It has been reported that different (TA)n genotypes (polymorphisms) at the promoter of UGT1A influence bilirubin levels at baseline and during hydroxyurea therapy. The polymorphic UGT1A genotypes may affect the ability of hydroxyurea to prevent gallstone formation in patients with sickle cell anemia (Heeney et al. J Lab Clin Med 141: 279-82, 2003). Patients with the UGT1A wild type/(TA)6/(TA)6 will normalize bilirubin levels, whereas heterozygous (TA)6/(TA)7 or homozygous (TA)7/(TA)7 genotypes are associated with failure to normalize bilirubin levels in response to hydroxyurea therapy. The (TA)7/(TA)7genotype is also associated with Gilbert syndrome. This laboratory performs repeat analysis for the UGT1A gene.