Causes of cystic fibrosis

Cystic fibrosis is a genetic inherited disease


Our bodies are made up of cells, and each cell contains around 20,000–25,000 genes.1,2 Genes are part of our DNA, the unique material inside all of our cells that is the molecular code for everything in our bodies. They are a set of instructions that determine our individual characteristics, such as eye colour and hair colour.2,3

Genes also contain the instructions for making proteins, which are the building blocks for everything in the body and are very important for keeping our bodies working properly.3 Everyone inherits two copies of each gene, one from each parent.2

Sometimes, a gene might have a change in it that causes it to behave differently to a normal gene. This change is called a mutation.4

Cystic fibrosis (CF) is a disease people are born with. It is a genetic disease, meaning it is inherited from your parents.3



  • One of the genes in our bodies is called the Cystic Fibrosis Transmembrane conductance Regulator (CFTR) gene. Everyone inherits two copies of this gene, which contains the instructions for making the CFTR protein.3
  • If one of the CFTR genes you inherit has a mutation (change) that causes cystic fibrosis, this means you are a “carrier” of the mutated gene, but you do not have CF.3
  • If both of the CFTR genes you inherit have a mutation that causes cystic fibrosis, you are born with CF.3


There are many different types of CFTR gene mutations

  • Not everyone with CF has the same mutations (changes) in their CFTR genes. We know of over 2,000 different CFTR gene mutations.5 At least 352 of these cause CF6, but most of them are extremely rare.7
  • People with CF can either have two copies of the same CF gene mutation (homozygous), or two different CF gene mutations (heterozygous).8
  • F508del is the most common CFTR gene mutation.7 Approximately 90% of people with CF in the UK have at least one copy of the F508del mutation.8
  • The next most common mutations, for example, G551D, R117HG542X, 621+1G->T, and N1303K, have a much lower prevalence.8

Knowing your CF genotype

The type of CFTR gene mutations you have is called your ‘genotype’, and this is something your doctor should know and be able to tell you.


  1. NIH Genetics Home Reference. What is a cell? Available at: Last accessed July April 2021.

  2. NIH Genetics Home Reference. What is a gene? Available at: Last accessed April 2021.

  3. Orenstein DM. Cystic Fibrosis: A Guide for Patient and Family. 3rd ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2004.

  4. NIH Genetics Home Reference. What is a gene mutation and how do mutations occur? Available at: Last accessed April 2021.

  5. The Clinical and Functional Translation of CFTR (CFTR2) resources. How is CF inherited. Available at: Last accessed April 2021.

  6. CFTR2. CFTR2 Variant List History. 10 January 2020. Available at: Last accessed April 2021.

  7. Castellani C, et alJ Cyst Fibros 2008; 7(3): 179 ̶ 196.

  8. Cystic Fibrosis Trust. UK Cystic Fibrosis Registry. Annual Data Report 2018. Published August 2019.