Overview of Porphyria
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 the key component of several important proteins in the body. One of the proteins is hemoglobin, which enables red blood cells to carry oxygen. Heme is also an important part of certain enzymes made by the liver.
Heme is produced in the bone marrow and liver through a complex process regulated by eight different enzymes. The enzymes work one after another in separate steps that take the starting compound through several different intermediate compounds (heme precursors, also called porphyrins), finally producing heme. If there is a deficiency in one of these enzymes, certain heme precursors may accumulate. They may accumulate in the bone marrow or liver, appear in excess in the blood, and get excreted in the urine or stool. The accumulated heme precursors cause symptoms. The specific heme precursors that accumulate and the symptoms that develop depend on which enzyme is deficient.
Porphyrias are a number of different disorders, each caused by a deficiency in one of the heme production enzymes. Each enzyme deficiency is caused by damage to the gene (a mutation) responsible for the production of the enzyme in question. The damaged gene is almost always inherited from one of the parents or, rarely, both.
Porphyrias are commonly divided into two types:
Acute porphyrias cause intermittent attacks of abdominal, mental, and neurologic symptoms. These attacks are typically triggered by prescription drugs (including oral contraceptives), alcohol, and other factors such as fasting, infections, or stress.
The most common acute porphyria is
Other acute porphyrias include
Some acute porphyrias (variegate porphyria and hereditary coproporphyria) also cause skin (cutaneous) symptoms.
Cutaneous porphyrias cause symptoms involving the skin after the skin is exposed to sunlight. In these porphyrias, certain porphyrins are deposited in the skin. When exposed to light and oxygen, these porphyrins generate a charged, unstable form of oxygen capable of damaging the skin.
Some cutaneous porphyrias cause symptoms that tend to be continuous or intermittent. These porphyrias include
Porphyria cutanea tarda, the most common cutaneous porphyria
Congenital erythropoietic porphyria
Hepatoerythropoietic porphyria (extremely rare)
People are often unaware of the connection between their symptoms and sun exposure. Their skin becomes fragile and blistered, generally on sun-exposed areas (such as the face, neck, hands, and forearms) or on damaged skin. Identical skin symptoms are also caused by two of the acute porphyrias (variegate porphyria and hereditary coproporphyria).
Other cutaneous porphyrias cause symptoms more immediately after a sun exposure. These porphyrias are
People develop a nonblistering, burning pain within minutes or hours after sun exposure. The pain can last for hours. The skin often has no change in appearance, but swelling and redness may occur.
Doctors diagnose porphyrias by measuring porphyrins and precursors in the urine. Several diseases unrelated to porphyrias, such as blood disorders, liver disorders, and exposures to toxins such as alcohol, benzene, and lead, may increase the amount of urine porphyrins. This phenomenon is described as secondary porphyrinuria.