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A group of disorders involving heme biosynthesis, characterized by excessive excretion of porphyrins or their precursors; may be inherited or may be acquired, as from the effects of certain chemical agents ( e.g., hexachlorobenzene).

- acute intermittent p., acute p. SYN: intermittent acute p..

- δ-aminolevulinate dehydratase p. an inherited disorder in which there is a deficiency of porphobilinogen synthase; δ-aminolevulinate levels are elevated, leading to neurologic disturbances. SYN: porphobilinogen synthase p..

- congenital erythropoietic p. [MIM*263700] enhanced porphyrin formation by erythroid cells in bone marrow, leading to severe porphyrinuria, often with hemolytic anemia and persistent cutaneous photosensitivity; caused by a deficiency of uroporphyrinogen III cosynthetase; autosomal recessive inheritance, caused by mutation in the uroporphyrinogen III synthase gene (UROS) on chromosome 10q; there is an overproduction of type I porphyrin isomers.

- p. cutanea tarda (PCT) [MIM*176090, MIM*176100] familial or sporadic p. characterized by liver dysfunction and photosensitive cutaneous lesions, with bullae, hyperpigmentation, and scleroderma-like changes in the skin and increased excretion of uroporphyrin; caused by a deficiency of uroporphyrinogen decarboxylase induced in sporadic cases by chronic alcoholism; autosomal dominant inheritance in familial cases. SYN: symptomatic p..

- p. cutanea tarda hereditaria See p. cutanea tarda.

- p. cutanea tarda symptomatica See p. cutanea tarda.

- erythropoietic p. a classification of p. that includes congenital erythropoietic p. and erythropoietic protoporphyria.

- hepatic p. [MIM*176100.0002] a category of p. that includes p. cutanea tarda, variegate p., and coproporphyria. SYN: p. hepatica.

- p. hepatica (he-pat′i-ka) SYN: hepatic p..

- hepatoerythropoietic p. an autosomal recessive disorder in which there is a deficiency or absence of uroporphyrinogen decarboxylase; results in photosensitivity and excessive hepatic production of 8- and 7-carboxylate porphyrins.

- intermittent acute p. (IAP) [MIM*176000] p. caused by hepatic overproduction of δ-aminolevulinic acid, with greatly increased urinary excretion of it and of porphobilinogen, and some increase of uroporphyrin, due to a deficiency of porphobilinogen deaminase; characterized by intermittent acute attacks of hypertension, abdominal colic, psychosis, and polyneuropathy, but with no photosensitivity; autosomal dominant inheritance, caused by mutation in the human porphobilinogen deaminase gene on 11q24; exacerbation caused by ingestion of certain drugs ( e.g., barbiturates). SYN: acute intermittent p., acute p..

- ovulocyclic p. acute episodic exacerbations of p. occurring in the premenstrual period.

- porphobilinogen synthase p. SYN: δ-aminolevulinate dehydratase p..

- South African type p. SYN: variegate p..

- symptomatic p. SYN: p. cutanea tarda.

- variegate p. (VP) [MIM*176200] p. characterized by abdominal pain and neuropsychiatric abnormalities, by dermal sensitivity to light and mechanical trauma, by increased fecal excretion of proto- and coproporphyrin, and by increased urinary excretion of δ-aminolevulinic acid, porphobilinogen, and porphyrins; due to a deficiency of protoporphyrinogen oxidase; autosomal dominant inheritance, caused by mutation in the gene for protoporphyrinogen oxidase (PPOX) on chromosome 1q. SYN: protocoproporphyria hereditaria, South African type p..

por·phyr·ia pȯr-'fir-ē-ə n any of several usu. hereditary abnormalities of porphyrin metabolism characterized by excretion of excess porphyrins in the urine and by extreme sensitivity to light

one of a group of rare disorders due to inborn error of metabolism in which there are deficiencies in the enzymes involved in the biosynthesis of haem. The accumulation of the enzyme's substrate gives rise to symptoms of the disorder. The defect may be primarily in the liver (hepatic porphyria) or in the bone marrow (erythropoietic porphyria) or both. The prominent features include the excretion of porphyrin and their derivatives in the urine, which may change colour on standing (see porphobilinogen); sensitivity of the skin to sunlight causing chronic inflammation or blistering; inflammation of the nerves (neuritis); mental disturbances; and attacks of abdominal pain. The commonest porphyria is porphyria cutanea tarda, which affects up to 1 in 5000 people in some countries. It is a hereditary or acquired hepatic porphyria in which light-exposed areas of the skin become blistered and fragile. Acute intermittent porphyria is a hereditary hepatic porphyria characterized by recurrent attacks of acute abdominal pain, severe constipation, and psychotic behaviour. Factors triggering attacks include alcohol and many drugs.