PORPHYRIA CUTANEA tarda (PCT) is the most common of the porphyrias, a group of metabolic disorders caused by derangements in the heme biosynthetic pathway. The sequence of events whereby glycine and succinyl coenzyme A are transformed into the tetrapyrrole heme depends on the decarboxylative and oxidative properties of 8 key intracellular enzymes. The chromosomal locations of all these enzymes have now been assigned, and the gene structures characterized.1 In normal heme synthesis, which occurs predominantly in erythrocytes and hepatocytes, these enzymes are regulated with utmost precision, resulting in a delicate balance of substrates and their porphyrin-heme products. When there is any aberration in normal enzyme function that disturbs this equilibrium, toxic porphyrin precursors accumulate in the liver and blood, and, depending on where the enzyme defect is in the pathway, certain porphyrins are excreted in patterns that are diagnostic of the different porphyrias.
Kim JJ, Lim HW. Hexachlorobenzene and Porphyria Cutanea Tarda. Arch Dermatol. 1999;135(4):459-460. doi:10.1001/archderm.135.4.459