Erythropoietic Protoporphyria and X-Linked Protoporphyria
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.
(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 liver.
The enzyme deficiency is inherited from one parent, but in order to develop the disorder people must also inherit a slightly abnormal gene for the enzyme from the other parent.
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 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.
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.
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.
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, such as afamelanotide, that may help people tolerate sunlight are being tested. Afamelanotide is available in some parts of Europe. However, sunlight should still be avoided.
Drugs that trigger acute porphyrias do not cause erythropoietic protoporphyria and need not be avoided.
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 hematin 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 them 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.