Porphyrias are heterogeneous disorders resulting from enzymatic defects in heme biosynthesis, as detailed in Figure 6. Porphyria cutanea tarda (PCT) is the most common nonacute (cutaneous) porphyria, caused by deficient uroporphyrinogen decarboxylase (UROD) in hepatocytes [10]. Here, UROD is linked to porphyria cutanea tarda.