This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: G.I.T., Subject name: Medicine
A 29-year-old woman is found, on routine annual blood testing, to have a small increase in unconjugated bilirubin. There is no evidence of hemolysis and her liver enzymes and function tests are otherwise normal. She has no prior history of liver disease and is not taking any medications. Her physical examination is completely normal with no signs of chronic liver disease. Which of the following is the most likely diagnosis? 
Select and explain. 
A. Crigler-Najjar syndrome, B. Dubin-Johnson syndrome, C. Rotor syndrome, D. Gilbert syndrome
D: Gilbert syndrome
Answer: D: Gilbert syndrome 
Explanation: Gilbert syndrome may be associated with impaired hepatic uptake of bilirubin. It is caused by hereditary decrease in the activity of glucuronosyltransferase in the uridine diphosphate glycosyltransferase 1 (UGT1) family. More severe enzyme deficits are the cause of the two variants of Crigler-Najjar syndrome and usually present in the neonatal period with very high elevations in unconjugated bilirubin, making it not the correct answer in this patient. She does not have Dubin-Johnson or Rotor syndrome since both of these entities have elevations of conjugated bilirubin.