Effects of Oral Zinc in Erythropoietic Protoporphyria

To the Editor.— Erythropoietic protoporphyria (EPP) is an inherited disorder of heme synthesis due to a defect in the enzyme activity of ferrochelatase, which results in the accumulation of free protporphyrin IX in erythrocytes and plasma, and is associated with cutaneous photosensitivity to UV light (around 400 nm). It is one of the two most common porphyrias, rivaling porphyria cutanea tarda in prevalence. Treatment of the cutaneous symptoms of EPP entail avoidance of sunlight and wearing of protective clothing. Beta carotene, used systemically in doses that produce clinical carotenodermia (recommended serum carotene levels above 400 μg/dL), affords most patients limited photoprotection. It has long been recognized that erythrocyte protoporphyrinis significantly increased in lead toxicity and some anemias without cutaneous photosensitivity.1In these cases, protoporphyrin is mainly bound to zinc in the form of zinc protoheme, whereas, in EPP, the accumulated protoporphyrin is metal free. The affinity of zinc for protoporphyrin, and the reduction in erythrocyte photohemolysis that results from cheletion of free protoporphyrin, has been previously demonstrated.2