An autosomal dominant porphyria presents with acute abdominal pain and motor neuropathy after drug exposure, together with mild photosensitive skin fragility. Stool analysis reveals markedly elevated coproporphyrin III. The deficient enzyme is:

• A Uroporphyrinogen III synthase
• B Protoporphyrinogen oxidase
• C Coproporphyrinogen oxidase ✓
• D Delta-aminolevulinic acid dehydratase

Explanation

Hereditary coproporphyria arises from partial deficiency of the mitochondrial enzyme coproporphyrinogen oxidase, causing accumulation of coproporphyrinogen III and its oxidised product coproporphyrin III, excreted chiefly in bile and stool. Clinically it resembles variegate porphyria but the biochemical hallmark is isolated fecal coproporphyrin excess. Protoporphyrinogen oxidase deficiency gives variegate porphyria with excess protoporphyrin rather than coproporphyrin.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.