The most common lethal genetic disease in the United States is cystic fibrosis, which strikes one out of every 2500 Caucasians. About 1 out of 20 Caucasian people (1), carries at least one of the fatal defective genes that cause cystic fibrosis, CF, or mucoviscidosis (in Europe) although carriers don't show any signs of the disease (inherited as recessive disease). Therefore, 10 million people in the United States alone carry the defective gene and are not aware of it because the dominant gene masks the recessive gene (2). Consequently, it makes it one of the most common genetic defect in the United States. Cystic Fibrosis is an autosomal recessive gene.
That means that it may, but does not always skip generations. In order to get this disease, both parents must be carriers. If one parent has CF and the other one is not a carrier than there is a 100% chance that their child will be a carrier. If one parent has CF and the other is a carrier than the child has a 50% chance of having CF and a 50% chance of just being a carrier. If both parents are carriers than their child will have a 25% of having CF, a 50% chance of being a carrier and a 25% chance of not being affected. CF is common in both males and females, there is not a specific sex that it is more common in.
However, the disease does occur less often in Blacks, and is rare in Asians and Native Americans. There are about 40,000 people living with cystic fibrosis in the U.S. today. The normal allele for the CF gene codes for a membrane protein that functions in chloride transport between certain cells and the extracellular fluid (CFTR gene). These chloride channels are defective or absent in the plasma membranes of children who have inherited two of the recessive alleles that cause cystic fibrosis (Mendelian recessive disease). This results in an abnormal concentration of extracellular chloride, which in turns causes the mucus that coats certain cells to become thicker and stickier than normal. The mucus builds up in the pancreas, lungs, digestive tract, and the other organs.
This condition favors pneumonia and other infections. Untreated, most children with cystic fibrosis die before their fifth birthday. How does a person know if they have cystic fibrosis? There are many symptoms to this deadly disease including: salty tasting skin, constant coughing, large amounts of mucus, trouble gaining weight, frequent greasy, foul smelling bowel, growths in the nose (nasal polyps) and clubbed or enlarged fingertips (see picture) and toe tips is another symptom. Now, there are many tests that can be done to find out if a person has cystic fibrosis.
One way which CF can be detected is to observe the symptoms. A person does not need to have all the symptoms in order to have cystic fibrosis, but they usually show most of them. Another way are different genetic testing. Doctors can now do genetic testing for CF, where about 10 years ago it was not possible. In 1989, the location of the defective gene on chromosome number 7 was discovered by Francis S. Collins from University of Michigan.
Identification of this gene raises hopes of eventually developing a drug or a form of gene therapy to treat the disease. Such treatments, currently in the experimental stage, are being closely studied. These treatments if successful could make the once incurable disease curable. Tests can now be taken to see if an unborn child is infected with CF such tests are amniocentesis, chronic villus biopsy (3) and a removal of cells from the embryo during in vitro. Many years ago, New York had a heat wave, and the hospitals became overwhelmed with dehydrated CF children (4). These children became dehydrated much quicker than children without the disorder.
Thus eventually resulting in the formation of the sweat test, which is now the standard test. Doctors place a pad or filter paper on a patients arm or back. A chemical called Pilocarpine, makes a burst of electricity to produce more sweat. Then the pad is wrapped in plastic and is sent to a lab to get analyzed. The doctors then would look for a high chloride content in the sweat. Another equally effective test is a blood test that is administered 3 days after a baby is born.
It is called Immunoreactive Trypsinogen (6) if that comes back positive it is then double checked with a sweat test. Furthermore, cystic fibrosis causes the sweat glands to release about 5 times as much salt as a normal person would (5). This is why the skin of a cystic fibrosis patients may taste salty. They do not sweat more, but when they perspire more salt is excreted. This causes the person to dehydrate.
X- ray examinations of the chest are also useful in diagnosis. CF is a disorder that causes the body to produce larger amount of mucus than normal. In a normal person, mucus in the lungs helps get rid of germs and bacteria in the air. In cystic fibrosis patients, the lungs become covered with a sticky mucus that is hard to remove and promotes infection from bacteria.
