Amino acid transport disorders: 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 disorders

Sample item

A 28-year-old man has recurrent flank pain with hexagonal crystals in the urine. The sodium nitroprusside test is positive. Which amino acids are excreted in excess?

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

The answer and the reasoning

A. Cystine, ornithine, lysine and arginine

Cystinuria is an autosomal recessive defect of the renal tubular and intestinal transporter for cystine and the dibasic amino acids ornithine, lysine and arginine (COLA). Cystine is poorly soluble and forms hexagonal crystals and calculi. Treatment includes hydration and urinary alkalinisation.

Option by option

  • A. Cystine, ornithine, lysine and arginine (correct)

    Correct. These dibasic amino acids and cystine share the defective transporter.

  • B. Phenylalanine and tyrosine

    Phenylalanine and tyrosine are involved in phenylketonuria and tyrosinaemias, not cystinuria.

  • C. Leucine, isoleucine and valine

    Branched-chain amino acids accumulate in maple syrup urine disease.

  • D. Glycine, proline and hydroxyproline

    These amino acids are excreted in excess in iminoglycinuria, which is 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 A, Cystine, ornithine, lysine and arginine. Cystinuria is an autosomal recessive defect of the renal tubular and intestinal transporter for cystine and the dibasic amino acids ornithine, lysine and arginine (COLA).

Why is "Phenylalanine and tyrosine" not the answer?

Phenylalanine and tyrosine are involved in phenylketonuria and tyrosinaemias, not cystinuria.

Why is "Leucine, isoleucine and valine" not the answer?

Branched-chain amino acids accumulate in maple syrup urine disease.

Why is "Glycine, proline and hydroxyproline" not the answer?

These amino acids are excreted in excess in iminoglycinuria, which is benign.

What concept does this question test?

It tests Amino acid transport disorders in Biochemistry. Cystine is poorly soluble and forms hexagonal crystals and calculi. Treatment includes hydration and urinary alkalinisation.

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 disorders?

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.