Organic acidaemias: isovaleric acidaemia: 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.

Try it

Biochemistry · Organic acidaemias: isovaleric acidaemia

Sample item

A 5-day-old neonate who fed well initially now has lethargy, vomiting, metabolic acidosis with ketosis, hyperammonaemia and pancytopenia. The nurse notes a distinctive sweaty-feet odour. Which enzyme is deficient?

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

The answer and the reasoning

B. Isovaleryl-CoA dehydrogenase

Isovaleric acidaemia is a defect in leucine catabolism, causing accumulation of isovaleryl-CoA and isovaleric acid, which smells of sweaty feet. Glycine supplementation conjugates isovaleryl-CoA to excretable isovalerylglycine, and carnitine adds a second route; leucine is restricted in the diet.

Option by option

  • A. Propionyl-CoA carboxylase

    Propionyl-CoA carboxylase deficiency causes propionic acidaemia, not the sweaty-feet odour.

  • B. Isovaleryl-CoA dehydrogenase (correct)

    Correct. Isovaleryl-CoA dehydrogenase deficiency leads to isovaleric acid, with the characteristic odour.

  • C. Methylmalonyl-CoA mutase

    Methylmalonyl-CoA mutase deficiency causes methylmalonic acidaemia without the sweaty-feet odour.

  • D. Glutaryl-CoA dehydrogenase

    Glutaryl-CoA dehydrogenase deficiency causes glutaric aciduria type 1 with macrocephaly and striatal injury.

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.

More Biochemistry questions

Questions about this Biochemistry question

What is the answer to this Biochemistry question?

The best answer is B, Isovaleryl-CoA dehydrogenase. Isovaleric acidaemia is a defect in leucine catabolism, causing accumulation of isovaleryl-CoA and isovaleric acid, which smells of sweaty feet.

Why is "Propionyl-CoA carboxylase" not the answer?

Propionyl-CoA carboxylase deficiency causes propionic acidaemia, not the sweaty-feet odour.

Why is "Methylmalonyl-CoA mutase" not the answer?

Methylmalonyl-CoA mutase deficiency causes methylmalonic acidaemia without the sweaty-feet odour.

Why is "Glutaryl-CoA dehydrogenase" not the answer?

Glutaryl-CoA dehydrogenase deficiency causes glutaric aciduria type 1 with macrocephaly and striatal injury.

What concept does this question test?

It tests Organic acidaemias: isovaleric acidaemia in Biochemistry. Glycine supplementation conjugates isovaleryl-CoA to excretable isovalerylglycine, and carnitine adds a second route; leucine is restricted in the diet.

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 Organic acidaemias: isovaleric acidaemia?

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.