The porphyrias have several different classification systems. The most accurate classification is by the specific enzyme deficiency. Another classification system distinguishes porphyrias that cause neurologic symptoms (acute porphyrias) from those that cause photosensitivity (cutaneous porphyrias). A third classification system is based on whether the excess precursors originate primarily in the liver (hepatic porphyrias) or primarily in the bone marrow (erythropoietic porphyrias). Some porphyrias are classified as more than one of these categories.
| Type of Porphyria | Deficient Enzyme |
|---|---|
| Acute Porphyrias | |
| ALAD porphyria | delta-aminolevulinic acid dehydratase |
| acute intermittent porphyria | porphobilinogen deaminase |
| hereditary coproporphyria | coproporphyrinogen oxidase |
| variegate porphyria | protoporphyrinogen oxidase |
| Cutaneous Porphyrias | |
| congenital erythropoietic porphyria | uroporphyrinogen III cosynthase |
| porphyria cutanea tarda | uroporphyrinogen decarboxylase (~50% deficiency) |
| hepatoerythropoietic porphyria | uroporphyrinogen decarboxylase (~90% deficiency) |
| hereditary coproporphyria | coproporphyrinogen oxidase |
| variegate porphyria | protoporphyrinogen oxidase |
| erythropoietic protoporphyria | ferrochelatase |
The most common type of porphyria overall is porphyria cutanea tarda. In the United States, acute intermittent porphyria is the most common acute porphyria.
What are the cutaneous porphyrias?
The cutaneous porphyrias affect the skin. People with cutaneous porphyria develop blisters, itching, and swelling of their skin when it is exposed to sunlight. The cutaneous porphyrias include the following types:
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