Metabolic: MCAD deficiency: practice question

A Pediatrics 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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Pediatrics · Metabolic: MCAD deficiency

Sample item

A 14-month-old has lethargy and seizures after a prolonged fast during a viral illness. Glucose is 25 mg/dl with absent urine ketones. Which condition is likely?

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

The answer and the reasoning

C. Medium-chain acyl-CoA dehydrogenase deficiency

Fatty acid oxidation defects such as MCAD cause hypoketotic hypoglycaemia during fasting because ketones cannot be made. Treatment is avoiding fasting and giving IV glucose in illness. In GSD I there is lactic acidosis, while hyperinsulinism also suppresses ketones but shows high glucose requirement.

Option by option

  • A. Congenital adrenal hyperplasia

    CAH shows electrolyte disturbance and ambiguous genitalia in girls.

  • B. Type I glycogen storage disease

    GSD I has hepatomegaly and lactic acidosis.

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

    Correct. Hypoketotic hypoglycaemia points to a fatty acid oxidation defect.

  • D. Hyperinsulinism

    Hyperinsulinism occurs mainly in neonates and has a high glucose infusion rate.

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 Pediatrics question

What is the answer to this Pediatrics question?

The best answer is C, Medium-chain acyl-CoA dehydrogenase deficiency. Fatty acid oxidation defects such as MCAD cause hypoketotic hypoglycaemia during fasting because ketones cannot be made.

Why is "Congenital adrenal hyperplasia" not the answer?

CAH shows electrolyte disturbance and ambiguous genitalia in girls.

Why is "Type I glycogen storage disease" not the answer?

GSD I has hepatomegaly and lactic acidosis.

Why is "Hyperinsulinism" not the answer?

Hyperinsulinism occurs mainly in neonates and has a high glucose infusion rate.

What concept does this question test?

It tests Metabolic: MCAD deficiency in Pediatrics. Treatment is avoiding fasting and giving IV glucose in illness. In GSD I there is lactic acidosis, while hyperinsulinism also suppresses ketones but shows high glucose requirement.

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 Metabolic: MCAD deficiency?

Memorise milestones and the vaccine schedule as tables and revise them often. Then use the flashcards and the other Pediatrics 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.