Gastrointestinal: Crigler-Najjar syndrome: practice question

A Physiology question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Physiology · Gastrointestinal: Crigler-Najjar syndrome

Sample item

A newborn develops severe unconjugated hyperbilirubinaemia with neurological signs in the first week. The bilirubin does not fall with phenobarbital. What is the defect?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

C. Complete absence of UDP-glucuronosyltransferase activity

In type I Crigler-Najjar syndrome the enzyme UGT1A1 is absent, so bilirubin cannot be conjugated and unconjugated bilirubin rises to levels that cause kernicterus. Phenobarbital induces the enzyme, but cannot help when it is absent. Type II has residual activity and responds.

Option by option

  • A. Neonatal haemolysis from G6PD deficiency

    Haemolysis raises the bilirubin load, but conjugation works and a partial phenobarbital response is expected.

  • B. Defective canalicular export of conjugated bilirubin

    Defective canalicular export causes conjugated hyperbilirubinaemia, as in Dubin-Johnson syndrome.

  • C. Complete absence of UDP-glucuronosyltransferase activity (correct)

    Correct. With no glucuronyl transferase, bilirubin cannot be conjugated, and phenobarbital cannot induce a missing enzyme.

  • D. Reduced hepatic uptake of conjugated bilirubin

    Uptake defects produce mild unconjugated rises, as in Gilbert syndrome.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

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Questions about this Physiology question

What is the answer to this Physiology question?

The best answer is C, Complete absence of UDP-glucuronosyltransferase activity. In type I Crigler-Najjar syndrome the enzyme UGT1A1 is absent, so bilirubin cannot be conjugated and unconjugated bilirubin rises to levels that cause kernicterus.

Why is "Neonatal haemolysis from G6PD deficiency" not the answer?

Haemolysis raises the bilirubin load, but conjugation works and a partial phenobarbital response is expected.

Why is "Defective canalicular export of conjugated bilirubin" not the answer?

Defective canalicular export causes conjugated hyperbilirubinaemia, as in Dubin-Johnson syndrome.

Why is "Reduced hepatic uptake of conjugated bilirubin" not the answer?

Uptake defects produce mild unconjugated rises, as in Gilbert syndrome.

What concept does this question test?

It tests Gastrointestinal: Crigler-Najjar syndrome in Physiology. Phenobarbital induces the enzyme, but cannot help when it is absent. Type II has residual activity and responds.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Gastrointestinal: Crigler-Najjar syndrome?

For each system, sketch the key graph (pressure–volume loop, oxygen dissociation curve, nephron handling) and explain it aloud. Then use the flashcards and the other Physiology questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.