Erythropoietic protoporphyria and X-linked protoporphyria are conditions related to deficiencies of enzymes involved in the production of heme and characterized by sensitivity to sunlight.
- The heme precursor protoporphyrin accumulates in the bone marrow, red blood cells, and other tissues, including skin.
- People have severe skin pain and swelling soon after exposure to sunlight.
- Doctors test blood to look for elevated levels of protoporphyrin.
- People should avoid exposure to sunlight.
- Sometimes, beta-carotene can help protect the skin.
- Afamelanotide, a drug that stimulates the production of more melanin, can decrease sensitivity to sunlight and improve quality of life.
Porphyrias are a group of disorders caused by deficiencies of enzymes involved in the production of heme. Heme is a chemical compound that contains iron and gives blood its red color. Heme is a key component of several important proteins in the body. (See also Overview of Porphyria.)
Accumulation of protoporphyrin in the skin results in extreme sensitivity to sunlight and severe pain soon after exposure. The sunlight activates the protoporphyrin molecules, which damage the surrounding tissue.
Accumulation of protoporphyrins in the liver can cause liver damage. Protoporphyrins excreted in the bile can often lead to gallstones.
Erythropoietic protoporphyria is uncommon. It usually appears in childhood.
In most people with erythropoietic protoporphyria, a deficiency of the enzyme ferrochelatase leads to accumulation of the heme precursor protoporphyrin in the bone marrow, red blood cells, blood plasma (the liquid component of blood), skin, and eventually the liver.
The enzyme deficiency is inherited from both parents..
About 10% of people who have the symptoms of erythropoietic protoporphyria actually have increased activity of a different enzyme. The increased activity leads to accumulation of the same heme precursor. However, the abnormal gene for this form of erythropoietic protoporphyria is carried on the X-chromosome, and thus the disorder, called X-linked protoporphyria, occurs mainly in boys.
Because X-linked protoporphyria is so similar to erythropoietic protoporphyria, it is sometimes regarded as a variant of erythropoietic protoporphyria.
Symptoms usually start in childhood. Severe skin pain and swelling develop soon after even brief exposure to sunlight. Crusting may develop around the lips and on the back of the hands after prolonged sun exposure. Because blistering and scarring do not occur, doctors usually do not recognize the disorder.
If skin protection is chronically neglected, rough, thickened, and leathery skin (lichenification) may develop, especially over the knuckles. Deep grooves may develop around the mouth (carp mouth).
People with X-linked protoporphyria tend to have higher levels of protoporphyrin in their red blood cells, plasma, and other tissues and, therefore, more severe reactions to sunlight and more severe liver disease than those with erythropoietic protoporphyria.
Children in whom erythropoietic protoporphyria and X-linked protoporphyria is unrecognized may develop psychosocial problems because they inexplicably refuse to go outdoors. The fear or anticipation of pain may be so distressing that children become nervous, tense, aggressive, or develop feelings of detachment from the surroundings or even suicidal thoughts.
Did You Know...
- Blood tests
Porphyrin levels in urine are not usually increased. The diagnosis is therefore made when increased levels of protoporphyrin are detected in red blood cells and blood plasma (the liquid portion of blood).
Genetic testing may be done. Family members may also be tested to determine whether they also have the gene mutation.
Prevention of Attacks
Extreme care should be taken to avoid exposure to sunlight. People should use protective clothing, hats, and light-opaque sunscreens containing titanium dioxide or zinc oxide. Accidental sun exposure is given the same treatment as is sunburn.
The drug afamelanotide helps people better tolerate sunlight. Beta-carotene, when taken in sufficient amounts to cause a slight protective yellowing of the skin, may make people more tolerant of sunlight. Several other drugs that may help people tolerate sunlight are being tested. However, sunlight should still be avoided.
Drugs that trigger acute porphyrias do not cause erythropoietic protoporphyria and need not be avoided.
- Relief of symptoms of attacks
- Treat gallstones and liver problems
Acute skin symptoms can be alleviated by cold baths or wet towels, analgesics, and topical and/or oral corticosteroids. Symptoms can take up to a week to resolve. If these measures are ineffective, doctors sometimes give heme and/or blood transfusions. Several other drugs such as afamelanotide, bile acids, cholestyramine resin, and charcoal are also effective.
People who develop gallstones that contain protoporphyrin may need to have the gallbladder surgically removed.
Porphyrin accumulation in red blood cells and the condition of the liver should be monitored yearly by testing blood, urine, and stool samples. Liver damage, if severe, may necessitate liver transplantation.
Stem cell transplantation may cure erythropoietic protoporphyria, but it is not usually done because the risks of transplantation typically outweigh the benefits.
The following is an English-language resource that may be useful. Please note that THE MANUAL is not responsible for the content of this resource.
- American Porphyria Foundation: Aims to educate and support patients and families affected by porphyrias
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