Porphyria is a group of disorders caused by abnormalities in the chemical steps that lead to heme production. Heme is a vital molecule for all of the body's organs. It is found mostly in the blood, bone marrow, and liver. Heme is a component of hemoglobin, the molecule that carries oxygen in the blood.
The major types of porphyria are each caused by mutations in one of the genes required for heme production. Forms of porphyria include ALAD deficiency porphyria, acute intermittent porphyria, congenital erythropoietic porphyria, erythropoietic protoporphyria, hepatoerythropoietic porphyria, hereditary coproporphyria, porphyria cutanea tarda, and variegate porphyria.
In addition to the genetic forms of porphyria, some cases of this disorder are caused by nongenetic factors such as infections or exposure to certain prescription drugs. These cases are described as sporadic or acquired porphyria.
The signs and symptoms of porphyria vary among the types. Some types of porphyria (called cutaneous porphyrias) cause the skin to become overly sensitive to sunlight. Areas of the skin exposed to the sun are fragile and easily damaged. Exposed skin may develop redness, blistering, infections, scarring, changes in pigmentation, and increased hair growth. Cutaneous porphyrias include congenital erythropoietic porphyria, erythropoietic protoporphyria, hepatoerythropoietic porphyria, and porphyria cutanea tarda.
Other types of porphyria (called acute porphyrias) mostly affect the nervous system. Appearing quickly and lasting from days to weeks, acute signs and symptoms include abdominal pain, vomiting, constipation, and diarrhea. During an attack, a person may also experience muscle weakness, seizures, fever, loss of sensation, and mental changes such as anxiety and hallucinations. These symptoms can be life-threatening in rare cases, especially if the muscles that control breathing become paralyzed. Acute porphyrias include acute intermittent porphyria and ALAD deficiency porphyria. Two other forms of porphyria, hereditary coproporphyria and variegate porphyria, have a combination of acute symptoms and symptoms that affect the skin.
Additional medical problems associated with some types of porphyria include a low number of red blood cells (anemia), enlargement of the spleen, abnormal liver function, and an increased risk of developing liver cancer.
Some people with the genetic changes that cause porphyria, particularly the acute forms of porphyria, never experience any features of this condition. Environmental factors can strongly influence the occurrence and severity of signs and symptoms in some types of porphyria. Alcohol, smoking, certain drugs, hormones, exposure to sunlight, other illnesses, stress, and dieting or periods without food (fasting) can all trigger the signs and symptoms of these disorders.
How common is porphyria?
The exact prevalence of this condition is unknown, but probably ranges from 1 in 500 to 50,000 people worldwide. Overall, porphyria cutanea tarda is the most common type of the disease, affecting 1 to 2 in 100,000 people. For some forms of porphyria, the incidence is uncertain because many people with a gene mutation never experience signs or symptoms.
Acute intermittent porphyria is the most common form of acute porphyria in most countries. It occurs most frequently in northern European countries, particularly Sweden, and in the United Kingdom. Another form of the disorder, hereditary coproporphyria, has been reported mostly in Europe and North America.
Variegate porphyria is most common in the Afrikaner (white) population of South Africa; about 3 in 1,000 people in this population are diagnosed each year. This form of the disorder occurs much less frequently in other parts of the world.