Porphyria cutanea tarda is a common form of porphyria, but is less frequently encountered in South Africa than variegate porphyria. This form of porphyria is unusual in that it is typically an acquired illness, rather than a genetically inherited disorder. It is also the only form of porphyria which is readily treatable.

Enzyme Defect
The defective enzyme is uroporphyrinogen decarboxylase. Deficient activity results in the accumulation of large amounts of water-soluble porphyrins (uroporphyrin, hepta-, hexa-, and pentacarboxylic porphyrin, and coproporphyrin). Accumulation of these photoactive porphyrins in the skin results in photosensitivity and skin disease. (See Introduction to porphyria). In the commoner, acquired form, the enzyme activity is diminished as a result of chemical inhibition. In the inherited form, reduced activity results from a mutation in the uroporphyrinogen decarboxylase gene, though the same risk factors as for the acquired form are usually present in clinically expressed cases.

Diagnosis
Porphyria cutanea tarda may be diagnosed by:

A positive plasma fluorescence peak at 619 nm on plasma fluoroscanning.
Demonstration of increased concentrations of the uroporphyrin, hepta-, hexa-, and pentacarboxylic porphyrin in urine and plasma on quantitative chromatography.
Identifying a characteristic porphyrin, isocoproporphyrin, on a stool porphyrin chromatography.

Source: Courtesy of Porphyria SA - UCT