What is porphyria?
The porphyrias are a group of uncommon diseases that produce signs and symptoms related to the skin, the nervous system, or both. They are caused by the accumulation of porphyrins within the body to unusually high levels. In all, there are seven types of porphyria.
Under normal conditions, porphyrins are made by the body in small amounts during the synthesis of heme. Heme is an essential component of hemoglobin, which is responsible for transporting oxygen through our bodies. It is produced in a sequence of chemical reactions, each one under the control of a specific enzyme. If one of these enzymes is defective, there is a buildup of porphyrins or their precursors, which may accumulate to toxic levels. Each porphyria is caused by deficiency of a specific enzyme in the pathway.
Porphyria cutanea tarda. The most common form of porphyria in the U.S. and elsewhere in the world is called porphyria cutanea tarda (PCT). PCT does not usually occur until middle age, and it affects the skin in sun-exposed areas, causing fluid-filled blisters to develop. Over time, the skin becomes scarred, brown, blotchy, and fragile. Sometimes excess hair grows in the affected areas. Most cases of PCT are sporadic, but the disease also can run in families. Even in cases where it appears to be inherited from a parent, another factor is usually required before it causes symptoms. The most common factor is excessive alcohol consumption, but the presence of other diseases such as hemochromatosis and hepatitis C may trigger PCT symptoms.
Acute intermittent porphyria. The next most common form of porphyria is acute intermittent porphyria (AIP). AIP causes only neurological symptoms and does not affect the skin. AIP is a hereditary disorder, but many people who inherit the gene for AIP never get any symptoms. AIP virtually never appears prior to puberty. Affected people get attacks that develop over hours or days and last for days or weeks if untreated.
The most common symptom is pain in the abdomen (often severe), but the pain may affect other areas of the body as well. Muscle weakness of the arms and legs may occur and, in severe cases, weakness of the breathing muscles may require the person to be placed on a ventilator. A variety of other symptoms may occur, depending upon which parts of the nervous system are affected. These include areas of reduced or altered sensation, confusion, seizures, palpitations, high blood pressure, and constipation or diarrhea. Attacks of AIP are often precipitated by drugs, hormones, starvation or crash diets, and the stress caused by infections, surgery, accidents or even psychological stress.
Erythropoietic protoporphyria. The third most common form of porphyria is erythropoietic protoporphyria (EPP). EPP is also inherited, and signs and symptoms usually start in childhood or adolescence. Children with EPP are unusually sensitive to the sun and develop itching, burning pain, redness and swelling in sun-exposed skin within minutes of sun exposure. Over time, the skin may become thickened and waxy in appearance, but permanent spots and scarring are unusual. A small number of affected children also develop gallstones and liver disease, which in some cases can be very serious.
Other forms of porphyria are very rare. Variegate porphyria (VP - more common in Caucasian people of South African ancestry) and hereditary coproporphyria (HCP) can cause neurological symptoms like AIP and skin symptoms like PCT. Most affected persons get either neurological or skin symptoms, but a few unlucky persons get both. Both of these diseases are inherited as autosomal dominant conditions like AIP. There are several even more rare forms of porphyria that cause some combination of the symptoms described above, sometimes in a more severe manner.