What Causes Cystic Fibrosis

Cystic fibrosis is caused by a mutation in the cystic fibrosis transmembrane regulator (CFTR) gene, one of thousands of genes found in the DNA in every person. The CFTR gene produces the CFTR protein, which controls the flow of water and certain salts in and out of the body’s cells. If the CFTR gene has a mutation that causes the protein to not work, this changes the movement of salt and water in and out of cells and results in thickened mucus throughout the body.

Cystic fibrosis is an autosomal recessive genetic disorder. That means both parents must have a mutation of the CFTR gene for a child to be born with the disorder. More than 10 million people in the United States are carriers of the cystic fibrosis gene. These people are typically not affected by the disease and most often don’t know they carry the gene. They can, however, pass the disorder on to their children.

In most cases, children with cystic fibrosis are born to parents with no known history of the disorder. In these cases, both parents unknowingly carried the CFTR mutation and passed it on to their child during conception. If both parents carry the CFTR mutation, they have a 1 in 4 chance of having a child with cystic fibrosis, and a 1 in 2 chance of having a child who is also a carrier for the disorder. If only one parent carries a CFTR mutation, each child born may become a cystic fibrosis carrier — and potentially pass the CFTR mutation on to his or her children — but will not have the disease.