Amino acid metabolism: isoniazid seizures and GABA synthesis: practice question

A Biochemistry 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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Biochemistry · Amino acid metabolism: isoniazid seizures and GABA synthesis

Sample item

A patient who swallowed a large quantity of isoniazid presents with refractory seizures. Which metabolic defect explains the fits, and what corrects it?

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

The answer and the reasoning

D. Impaired GABA synthesis by glutamate decarboxylase, corrected by pyridoxine

Isoniazid forms a hydrazone with pyridoxal and inhibits pyridoxal kinase, causing functional pyridoxal phosphate deficiency. Glutamate decarboxylase needs pyridoxal phosphate, so GABA falls and seizures follow. Intravenous pyridoxine is the antidote.

Option by option

  • A. Impaired acetylcholine synthesis by choline acetyltransferase, corrected by thiamine

    Choline acetyltransferase does not require thiamine, and acetylcholine deficiency is not the cause of these fits.

  • B. Impaired noradrenaline synthesis by dopamine beta-hydroxylase, corrected by ascorbate

    Dopamine beta-hydroxylase needs copper and ascorbate, and its failure does not explain isoniazid seizures.

  • C. Impaired glutamate formation by glutamate dehydrogenase, corrected by riboflavin

    Glutamate dehydrogenase uses NAD(P) and its loss would not cause seizure through this route; riboflavin is not the antidote.

  • D. Impaired GABA synthesis by glutamate decarboxylase, corrected by pyridoxine (correct)

    Correct. PLP is the cofactor of glutamate decarboxylase, and pyridoxine restores it.

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 Biochemistry question

What is the answer to this Biochemistry question?

The best answer is D, Impaired GABA synthesis by glutamate decarboxylase, corrected by pyridoxine. Isoniazid forms a hydrazone with pyridoxal and inhibits pyridoxal kinase, causing functional pyridoxal phosphate deficiency.

Why is "Impaired acetylcholine synthesis by choline acetyltransferase, correc…" not the answer?

Choline acetyltransferase does not require thiamine, and acetylcholine deficiency is not the cause of these fits.

Why is "Impaired noradrenaline synthesis by dopamine beta-hydroxylase, correc…" not the answer?

Dopamine beta-hydroxylase needs copper and ascorbate, and its failure does not explain isoniazid seizures.

Why is "Impaired glutamate formation by glutamate dehydrogenase, corrected by…" not the answer?

Glutamate dehydrogenase uses NAD(P) and its loss would not cause seizure through this route; riboflavin is not the antidote.

What concept does this question test?

It tests Amino acid metabolism: isoniazid seizures and GABA synthesis in Biochemistry. Glutamate decarboxylase needs pyridoxal phosphate, so GABA falls and seizures follow. Intravenous pyridoxine is the antidote.

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 Amino acid metabolism: isoniazid seizures and GABA synthesis?

Build one table of enzyme deficiency, disease, inheritance and key finding, then revise it by spaced recall. Then use the flashcards and the other Biochemistry 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.