Amino acid metabolism: primary hyperoxaluria: 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 metabolism: primary hyperoxaluria

Sample item

A 6-year-old child has recurrent flank pain, haematuria and calcium oxalate stones, with nephrocalcinosis on ultrasound. Urinary oxalate and glycolate are raised. A defect in which enzyme is likely?

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

The answer and the reasoning

D. Alanine-glyoxylate aminotransferase

Primary hyperoxaluria type 1 results from deficiency of the pyridoxal phosphate-dependent peroxisomal enzyme alanine-glyoxylate aminotransferase, which converts glyoxylate to glycine. Glyoxylate is instead oxidised to oxalate, which precipitates as calcium oxalate in the kidney, leading to stones, nephrocalcinosis and renal failure. Some patients respond to pyridoxine.

Option by option

  • A. Fumarylacetoacetate hydrolase

    Fumarylacetoacetate hydrolase deficiency causes tyrosinaemia type I with liver failure.

  • B. Cystathionine beta-synthase

    Cystathionine beta-synthase deficiency causes homocystinuria with lens dislocation and thrombosis.

  • C. Glycine cleavage enzyme complex

    Glycine cleavage complex deficiency causes nonketotic hyperglycinaemia with neonatal encephalopathy and not stones.

  • D. Alanine-glyoxylate aminotransferase (correct)

    Correct. Failure to transaminate glyoxylate diverts it to oxalate.

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 D, Alanine-glyoxylate aminotransferase. Primary hyperoxaluria type 1 results from deficiency of the pyridoxal phosphate-dependent peroxisomal enzyme alanine-glyoxylate aminotransferase, which converts glyoxylate to glycine.

Why is "Fumarylacetoacetate hydrolase" not the answer?

Fumarylacetoacetate hydrolase deficiency causes tyrosinaemia type I with liver failure.

Why is "Cystathionine beta-synthase" not the answer?

Cystathionine beta-synthase deficiency causes homocystinuria with lens dislocation and thrombosis.

Why is "Glycine cleavage enzyme complex" not the answer?

Glycine cleavage complex deficiency causes nonketotic hyperglycinaemia with neonatal encephalopathy and not stones.

What concept does this question test?

It tests Amino acid metabolism: primary hyperoxaluria in Biochemistry. Glyoxylate is instead oxidised to oxalate, which precipitates as calcium oxalate in the kidney, leading to stones, nephrocalcinosis and renal failure. Some patients respond to pyridoxine.

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 metabolism: primary hyperoxaluria?

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.