Lipid metabolism: fatty acid oxidation: 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 · Lipid metabolism: fatty acid oxidation

Sample item

A toddler becomes lethargic and hypoglycaemic after a prolonged fast, with a low urinary ketone level and raised urinary dicarboxylic acids. What is the most likely diagnosis?

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

The answer and the reasoning

D. Medium-chain acyl-CoA dehydrogenase deficiency

In MCAD deficiency, fasting causes hypoketotic hypoglycaemia because fatty acid beta-oxidation is blocked, and medium-chain acylcarnitines and dicarboxylic acids accumulate. It is the most common fatty acid oxidation defect, and it is managed by avoiding fasting.

Option by option

  • A. Maple syrup urine disease

    Maple syrup urine disease gives ketoacidosis and sweet-smelling urine.

  • B. Von Gierke disease

    Von Gierke disease gives hypoglycaemia with lactic acidosis, hyperuricaemia and hepatomegaly.

  • C. Hereditary fructose intolerance

    Fructose intolerance is triggered by fructose ingestion.

  • D. Medium-chain acyl-CoA dehydrogenase deficiency (correct)

    Correct. Hypoketotic hypoglycaemia is characteristic.

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, Medium-chain acyl-CoA dehydrogenase deficiency. In MCAD deficiency, fasting causes hypoketotic hypoglycaemia because fatty acid beta-oxidation is blocked, and medium-chain acylcarnitines and dicarboxylic acids accumulate.

Why is "Maple syrup urine disease" not the answer?

Maple syrup urine disease gives ketoacidosis and sweet-smelling urine.

Why is "Von Gierke disease" not the answer?

Von Gierke disease gives hypoglycaemia with lactic acidosis, hyperuricaemia and hepatomegaly.

Why is "Hereditary fructose intolerance" not the answer?

Fructose intolerance is triggered by fructose ingestion.

What concept does this question test?

It tests Lipid metabolism: fatty acid oxidation in Biochemistry. It is the most common fatty acid oxidation defect, and it is managed by avoiding fasting.

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 Lipid metabolism: fatty acid oxidation?

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.