Blood and immunity: lead and haem synthesis: practice question

A Physiology 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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Physiology · Blood and immunity: lead and haem synthesis

Sample item

A 6-year-old living in an old house has abdominal colic, a pale appearance, basophilic stippling of red cells and a blue line on the gums. Which enzymes of haem synthesis are inhibited most characteristically?

ADelta-aminolevulinic acid synthase and heme oxygenaseBDelta-aminolevulinic acid dehydratase and ferrochelataseCPorphobilinogen deaminase and biliverdin reductaseDUroporphyrinogen decarboxylase and glucuronyl transferase

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

The answer and the reasoning

B. Delta-aminolevulinic acid dehydratase and ferrochelatase

Lead inhibits ALA dehydratase and ferrochelatase, so ALA and protoporphyrin accumulate and haem formation falls, causing a microcytic anaemia with basophilic stippling from inhibited pyrimidine 5-nucleotidase. Colic and gum lines reflect chronic lead exposure.

Option by option

A. Delta-aminolevulinic acid synthase and heme oxygenase
ALA synthase is the rate-limiting first step and heme oxygenase degrades haem, so neither is the typical lead target.
B. Delta-aminolevulinic acid dehydratase and ferrochelatase (correct)
Correct. Lead blocks ALA dehydratase and ferrochelatase.
C. Porphobilinogen deaminase and biliverdin reductase
Porphobilinogen deaminase is affected in acute intermittent porphyria, and biliverdin reductase acts in haem breakdown.
D. Uroporphyrinogen decarboxylase and glucuronyl transferase
Uroporphyrinogen decarboxylase is deficient in porphyria cutanea tarda, and glucuronyl transferase conjugates bilirubin.

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.

Questions about this Physiology question

What is the answer to this Physiology question?

The best answer is B, Delta-aminolevulinic acid dehydratase and ferrochelatase. Lead inhibits ALA dehydratase and ferrochelatase, so ALA and protoporphyrin accumulate and haem formation falls, causing a microcytic anaemia with basophilic stippling from inhibited pyrimidine 5-nucleotidase.

Why is "Delta-aminolevulinic acid synthase and heme oxygenase" not the answer?

ALA synthase is the rate-limiting first step and heme oxygenase degrades haem, so neither is the typical lead target.

Why is "Porphobilinogen deaminase and biliverdin reductase" not the answer?

Porphobilinogen deaminase is affected in acute intermittent porphyria, and biliverdin reductase acts in haem breakdown.

Why is "Uroporphyrinogen decarboxylase and glucuronyl transferase" not the answer?

Uroporphyrinogen decarboxylase is deficient in porphyria cutanea tarda, and glucuronyl transferase conjugates bilirubin.

What concept does this question test?

It tests Blood and immunity: lead and haem synthesis in Physiology. Colic and gum lines reflect chronic lead exposure.

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 Blood and immunity: lead and haem synthesis?

For each system, sketch the key graph (pressure–volume loop, oxygen dissociation curve, nephron handling) and explain it aloud. Then use the flashcards and the other Physiology 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.