An abnormality in the gene known as cystic fibrosis transmembrane conductance regulator (CFTR) causes cystic fibrosis. This gene is responsible for making a protein that regulates the movement of salt and water into and out of the body's cells. When this gene is defective, it causes the body to produce the thick, sticky mucus and salty perspiration characteristic of cystic fibrosis.

Everyone inherits one CFTR gene from each parent. When both parents pass on an abnormal CFTR gene, the child will have cystic fibrosis. Children who inherit one abnormal gene and one normal gene will not develop cystic fibrosis and will experience no symptoms. However, they will be carriers of the condition and may pass it on to any future children. About 12 million Americans are carriers of this abnormal gene, according to the National Institutes of Health (NIH).

It is important to remember that parents who are carriers have both normal and abnormal CFTR genes. Therefore, even if both parents are carriers, it does not mean they will always pass the abnormal CFTR gene on to their child. When two people who are both carriers of an abnormal CFTR gene (but who do not have the condition) have a baby, the child has the following odds of developing cystic fibrosis:

• One in four chance of inheriting two abnormal CFTR genes and developing cystic fibrosis.
  
  
• One in four chance of inheriting two normal CFTR genes and not developing cystic fibrosis and not becoming a carrier.
  
  
• Two in four chance of inheriting one normal CFTR gene and one abnormal CFTR gene. In this instance, the child will not develop cystic fibrosis but will be a cystic fibrosis carrier.

Cystic fibrosis affects both males and females and people from all racial and ethnic groups. However, it is most common among Caucasians of Northern European descent. It also is relatively common among Latinos and Native Americans (particularly the Pueblo and Zuni). It is less common among people of African and Asian descent.