A 7-year-old child with abdominal pain, constipation, and basophilic stippling on the peripheral smear has a blood lead level of 65 mcg/dL. Lead inhibits which enzymes of heme synthesis, explaining both the anemia and the elevated free erythrocyte protoporphyrin?

• A ALA synthase and uroporphyrinogen decarboxylase
• B ALA dehydratase and ferrochelatase ✓
• C Ferrochelatase and coproporphyrinogen oxidase
• D ALA dehydratase and porphobilinogen deaminase

Explanation

Lead directly inhibits ALA dehydratase and ferrochelatase. Ferrochelatase blockade prevents iron incorporation into protoporphyrin IX, raising free erythrocyte protoporphyrin and zinc protoporphyrin, while ALA dehydratase inhibition elevates urinary ALA. Basophilic stippling reflects ribosomal aggregation from lead toxicity. Porphyria cutanea tarda involves uroporphyrinogen decarboxylase, unrelated to lead.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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