'Time bomb' that has no cure

Cystic fibrosis is the most common inherited and life-threatening disease in the UK and affects about 7,500 people.

Caused by a genetic defect, there is no cure and one in 25 people in Britain - 2.3 million - are carriers of the DNA "time bomb". Both parents need to be carriers before it can be passed on to a child.

Sufferers tend to have digestive disorders and their lungs become covered with a sticky mucus that makes breathing extremely difficult and leaves them vulnerable to bacterial infections. Frequent hospital treatment is necessary, along with regular physiotherapy to strengthen the lungs and clear excess mucus.

Around three people under the age of 30 die from the disease every seven days. Life expectancy is around 30 years. Before recent medical advances many children did not live beyond the age of eight.