PPOX and glioma: In this sense, different gene expression between WHO grade II and grade IV gliomas was found in the Solute Carrier Family 15 Member 2 (SLC15A2), ALA-Dehydratase (ALAD), Hydroxymethylbilane Synthase (HMBS), Uroporphyrinogen-III-Synthase (UROS), Uroporphyrinogen-Decarboxylase (UROD), ATP-binding Transporter Cassette Subfamily B Member 6 (ABCB6), Protoporphyrinogen-Oxidase (PPOX), and Ferrochelatase (FECH) [13].