People who inherit one copy of the CFTR gene that contains a mutation and one normal copy are considered CF carriers. CF carriers do not have the disease but can pass their copy of the defective gene on to their children.
Our Genetic Encyclopedia
Each of our cells contains genetic information that provides the body with coded instructions to make proteins, which determine how the body looks, develops, and works.
Genetic information is stored in chromosomes, which can be thought of as different volumes of our genetic encyclopedia. Humans have 23 pairs of chromosomes. Each pair is made up of one copy of a chromosome from the mother and one from the father.
Most cells in the body have a full copy of the genetic encyclopedia, which includes 23 pairs of chromosomes. However, eggs and sperm have only a single copy of each chromosome, rather than the pairs found in other cells in the body.
Each chromosome is made up of many genes, which are the entries, or topics, in the encyclopedia. The genes supply the body with instructions for making proteins.
All of this genetic information that makes up our genes is in code and stored as a molecule called deoxyribonucleic acid (DNA). The DNA code is made up of letters that spell out the entries of our genetic encyclopedia.
If we all shared 100 percent of our genetic material then we would all be as alike as identical twins are. But not every single letter in the genetic encyclopedia is the same in all of us, which helps to explain why we are not all exactly alike.
How Changes in the CFTR Gene Affect the Body
Different types of changes, or mutations, in our genes affect the body in different ways. Within our genetic encyclopedia, there are small differences in our genes. Sometimes the differences are minor or do not affect a person's health — like two encyclopedia entries that are worded in slightly different ways but still say the same thing. In these cases, people's genes may differ or the protein made by the gene is slightly different — resulting in a different eye color — but the genes and the proteins work correctly.
At other times, the change in a gene may cause the protein to not work or not be made at all. Cystic fibrosis is caused by mutations in the gene that produces the cystic fibrosis transmembrane conductance regulator (CFTR) protein. This protein is responsible for regulating the flow of salt and fluids in and out of the cells in different parts of the body.
In people with CF, mutations in the CFTR gene can disrupt the normal production or functioning of the CFTR protein found in the cells of the lungs and other parts of the body.
Mutations in the CFTR gene cause the CFTR protein to malfunction or not be made at all, leading to a buildup of thick mucus, which in turn leads to persistent lung infections, destruction of the pancreas, and complications in other organs.
Cystic fibrosis is an example of a recessive disease. That means a person must have a mutation in both copies of the CFTR gene to have CF. If someone has a mutation in only one copy of the CFTR gene and the other copy is normal, he or she does not have CF and is a CF carrier. About 10 million people in the United States are CF carriers.
CF carriers can pass their copy of the CFTR gene mutation to their children. Each time two CF carriers have a child together, the chances are:
- 25 percent (1 in 4) the child will have CF
- 50 percent (1 in 2) the child will be a carrier but will not have CF
- 25 percent (1 in 4) the child will not be a carrier of the gene and will not have CF
People with CF can also pass copies of their CFTR gene mutations to their children. If someone with CF has a child with a CF carrier, the chances are:
- 50 percent (1 in 2) the child will have CF
- 50 percent (1 in 2) the child will be a carrier but will not have CF
Children of two carriers may be CF carriers like their parents. In a family with four children, it is possible that none of the children, some of the children, or all of the children will have CF. Each baby has the same chance to inherit CFTR mutations from both parents, no matter whether any of the other siblings are carriers or have CF. When someone with CF has children with a CF carrier, the children will either be CF carriers or have CF.