Haematology: lead poisoning: practice question

A General Medicine 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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General Medicine · Haematology: lead poisoning

Sample item

A 6-year-old child living near an informal battery-recycling unit has colicky abdominal pain, constipation, irritability and anaemia. The blood film shows coarse basophilic stippling of red cells, and blood lead is markedly raised. Which pair of haem synthesis enzymes is inhibited by lead?

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

The answer and the reasoning

C. Delta-aminolevulinic acid dehydratase and ferrochelatase

Lead inhibits ALA dehydratase and ferrochelatase, so delta-aminolevulinic acid and free erythrocyte protoporphyrin accumulate and haem synthesis falls. It also inhibits pyrimidine 5'-nucleotidase, which causes basophilic stippling from retained ribosomal RNA. Lead lines on the gums, wrist drop and encephalopathy are other features, and chelation with succimer or calcium EDTA is used.

Option by option

  • A. Porphobilinogen deaminase and uroporphyrinogen III synthase

    Porphobilinogen deaminase deficiency causes acute intermittent porphyria and uroporphyrinogen III synthase deficiency causes congenital erythropoietic porphyria.

  • B. Heme oxygenase and biliverdin reductase

    Haem oxygenase and biliverdin reductase belong to haem degradation, not synthesis.

  • C. Delta-aminolevulinic acid dehydratase and ferrochelatase (correct)

    Correct. Inhibition of these two enzymes explains raised ALA and protoporphyrin with anaemia.

  • D. Delta-aminolevulinic acid synthase and uroporphyrinogen decarboxylase

    ALA synthase is the rate-limiting step and is regulated by haem; uroporphyrinogen decarboxylase is deficient in porphyria cutanea tarda.

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 General Medicine question

What is the answer to this General Medicine question?

The best answer is C, Delta-aminolevulinic acid dehydratase and ferrochelatase. Lead inhibits ALA dehydratase and ferrochelatase, so delta-aminolevulinic acid and free erythrocyte protoporphyrin accumulate and haem synthesis falls.

Why is "Porphobilinogen deaminase and uroporphyrinogen III synthase" not the answer?

Porphobilinogen deaminase deficiency causes acute intermittent porphyria and uroporphyrinogen III synthase deficiency causes congenital erythropoietic porphyria.

Why is "Heme oxygenase and biliverdin reductase" not the answer?

Haem oxygenase and biliverdin reductase belong to haem degradation, not synthesis.

Why is "Delta-aminolevulinic acid synthase and uroporphyrinogen decarboxylase" not the answer?

ALA synthase is the rate-limiting step and is regulated by haem; uroporphyrinogen decarboxylase is deficient in porphyria cutanea tarda.

What concept does this question test?

It tests Haematology: lead poisoning in General Medicine. It also inhibits pyrimidine 5'-nucleotidase, which causes basophilic stippling from retained ribosomal RNA. Lead lines on the gums, wrist drop and encephalopathy are other features, and chelation with succimer or calcium EDTA is used.

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 Haematology: lead poisoning?

For each disease know the classic presentation, the best test, and the first-line treatment. Then use the flashcards and the other General Medicine 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.