Cystic fibrosis (CF) is a genetic condition. Alterations in the CFTR gene, which a person inherits from their parents, affect the function of the CFTR protein, causing thick, sticky mucus.

CF can affect the lungs, digestive system, and other organs. It occurs due to a gene variation in the cystic fibrosis transmembrane conductance regulator (CFTR) gene.

This gene is responsible for the CFTR protein, which plays an important role in producing mucus. When there is a problem with this protein, it can cause mucus to thicken.

This thick mucus may clog the airways, increasing the risk of infections and making breathing difficult. It can also affect other organs, such as the pancreas, which can lead to malnutrition and insufficient growth.

Read on to learn more about the genetics of cystic fibrosis.

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CF is a progressive genetic condition that typically affects the lungs and pancreas. It is hereditary, as people inherit a gene alteration from both parents that results in the condition.

Alterations in the CFTR gene, which codes for the CFTR protein, are responsible for the condition.

Alterations in the CFTR gene result in CF due to how these variations affect the CFTR protein. Variations in this gene can disrupt the usual production or functioning of the CFTR protein, which results in a buildup of thick mucus.

The CFTR protein is responsible for regulating the flow of salt and fluids in and out of the cells in various parts of the body, such as the lungs.

Specifically, healthy CFTR protein moves chloride ions between the inside of a cell and the space surrounding it. By regulating the balance of salt and water, this protein is able to maintain a healthy layer of mucus.

However, when the CFTR protein is not working correctly, salt and water get out of balance. As a result, mucus becomes too thick.

This thick mucus can clog the airways, making it difficult to breathe. It can also trap bacteria, which may lead to recurrent lung infections and inflammation. The thick mucus can also affect the release of digestive enzymes from the pancreas. This can impair the digestion and absorption of nutrients from food, which can lead to malnutrition.

Evidence notes there are almost 2,000 known disease-causing variations of the CFTR gene that can result in CF. Health experts can categorize these variations into five classes, depending on how the alteration affects the CFTR protein.

Typically, the first three classes cause a complete loss of CFTR function and a more severe form of CF. The last two classes result in a milder reduction in CFTR function.

The five different classes include:

  • Class I (protein production alterations): This type includes nonsense and splice variations. Nonsense variations occur when the cell mistakenly thinks the protein is finished and stops production too soon. Splice variations interrupt the correct sequence of instructions, meaning a cell cannot build a correct CFTR protein.
  • Class II (protein processing alterations): This occurs due to either a deletion of an amino acid or the addition of an incorrect amino acid. Both result in the protein not having the correct shape to function correctly and transport chloride. The most common CF alteration, known as F508del, occurs due to removing a single amino acid from the CFTR protein.
  • Class III (gating alterations): The shape of the CFTR protein includes a channel with a gate. The gate opens when chloride needs to flow through the channel. However, gating variations mean this gate cannot open, meaning chloride is unable to get through.
  • Class IV (conduction variations): In some cases, a change in amino acids does not change the shape of the protein but affects the shape of the chloride channel. This change in shape means that chloride cannot move through as easily as it needs.
  • Class V (insufficient protein levels): This variation results in a lower amount of typical CFTR protein. As these individuals only produce a small amount of functioning CFTR protein, the mucus becomes thick.

CF can affect people of every racial and ethnic group. However, it occurs most frequently within white populations. Evidence suggests there are approximately 30,000 people with CF in the United States. In addition, roughly 1 in 30 people in the United States are a carrier for a CF variation.

A person inherits the condition in an autosomal recessive pattern. This means both parents must carry and pass on one copy of a CF gene alteration.

If both parents are carriers of a CFTR gene alteration, their child will have a 25% chance of having CF. In the same circumstance, there is a 50% chance that the child will also be a carrier and a 25% chance they will not carry the CF gene alteration.

In every U.S. state, testing for CF is a part of newborn screening. While a positive result is not a diagnosis of CF, it indicates that more testing is necessary. Typically, the screen involves testing a sweat, blood, or saliva sample.

However, if people have a standard test result, there is a small risk that they may still be a carrier for rare CF gene variations.

Additionally, if both individuals are carriers of CF, prenatal testing is available at either 10–14 or 16–20 weeks to determine whether the fetus has two copies of a CF gene alteration. Before conceiving, individuals can also meet with a genetic counselor to discuss any issues.

Cystic fibrosis is a genetic condition. It occurs when an individual inherits two gene variations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene from both parents.

The CFTR gene produces the CFTR protein, which is responsible for regulating mucus. When this gene does not function correctly, mucus becomes too thick, which can negatively affect the lungs, pancreas, and other organs.

In the United States, checking for CF is part of newborn screening. Individuals who are either pregnant or considering pregnancy can also test if they are carriers for CF gene variations or if the fetus has two copies of a CF gene alteration.