Cystic Fibrosis and what causes it

Cystic fibrosis is caused by an issue with the cystic fibrosis transmembrane conductance regulator (CFTR) protein and occurs when a child inherits 2 copies of a CFTR gene that contains a mutation.

So what does the CFTR protein do in a ‘healthy’ person?

Proteins are tiny ‘machines’ that do specific jobs within a cell. They are assembled from building blocks called amino acids. There are 20 different amino acids that are connected together in different orders to form the many different proteins within the body. The CFTR protein is made up of a chain of 1,480 amino acids. Once the CFTR protein chain is made, it is folded into a kind of 3-D tube shape that goes through the membrane surrounding the cell - just like a straw that goes through the plastic top on a cup.

The CFTR protein is an ion channel - it is responsible for moving chloride ions out from inside the cell to outside, or from outside the cell to inside. When this happens, the chloride ions move through the center of the tube that is formed by the CFTR protein.

The chloride ions attract a layer of water. This is crucial to maintain the balance of salt and water on many surfaces in the body including the lungs and pancreas. Without the correct movement of ions, mucus is able to build up.

When a person has cystic fibrosis the issue with the CFTR protein differs depending on the mutation that has been inherited - with some mutations the CFTR protein is not made correctly and with others it is actually not made at all.

There are over 1,800 different CF mutations currently on record including some incredibly rare ‘nonsense’ mutations. But the full list is thought to be over 2,000.

The more common mutations have been categorised into classes from 1 to 6 with each class representing a different defect in the CFTR protein. The table on this page shows the differences between the classes.