Porphyria cutanea tarda
Porphyria cutanea tarda
Description, Causes and Risk Factors:
Porphyrias are a group of rare metabolic disorders in which excessive quantities of porphyrins, or their precursors are produced. Porphyrins are complex molecules in the body that combine with iron to produce heme, which is responsible for giving blood its red color. They combine with globin to form hemoglobin. Porphyria is the name of group of disease caused by an excess of porphyrins in the blood. Porphyria cutanea tarda is one of the most common types of porphyria, triggered by a deficiency of an enzyme called uroporphyrinogen decarboxylase (UROD). They reduce activity of UROD results in an overproduction and buildup of the protein uroporphyrinogen in the blood and urine of patients. This results is an abnormal production of heme, a compound found in all body tissue and especially in the liver, bone marrow, and red blood cells.
PCT can be caused or triggered by hemochromatosis (accumulation of iron in the liver), heavy alcohol use, estrogens (oral contraceptives, and prostate cancer treatment), viral infections (HIV and HCV), and possibly smoking. Hepatitis C is the most common infection associated with viral infection. In fact, some studies have found that, in people who have PCT that can be traced to a viral infection, greater than 50% are the result of the hepatitis C virus. An inherited deficiency of UROD (uroporphyrinogen decarboxylase) is responsible for about 20% of cases of PCT.
Familial porphyria cutanea tarda (Type II or inherited) - It comprises 16% to 28% of cases. Urod activity is reduced to half normal in all tissues (erythrocytes and liver) due to reduction in enzyme synthesis or stability. Differentiation between PCT types I and II cannot be solely based on erythrocyte Urod activity, which may be at the lower limit in PCT type II and below the normal interval in PCT type I.
Type III porphyria cutanea tarda - It is biochemically indistinguishable from type I (normal erythrocyte Urod), but it affects more than one family member. It occurs in a small number of patients (<5%). The promoter region and the coding DNA sequence of Urod are normal, suggesting that other loci are involved in its pathogenesis, and these may be genes affecting tissue iron. It is not proven that type III PCT is a distinct form of the disease or if it would be PCT type I with inherited contribution.
Toxic porphyria cutanea tarda - It occurs after the exposure to hexachlorobenzene (HCB) and tetrachlorodibenzo-p-dioxin (TCDD), which diminish hepatic Urod activity.
Sporadic porphyria cutanea tarda (Type I, symptomatic or acquired) - It encompasses 72% to 84% of cases, and the enzyme deficiency is restricted to the liver, with normal erythrocyte Urod activity. There is no family history. The specific enzyme defect is not caused by mutation in the Urod locus; and the cDNA sequences of hepatic, extra-hepatic Urod, as well as the promoter region of the gene are normal.
The number of people who have been diagnosed with PCT is unknown, but it is estimated that about 1 in 50,000 have PCT that can be traced to a viral infection, greater than 50% are the result of hepatitis C virus. An inherited deficiency of UROD responsible for about 20% of cases.
The symptoms of porphyria cutanea tarda are mostly confined to the skin.Skin lesions or blisters are most often seen on thehands, forearms, back of the neck and face and areasexposed to the sun. The skin may become red, blisterand peel after exposure to the sun or minor trauma.Porphyria cutanea tarda can also cause either darkening or lightening ofthe skin, increased facial hair, scarring, alopecia (hairloss), thickening of the skin, itching and prematureaging of the skin. In severe cases calcium may bedeposited in the skin causing non-healing ulcers.
Porphyria cutanea tarda is usually diagnosed by a blood test that measuresporphyrins in the blood, and the diagnosis is confirmedby testing for porphyrins in the urine and feces.
Mutation analysis of genes encoding UROD is considered the criterion standard for diagnosis of familial porphyria cutanea tarda. It is most often available at specialized porphyria research centers and is commercially available in the United States. Molecular analysis for hemochromatosis gene (HFE) mutations may be positive.
A thorough evaluation requires determination of hematologic and iron profiles, including serum ferritin, liver function profile, and screening for hepatitis viruses and the human immunodeficiency virus.
Imaging: Evaluation of the liver for size, iron content, or tumors is indicated in selected cases.
The signs and symptoms of porphyria cutanea tarda can be managed, but there is no cure; however it is one of the easiest of the porphyria conditions to manage and treat. The most common management techniques include:
Avoiding the sun when possible, use sunscreen and protective clothing such as gloves, hats, pants, and long-sleeved shirts when outside.
Low doses of chloroquine or hydroxychloroquine (drugs that are used to treat malaria).
Restriction of foods that contain iron.
Treatment of the underlying disease (HCV) with interferon plus ribavirin has also been found to decrease skin lesions as well as the amount of UROD's found in urine.
Phlebotomies (the removal of blood) to reduce iron in the liver. Phlebotomies are given until the level of serum ferritin is reduced to about 20ng/mL. Phlebotomies can also reduce the porphyrins to normal levels in the blood. Once levels of ferritin and porphyrins have normalized PCT does not usually recur.
NOTE: The above information is for processing purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.
DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.
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