CEP is autosomal recessive and results from a markedly deficient activity of the uroporphyrinogen III synthase (UROIIIS; EC 4.2.1.75) that leads to the accumulation of type I porphyrins, specifically uroporphyrin I (URO I) and coproporphyrin I (COPRO I) [9]. This evidence concerns the gene UROS and Congenital erythropoietic porphyria.