This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Bilirubin Metabolism, Subject name: Pathology
Complete deficiency of UDP glucoronyl transferase (UGT) is seen in: 
Select and explain. 
A. Criggler - Najjar Type I, B. Criggler - Najjar Type II, C. Gilbe's syndrome, D. Dubin-Johnson syndrome
A: Criggler - Najjar Type I
Answer: A: Criggler - Najjar Type I 
Explanation: 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