A young woman reports severe throbbing burning pain in her hands and feet within minutes of sun exposure, but never develops blisters. Erythema and swelling appear on exposed skin. Urine porphyrins are normal, and red fluorescence of plasma is seen. The enzyme deficient in this condition is:

• A Uroporphyrinogen III synthase
• B Uroporphyrinogen decarboxylase
• C ALA dehydratase
• D Ferrochelatase ✓

Explanation

Erythropoietic protoporphyria results from ferrochelatase deficiency, causing accumulation of free protoporphyrin in erythrocytes. It produces acute painful non-blistering phototoxic reactions, gallstones, and sometimes liver failure. Uroporphyrinogen decarboxylase deficiency causes porphyria cutanea tarda with blistering and fragility on the dorsa of hands, and uroporphyrinogen III synthase deficiency causes congenital erythropoietic porphyria with red urine and haemolysis.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.