Porphyria
Any of a group of diseases characterized by the marked overproduction and excretion of porphyrins or of one or another of their precursors. The porphyrins are reddish constituents of heme, the deep red iron-containing pigment of hemoglobin, the oxygen-carrying protein of the red blood cells. The deposition of porphyrin compounds in body tissues, notably the skin, gives rise to a variety of symptoms, the nature of which depends on the specific compound that is abnormally metabolized.
Two main groups of porphyria are recognized: (1) erythropoietic and (2) hepatic. In the first, the overproduction occurs in relation to hemoglobin synthesis by cells in the bone marrow; in the second, the disturbance is in the liver.
There are two principal types of erythropoietic porphyria: (1) In congenital erythropoietic porphyria, or Günther's disease, the excretion of pinkish urine is noted shortly after birth; later, the skin becomes fragile, and blisters may appear in body areas exposed to light; the teeth and bones are reddish brown. Anemia and enlargement of the spleen are frequently noted. The condition is thought to be transmitted as a recessive trait. (2) In erythropoietic protoporphyria, the skin becomes inflamed and itchy after short exposures to sunlight, but usually there are no other impairments, and this form of porphyria, which is transmitted as a dominant trait, is compatible with normal life expectancy.
There are three types of hepatic porphyria: (1) In acute intermittent porphyria, also called porphyria hepatica, affected persons have recurrent attacks of abdominal pain and vomiting, weakness or paralysis of the limbs, and psychic changes resembling hysteria. Attacks may be precipitated by a variety of drugs, including barbiturates and contraceptives and possibly alcohol. This condition is transmitted as a dominant trait; it is possibly the most common form of porphyria, with an overall incidence of approximately one per 100,000 population; people of Scandinavian, Anglo-Saxon, and German ancestry seem more susceptible than others. (2) In variegate porphyria, affected individuals suffer from chronic skin lesions that tend to heal slowly. Acute transient attacks of abdominal pain and nervous-system symptoms may also be present. The condition is inherited as a dominant trait, being especially common in the white population of South Africa. (3) Porphyria cutanea tarda symptomatica, or cutaneous porphyria, is more common in males and usually begins insidiously later in life, in the fourth to eighth decade. The exposed skin is fragile and sensitive to light and other factors. Liver function impairment, if the patient also suffers from chronic alcoholism, is present in the majority of affected individuals; abstinence, in alcoholic patients, results in marked improvement or disappearance of the porphyria; the tendency to develop this form of porphyria also appears to be inherited.
In addition to hereditary porphyria, there have also been rare instances of acquired hepatic porphyria, caused by intoxications. There is generally no specific treatment for porphyria; therapy is aimed at alleviating the symptoms and preventing skin injury and attacks.
Copyright © 1994-2002 Encyclopædia Britannica, Inc.
Sources
- Encylopedia Britannica 2002, Expanded Edition DVD
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