Complete deficiency of UDP glucoronyl transferase (UGT) is seen in:

UGT1A1, generated from the UGT1A1 gene, is responsible for bilirubin glucuronidation. Mutations of UGT1A1 cause hereditary unconjugated hyperbilirubinemias: Crigler-Najjar type 1 is caused by severe UGT1A1 deficiency and is fatal around the time of bih, Crigler-Najjar type II and Gilbe syndrome there is some UGT1A1 activity and the phenotypes are much milder