Porphyria Cutanea Tarda is a rare enzyme deficiency that causes sensitivity to sunlight and skin blistering. It is often asymptomatic and caused by an abnormally high demand for heme. Treatment involves avoiding triggers and relieving symptoms.
Porphyria Cutanea Tarda is the most common type of the group of enzyme deficiencies classified as porphyrias. It is caused by insufficient levels of uroporphyrinogen III decarboxylase, or UROD, which codes for the fifth enzyme required in the production of heme, an important molecule in human physiology. Heme is part of the hemoglobin molecule that carries oxygen through the blood. Porphyria Cutanea Tarda is characterized by sensitivity to sunlight, which causes the skin to blister when exposed to too much sun.
Although porphyria tatata occurs more often than other types of porphyria, it is very rare, affecting only one in 25,000 people. About 80% of cases are sporadic or non-inherited. Furthermore, the disorder is often asymptomatic.
Blisters caused by photosensitivity in patients with this disease most often affect the face, lower legs and forearms. They heal slowly and often scar. In some patients, photosensitivity manifests itself not as blisters but as hyperpigmentation, or darkening of the skin, or as hypertrichosis, abnormal hair growth, often on the face. In patients who have not inherited the disease, liver inflammation and scarring are common.
Sporadic PCT differs from the hereditary disease in that the UROD gene does not show mutations. Rather, the body has an abnormally high demand for heme, as well as for enzymes involved in heme production. Risk factors for PCT include alcoholism, excessive iron or estrogen, hepatitis C infection, cancer, and mutations in the hemochromatosis protein or the HFE gene. These risk factors can also exacerbate the disease in people with an inherited mutation in the UROD gene.
Hereditary or familial PCT is sometimes referred to as type I, while the sporadic variety is classified as type II. The rarest subtype, type III, shows a familial pattern in that more than one family member is affected, but does not involve a mutation in the UROD gene. Mutations of the HFE gene may be the genetic factor in such a case.
PPC is usually diagnosed through a urine test that reveals high levels of uroporphyrinogen. If laboratory tests reveal no signs of the disease, but the patient has symptoms, the diagnosis is often pseudoporphyria. This condition isn’t well understood, but it can be caused by an allergic reaction to medications or excessive exposure to long-wave ultraviolet (UVA) light, such as in a tanning booth.
Porphyria Cutanea Tarda is a chronic condition with no known cure, so treatment is aimed at relieving symptoms. Patients are advised to avoid alcohol, iron-rich foods, sunlight, and estrogen. Treatment may also involve treating hepatitis C if needed, bloodletting to reduce iron in the body, and chloroquine medications, also used to treat and prevent malaria.
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