Gilbertʹs syndrome and hyperbilirubinaemia in ABO-incompatible neonates

We asked whether UDP glucuronosyltransferase (UGT) gene promoter polymorphism (Gilbertʹs syndrome) would increase hyperbilirubinaemia in direct Coombsʹ negative ABO-incompatible neonates, as seen in other combinations with this condition. 40 ABO-incompatible and 344 ABO-compatible controls had an allele frequency of 0·35 for the variant promoter gene. The incidence of hyperbilirubinaemia was significantly higher only in the former who were also homozygotes for the variant UGT promoter, compared with ABO-incompatible babies homozygous for the normal UGT promoter (43% vs 0, p=0·02), and with ABO-compatible controls of all UGT genotypes combined (relative risk 5·65, 95% Cl 2·23·14·31). Gilbertʹs syndrome is a determining factor for neonatal hyperbilirubinaemia ABO incompatibility.