What Causes cystic fibrosis?
The CFTR gene makes a protein that controls the movement of salt and water in and out of the cells. In people who have cystic fibrosis, the gene makes a protein that doesn't work well. This causes thick, sticky mucus and very salty sweat. More than a thousand defects are known that can affect the CFTR gene. The type of defect may affect the severity of cystic fibrosis. </s>