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What Causes Cystic Fibrosis?

A defect in the CFTR gene causes cystic fibrosis (CF). This gene makes a protein that controls the movement of salt and water in and out of your body's cells. In people who have CF, the gene makes a protein that doesn't work well. This causes thick, sticky mucus and very salty sweat.

Research suggests that the CFTR protein also affects the body in other ways. This may help explain other symptoms and complications of CF.

More than a thousand known defects can affect the CFTR gene. The type of defect you or your child has may affect the severity of CF. Other genes also may play a role in the severity of the disease.

How Is Cystic Fibrosis Inherited?

Every person inherits two CFTR genes—one from each parent. Children who inherit a faulty CFTR gene from each parent will have CF.

Children who inherit one faulty CFTR gene and one normal CFTR gene are "CF carriers." CF carriers usually have no symptoms of CF and live normal lives. However, they can pass the faulty CFTR gene to their children.

The image below shows how two parents who are both CF carriers can pass the faulty CFTR gene to their children.

Example of an Inheritance Pattern for Cystic Fibrosis

    The image shows how CFTR genes are inherited. A person inherits two copies of the CFTR gene—one from each parent. If each parent has a normal CFTR gene and a faulty CFTR gene, each child has a 25 percent chance of inheriting two normal genes; a 50 percent chance of inheriting one normal gene and one faulty gene; and a 25 percent chance of inheriting two faulty genes.
The image shows how CFTR genes are inherited. A person inherits two copies of the CFTR gene—one from each parent. If each parent has a normal CFTR gene and a faulty CFTR gene, each child has a 25 percent chance of inheriting two normal genes; a 50 percent chance of inheriting one normal gene and one faulty gene; and a 25 percent chance of inheriting two faulty genes.
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Last Updated: December 26, 2013