The predominant enzyme is UGT1A1, the enzyme that conjugates bilirubin.5 In the promoter region of the UGT1A1 gene, an extra TA dinucleotide characterises the genotype associated with Gilbert’s syndrome (chronic non-conjugated hyperbilirubinemia due to reduced UGT1A1 activity). The gene discussed is UGT1A1; the disease is Gilbert syndrome.