What Causes Cystic Fibrosis

Cystic Fibrosis affects both males and females. It's not contagious, so you can't catch CF from another person.

Cystic fibrosis is an inherited disease caused by mutations (changes) in a gene on chromosome 7, one of the 23 pairs of chromosomes that children inherit from their parents.

“genetic testing for CF

won't detect everyone”

Cystic fibrosis occurs because of mutations in the gene that makes a protein called CFTR (cystic fibrosis transmembrane regulator). A person with CF produces abnormal CFTR protein - or no CFTR protein at all, which causes the body to make thick, sticky mucus instead of the thin, watery kind.

Humans have 23 pairs of chromosomes made of the inherited genetic chemical called DNA. The CF gene is found on chromosome number 7. It takes two copies of a CF gene - one inherited from each parent - for a child to show symptoms of CF. Persons born with only one CF gene (inherited from only one parent) and one normal gene are CF carriers . CF carriers do not show CF symptoms themselves, but can pass the problem CF gene to their children. Scientists estimate that about 12 million Americans are currently CF carriers. If two CF carriers have a child, there is a one in four chance that the child will have CF.

There are more than 1,200 different mutations of the CF gene that can lead to cystic fibrosis (some mutations cause milder symptoms than others). About 70% of people with CF have the disease because they inherited the mutant gene Delta F508 from both of their parents. This can be detected by genetic testing, which can be done in children, both before and after birth, and in adults who are thinking about starting their families.

Of all ethnic groups, Caucasians have the highest inherited risk for CF, and Asian Americans have the lowest. In the United States today, about one of every 3,600 Caucasian children is born with CF. This compares with one of every 17,000 African Americans and only one of every 90,000 Asian Americans. Although the chances of inherited risk may vary, CF has been described in every geographic area of the world among every ethnic population.

And most of them don't know it. Parents can be tested to see if they carry the CF gene, but because there are hundreds of specific CF gene mutations (not all of which are known), genetic testing for CF won't detect everyone who is carrying a CF gene. Doctors can also perform tests during pregnancy so prospective parents can find out more about the chances that their child will have CF. However, these tests also won't always detect a CF gene.

Scientists don't know exactly why the CF gene evolved in humans, but they have some evidence to show that it helped to protect earlier generations from the bacteria that cause cholera, a severe intestinal infection.

Carriers
People who carry the cystic fibrosis gene are healthy and have no symptoms — they may be carriers and not know it. Although parents often blame themselves when a child is born with cystic fibrosis, it's important to remember that nothing a parent consciously does causes this disease.