Porphyria diseases are a group of metabolic disorders caused by abnormal functioning of
heme biosynthesis
enzymes and characterized by excessive accumulation and excretion of
porphyrins and their precursors. Precisely which of these chemicals builds up depends on the type of
porphyria.
Porphyria is not a single disease but a group of nine disorders:
acute intermittent porphyria (AIP),
hereditary coproporphyria (HCP),
variegate porphyria (VP), δ-
aminolevulinic acid dehydratase deficiency
porphyria (
ADP),
porphyria cutanea tarda (PCT),
hepatoerythropoietic porphyria (HEP),
congenital erythropoietic porphyria (CEP),
erythropoietic protoporphyria (EPP), and X-linked protoporphyria (XLP). Each
porphyria results from overproduction of
heme precursors secondary to partial deficiency or, in XLP, increased activity of one of the
enzymes of
heme biosynthesis. Taken together, all forms of
porphyria afflict fewer than 200,000 people in the United States. Based on European studies, the most common
porphyria, PCT, has a prevalence of 1 in 10,000, the most common
acute porphyria, AlP, has a prevalence of ∼1 in 20,000, and the most common
erythropoietic porphyria, EPP, is estimated at 1 in 50,000 to 75,000. CEP is extremely rare, with prevalence estimates of 1 in 1,000,000 or less. Only six cases of
ADP are documented. The current
porphyria literature is very exhaustive and a brief overview of
porphyria diseases is essential in order for the reader to better appreciate the relevance of this area of research prior to undertaking biochemical diagnostics procedures. This unit summarizes the current knowledge on the classification, clinical features, etiology, pathogenesis, and genetics of
porphyria diseases.