What are the causes of cystic fibrosis?
People have cystic fibrosis (CF) because they have inherited a faulty gene from both of their parents. Find out more about the CF gene, genotypes and the different mutations that people with CF have.
How do you get cystic fibrosis?
People who have CF are born with it. It can't be caught or developed.
If you are not born with CF you will never have it, but you could be a CF gene carrier.
One in 25 people carry the CF gene. For someone to be born with CF, both parents must carry the faulty gene. If both parents have the gene, there is a 25% chance the child will have CF. If both parents carry the gene there is also a 50% chance of the child being a gene carrier but not having CF and a 25% chance they will not have the CF gene.
Nowadays, all babies are offered a screening test when they are five days old. Because of this, most people with CF are diagnosed at birth. However, some people with CF are not diagnosed until later in life.
What is a mutation?
Everyone with CF will have two faulty or ‘mutated’ CF genes.
These mutations may also be known as 'variants'.
There are over 2,000 known mutations that can cause CF.
The two genes could be the same mutation, or you could have two different ones. The specific mutations and combination you have is known as your ‘genotype’.
Your genotype and other factors will dictate how severe the condition is for you, and which organs in the body are most affected.
It’s important to know which mutations you have, as it might affect what kind of treatments you can have. Research is underway into medicines that work for people with specific CF genotypes, as well as treatments that will work for everyone with CF ('genotype agnostic' treatments).
Why do the mutations cause CF?
Genes instruct the body on how to make proteins and where to send them in cells in order for them to work. CF mutations affect the body’s ability to make or direct the CFTR protein, which helps salt and water move into and out of cells. You can find out more about how CF affects the body here.
What types of mutation are there?
The mutations that cause CF can be split into five different categories depending on how they affect the CFTR protein.
The first three classes generally lead to complete loss of CFTR function and a more severe form of the disease. The last two classes cause a milder reduction in function.
Class I – shortened protein
Around 7% of people with cystic fibrosis in Europe have this type of mutation, which results in a shortened CFTR protein.
Class II – protein fails to reach membrane
Around 85% of people with cystic fibrosis in Europe have this type of mutation, which results in the CFTR protein not being transported to the surface of the cells in which it is required. The most common of this type of mutation is F508del.
Class III – protein cannot be regulated
Less than 3% of people with cystic fibrosis in Europe have this type of mutation. The CFTR protein forms a channel in the cell surface – in people with this mutation the gate at the end of the channel doesn’t open and close at the right times.
Class IV – reduced chloride conductance
Less than 3% of people with cystic fibrosis in Europe have this type of mutation, which changes the shape of the protein channel so that chloride cannot move easily in and out of the cells.
Class V – reduced protein levels
Less than 3% of people with cystic fibrosis in Europe have this type of mutation, which results in a reduction in the amount of CFTR protein produced by the cells.
Where can I find out more about my genotype?
CFTR2 provides information about specific variants in the CF gene.
You must accept the site usage agreements before using the site.
You can enter your genetic variants to find information about:
- sweat chloride in people with your genotype
- lung function in people with your genotype
- pancreatic insufficiency in people with your genotype
- P. aeruginosa infection rate in people with your genotype
This information is not a substitute for information from your CF team. It's only a representation of the average health outcomes of people with your genotype, and cannot account for individual experience.
How is cystic fibrosis diagnosed?
Our page on how people with cystic fibrosis are diagnosed with the condition also includes information on newborn screening, carrier testing and late diagnosis.
How is cystic fibrosis treated?
Find out more about medication, exercise, nutrition, transplant and transition on our treatment page.
How cystic fibrosis affects the body
Explore our interactive body to find out all about the different ways CF affects the body, from the lungs and digestive system to the bones and the reproductive system.