Gilbert's syndrome is the most commonly inherited disorder of bilirubin metabolism, affecting 3-12% of the general population, mainly characterized by intermittent unconjugated hyperbilirubinemia in the absence of hepatocellular disease or hemolysis.
Healthy carriers of the UGT1A1*28 promoter mutation, that is characteristic for the benign condition of Gilbert’s syndrome (GS; i.e. M. Meulengracht), present with moderate unconjugated hyper-bilirubinaemia. The underlying polymorphism is characterised by an additional –TA repeat in the TATA-sequence of the UGT1A1 promoter, to yield (TA)7/(TA)7 instead of (TA)6/(TA)63. This missense mutation results in a reduced UGT1A1 enzyme function, leading to a decreased conjugation of bilirubin. Next to higher levels of unconjugated bilirubin (UCB) and in the absence of any other adverse symptoms, significantly lower body mass indices (BMI)4, improved glucose and lipid profiles5, and a resulting lower prevalence of DM II and of other chronic metabolic/inflammatory disorders6,7,8 have been reported specifically for this group.