Table 1.

Summary of the heme biosynthetic enzymes and associated porphyrias, noting their predominant mode of inheritance and clinical features

Enzyme	Disorder	Inheritance	Clinical features
Aminolevulinate synthase	X-linked protoporphyria	X-linked	Immediate photosensitivity, liver disease secondary to protoporphyrin accumulation
	X-linked sideroblastic anemia	X-linked	Anemia with ringed sideroblasts, some pyridoxine responsive
Porphobilinogen synthase	Aminolevulinate dehydratase porphyria	Recessive	Acute neurological attacks
Hydroxymethylbilane synthase	Acute intermittent porphyria	Dominant	Acute neurological attacks
Uroporphyrinogen-III synthase	Congenital erythropoietic porphyria	Recessive	Severe vesiculoerosive skin disease
Uroporphyrinogen decarboxylase	Porphyria cutanea tarda	Acquired, but may be associated with a dominantly inherited mutation in up to approximately 30%	Vesiculoerosive skin disease; usually coexists with iron overload and a number of precipitating factors, particularly alcohol exposure, liver disease, and renal failure
Coproporphyrinogen oxidase	Hereditary coproporphyria	Dominant	Acute neurological attacks and vesiculoerosive skin disease
Protoporphyrinogen oxidase	Variegate porphyria	Dominant	Acute neurological attacks and vesiculoerosive skin disease
Ferrochelatase	Erythropoietic protoporphyria	Recessive, but more common than most recessive disorders because the disease-associated mutation is frequently inherited with a low-expression polymorphism that is common in populations of European extraction	Immediate photosensitivity