Haem synthesis: delta-aminolevulinate synthase: 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 · Haem synthesis: delta-aminolevulinate synthase

Sample item

A 20-year-old man has a hypochromic microcytic anaemia with ring sideroblasts, iron overload and a maternal uncle with the same condition. His haemoglobin improves with pyridoxine. Which erythroid enzyme carries the mutation?

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

The answer and the reasoning

D. Delta-aminolevulinate synthase

X-linked sideroblastic anaemia arises from mutations in the erythroid isoform of the first haem enzyme, and many are pyridoxine-responsive because the mutations impair cofactor binding. Iron accumulates in mitochondria around the nucleus. X-linked inheritance fits the affected maternal uncle.

Option by option

  • A. Porphobilinogen deaminase

    Porphobilinogen deaminase deficiency causes acute intermittent porphyria, not anaemia.

  • B. Ferrochelatase

    Ferrochelatase deficiency causes erythropoietic protoporphyria with painful photosensitivity.

  • C. Uroporphyrinogen III synthase

    Uroporphyrinogen III synthase deficiency causes congenital erythropoietic porphyria with photosensitivity.

  • D. Delta-aminolevulinate synthase (correct)

    Correct. A mutant erythroid isoform on the X chromosome gives pyridoxine-responsive sideroblastic anaemia.

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, Delta-aminolevulinate synthase. X-linked sideroblastic anaemia arises from mutations in the erythroid isoform of the first haem enzyme, and many are pyridoxine-responsive because the mutations impair cofactor binding.

Why is "Porphobilinogen deaminase" not the answer?

Porphobilinogen deaminase deficiency causes acute intermittent porphyria, not anaemia.

Why is "Ferrochelatase" not the answer?

Ferrochelatase deficiency causes erythropoietic protoporphyria with painful photosensitivity.

Why is "Uroporphyrinogen III synthase" not the answer?

Uroporphyrinogen III synthase deficiency causes congenital erythropoietic porphyria with photosensitivity.

What concept does this question test?

It tests Haem synthesis: delta-aminolevulinate synthase in Biochemistry. Iron accumulates in mitochondria around the nucleus. X-linked inheritance fits the affected maternal uncle.

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 Haem synthesis: delta-aminolevulinate synthase?

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.