What is Cystic Fibrosis?

 

What is cystic fibrosis?

Cystic fibrosis (CF) is an inherited disease caused by an abnormality in the body’s regulation of salt and water movement through certain cells. It is chronic, progressive and life shortening. In 2008, the average expected age for death for patients with CF was age 38.

Children with CF have an abnormality in the function of a cell protein called the cystic fibrosis transmembrane conductance regulator (CFTR). CFTR controls the flow of water and certain salts in and out of the body's cells. As the movement of salt and water in and out of cells is altered, secretions become thickened. The thickened secretions can affect many organs and body systems, including:

  • Respiratory—sinuses and lungs
  • Digestive—pancreas, liver, gallbladder and intestines
  • Reproductive—primarily in the male, where sperm-carrying ducts become clogged
  • Sweat glands

Nearly 30,000 people in the U.S. are affected with the disease, including 1,000 infants. It occurs mainly in Caucasians, although it also can occur in Hispanics, African-Americans, Asian Americans and Native Americans.

Approximately one-in-31 people in the U.S. are carriers of the cystic fibrosis gene. These people are not affected by the disease and usually do not know they are carriers.

CF is a complicated illness that requires clinical care by a doctor and healthcare professionals specializing in the disease. Multidisciplinary teams organized at CF centers are best suited to care for children and adults with CF and have been shown to help reduce the severity of the illness and to provide treatment that may lead to longer life spans for CF patients.

The Genetics of Cystic Fibrosis

CF is a genetic disease. This means that CF is inherited. A child will be born with CF only if two CF genes are inherited—one from the mother and one from the father. A person who has only one CF gene is healthy and is said to be a "carrier" of the disease. A carrier has an increased chance of having a child with CF. This gene inheritance is called "autosomal recessive." Autosomal means the gene is on one of the first 22 pairs of chromosomes that do not determine gender—the disease affects males and females equally. "Recessive" means that two copies of the gene, one inherited from each parent, are necessary to have the condition. Once parents have had a child with CF, there is a 25 percent chance with each subsequent pregnancy for another child to be born with the disease.

The birth of a child with CF is sometimes a surprise to a family because there may be no family history of the disease. Many autosomal recessive conditions occur this way. Because both parents are healthy, they have no prior knowledge they carried the gene or that they passed the gene to their child during pregnancy.

Genes are found on structures called chromosomes in the cells of our body. There are normally 46 total chromosomes (23 pairs) in each cell of our body. The seventh pair of chromosomes contains the cystic fibrosis transmembrane conductance regulator (CFTR) gene. Mutations or errors in this gene cause CF, and it is quite large and complex. More than 1,000 different mutations in this gene cause CF.

The risk for having a mutation in the gene for CF depends on your ethnic background (for persons without a family history of CF):

Ethnic Background

Risk of CF Mutation

Risk of Child with CF

Caucasian

1 in 29

1 in 3,300

Hispanic

1 in 46

1 in 8,000 to 9,000

African-American

1 in 65

1 in 15,300

Asian

1 in 90

1 in 32,100

Testing for the CF gene can be done with a small blood sample or from a cheek swab, which is a brush rubbed against the inside of your cheek to obtain cells for testing. Laboratories generally test for the most common mutations—anywhere from 30 to 100 total mutations. The detection rate depends on the person's ethnic background. In general, the detection rate for the Caucasian population is about 90 percent, 57 percent for Hispanics, 75 percent for African-Americans and 30 percent for Asians. The detection rate differs because CF is more common in certain geographical areas and certain populations of the world. The diagnosis is confirmed by another test called a sweat chloride test.

Many people with CF have mutations that have not been identified. In other words, not all of the genetic errors that cause the disease have been discovered. Because not all mutations are detectable, a person can still be a CF carrier even if no mutations were found through testing. In recent years, however, more sophisticated gene testing has helped doctors identify the vast majority of genetic defects.

Testing for the CF gene is recommended for anyone who has a family member with the disease, or whose partner is a known carrier of or affected with CF.