Gilbert's syndrome is a finding, not a disease. It is found in about 5 per cent of the population and is due to raised levels of a natural pigment called bilirubin in the blood.

Bilirubin is the natural waste product the body produces in the breakdown of haemoglobin - the oxygen-carrying compound present within red blood cells. New red blood cells are continuously being manufactured in the bone marrow and old cells broken down; each red cell lasts about 120 days.

Bilirubin is eliminated in the bile fluids produced by the liver, but in Gilbert's syndrome the enzyme reactions involved in this process are slower than average. Because bilirubin has a yellow colour, an excess in the blood causes the person to be jaundiced.

Gilbert's syndrome is determined by a particular liver enzyme, and the tendency for this to be slower in action can be passed on genetically. For this reason, it can be found more commonly in family members of someone who has the condition. Males are affected more often than females.