UGT1A1 and cholelithiasis: UGT1A promoter polymorphisms act as an important genetic modifier of hepatobiliary disease in SCA, influencing baseline bilirubin levels and the incidence of cholecystectomy.101 This suggests that symptomatic cholelithiasis is more common in carriers of this genotype.101,102 When treated with HU, children with the 6/6 UGT1A genotype had normal bilirubin levels compared with individuals with the 6/7 or 7/7 genotypes.