Chronic hepatic porphyrias represent a sub-group of porphyrias (see this term). They are characterized by bullous photodermatitis caused by a deficiency of uroporphyrinogen decarboxylase (URO-D; the fifth enzyme in the heme biosynthesis pathway). Chronic hepatic porphyria encompasses two diseases: porphyria cutanea tarda and hepatoerythropoietic porphyria (extremely rare) (see these terms).