The UGT1A1 gene contains instructions for creating (encoding) a liver enzyme known as uridine disphosphate-glucuronosyltransferase-1A1 (UGT1A1). This enzyme is required for the conversion (conjugation) and subsequent excretion of bilirubin from the body. Mild jaundice associated with Gilbert syndrome occurs due to reduced amounts of this enzyme, which results in the accumulation of unconjugated bilirubin in the body. Bilirubin is an orange-yellow bile pigment that is mainly a byproduct of the natural breakdown (degeneration) of red blood cells (hemolysis). Bilirubin circulates in the liquid portion of the blood (plasma) bound to a protein called albumin; this is called unconjugated bilirubin, which does not dissolve in water (water-insoluble). Normally, this unconjugated bilirubin is taken up by the liver cells and, with the help of the UGT1A1 enzyme, is converted to form water-soluble bilirubin glucuronides (conjugated bilirubin), which are then excreted in the bile. The bile is stored in the gall bladder and, when called upon, passes into the common bile duct and then into the upper portion of the small intestine (duodenum) and aids in digestion. Most bilirubin is eliminated from the body in the feces.