Over time, infections cause the lungs to become extremely weak, therefore ending in respiratory failure. Moreover, cystic fibrosis also affects the digestive tract. The overproduction of mucus causes the pancreatic ducts to be clogged. In result, preventing necessary enzymes to digest fats and proteins.
Without those enzymes, cystic fibrosis patients can not gain weight. The undigested proteins and fats pass right through the body creating smelly bowel. In some cases, this malnutrition causes people to die when they are only children. Furthermore, it is more common for people with cystic fibrosis to develop digestive tract cancer (10).
High levels of the protein CFTR (which the gene makes) are found in the digestive tissues. Doctors explain this increased risk of cancer because CF induces change in the digestive tract organs that causes the cell turnover. Patients with gastrointestinal tract problem should get examined for such tumors. Women with CF can have children, but it is not very common. Giving birth is a vigorous process and puts the mother's health at risk. It may also be hard for a women to get pregnant though because the mucus blocks the sperm from entering the uterus to the fallopian tubes.
About 98% of men with CF are infertile (2). Even though sperm are produced, they can not get to the semen because the vas deferens are blocked. In some new research, it has been thought that men who are sterile have a different form of CF that doesn't involve the digestive system and the lungs. There are now many drugs that are in the market and many more that are in development.
Treatments mainly depends on what organs are effected. The first new drug therapy in 30 years was approved by the Food and Drug Administration in December of 1993. It's a mucus-thinning drug called Pulmozyme. Pulmozyme has reduced the number of respiratory infections and improved lung function.
There is also postural drainage or thumps. This treatment is when the patient is hit on the back and chest with cupped hands to loosen the mucus so it can be coughed up easier. There are many antibiotics that help treat lung infections. Also, medicated vapors are inhaled to open clogged airways.
Since mucus in the intestines causes the food not to get digested, there are enzyme supplements to help. Those enzymes allow patients to go back to a normal diet. Due to the high concentration of the enzymes the end result is deterioration of the pancreas leading to diabetes. With the supplements, patients with cystic fibrosis can eat normal food. There are now many studies that show the medicine ibuprofen (Advil, Motrin IB, Nu prin) prevents serious damage to lungs in children who have cystic fibrosis. The trials involved 85 patients between the ages of 5 and 39 with FEV 1 equal or greater than 60% (11).
In this study, patients that took ibuprofen had a slower rate of decline of FEV 1. Patients that took it for 4 years consistently had even better results and showed best in patients under the age of 13. The dose of ibuprofen was selected between 50 and 100 up / m L because the anti-neutrophil effects of ibuprofen are only attained at these levels. There are some side effects, including conjunctivitis (unknown reason) and epistaxis (due to the anti-platelet action in the ibuprofen. Doctors say that they are not sure if the stomach pains are due to the ibuprofen, but they recommend cystic fibrosis patients to stay on the medicine and to take antacids with magnesium and aluminum and not those containing calcium. Many adults with cystic fibrosis are now living into early middle age (27 years of age) and beyond.
Close attention to medication, physical therapy, exercise and nutrition make cystic fibrosis a far more controllable, less debilitating, and survivable disease. Today, many adults with cystic fibrosis lead fulfilling lives that include college, varied careers, marriage, and families. In the mean time, medical science is making steady progress toward a cure as it explores gene therapy, mucus- thinning drugs and other promising therapies. In 1990, two teams of researchers were able to correct cystic fibrosis cells in a petri dish (8). The next huge step happened in 1993, when the first experimental dose of gene therapy was administered to a human (8). These were milestones in finding a cure or a preventive treatment.
They were huge steps because it marked the first time that scientists were able to test new technology in people with the disease. Also in October of 1993, scientists at the University of Iowa made another big step, they determined that the CF gene treatment worked (8). It had repaired the defective CF cells. This too was the first time that the basic defect was corrected in people with the disease.
