Some features are shared with the other, less common porphyrias, which include delta-aminolevulinic acid dehydratase deficiency, congenital erythropoietic porphyria, hepatoerythropoietic porphyria, hereditary coproporphyria, and variegate porphyria. All porphyrias except porphyria cutanea tarda are hereditary. All people with a particular hereditary porphyria have a deficiency of the same enzyme. However, unless they come from the same family, they are likely to have different mutations in the gene for that enzyme. Porphyrias can be classified in several ways.
Classification according to the specific enzyme deficiency is preferred.
Another classification system distinguishes acute porphyrias, which cause neurologic symptoms, from cutaneous porphyrias, which cause skin photosensitivity. A third classification system is based on whether the excess precursors originate primarily in the liver, in which case the porphyria is hepatic, or primarily in the bone marrow, in which case the porphyria is erythropoietic. A person who has symptoms of porphyria will have markedly abnormal laboratory test results. But the tests must be properly selected and interpreted to confirm or exclude the presence of porphyria. In most cases, doctors measure the levels of delta-aminolevulinic acid and porphobilinogen in urine when they suspect an acute porphyria, and they measure the levels of porphyrin in the blood plasma when they suspect a cutaneous porphyria.