The Porphyrias

Abstract

Porphyrias are metabolic disorders due to deficiencies of specific enzymes of the heme biosynthetic pathway. They are associated with striking accumulations and excess excretion of heme pathway intermediates and their oxidized products. Symptoms and signs are almost all due to effects on the nervous system or skin. The three most common porphyrias, acute intermittent porphyria, porphyria cutanea tarda and erythropoietic protoporphyria, differ considerably from each other. The first presents with acute neurovisceral symptoms and can be aggravated by some drugs. Its treatment comprises intravenous heme administration and liberal amounts of glucose. In the latter two porphyrias the skin is affected, though with different lesions. Treatment differs also, from reducing excess iron for the first, and administration of β-carotene for the last porphyria. These disorders are more often manifest in adults than are most metabolic diseases. All porphyrias are inherited, with the exception of porphyria cutanea tarda, which is due to an acquired enzyme deficiency in liver, although an inherited deficiency is a predisposing factor in some cases.