A 6-year-old child from a rural area presents with anaemia, abdominal pain, peripheral neuropathy, and 'lead lines' on the gums. Blood lead level is 65 mcg/dL. The MECHANISM by which lead causes anaemia is:

• A Lead causes haemolysis by oxidising RBC membrane lipids similar to G6PD deficiency
• B Lead inhibits iron absorption in the duodenum by competing with DMT-1
• C Lead inhibits erythropoietin synthesis in the renal cortex
• D Lead inhibits delta-aminolevulinic acid dehydratase (ALAD) and ferrochelatase, blocking haeme synthesis and causing sideroblastic-like anaemia with elevated erythrocyte protoporphyrin ✓

Explanation

Lead inhibits two key enzymes of haeme biosynthesis: (1) delta-aminolevulinic acid dehydratase (ALAD), blocking ALA→porphobilinogen condensation (most sensitive enzyme), and (2) ferrochelatase, blocking Fe2+ insertion into protoporphyrin IX. This causes accumulation of delta-ALA, coproporphyrin III in urine, and erythrocyte zinc protoporphyrin (ZPP). The resulting anaemia is microcytic hypochromic with elevated free erythrocyte protoporphyrin, basophilic stippling of RBCs, and elevated urinary ALA — the classic biochemical pattern of lead poisoning.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.