The Porphyrias

The porphyrias are uncommon disorders caused by deficiencies in the activities of the enzymes of the heme biosynthetic pathway. The enzymatic defects that cause porphyrias may be either inherited or acquired, and there is significant interplay between the genetic defect and acquired or environmental factors. Acute forms of the porphyrias may be life threatening and may be misdiagnosed because of the nonspecific nature of the clinical presentation (e.g., acute abdominal pain, psychiatric disturbances, and polyneuropathies). The course of the acute forms of disease is characterized by long latent periods interrupted by acute attacks, which are associated with substantial morbidity and mortality. Porphyrias may be classified as neurovisceral or photosensitive, depending on their prominent clinical characteristic, but in some cases of porphyria, both symptoms are present. Alternatively, the porphyrias can be classified as hepatic or erythropoietic, depending on the principal site of expression of the specific enzymatic defect involved, but the expressions overlap in some porphyrias. The neurovisceral porphyrias correspond with the hepatic porphyrias (ie, acute intermittent porphyria [A