The porphyrias are a group of rare and ultra-rare devastating disorders of heme biosynthesis. The majority of these disorders are inherited, and patients present with disabling symptoms that have a profound effect on their quality of life. The subtypes of acute hepatic porphyria - including acute intermittent porphyria (the most common subtype), hereditary coproporphyria, variegate porphyria, and delta-aminolevulinic acid (ALA) dehydratase-deficiency porphyria - are characterized by the occurrence of severe neurovisceral attacks. The genetic deficit that causes acute hepatic porphyria reduces heme availability under conditions of increased heme demands, which leads to activation of the heme-synthesis pathway and up-regulation of . . .