A 62-year-old woman with a diet chronically poor in meat and legumes presents with progressive fatigue. Hemogram shows microcytic hypochromic anemia, and bone marrow reveals ringed sideroblasts. Her anemia improves after supplementation with a single vitamin. Which enzyme was functioning suboptimally?

• A ALA dehydratase
• B Ferrochelatase
• C Delta-aminolevulinic acid synthase ✓
• D Uroporphyrinogen decarboxylase

Explanation

Pyridoxal phosphate, the active form of vitamin B6, is the obligatory cofactor for delta-aminolevulinic acid synthase, the rate-limiting first enzyme of heme synthesis in mitochondria. Dietary B6 deficiency impairs ALA formation, iron cannot be inserted into protoporphyrin, and iron-laden mitochondria accumulate around the nucleus forming ringed sideroblasts. Ferrochelatase is inhibited by lead, and ALA dehydratase deficiency causes lead poisoning or acute intermittent porphyria patterns, both distinct entities.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.