It is possible that several hundred different mutations of the gene exist than can cause cystic fibrosis. The gene was discovered in 1989. The underlying defect stems from a mutation in a gene on the long arm (q) of chromosome 7. The protein product acts as a chloride channel. It is called the cystic fibrosis trans membrane conductance regulator (CFTR). This controls the cellular transport of sodium chloride and water. It is inherited and is a recessive gene. Some may be unique to certain families so testing of families in which the disease is present may yield results that will help to determine the specific mutation. People having this disease in the past were not expected to live long enough to reach adulthood but improved diagnoses and treatment now allows them to live even beyond fifty years of age. The usual form of death is from respiratory failure.
In normal people chloride the chloride and sodium that is presented in sweat are reabsorbed by epithelial cells in the sweat dust as the sweat finds its way to the surface of the skin. In people with cystic fibrosis the defective gene inhibits the reabsorbing of chloride and sodium ions resulting in an excess of sodium chloride or very salty sweat.
In normal people, the function of respiratory tract epithelial cells is to transport chloride ions into the lumen thereby maintaining the adequate hydration of mucus. In the respiratory tract of persons with cystic fibrosis there is a reduction of the secretion of sodium ions and water caused from the inability of epithelial cell membranes to influence the hydration of mucus. Consequently the mucus becomes very thick. This mucus affects the clearance of irritation and micro-organisms from the lungs. The following events occur in the lungs.
Genetic testing is now available. Cells are collected from inside the cheek of patients and then examined for the