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glossary:porphyria

A diverse group of diseases in which the production of heme is disrupted. Porphyria is derived from the Greek word “porphyra”, which means purple. When heme production is faulty, porphyrins are overproduced and lend a reddish-purple color to urine. All forms of porphyrias are inherited. The key clinical features are skin sensitivity to sunlight and/or by intermittent acute attacks of abdominal and nerve pain.

Heme is composed of porphyrin, a large circular molecule made from four rings linked together with an iron atom at its center. Heme is the oxygen-binding part of hemoglobin, giving red blood cells their color. It is also a component of several vital enzymes in the liver including the group known as cytochrome P450. This enzyme family is important in converting potentially harmful substances such as drugs to inactive products destined for excretion.

Heme synthesis takes place in several steps, each of which requires a specific enzyme of which there are 8 in total. The genes that encode these enzymes are located on different chromosomes, and mutations of these genes can be inherited in either an autosomal dominant or autosomal recessive fashion, depending on the gene concerned. Affected individuals are unable to complete heme synthesis, and intermediate products, porphyrin or its precursors, accumulate.

Not all persons with porphyria experience acute attacks. In those that do suffer them, the attack may range from mild to severe. Besides abdominal and nerve pain, the victim may suffer rapid heartbeat, mania, muscle cramps, muscle weakness, breathing problems, hallucinations and coma. Acute attacks are often precipitated by the following:

  • The use of certain drugs such as barbiturates, sulphonamides and birth-control pills;
  • Alcohol use;
  • Hormonal changes during menstruation or pregnancy;
  • Dieting or fasting; and
  • Infections.

Diagnosis requires a thorough physical exam and laboratory tests that include analysis of blood, urine, and stools.

Treatment involves appropriate measures to relieve symptoms. A high-carbohydrate diet and avoidance of precipitating factors, wherever possible, can help patients reduce their risk of suffering an acute attack. Severe acute attacks may require hospitalization to stabilize the patient, relieve pain and monitor the body's fluid levels.

Source - MedTerms

glossary/porphyria.txt · Last modified: 2012/10/16 14:40 (external edit)