Gilbert's syndrome and hyperbilirubinaemia in ABO-incompatible neonates.

We asked whether UDP glucuronosyltransferase (UGT) gene promoter polymorphism (Gilbert's syndrome) would increase hyperbilirubinaemia in direct Coombs' 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% CI 2.23-14.31). Gilbert's syndrome is a determining factor for neonatal hyperbilirubinaemia ABO incompatibility.