Causes

Cystic fibrosis is caused by a faulty gene that a child inherits from both their parents.

The faulty gene means that some cells struggle to move salt and water across the cell wall. This, along with recurrent infections, can result in a build-up of thick, sticky mucus in the body's tubes and passageways particularly the lungs and digestive system.

The condition is present from birth and cannot be caught from someone else who has it.

How cystic fibrosis is inherited

Genes come in pairs. You inherit one set from your mother and one set from your father.

To be born with cystic fibrosis, a child has to inherit a copy of the faulty gene from both of their parents.

This can happen ifthe parents are "carriers" of the faulty gene. This means they don't have cystic fibrosis themselves, but they can have a child with the condition if their partner also carries the faulty gene.

It's estimated that around 1 in every 25 people in the UK are carriers of the faulty gene that causes cystic fibrosis.

If both parents are carriers, there's a:

• 25% chance that each child they have will not inherit any faulty genes and won't havecystic fibrosisor be able to pass it on
• 50% chance that each child they have will just inherit one copy of the faulty gene from one parent and be a carrier
• 25% chance that each child they have will inherit copies of the faulty gene from both parents and will havecystic fibrosis

This is known as an autosomal recessive inheritance pattern.

Chromosome

Chromosomes are the parts of a body cell that carry genes. A human cell usually has 23 pairs of chromosomes.

Gene

Genes contain information that you inherit from your parents, such as eye or hair colour. They are carried by chromosomes.