In porphyria cutanea tarda (PCT), the enzyme deficiency leads to accumulation of which compound that causes photosensitisation?
- A Uroporphyrin I and III (derived from uroporphyrinogen accumulation due to uroporphyrinogen decarboxylase deficiency) ✓
- B Protoporphyrin IX
- C Coproporphyrin III
- D Delta-aminolevulinic acid (ALA)
Correct answer: A. Uroporphyrin I and III (derived from uroporphyrinogen accumulation due to uroporphyrinogen decarboxylase deficiency)
Explanation
PCT involves deficiency of uroporphyrinogen decarboxylase (UROD), leading to accumulation of uroporphyrinogens (predominantly type I and III). These are oxidised to uroporphyrins, which are highly photosensitising — they absorb visible light (400–410 nm Soret band) and generate reactive oxygen species in the skin, causing blistering, hyperpigmentation, and hypertrichosis on sun-exposed areas. PCT is the most common porphyria; hepatitis C, alcohol, oestrogens, and iron overload are common precipitants.
Reference: Harper's Illustrated Biochemistry, 32nd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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