ALAS2 and X-linked lymphoproliferative disease: Erythropoietic protoporphyria (EPP; OMIM 177000) and X-linked protoporphyria (XLP; MIM 300752) are two rare disorders, triggered, respectively, by the deficiency of the enzyme ferrochelatase (FECH; EC 4.99.1.1) or the activation of the erythroid-specific form of 5-aminolevulinate synthase 2 (ALAS2; EC 2.3.1.37) in the heme biosynthesis pathway (15, 16).