A 10-year-old boy complains of burning pain and redness on sun-exposed skin beginning within minutes of exposure and settling over hours. There are no blisters. Examination shows mild pitting of dental enamel. The most likely enzyme defect is:
- A Ferrochelatase ✓
- B Uroporphyrinogen decarboxylase
- C Uroporphyrinogen III synthase
- D Delta-aminolevulinic acid dehydratase
Correct answer: A. Ferrochelatase
Explanation
Erythropoietic protoporphyria is caused by deficient ferrochelatase, leading to accumulation of free protoporphyrin in erythrocytes. It presents in childhood with immediate painful photosensitivity without blistering, and cholelithiasis from protoporphyrin gallstones is common. Uroporphyrinogen decarboxylase deficiency causes PCT with fragile blistering skin in adults, uroporphyrinogen III synthase deficiency causes congenital erythropoietic porphyria with mutilating scarring, and ALA dehydratase deficiency is an extremely rare acute hepatic porphyria.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.