Cystic Fibrosis and Chloride Channels

The inherited disease cystic fibrosis (CF) involves defective plasma membrane proteins that affect chloride ion (Cl − ) channels in the membrane. These channels are transport proteins that use facilitated diffusion to move chloride ions across the plasma membrane. The genetic defect that causes CF results in the formation of abnormal chloride channel proteins in the membranes of cells lining the respiratory passageways and ducts in glands, such as the pancreas. The primary defect in these chloride channels results in an abnormal flow of chloride ions across the membrane, causing salt to be trapped within the cytoplasm of affected cells.
Ultimately, the normal osmotic flow of water across the plasma membrane breaks down. The concentration of salt within the cytoplasm of these cells causes an increase in the osmotic flow of water into the cell, thereby resulting in thickening of the mucus in the respiratory passageways and the pancreatic ducts. The aggregation of thickened mucus plugs the airways of the lungs, leading to breathing problems and increasing the risk of infection.
Therefore, a single genetic and biochemical defect in a transport protein produces significant health problems.

source : human anatomy