<prompt> Complete deficiency of UDP glucuronyl transferase is seen in -Criggler - Najjar type - 1Criggler - Najjar type - 2Gilbes syndromeDubin-Jhonson syndrome  <response>: Ans. is a i.e.,Criggler - Najjar type - 1Crigler-Najjar syndrome type 1 CNS1 is the most severe form of CNS see this term, a hereditary disorder of hepatic bilirubin conjugation, characterized by severe neonatal unconjugated hyperbilirubinemia due to a complete absence of hepatic bilirubin glucuronosyltransferase BGT.Mutations in the UGT1A1 gene that cause Crigler-Najjar syndrome result in reduced or absent function of the bilirubin-UGT bilirubin uridine diphosphate glucuronosyl transferaseenzyme.People with CN1 have no enzyme function, while people with CN2 have less than 20 percent of normal function.The loss of bilirubin-UGT function decreases glucuronidation of unconjugated bilirubin.This toxic substance then builds up in the body, causing unconjugated hyperbilirubinemia and jaundice. 