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MBBS QUESTION #10325
Question 1
Lead poisoning classically inhibits which two enzymes of the heme biosynthetic pathway, producing a microcytic anemia with basophilic stippling of red blood cells?
  • ALA dehydratase and ferrochelatase✔️
  • ALA synthase and porphobilinogen deaminase
  • Uroporphyrinogen synthase and coproporphyrinogen oxidase only
  • Enzymes of globin chain synthesis exclusively, sparing heme synthesis entirely
Correct Answer Explanation
Lead inhibits both ALA dehydratase (early pathway) and ferrochelatase (final step, insertion of iron into protoporphyrin IX), impairing heme synthesis and causing accumulation of protoporphyrin and delta-ALA; the resulting sideroblastic-type microcytic anemia with basophilic stippling is a classic finding in childhood lead poisoning.