Cystic Fibrosis Essay, Research Paper

CYSTIC FIBROSIS

According to old northern European folklore, a child that tasted salty when kissed upon the forehead was bewitched and would soon die. Today we know the reason -the genetic disease, cystic fibrosis or CF. It is a chronic, progressive disease and the most common, fatal inherited disorder in the United States.

About 30,000 Americans suffer from cystic fibrosis, and 2500 babies are born in the U.S. with the disease each year. While all races and ethnic groups may suffer from the disease, it occurs most often in whites whose ancestors came from northern Europe. About 1 in every 20 Americans is an unaffected carrier of the disease because they have one abnormal ?CF gene?.

Patients with CF produce a thick, sticky mucus; much thicker than a healthy person. The buildup of this mucus clogs ducts and body tubes, leading to chronic tissue inflammation and the replacement of injured cells with scar tissue which blocks the airways of the lungs and ducts in the pancreas and liver. In the lungs, this mucus impairs breathing and causes chronic bacterial infections. Lung disease is the main cause of death from cystic fibrosis. Occlusion of ducts in the pancreas prevents digestive enzymes produced by the pancreas from reaching the intestines where they are required for proper digestion. Cirrhosis of the liver and male infertility are also associated with the disease.

Until recently, most of the information known about cystic fibrosis was gained from observation. In 1938, Dorothy H. Anderson of Columbia University, provided the first descriptions of body changes produced by CF. From autopsies performed on infants and children, she described destruction of the lungs and pancreas. A decade later, physicians had connected the clogged ducts and passageways to the body?s inability to digest nutrients and respiratory failure.

By 1946, studies about family patterns of disease inheritance led researchers to realize that cystic fibrosis was probably caused by a single gene mutation. It is called an autosomal recessive condition. The function of most genes is to instruct the cells to make particular proteins, most of which are needed to keep us alive. If the basic building blocks of a gene (called base pairs) are altered or mutated, the protein that the gene codes for will be defective or not produced at all. Researchers concluded that if a child inherited an altered copy of the gene from both parents (making no normal molecules of the protein coded for by that gene), the child became sick; however, a good gene from one parent and an altered gene from the other parent did not produce the disease. This means that each time two carriers produce a child, there is a 25 percent chance the child will have CF; a 50 percent chance the child will be a carrier; and a 25 percent chance the child will be a non-carrier (completely free of the altered gene).

About seven years after the inheritance pattern was discovered, a New York City heat wave caused doctors to see a large number of children with cystic fibrosis who were dehydrated. At Columbia University, researchers concluded that children with CF lose an excessive amount of salt in their sweat. While the reason for the salty skin was still a mystery, the information became the basis for the test used to tell if a child has cystic fibrosis: measurement of the salt content in sweat. In 1985, Paul Quinton answered the salty skin question. Sweat, which is normally produced at the base of the sweat gland, has high concentrations of sodium and chloride ions (the ingredients in salt). As sweat flows to the skin surface the ions escape, through channels, to the epithelial tissue surrounding the glands. The sweat that emerges to cool the skin is then only slightly salty. In patients with cystic fibrosis, the epithelial tissue was impermeable to chloride. The chloride-transporting channel in the epithelial tissue did not function causing the sweat to remain very salty. In addition, the salt build-up caused water to be drawn into these cells by osmosis, making the mucus very thick.

In 1989, a team of scientists isolated the gene (located on chromosome 7) that produces the protein responsible for the movement of chloride ions through the cell membrane. They named the protein ?cystic fibrosis transmembrane conductance regulator? or CFTR. This protein forms a channel in the cell membrane to transport chloride. The team also found that the gene mutation involved in 70-80 percent of cystic fibrosis cases was due to the deletion of three base pairs from the gene. Because of this base pairs deletion, the CFTR protein produced by the defective gene, lacks a single amino acid: phenylalanine at position 508. The mutated protein is called deltaF508

CFTR. Various other mutations on this gene- over 400 at last count- seem to be responsible for the remaining cystic fibrosis cases.

Since these latest discoveries, CF research has greatly increased. Cystic fibrosis was once considered a fatal childhood disease. Thirty years ago the median life expectancy was 8 years. Today better treatment and drugs have increased the life span of CF patients to 29 years. Antibiotics, enzyme supplements, vitamins, special enriched diets, bronchodialators, mucolytics, and decongestants have all proven helpful in treating the disease. Physical therapy, consisting of bronchial, or postural drainage procedures, and exercise are also helpful. INS365, a new drug, is being studied for its ability to stimulate cells to secrete chloride. This in turn would lead to mucus that is thinner and less sticky. One treatment strategy, now in clinical trials, is to correct the protein product of the gene. The CF sufferer would actually be given the active form of the protein. While the length and quality of a CF victims life has been improved, there is still no cure. Those who suffer from cystic fibrosis face a new set of problems- going to college, getting a job, finding health insurance, and building permanent relationships-while still maintaining medications and treatments.

Since cystic fibrosis is a genetic disease, the best hope for a future cure is through gene therapy at an early age. Gene therapy could repair or replace the defective gene. In 1990, scientists were able to grow cells from the nasal passages of CF patients. By introducing the normal gene into these cells, researchers corrected the cells chloride transport abnormality. In 1993, researchers modified a common cold virus to act as a delivery vehicle-carrying the genes to the CF cells in the respiratory airways of patients. Several studies, supported by the Cystic Fibrosis Foundation, are underway to test new gene delivery methods. Hopefully, a cure for CF is not far away.

BIBLIOGRAPHY

TEXT:

1. NHLBI, Facts About Cystic Fibrosis; http://www.nhlbi.nih.gov/health/public/lung/other/cf.htm

2. About Cystic Fibrosis; http://cf-web.mit.edu/what-is-cf.html

3. Facts About Cystic Fibrosis; http://www.cff.org/facts.htm

4. Cystic Fibrosis; Welsh Michael J. and Smith, Alan E. http://www.people.virginia.edu/~rjh9u/cfsciam.html

DIAGRAM:

1. Diagram of base pairs deletion; http://www.people.virginia.edu/~rjh9u/cfsciam.html

PHOTOGRAPHS:

1. Photographs of ?olden? treatments (3); http://www.talkcity.com/StudioDr/normap

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TEXT:

1. NHLBI, Facts About Cystic Fibrosis; http://www.nhlbi.nih.gov/health/public/lung/other/cf.htm

2. About Cystic Fibrosis; http://cf-web.mit.edu/what-is-cf.html

3. Facts About Cystic Fibrosis; http://www.cff.org/facts.htm

4. Cystic Fibrosis; Welsh Michael J. and Smith, Alan E. http://www.people.virginia.edu/~rjh9u/cfsciam.html