UGT1A1 and Gilbert syndrome: Gilbert syndrome is associated with various mutations, but in European populations, homozygosity for a two base pair TA insertion into the promoter of the UGT1A1 (rs3064744, also known as UGT1A*28) is the most common.9 This mutation impairs transcription of UGT1A1 leading to around 20-30% of normal transcriptional values and a subsequent reduced amount of enzyme.