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INTRODUCTION

  • The porphyrias are inherited or acquired disorders due to altered activities of enzymes in the heme biosynthetic pathway. Metabolic intermediates are produced in excess, initially either in the marrow or the liver, and result in neurologic and/or photocutaneous symptoms and signs.

CLASSIFICATION

  • See Table 28–1.

  • The two organs most active in heme biosynthesis are the marrow and the liver. Photosensitivity, indicated below as either blistering (*) or nonblistering (), and/or neurovisceral symptoms () may be components of the different porphyria phenotypes. Based on these features, porphyrias are classified as erythropoietic or hepatic and as cutaneous or acute.

TABLE 28–1HUMAN PORPHYRIAS: SPECIFIC ENZYMES AFFECTED BY MUTATIONS, MODES OF INHERITANCE, CLASSIFICATION, AND MAJOR CLINICAL FEATURES OF EACH OF THE HUMAN PORPHYRIAS

Erythropoietic Porphyrias

  • Principal site of initial accumulation of pathway intermediates: erythroblasts and reticulocytes

  • Major types:

    — Congenital erythropoietic porphyria (CEP)*

    — Erythropoietic protoporphyria (EPP)

    — X-linked protoporphyria (XLP)

Hepatic Porphyrias

  • Principal site of initial accumulation of pathway intermediates: hepatocytes

  • Major types

    — Acute hepatic porphyrias

    • δ-Aminolevulinic acid dehydratase porphyria (ADP)

    • Acute intermittent porphyria (AIP)

    • Hereditary coproporphyria (HCP)*‡

    • Variegate porphyria (VP)...

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