What causes porphyria cutanea tarda?

The porphyrias are due to specific enzyme deficiencies that lead to accumulation of porphyrins. Porphyrins absorb light in the 400- to 410-nm (Soret band) range, in the lower range of visible light. This absorbed light energy is then transferred to cellular structures or to molecular oxygen, causing damage to tissues. PCT is due to a deficiency of the enzyme uroporphyrinogen decarboxylase. There are two main categories of PCT patients, acquired and hereditary. Patients with acquired PCT have the enzyme deficiency in the liver only and often have attacks triggered by agents such as alcohol, estrogen, hexachlorobenzene, and iron. PCT may also develop in patients with chronic liver disease (e.g., hepatitis C infection or hemochromatosis). In hereditary PCT, uroporphyrinogen decarboxylase is deficient in most tissues, not just the liver. Both heterozygous and homozygous inheritances of enzyme deficiencies have been described.