Cystic fibrosis: Causes, symptoms, diagnosis, treatment

What is cystic fibrosis?

Cystic fibrosis (CF) is a chronic, progressive condition that primarily affects the body's respiratory and digestive systems. It is due to a gene defect that causes the body to produce abnormally thick mucus.

The condition affects more than 8,500 children and young adults in the UK. 1 in 25 people carry the faulty gene. The charity Cystic Fibrosis Trust says it is the UK's most common life-threatening inherited disease.

In the past, children born with CF died early in childhood. Today, thanks to improved medical treatments, people with CF often live into their 30s and possibly beyond.

People who have CF produce abnormally thick, sticky mucus, which clogs the lungs and leads to recurring lung and sinus infections as well as difficulty breathing. Reduced oxygen in the blood also leads to a characteristic rounding and enlargement of the nail bed in the fingers and toes, called clubbing. Those with the disease may also develop a barrel-shaped chest as a result of their increased work to breathe. Repeated infections often lead to fleshy growths inside the nose, called nasal polyps.

The thick mucus also obstructs the ducts of the pancreas, preventing digestive enzymes from reaching the intestines. So those with CF do not absorb nutrients from their food well, and they eliminate undigested food through the bowel, resulting in very large, smelly stools. Because so little food is absorbed, children with CF have difficulty gaining and maintaining weight, despite a healthy appetite and diet.

CF also affects the reproductive systems of both males and females. Although females with CF have normal fallopian tubes and ovaries, their thick cervical secretions may block sperm entry and prevent them from getting pregnant. Males with CF are almost always sterile because they produce relatively few or no sperm. Abnormally thick secretions may block the ducts that carry sperm, or the ducts may not develop properly.

Another hallmark of CF is an unusually high concentration of sodium and chloride (salt) in the sweat. The defective CF gene causes faulty chloride movement in CF cells. As a result, parents often report that their babies "taste very salty" when they kiss them.

What causes cystic fibrosis?

Cystic fibrosis occurs in children who have inherited two abnormal copies of a specific gene, one from each parent. A parent who does not have CF but has one normal copy of this gene and one abnormal copy is called a CF carrier. The normal copy dominates, so the parent shows no sign of CF. In some cases, carriers pass on their normal gene to their child. In other instances, they pass on their abnormal copy. A child who receives a normal copy from one parent and an abnormal copy from the other will be a CF carrier and won't have the disease. A child who receives an abnormal gene from both parents will develop CF.