For a child with cystic fibrosis life is mostly a series of respitory infections doctors visits and medications. Cystic fibrosis causes a build up of mucus in th lungs making breathing difficult . The thick mucus coats the hairlike projections lining air passage weakening the bodys immune system .Excess mucus interfers with the functioning of other oragns too.In the liver and pancreas mucus blocks the flow of the digestive enzymes in the intestine so food is not digested properly. Worn down by the repeated bouts of illness a cystic fibrosis patient rarely lives beyond his or her twenties. Cystic fibrosis is most common inherited disorder among Caucasian people. The disease which begins in infancy afflicts more than 25,000 Americans and causes more than 500 deaths every year. Forty years ago the average life span of a cystic fibrosis patient was five years .Today improved medical therapies and nurtrient rich diets have enabled cystic fibrosis suffers to survive into adulthood. Research into the cause of cystic fibrosis reads like a detective story. One clue is that cystic fibrosis patients have excess amounts of sodium and chloride in their sweat making it vey salty . At the University of North Carolina researchers found that salt imbalance caues thick mucus to accumulate in the patients lungd. High level of salt in lung cells draw water out of the mucus causing it to thicken.The level of salt in a cell is determained by the movement of ions across the cell membrane.Ions are carried across call memebranes by protein channels embedded in the cell membrane. Since the stucture and functions of proteins are determained by genes problems with ion transport can be assumed to have a genetic basis. In 1989 an American Canadian research team found thre defect in the gene called the cystic fibrosis transmembrane conductance regulator gene ,produces a protein that usually helps maintain normal levels of chloride. In about 60% of cystic fibrosis pateints the protein made by the CFTR gene is missing an amino acid called phenylalanine
.When this amino acid is missing the protein doesnt fold into its correct shape and loses its function. Researchers are not certain whether the defective protein is actually in tranport molecule. Some research data indicates that proteins might instead be involved in the regulatory network that controls ion transport. Although most cystic fibrosis pateins have the mutation causing the defective protein described above another 61 mutations in the CFTR gene have been identified.