Sequencing of the UGT1A1 gene in patients with Gilbert’s syndrome, associated with unconjugated hyperbilirubinemia, revealed that an important modulator of enzyme activity is the length of TA repeats in the promoter region; the greater the number of repeats being associated with the highest serum bilirubin levels and cholelithiasis risk [8], [9]. The gene discussed is UGT1A1; the disease is Gilbert syndrome.