IS PORPHYRIA-CUTANEA-TARDA A PARANEOPLASTIC DISORDER

The term porphyria cutanea tarda (PCT) encompasses a group of inherited or acquired metabolic disorders of the heme biosynthetic pathway characterized by deficient activity of the enzyme uroporphyrinogen decarboxylase (URO-D). The resultant excess accumulation and excretion of several polycarboxylated porphyrin by-products of the pathway, most prominently uroporphyrin (8-COOH), heptacarboxylic porphyrin, and isocoproporphyrin (4-COOH), biochemically characterize these disorders. In acquired, or sporadic, PCT (type I) reduced activity of URO-D can be detected in liver tissue.1 In familial PCT (type II), heterozygous inheritance of a gene defect encoding altered URO-D protein results in reduced enzyme activity that can be detected in erythrocytes as well as in liver .2 Heterozygous familial PCT in which erythrocyte URO-D activity is normal (type III) has also been described.3,4 Hepatoerythropoietic porphyria (HEP) is a disorder resulting from inheritance of two mutant genes, each encoding defective URO-D, typically yielding a profoundly reduced residual enzyme activity.5,6 Epidemic forms of PCT resulting from exposure to hepatotoxic polychlorinated aromatic hydrocarbons compounds such as hexachlorobenzene7 and dioxin8 have also been described.