Mutations in the ALAD, HMBS, CPOX, PPOX genes cause different forms of acute hepatic porphyrias: Alad-deficiency porphyria (ADP; OMIM: #612740), acute intermittent porphyria (AIP; OMIM: #176000), hereditary coproporphyria (HCP; OMIM: #121300) and porphyria variegate (VP; OMIM: #176200), respectively. The gene discussed is HMBS; the disease is hereditary coproporphyria.