Porphyria Cutanea Tarda
What is porphyria cutanea tarda?
Porphyria cutanea tarda is the most common type of porphyria. The disorder results from low levels of the enzyme responsible for the fifth step in haeme production. Haeme is a vital molecule for all of the body's organs. It is a component of haemoglobin, the molecule that carries oxygen in the blood.
Porphyria cutanea tarda is a subtype of porphyria.
When signs and symptoms occur, they usually begin in adulthood and result from the skin becoming overly sensitive to sunlight. Areas of skin exposed to the sun develop severe blistering, scarring, changes in pigmentation, and increased hair growth. Exposed skin becomes fragile and is easily damaged. People with porphyria cutanea tarda also have increased iron levels in the liver. They face a higher risk of developing abnormal liver function and liver cancer. The signs and symptoms of this condition are triggered by nongenetic factors such as alcohol abuse, excess iron, certain hormones, and viral infections.
How common is porphyria cutanea tarda?
This type of porphyria occurs in an estimated 1 in 25,000 people, including both inherited and sporadic (noninherited) cases. An estimated 80 percent of porphyria cutanea tarda cases are sporadic. The exact frequency is not clear because many people with the condition never experience symptoms.
What genes are related to porphyria cutanea tarda?
Mutations in the UROD gene cause porphyria cutanea tarda.
Variations of the HFE gene increase the risk of developing porphyria cutanea tarda.
Inherited mutations in the UROD gene cause about 20 percent of cases. (The other 80 percent of cases do not have mutations in UROD, and are classified as sporadic.) UROD makes an enzyme called uroporphyrinogen decarboxylase, which is critical to the chemical process that leads to haeme production. The activity of this enzyme is usually reduced by 50 percent in all tissues in people with the inherited form of the condition. Nongenetic factors such as alcohol abuse, excess iron, and others listed above can increase the demand for haeme and the enzymes required to make haeme. The combination of this increased demand and reduced activity of uroporphyrinogen decarboxylase disrupts haeme production and allows byproducts of the process to accumulate in the body, triggering the signs and symptoms of porphyria cutanea tarda.
The HFE gene makes a protein that helps cells regulate the absorption of iron from the digestive tract and into the cells of the body. Certain mutations in the HFE gene cause haemochromatosis (an iron overload disorder). People who have these mutations are also at an increased risk of developing porphyria cutanea tarda.
How do people inherit porphyria cutanea tarda?
Porphyria cutanea tarda is inherited in an autosomal dominant pattern, which means one copy of the altered gene is sufficient to decrease enzyme activity and cause the signs and symptoms of the disorder.
What other names do people use for porphyria cutanea tarda?
* Familial PCT
* PCT
* Porphyria cutanea tarda symptomatica
* Porphyria, hepatocutaneous type
* UROD deficiency
* Uroporphyrinogen decarboxylase deficiency
