Porphyria

Porphyria is a group of disorders caused by inherited or acquired defects in heme biosynthesis. These defects can cause porphyrins or their precursors to accumulate, producing neurological, abdominal, or skin symptoms.

Heme biosynthesis: The multistep pathway that produces heme from glycine and succinyl-CoA. Each porphyria stems from reduced activity at a particular step in this pathway.
Acute intermittent porphyria: An inherited hepatic porphyria caused by deficient hydroxymethylbilane synthase activity. It is a common cause of acute abdominal and neurological attacks without photosensitivity.
Porphyria diagnosis: The process of identifying porphyria through symptoms, biochemical testing, and genetic analysis. Testing during symptoms can distinguish an acute attack from other causes of abdominal or neurological illness.
Enzyme deficiency: A reduction or absence of an enzyme’s activity that disrupts a biochemical reaction. Most porphyrias arise from deficient activity of a specific heme-synthesis enzyme.
Lead poisoning: Illness caused by exposure to lead, which disrupts heme synthesis and damages multiple organ systems. It can elevate heme precursors and mimic biochemical or neurological features of acute porphyria.
Porphyrin: A family of ring-shaped organic molecules that bind metal ions and include intermediates in heme synthesis. Porphyrins accumulate in several forms of porphyria and can make skin light-sensitive.
Porphyria cutanea tarda: A hepatic porphyria caused by deficient uroporphyrinogen decarboxylase activity. Its characteristic blistering skin fragility contrasts with acute intermittent porphyria.
Urinary porphobilinogen: A laboratory measurement of porphobilinogen excreted in urine. A marked rise during symptoms supports diagnosis of an acute hepatic attack.
Autosomal dominant inheritance: An inheritance pattern in which one altered gene copy can cause a trait or disorder. Several acute porphyrias are inherited this way, though many carriers never develop attacks.
Phototoxicity: Tissue injury caused when light activates a chemical substance in the body or on the skin. Porphyrin-related skin disease is one specific cause of phototoxic injury.

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