This hereditary metabolic disorder of porphyrin metabolism is unique among the porphyrias in that porphyrins or porphyrin precursors are not excreted in the urine. Also, erythropoietic protoporphyria (EPP) is characterized by an acute sunburn-like photosensitivity, in contrast to the other common porphyrias (porphyria cutanea tarda or variegate porphyria), in which obvious acute photosensitivity is not a presenting complaint.
The specific enzyme defect occurs at the step in porphyrin metabolism in which protoporphyrin is converted to heme by the enzyme ferrochelatase. This leads to an accumulation of protoporphyrin that is highly photosensitizing.
First symptoms usually appear in infancy or early childhood and present as an uncomfortable or painful burning sensation of the skin after sun exposure. It occurs most often on the tops of the hands and feet, face and ears. In most cases visible changes to the skin are mild. The affected skin may become red and swollen and blistered. Later there are pitted scars and sometimes crusty thickened skin, particularly over the cheeks, nose and knuckles of the hands.
Joke and Humors
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