Learn More - Overview of the Porphyrias
The Cutaneous Porphyrias
Cutaneous porphyrias primarily affect the skin. Areas of skin exposed to the sun become fragile and blistered, which can lead to infection, scarring, changes in skin coloring (pigmentation), and increased hair growth. Cutaneous porphyrias include congenital erythropoietic porphyria, erythropoietic protoporphyria and X-linked protoporphyria, porphyria cutanea tarda, and hepatoerythropoietic porphyria.
Cutaneous Porphyrias: Porphyria Cutanea Tarda (PCT)
What is PCT?
PCT is a deficiency of the enzyme uroporphyrinogen decarboxylase. Cutaneous blisters develop on sun-exposed areas of the skin, such as the hands and face. The skin in these areas may blister or peel after minor trauma. Increased hair growth, as well as darkening and thickening of the skin may also occur. Neurological and abdominal symptoms are not characteristic of PCT.
Liver function abnormalities are common, but are usually mild. PCT is often associated with hepatitis C infection, which also can cause these liver complications. However, liver tests are generally abnormal even in PCT patients without hepatitis C infection. Progression to cirrhosis and even liver cancer occurs in some patients.
Who gets PCT?
Porphyria cutanea tarda (PCT) is the most common type of porphyria, with a prevalence of approximately 1 case for every 10,000 people. PCT develops when the activity of an enzyme involved in synthesis of heme, uroporphyrinogen decarboxylase (URO-decarboxylase), becomes severely deficient (less than 20% of normal activity) in the liver. In most cases of PCT, patients do not have inherited URO-decarboxylase gene mutations and are said to have sporadic (or Type I) PCT (s-PCT) A URO-decarboxylase inhibitor generated only in the liver accounts for the severely deficient enzyme activity in s-PCT. About 20 percent of cases have familial (or Type II) PCT (f -PCT). Such individuals have inherited a URO-decarboxylase gene mutation from one parent, which has reduced the amount of URO-decarboxylase in all tissues from birth. However, to develop PCT symptoms, other factors must be present to further reduce URO-decarboxylase level in the liver to less than 20% of normal. Such f-PCT patients may develop blisters at an early age or have relatives with the disease. Excess iron and multiple other susceptibility factors contribute to the development of PCT. These susceptibility factors include excess use of alcohol, use of estrogens, chronic hepatitis C, smoking, HIV (human immunodeficiency virus) infections, and mutations of the HFE gene which is associated with the disease hemochromatosis in which excess iron accumulates in the liver. Other susceptibility factors exist but are as of yet unidentified.
What causes PCT?
PCT develops when the activity of the enzyme uroporphyrinogen decarboxylase (URO-decarboxylase) becomes severely deficient (less than 20% of normal) in the liver.
How is PCT Diagnosed?
The diagnosis of PCT can be made by finding an abnormally high concentration of porphyrins in urine or plasma. Abnormally high porphyrins in feces may also be observed.
Patients with f-PCT usually have no family history of the disease, but can be recognized by finding half-normal URO-decarboxylase activity in red blood cells, or preferably by DNA studies.
- Also see FAQ: What diagnostic tests are available?
What are treatments for PCT?
PCT, both familial and sporadic, can be treated either with regularly scheduled phlebotomies (removal of blood) to lower the amount of porphyrins in the liver or with a low dose regimen of hydroxychloroquine. In addition, the susceptibility mentioned above (see Who gets PCT?) need to be eliminated. PCT is the most treatable of the porphyrias. Treatment seems to be equally effective in f-PCT and s-PCT. Relapses that occur after the initial treatment can be treated in the same manner as the initial treatment.