Most cells in the body contain over 100,000 genes. They are grouped together on chromosomes, long strings of genes. Each gene contains a code that can be translated by the cell to make a protein.  The type of protein that is made decides a particular characteristic of a person such as eye colour or blood type.

Both X-linked and autosomal CGD affect the enzyme NADPH oxidase, which contains five proteins called Gp91-phox, p22-phox, p47-phox, p67-phox and p40-phox. This enzyme makes it possible for white blood cells to kill infections.

If someone has CGD, one of these five proteins is missing or defective, due to a genetic mutation.

In X-Linked CGD, the Gp91-phox protein is affected. This is the most common type of CGD, affecting around 65 per cent of people with the condition. It only affects males.

In autosomal recessive CGD,other parts of the enzyme are affected. This type of CGD affects both males and females, and there are four sub-types:

- the p47-phox form, affecting around 25 per cent of people affected by CGD.
- p22-phox and p67-phox, affecting around 10 per cent of people with CGD. The p40-phox form of CGD is extremely rare.

 Reviewed by the Medical Advisory Panel, February 2020