The porphyrias are a group of inherited or acquired disorders of certain enzymes in the heme bio-synthetic pathway (also called porphyrin pathway). They manifest with either neurological complications (“acute”) or skin problems (“cutaneous”), or occasionally both. The porphyrias may be classified by the primary site of the overproduction and accumulation of the porphyrins (or their chemical precursors) as hepatic porphyrias, where porphyrins are overproduced in the liver predominantly, or erythropoietic porphyrias, where the overproduction is confined to the bone marrow and the erythrocye (red blood cell) and its precursors.
The term derives from the Greek πορφύρα, porphyra, meaning “purple pigment”. The name is likely to have been a reference to the purple discolouration of feces and urine when exposed to light in patients during an attack. Although original descriptions are attributed to Hippocrates, the disease was first explained biochemically by Felix Hoppe-Seyler in 1871, and acute porphyrias were described by the Dutch physician Barend Stokvis in 1889.
The prevalence of all types of porphyria taken together has been estimated to be approximately 1 in 25,000 in the United States. The worldwide prevalence has been estimated to be somewhere between 1 in 500 to 1 in 50,000 people.
The cutaneous, or erythropoietic, porphyrias primarily affect the skin, causing photosensitivity (photodermatitis), blisters, necrosis of the skin and gums, itching, and swelling, and increased hair growth on areas such as the forehead. Often there is no abdominal pain, distinguishing it from other porphyrias.
In some forms of porphyria, accumulated heme precursors excreted in the urine may cause various changes in color, after exposure to sunlight, to a dark reddish or dark brown color. Even a purple hue or red urine may be seen.
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