What is Porphyria Cutanea Tarda (PCT)
Porphyria cutanea tarda (PCT) is the most common type of porphyria, with a prevalence of approximately 1 case for every 20,000 people. PCT is caused by low levels of the enzyme uroporphyrinogen decarboxylase (UROD), the fifth step in heme production. There are two types of PCT, one is inherited and called Familial PCT, and the other is not inherited and called Sporadic PCT. The sporadic type is more common. Developing PCT symptoms, of either type, requires other factors to be present causing the activity of this enzyme to drop to less than 20% of normal. The organ most affected in people with PCT is the liver. Some of these other risk factors include; excessive alcohol use, smoking, use of oral estrogens (birth control pills, hormone replacement therapy, etc.), hepatitis C infection, HIV (human immunodeficiency virus) infection, and a disease called hemochromatosis which causes iron overload.
Patients with PCT are generally adults that develop skin blisters on sun-exposed areas, such as the back of the hands and face and. The skin may also become fragile and/or peel after minor bumping or injury. People with PCT can also have increased hair growth, as well as darkening and thickening of the skin. Acute attacks that are seen in patients with AIP do NOT occur in patients with PCT.
Abnormal liver function tests can be seen in patients with PCT, but they are usually mild. PCT is often associated with hepatitis C infection, which also causes liver complications. However, liver tests are generally abnormal even in PCT patients without hepatitis C infection. Progression to cirrhosis and even liver cancer has been reported in some patients.
How is Porphyria Cutanea Tarda Diagnosed?
There are two types of testing; biochemical- meaning looking for “biomarkers” in the blood or urine, or genetic- meaning looking at the sequence of the UROD gene to see where the mutation is.
Biochemical: To diagnose PCT, measurements of total porphyrins in the urine or blood should be done at a reference laboratory. These levels are generally very high in people with PCT.
Genetic: A blood sample is used to make DNA to look at a person’s genes and by doing this it is possible to see if their genes have changes that can cause disease, called mutations. The gene that causes the familial form of PCT is called UROD. Genetic testing is recommended for all patients with PCT in addition to biochemical testing to help establish the type of PCT, sporadic versus familial form.
If a patient has a mutation, their immediate family members should be tested for that same mutation; including their parents, siblings, and children. This will allow all family members to receive appropriate counseling even though many people with a mutation in the UROD gene will not have symptoms of PCT.
What are treatments for Porphyria Cutanea Tarda?
Treatment and management are the same for both types of PCT. They can be treated either with regularly scheduled phlebotomies (like giving blood to a blood bank), or with a low dose of the drug hydroxychloroquine, a medication normally given for malaria. In addition, patients should be tested to see if they have any of the infections listed above and treated accordingly. Other susceptible factors including alcohol use, smoking, estrogen exposure should be avoided. PCT is the most treatable of the porphyrias; however, some patients can have relapse of symptoms after completing treatment. Treatment is the same for recurrences.
How is Porphyria Cutanea Tarda Inherited?
As mentioned above, only the familial form of PCT can be inherited, and even in this form patients with PCT may not have any family members with symptoms. Familial PCT is an autosomal dominant condition. Autosomal means that the defect is not on the chromosomes that determine sex, and dominant means that you only need to inherit one mutated gene to manifest the disease. The gene responsible for familial PCT is called UROD.
Genes are inherited randomly, so a parent has an equal chance of passing on either copy of each gene. Since most Familial PCT patients have one mutated copy and one normal copy, this means that each of their children will have a 50% chance of inheriting the mutated copy and 50% chance of inheriting the working copy.