What is the CTFR gene responsible for and what happens when there is a mutation in that gene?

Controls movement of chloride ions in and out of cells. Mutation in the gene cause the CFTR protein to malfunction or not be made at all, leading to a buildup of thick mucus and flattened cilia which cant sweep away the mucous, which in turn leads to persistent lung infections, destruction of the pancreas, and complications in other organs.