The porphyrias are inherited or acquired disorders in which the activity of an enzyme in the heme biosynthetic pathway is altered. Metabolic intermediates are produced in excess, initially either in the marrow or the liver, and result in neurologic and/or photocutaneous symptoms and signs.
See Table 28–1.
The two organs most active in heme biosynthesis are the marrow and the liver. Photosensitivity (indicated below with the following symbols as either blistering* or nonblistering†) and/or (indicated below with the following symbol as) neurovisceral symptoms‡ may be part of the porphyria phenotype. Therefore, 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 |Favorite Table|Download (.pdf) TABLE 28–1 HUMAN PORPHYRIAS: SPECIFIC ENZYMES AFFECTED BY MUTATIONS, MODES OF INHERITANCE, CLASSIFICATION, AND MAJOR CLINICAL FEATURES OF EACH OF THE HUMAN PORPHYRIAS
|Porphyriaa ||Affected Enzyme ||Known Mutations ||Inheritance ||Classification ||Principal Clinical Features |
|X-linked protoporhyria (XLP) ||δ-Aminolevulinic acid (ALA) synthase erythroid-specific form (ALAS2) ||4 (gain of function) ||Sex-linked recessive ||Erythropoietic ||Nonblistering photosensitivity |
|δ-Aminolevulinic acid dehydratase porphyria (ADP) ||ALA dehydratase (ALAD) ||10 ||Autosomal recessive ||Hepaticb ||Neurovisceral |
|Acute intermittent porphyria (AIP) ||PBG deaminase (PBGD) ||273 ||Autosomal dominant ||Hepatic ||Neurovisceral |
|Congenital erythropoietic porphyria (CEP) ||Uroporphyrinogen III synthase (UROS) ||36 ||Autosomal recessive ||Erythropoietic ||Neurovisceral |
|Porphyria cutanea tarda (PCT) ||Uroporphyrinogen decarboxylase (UROD) ||70 (includes HEP) ||Autosomal dominantc ||Hepatic ||Blistering photosensitivity |
|Hepatoerythropoietic porphyria (HEP) ||UROD ||— ||Autosomal recessive ||Hepaticb ||Blistering photosensitivity |
|Hereditary coproporphyria (HCP) ||Coproporphyrinogen oxidase (CPO) ||42 ||Autosomal dominant ||Hepatic ||Neurovisceral; blistering photosensitivity (uncommon) |
|Variegate porphyria (VP) ||Protoporphyrinogen oxidase (PPO) ||130 ||Autosomal dominant ||Hepatic ||Neurovisceral; blistering photosensitivity (common) |
|EPP – classic form ||Ferrochelatase (FECH) ||90 ||Autosomal recessived ||Erythropoietic ||Nonblistering photosensitivity |
Principal site of initial accumulation of pathway intermediates: the erythroblast
Congenital erythropoietic porphyria (CEP)*
Erythropoietic protoporphyria (EPP)†
X-linked protoporphyria (XLP)†
Principal site of initial accumulation of pathway intermediates: the liver
δ-Aminolevulinic acid dehydratase porphyria (ADP)‡
Acute intermittent porphyria (AIP)‡
Hereditary coproporphyria (HCP)*‡
Variegate porphyria (VP)...
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