Fatty acid oxidation: toxic hypoglycaemic 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 · Fatty acid oxidation: toxic hypoglycaemic syndrome

Sample item

After eating unripe ackee fruit, a child develops repeated vomiting followed by severe hypoglycaemia with no urinary ketones. Which mechanism best explains the hypoglycaemia?

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

The answer and the reasoning

D. A hypoglycin metabolite inhibits acyl-CoA dehydrogenases and so blocks fatty acid oxidation

Unripe ackee contains hypoglycin A, whose metabolite methylenecyclopropylacetyl-CoA inhibits the acyl-CoA dehydrogenases of beta-oxidation. Without fatty acid oxidation the liver lacks ATP, NADH and acetyl-CoA for gluconeogenesis and ketone synthesis, so hypoketotic hypoglycaemia follows, with dicarboxylic and medium-chain acids in urine. This is Jamaican vomiting sickness.

Option by option

  • A. The toxin stimulates insulin release from pancreatic beta cells

    Hyperinsulinism would suppress ketones too but fatty acid oxidation would be intact, and the hypoglycaemia here arises from a toxin acting on oxidation.

  • B. The toxin inhibits glucose-6-phosphatase in the liver and blocks glucose release

    Glucose-6-phosphatase inhibition would cause ketosis with lactic acidosis, as in von Gierke disease.

  • C. Fructose-1-phosphate accumulates and inhibits aldolase B in the liver

    Aldolase B inhibition is the mechanism of hereditary fructose intolerance, which requires fructose ingestion.

  • D. A hypoglycin metabolite inhibits acyl-CoA dehydrogenases and so blocks fatty acid oxidation (correct)

    Blocking beta-oxidation removes the fuel for gluconeogenesis and ketogenesis, causing hypoketotic hypoglycaemia.

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, A hypoglycin metabolite inhibits acyl-CoA dehydrogenases and so blocks fatty acid oxidation. Unripe ackee contains hypoglycin A, whose metabolite methylenecyclopropylacetyl-CoA inhibits the acyl-CoA dehydrogenases of beta-oxidation.

Why is "The toxin stimulates insulin release from pancreatic beta cells" not the answer?

Hyperinsulinism would suppress ketones too but fatty acid oxidation would be intact, and the hypoglycaemia here arises from a toxin acting on oxidation.

Why is "The toxin inhibits glucose-6-phosphatase in the liver and blocks gluc…" not the answer?

Glucose-6-phosphatase inhibition would cause ketosis with lactic acidosis, as in von Gierke disease.

Why is "Fructose-1-phosphate accumulates and inhibits aldolase B in the liver" not the answer?

Aldolase B inhibition is the mechanism of hereditary fructose intolerance, which requires fructose ingestion.

What concept does this question test?

It tests Fatty acid oxidation: toxic hypoglycaemic syndrome in Biochemistry. Without fatty acid oxidation the liver lacks ATP, NADH and acetyl-CoA for gluconeogenesis and ketone synthesis, so hypoketotic hypoglycaemia follows, with dicarboxylic and medium-chain acids in urine. This is Jamaican vomiting sickness.

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 Fatty acid oxidation: toxic hypoglycaemic 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.