Doctors and scientists know that the gene number 7 is the gene that CF is found upon. They also know that gene's protein product most likely induces the movement of chloride directly or indirectly. They named the protein, cystic fibrosis transmembrane conductance regulator (CFTR). While scientists and doctors were looking for the gene, they also discovered that there is an abnormality in the DNA of 70% of cystic fibrosis cases (8). It is important to note that at the DNA level, cystic fibrosis is caused by a mutation of nucleotides. The mutation of even one nucleotide can make a functional gene not function anymore by coding for the wrong amino acid (three nucleotides together code for an amino acid).
This is the case in cystic fibrosis. For instance, the normal DNA code of non- affected individual (normal CFTR protein production) is GG ATCC whereas the defective code of an affected individual is GG A. Thymine in the normal code is replaced with Cytosine in the defective code. The defective code in the DNA causes an abnormality in cystic fibrosis patients often called AF 508 mutation. The AF 508 is made of the deleting of 3 nucleotides from that gene, that then causes the protein product to be missing an amino acid named phenylalanine at position 508. Doctors are now trying to get to this gene mutation and fix it. Scientists are trying to think of a way to administer healthy CFTR genes to the patients through gene therapy.
If all goes as planned, the DNA injected will help the cells to make the normal CFTR protein and cystic fibrosis will then be terminated. Doctors have many "delivery vans" that deliver the good genes. Doctors transport them in viruses, fat capsules and synthetic vectors (8). They are put in the body through the nose or bronchial tubes.
Nine human gene therapy research studies are in the works as of now. Six of these nine are using the "delivery vans" to deliver healthy genes to the lungs or the nose. In one study, the patients are given repeated doses of the CF gene therapy treatment to the lungs. While other studies gave repeated doses of the gene therapy to the nasal tissue of the patients. The remaining studies are using the fat capsules for delivery. One in particular is making the fat capsule in air form to be breathed in by the CF patients.
Putting the good genes in AAV (ade no-associated virus) is another way of getting the genes in the body. They use the AAV to get the healthy genes into the lungs. There are about ninety people with CF who have gone through some sort of gene therapy. "There is a long way still to go before we have a cure for cystic fibrosis, but we are moving in the right direction", says David Porte ous of the Medical Research Council's Human Genetics Units at Edinburgh University. Recently, a grant has just been given to a company named Aradigm that might get us closer to a better delivery vector (8). Dr. Igor Gond a, Aradigm's Vice President of research and development says, "By combining gene therapy with the A ERx delivery system, our research could ultimately lead to a broadly-applicable technology for delivery of genes and oligonucleotides to the respiratory tract.
Diseases which might be treated by such genetic therapies include respiratory infections, lung cancer, emphysema, asthma and cystic fibrosis". (12) Cystic fibrosis is a genetic disorder that affects not only it's victims, but it's victims family and friends. Thanks to modern medicine and new techniques, the median survival rate has gone from 8 years old in 50's to 30 years old in the late 90's (4). Unfortunately, all this new medication and discoveries has come to late for many people. One such individual is Alex Deford (7).
She died when she was only 8 years old. Her father, Frank, wrote a book based on her life and their many struggles, from ignorant doctors who wouldn't believe a dying child about a collapsed lung and the disease itself. Many times with any genetic disorder, the parents blame themselves. After all it was their bad genes that caused it.
Actually, when Alex first went into the hospital to get a sweat test, it came back negative, when in reality, it was positive. That was back in the early 70's though. Now sweat tests have few oversights. Cystic fibrosis is a disease that doesn't take any prisoners. All victims will eventually die from complication due to CF. There are approximately 30,000 children and adults that are living with this disorder (1).
Now that scientists have found the gene in which CF is located, new medicines and new therapies will hopefully be invented. Perhaps in the next century, we can say that cystic fibrosis is completely abolished. Maybe, the new medications and therapies will not have to be as painful as they are now. Why should these individuals with CF be made to suffer in order to get better?
Frank Deford says about chest physiotherapy and the disease, "Two thousands times I had to beat my sick child, make her cry and plead... and in the end for what?".