Substance use: biochemical lesion in Wernicke encephalopathy: practice question

A Psychiatry 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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Psychiatry · Substance use: biochemical lesion in Wernicke encephalopathy

Sample item

A chronic drinker with nystagmus, ataxia and confusion is found to have a reduced red-cell enzyme activity that improves after parenteral vitamin therapy. Which enzyme activity is reduced?

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

The answer and the reasoning

C. Transketolase

Thiamine pyrophosphate is a cofactor for transketolase, pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase. Reduced red-cell transketolase activity and its correction after thiamine are the biochemical basis of Wernicke encephalopathy.

Option by option

  • A. Methylmalonyl-CoA mutase

    Methylmalonyl-CoA mutase depends on vitamin B12, not thiamine.

  • B. Glucose-6-phosphate dehydrogenase

    Glucose-6-phosphate dehydrogenase does not depend on thiamine and is the enzyme in favism.

  • C. Transketolase (correct)

    Correct. Transketolase needs thiamine as a cofactor, and its activity falls in thiamine deficiency.

  • D. Cystathionine beta-synthase

    Cystathionine beta-synthase depends on pyridoxine (vitamin B6).

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 Psychiatry question

What is the answer to this Psychiatry question?

The best answer is C, Transketolase. Thiamine pyrophosphate is a cofactor for transketolase, pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase.

Why is "Methylmalonyl-CoA mutase" not the answer?

Methylmalonyl-CoA mutase depends on vitamin B12, not thiamine.

Why is "Glucose-6-phosphate dehydrogenase" not the answer?

Glucose-6-phosphate dehydrogenase does not depend on thiamine and is the enzyme in favism.

Why is "Cystathionine beta-synthase" not the answer?

Cystathionine beta-synthase depends on pyridoxine (vitamin B6).

What concept does this question test?

It tests Substance use: biochemical lesion in Wernicke encephalopathy in Psychiatry. Reduced red-cell transketolase activity and its correction after thiamine are the biochemical basis of Wernicke encephalopathy.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. 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 Substance use: biochemical lesion in Wernicke encephalopathy?

Learn each diagnosis by its core features and its first-line treatment. Then use the flashcards and the other Psychiatry 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.