Amino acid transport: Hartnup disease: 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 · Amino acid transport: Hartnup disease

Sample item

An 8-year-old boy has episodic photosensitive pellagra-like rash, intermittent cerebellar ataxia and emotional lability, which are triggered by poor diet and illness. Serum niacin is low but his diet is adequate. Which urinary finding confirms the diagnosis?

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

The answer and the reasoning

B. Excess neutral amino acids with sparing of cystine and dibasic amino acids

Hartnup disease is an autosomal recessive defect of the SLC6A19 neutral amino acid transporter in the intestinal and renal tubular brush border. Loss of tryptophan reduces endogenous niacin synthesis, causing pellagra-like features. Nicotinamide supplementation and a high-protein diet help.

Option by option

  • A. Excess glutamate and aspartate

    Dicarboxylic aminoaciduria involves glutamate and aspartate and causes no pellagra.

  • B. Excess neutral amino acids with sparing of cystine and dibasic amino acids (correct)

    Correct. Neutral aminoaciduria with sparing of dibasic amino acids and cystine marks the SLC6A19 defect.

  • C. Excess cystine, ornithine, lysine and arginine

    Cystine with dibasic amino acids describes cystinuria, due to the SLC3A1 and SLC7A9 transporters.

  • D. Excess glycine, proline and hydroxyproline

    Glycine, proline and hydroxyproline in urine is iminoglycinuria, which is usually benign.

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 B, Excess neutral amino acids with sparing of cystine and dibasic amino acids. Hartnup disease is an autosomal recessive defect of the SLC6A19 neutral amino acid transporter in the intestinal and renal tubular brush border.

Why is "Excess glutamate and aspartate" not the answer?

Dicarboxylic aminoaciduria involves glutamate and aspartate and causes no pellagra.

Why is "Excess cystine, ornithine, lysine and arginine" not the answer?

Cystine with dibasic amino acids describes cystinuria, due to the SLC3A1 and SLC7A9 transporters.

Why is "Excess glycine, proline and hydroxyproline" not the answer?

Glycine, proline and hydroxyproline in urine is iminoglycinuria, which is usually benign.

What concept does this question test?

It tests Amino acid transport: Hartnup disease in Biochemistry. Loss of tryptophan reduces endogenous niacin synthesis, causing pellagra-like features. Nicotinamide supplementation and a high-protein diet help.

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 Amino acid transport: Hartnup disease?

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.