Individuals with Gilbert's syndrome (GS) exhibit genetic polymorphisms in the region of uridine diphosphate glucuronosyltransferase 1A1 (UGT1A1), causing a 60%–70% reduction in the liver's ability to conjugate bilirubin, and thus leading to substantially higher serum bilirubin levels.4 The gene discussed is UGT1A1; the disease is Gilbert syndrome.