Genetic and metabolic disorders: Canavan disease: 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 · Genetic and metabolic disorders: Canavan disease

Sample item

A 6-month-old has macrocephaly, marked head lag, poor visual following and progressive hypotonia that later turns into spasticity. MRI shows diffuse symmetrical subcortical white matter change and brain biopsy shows spongy degeneration. Which biochemical marker is characteristically raised?

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

The answer and the reasoning

A. N-acetylaspartic acid in urine

Canavan disease is an aspartoacylase deficiency leaving N-acetylaspartic acid to accumulate, causing spongy leukodystrophy with macrocephaly. Urinary N-acetylaspartic acid is markedly raised and is the diagnostic marker.

Option by option

  • A. N-acetylaspartic acid in urine (correct)

    Correct. Aspartoacylase deficiency causes N-acetylaspartic acid to accumulate in urine and brain.

  • B. Sulfatides in urine

    Raised urinary sulfatides indicate metachromatic leukodystrophy, which does not feature macrocephaly with spongy change.

  • C. Glycosaminoglycans in urine

    Raised glycosaminoglycans point to a mucopolysaccharidosis, with coarse facies and skeletal dysplasia.

  • D. Very long chain fatty acids in plasma

    Raised very long chain fatty acids point to X-linked adrenoleukodystrophy or a peroxisomal disorder.

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 A, N-acetylaspartic acid in urine. Canavan disease is an aspartoacylase deficiency leaving N-acetylaspartic acid to accumulate, causing spongy leukodystrophy with macrocephaly.

Why is "Sulfatides in urine" not the answer?

Raised urinary sulfatides indicate metachromatic leukodystrophy, which does not feature macrocephaly with spongy change.

Why is "Glycosaminoglycans in urine" not the answer?

Raised glycosaminoglycans point to a mucopolysaccharidosis, with coarse facies and skeletal dysplasia.

Why is "Very long chain fatty acids in plasma" not the answer?

Raised very long chain fatty acids point to X-linked adrenoleukodystrophy or a peroxisomal disorder.

What concept does this question test?

It tests Genetic and metabolic disorders: Canavan disease in Pediatrics. Urinary N-acetylaspartic acid is markedly raised and is the diagnostic marker.

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 Genetic and metabolic disorders: Canavan disease?

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.