People have cystic fibrosis because a faulty gene is passed from the parents to the child.

One in 25 people carry the faulty cystic fibrosis gene. For someone to be born with cystic fibrosis, both parents must carry the faulty gene. If both parents have the gene, there is a 25% chance the child will have cystic fibrosis. If both parents carry the gene there is also a 50% chance of the child being a gene carrier and a 25% chance they will not have the faulty cystic fibrosis gene.

Symptoms of cystic fibrosis can include a troublesome cough, repeated chest infections, prolonged diarrhoea and poor weight gain. These symptoms are not unique to cystic fibrosis.

Cystic fibrosis is a complex disease that affects many different organs.

Lungs
It is common for people with cystic fibrosis to experience some problems with lung function, although not everyone is affected.

A combination of physiotherapy and medication can help control lung infections and prevent the build up of mucus that damages the lung.

To avoid the risk of cross-infection people with cystic fibrosis should not meet or come into close contact with one another.

Digestive system
Cystic fibrosis affects the pancreas because a build up of thick, sticky mucus blocks the ducts, reducing the amount of insulin produced and stopping digestive enzymes from reaching the intestines to aid digestion. This can cause malnutrition, leading to poor growth, physical weakness and delayed puberty.

Medication can help compensate for the failure of the pancreas, such as digestive enzymes that most people with cystic fibrosis take with each meal to help digest food.

In older people with cystic fibrosis insulin production can become deficient due to increasing pancreatic disease. Some people develop cystic fibrosis related diabetes mellitus and their blood sugar levels are no longer controlled, although this is rare in children.

Common symptoms of diabetes include thirst, hunger, weight loss and an excessive need to urinate, but not everyone will show obvious symptoms.

Other parts of the body
One in every ten babies born with cystic fibrosis develops a bowel obstruction called meconium ileus at birth or within the first few days of life. In these cases the meconium (a thick black material present in bowels of all newborn babies) is so thick that it blocks the bowel instead of passing through. Babies with meconium ileus often need an urgent operation to relieve and bypass the blockage.

People with cystic fibrosis are prone to developing bone disease (thin, brittle bones) due to a lack of nutrition (which is lost through stools because of the damaged pancreas), and other complaints related to the disease. Adults with cystic fibrosis also have an increased risk of bone disease, which is a side effect of the steroids taken to control lung disease.

Cystic fibrosis can cause fertility problems, although it does not cause sexual impotency. In most men with cystic fibrosis the tubes that carry the sperm are blocked, causing infertility. The nutritional issues associated with cystic fibrosis may affect female fertility because underweight women are more likely to have irregular menstrual cycles and thicker vaginal mucus. Women with cystic fibrosis do produce healthy, fertile eggs, and so effective contraception is necessary.

Cystic fibrosis can cause the blockage of small ducts in the liver, leading to liver disease. Although this only happens in about eight per cent of people with cystic fibrosis and can sometimes be managed by drugs, it is a serious health risk and could require a liver transplant.