Cystic Fibrosis Causes

What causes cystic fibrosis?

Cystic fibrosis is an

inherited

inherited

(in-HAYR-ih-ted):

The passing of genetic information from a parent to a child through genes.

disease caused by

mutations

mutation

(myoo-TAY-shun):

Any change in a nucleic acid sequence, such as DNA or RNA.

in a

gene

gene

(jeen):

The unit that passes heredity from parents to children. Genes are pieces of DNA and contain information for making a specific protein.

called the cystic fibrosis transmembrane conductance regulator (CFTR). The CFTR gene provides instructions for the CFTR

protein

protein

(PRO-teen):

Large molecule made up of building blocks called amino acids. Proteins make up the structure of a cell. Proteins are involved in structures, hormones, enzymes, muscle contraction, immune system responses, and other essential life functions. The amino acids involved are generally determined by a gene.

.

People who inherit two copies of a mutated CFTR gene (one copy from each biological parent) will have cystic fibrosis. Having two mutated CFTR genes means that the body makes a CFTR protein that doesn’t work like it should.

In cystic fibrosis, the faulty CFTR protein changes how much salt moves in and out of cells. These changes cause thick and sticky

mucus

mucus

(MYOO-kus):

A clear, thick secretion made by the membranes that line some organs of the body, including the nose, mouth, throat, and vagina.

and increase the amount of salt in sweat. Thick mucus can block and damage the airways of the lungs, making it hard to breathe. It can also clog the digestive system and other organs of the body.

Learn more in How the Lungs Work.

How do CFTR mutations cause cystic fibrosis?

More than 2,000 mutations of the CFTR gene can cause cystic fibrosis. Different mutations affect how much CFTR protein the cells make and how well the protein works. With the most common gene mutation, part of the CFTR gene is missing. The mutation makes a CFTR protein that can’t stay in the correct shape. Some CFTR mutations cause cells to make hardly any CFTR protein at all.

Normally, the CFTR protein controls how salt and water move in and out of cells. In people who have cystic fibrosis, the CFTR protein does not work properly. The faulty CFTR protein causes mucus to become thick and sticky, because it contains less water. Also, the sweat glands make extra-salty sweat.

How is cystic fibrosis inherited?

Every person inherits two CFTR genes: one gene from each parent. Children who inherit a CFTR gene with a mutation from each parent will have cystic fibrosis.

When a mutated CFTR gene is inherited from one parent and a normal CFTR gene is inherited from the other, the person will be a cystic fibrosis carrier. Cystic fibrosis carriers can pass the mutated CFTR gene on to their children. Carriers are generally healthy, but they may have some mild symptoms of cystic fibrosis.

The image below shows how two parents who are both cystic fibrosis carriers can pass a CFTR gene mutation on to their children.

If both parents have a normal CFTR gene and a mutated CFTR gene, each of their children has a:

• 25% (1 in 4) chance of inheriting two normal CFTR genes
• 50% (1 in 2) chance of being a cystic fibrosis carrier, because they inherit one normal gene and one mutated gene
• 25% (1 in 4) chance of inheriting two genes with mutations and having cystic fibrosis

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What Is Cystic Fibrosis?

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Symptoms

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