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Chapter 057. Photosensitivity and Other Reactions to Light (Part 7)

Porphyria cutanea tarda is the most common type of human porphyria and is associated with decreased activity of the enzyme uroporphyrinogen decarboxylase associated with a number of gene mutations. There are two basic types of PCT: (1) the sporadic or acquired type, generally seen in individuals ingesting ethanol or receiving estrogens; and (2) the inherited type, in which there is autosomal dominant transmission of deficient enzyme activity. Both forms are associated with increased hepatic iron stores. In both types of PCT, the predominant feature is a chronic photosensitivity characterized by increased fragility of sun-exposed skin, particularly areas subject to repeated. | Chapter 057. Photosensitivity and Other Reactions to Light Part 7 Porphyria cutanea tarda is the most common type of human porphyria and is associated with decreased activity of the enzyme uroporphyrinogen decarboxylase associated with a number of gene mutations. There are two basic types of PCT 1 the sporadic or acquired type generally seen in individuals ingesting ethanol or receiving estrogens and 2 the inherited type in which there is autosomal dominant transmission of deficient enzyme activity. Both forms are associated with increased hepatic iron stores. In both types of PCT the predominant feature is a chronic photosensitivity characterized by increased fragility of sun-exposed skin particularly areas subject to repeated trauma such as the dorsa of the hands the forearms the face and the ears. The predominant skin lesions are vesicles and bullae that rupture producing moist erosions often with a hemorrhagic base that heal slowly with crusting and purplish discoloration of the affected skin. Hypertrichosis mottled pigmentary change and scleroderma-like induration are associated features. Biochemical confirmation of the diagnosis can be obtained by measurement of urinary porphyrin excretion plasma porphyrin assay and by assay of erythrocyte and or hepatic uroporphyrinogen decarboxylase. Multiple mutations of the uroporphyrinogen decarboxylase gene have been identified in human populations including exon skipping and base substitutions. Some patients with PCT have associated mutations in the HFE gene linked to hemochromatosis. This could contribute to the iron overload seen in PCT although iron status as measured by serum ferritin iron levels and transferrin saturation is no different from that in PCT patients without HFE mutations. Prior hepatitis C virus infection appears to be an independent risk factor for PCT. Treatment of PCT consists of repeated phlebotomies to diminish the excessive hepatic iron stores and or intermittent low doses of the antimalarial .