Gilbert syndrome: A common, harmless genetic condition in which a liver enzyme essential to the disposal of bilirubin (the chemical that results from the normal breakdown of hemoglobin from red blood cells) is abnormal. The abnormality is caused by a mutation the UDP-glucuronosyltransferase gene. This enzyme abnormality results in mild elevations of bilirubin pigment in the blood, and the elevated bilirubin pigment can sometimes cause mild yellowing (jaundice) of the eyes. Gilbert’s syndrome is a frequent finding in people in North America and Europe. The condition is usually detected serendipitously (purely by accident) in the course of routine blood screening. People with Gilbert syndrome are otherwise entirely normal with no other signs or symptoms and their liver enzyme levels in blood serum are also entirely normal. Treatment is not necessary. The condition has also been referred to as constitutional hepatic dysfunction and familial nonhemolytic jaundice.