Amino acid metabolism: Reye syndrome: 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: Reye syndrome

Sample item

A 7-year-old given aspirin during influenza develops vomiting, confusion, hypoglycaemia and a markedly raised plasma ammonia. Biopsy shows microvesicular fatty change in the liver. Which biochemical problem best explains the hyperammonaemia?

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

The answer and the reasoning

B. Mitochondrial injury impairing CPS I, OTC and fatty acid oxidation

Reye syndrome is an acute mitochondrial injury in the liver. The two mitochondrial urea cycle enzymes, carbamoyl phosphate synthetase I and ornithine transcarbamylase, fail, ammonia builds up, and impaired fatty acid oxidation produces the microvesicular steatosis and hypoglycaemia.

Option by option

  • A. Inherited absence of argininosuccinate lyase in the cytosol

    Argininosuccinic aciduria is an inherited disorder presenting early in life and does not follow aspirin during a viral illness.

  • B. Mitochondrial injury impairing CPS I, OTC and fatty acid oxidation (correct)

    Correct. Damaged hepatic mitochondria cannot run the first two urea cycle steps or beta-oxidation.

  • C. Failure of renal glutaminase to release ammonia into urine

    Reduced renal ammonia release would affect acid handling, not cause fulminant hyperammonaemia with fatty liver.

  • D. Over-activity of glutamine synthetase in the hepatocytes

    More glutamine synthetase would trap ammonia as glutamine and lower ammonia, not raise 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 B, Mitochondrial injury impairing CPS I, OTC and fatty acid oxidation. Reye syndrome is an acute mitochondrial injury in the liver.

Why is "Inherited absence of argininosuccinate lyase in the cytosol" not the answer?

Argininosuccinic aciduria is an inherited disorder presenting early in life and does not follow aspirin during a viral illness.

Why is "Failure of renal glutaminase to release ammonia into urine" not the answer?

Reduced renal ammonia release would affect acid handling, not cause fulminant hyperammonaemia with fatty liver.

Why is "Over-activity of glutamine synthetase in the hepatocytes" not the answer?

More glutamine synthetase would trap ammonia as glutamine and lower ammonia, not raise it.

What concept does this question test?

It tests Amino acid metabolism: Reye syndrome in Biochemistry. The two mitochondrial urea cycle enzymes, carbamoyl phosphate synthetase I and ornithine transcarbamylase, fail, ammonia builds up, and impaired fatty acid oxidation produces the microvesicular steatosis and hypoglycaemia.

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: Reye syndrome?

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.