronchiektasien," Wien. Med. Wschr., 1936, 86:753–756.
  70. ^ PA Di Sant' Agnese, RC Darling, GA Perera, et al., "Abnormal Electrolyte Composition of Sweat in Cystic Fibrosis of the Pancreas: Clinical Implications and Relationship to the Disease," Pediatrics, 1953, 12:549–563.
  71. ^ JR Riordan, JM Rommens, B Kerem, N Alon, R Rozmahel, Z Grzelczak, J Zielenski, S Lok, N Plavsic, JL Chou, et al. "Identification of the Cystic Fibrosis Gene: Cloning and Characterization of Complementary DNA," Science," 1989 Sep 8, 245(4922):1066–73. Erratum in Science, 1989 Sep 29, 245(4925):1437. PMID 2475911.
  72. ^ JM Rommens, MC Iannuzzi, B Kerem, ML Drumm, G Melmer, M Dean, R Rozmahel, JL Cole, D Kennedy, N Hidaka, et al. "Identification of the Cystic Fibrosis Gene: Chromosome Walking and Jumping," Science, 1989 Sep 8, 245(4922):1059–65. PMID 2772657.
  73. ^ Wiuf C. Do delta F508 heterozygotes have a selective advantage? Genet Res. 2001 Aug;78(1):41-7. PMID 11556136
  74. ^ Gabriel SE, Brigman KN, Koller BH, Boucher RC, Stutts MJ. Cystic fibrosis heterozygote resistance to cholera toxin in the cystic fibrosis mouse model. Science. 1994 Oct 7;266(5182):107-9. PMID 7524148
  75. ^ Cuthbert AW, Halstead J, Ratcliff R, Colledge WH, Evans MJ. The genetic advantage hypothesis in cystic fibrosis heterozygotes: a murine study. J Physiol. 1995 Jan 15;482 (Pt 2):449-54. PMID 7714835
  76. ^ Hogenauer C, Santa Ana CA, Porter JL, Millard M, Gelfand A, Rosenblatt RL, Prestidge CB, Fordtran JS. Active intestinal chloride secretion in human carriers of cystic fibrosis mutations: an evaluation of the hypothesis that heterozygotes have subnormal active intestinal chloride secretion. Am J Hum Genet. 2000 Dec;67(6):1422–7. Epub 2000 Oct 30. PMID 11055897.
  77. ^ Pier GB, Grout M, Zaidi T, Meluleni G, Mueschenborn SS, Banting G, Ratcliff R, Evans MJ, Colledge WH. Salmonella typhi uses CFTR to enter intestinal epithelial cells. Nature. 1998 May 7;393(6680):79–82. PMID 9590693
  78. ^ Modiano G, Ciminelli BM, Pignatti PF. Cystic Fibrosis: Cystic fibrosis and lactase persistence: a possible correlation. Eur J Hum Genet. 2007 Mar;15(3):255-9. PMID: 17180122.
  79. ^ Cystic fibrosis gene protects against tuberculosis
  80. ^ Footprint fears for new TB threat
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