Genetic and metabolic disorders: Hartnup 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.

Try it

Pediatrics · Genetic and metabolic disorders: Hartnup disease

Sample item

A 7-year-old has episodic photosensitive pellagra-like rash, intermittent cerebellar ataxia and emotional lability during fasting and illness, despite adequate dietary niacin. Urine chromatography shows excess alanine, serine, threonine, leucine and tryptophan, with normal plasma levels and no excess cystine or lysine. What is the basic defect?

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

The answer and the reasoning

B. Defective transport of neutral amino acids across the renal tubule and gut

Hartnup disease is an autosomal recessive defect of the neutral amino acid transporter in the renal tubule and intestine. Tryptophan loss reduces niacin synthesis, producing a pellagra-like rash and ataxia. Niacin supplements and sun protection are treatment.

Option by option

  • A. Deficient branched-chain ketoacid dehydrogenase activity in the liver

    Branched-chain ketoacid dehydrogenase deficiency causes maple syrup urine disease, with encephalopathy and a sweet odour.

  • B. Defective transport of neutral amino acids across the renal tubule and gut (correct)

    Correct. Loss of neutral amino acid transport removes tryptophan and gives pellagra-like features with a typical urinary pattern.

  • C. Defective transport of dibasic amino acids and cystine in the renal tubule

    This transport defect causes cystinuria, with excess cystine, ornithine, lysine and arginine and stone formation.

  • D. Deficient phenylalanine hydroxylase activity in the liver

    Phenylalanine hydroxylase deficiency causes phenylketonuria, with intellectual disability and a musty odour, not this pattern.

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 Pediatrics questions

Questions about this Pediatrics question

What is the answer to this Pediatrics question?

The best answer is B, Defective transport of neutral amino acids across the renal tubule and gut. Hartnup disease is an autosomal recessive defect of the neutral amino acid transporter in the renal tubule and intestine.

Why is "Deficient branched-chain ketoacid dehydrogenase activity in the liver" not the answer?

Branched-chain ketoacid dehydrogenase deficiency causes maple syrup urine disease, with encephalopathy and a sweet odour.

Why is "Defective transport of dibasic amino acids and cystine in the renal t…" not the answer?

This transport defect causes cystinuria, with excess cystine, ornithine, lysine and arginine and stone formation.

Why is "Deficient phenylalanine hydroxylase activity in the liver" not the answer?

Phenylalanine hydroxylase deficiency causes phenylketonuria, with intellectual disability and a musty odour, not this pattern.

What concept does this question test?

It tests Genetic and metabolic disorders: Hartnup disease in Pediatrics. Tryptophan loss reduces niacin synthesis, producing a pellagra-like rash and ataxia. Niacin supplements and sun protection are treatment.

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 Genetic and metabolic disorders: Hartnup 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.