What is erythropoietic protoporphyria?
Erythropoietic protoporphyria (EPP) is one of a group of genetic diseases called the porphyrias. EPP is due to an inherited deficiency of the enzyme ferrochelatase. Reduced activity of this enzyme causes a build-up of the chemical protoporphyrin in the skin; resulting in photosensitivity i.e. the skin is damaged by light. Abnormally high levels of protoporphyrin can rarely cause liver disease.
Who gets EPP?
EPP is thought to be due to a compound mutation in the gene encoding ferrochelatase (FECH; 612386) found on chromosome 18q21. Inheritance can be autosomal dominant with incomplete penetrance or autosomal recessive. Both males and females are equally affected. People of all races may get EPP.
What are the clinical features of EPP?
Cutaneous symptoms and signs of EPP
First symptoms usually appear in infancy or early childhood and present as an uncomfortable or painful burning sensation of the skin after sun exposure. It occurs most often on the tops of the hands and feet, face and ears. In most cases visible changes to the skin are mild. The affected skin may become red and swollen and blistered. Later there are pitted scars and sometimes crusty thickened skin, particularly over the cheeks, nose and knuckles of the hands.
Liver disease in EPP
People with EPP-induced liver disease often have mild changes in liver blood tests. About 10% develop more severe liver disease, presenting with malaise, pain under the ribs on the right, jaundice and increasing photosensitivity.
Gallstones are common in patients with EPP.
How is EPP diagnosed?
The red blood cells may be noted to fluoresce by ultraviolet microscopy. Diagnosis is confirmed by finding increased levels of protoporphyrin in the blood and reduced ferrochelatase enzyme activity. The severity of the biochemical findings is variable.
Biopsy can also be useful, as EPP has some characteristic features on histopathology.
What treatment is available for EPP?
Lifelong photosensitivity is the major problem for EPP uncomplicated by liver disease.
- Avoid unnecessary exposure to sunlight and wear protective clothing and wide-brimmed hats. Consider tinting windows.
- Other strong sources of light may also cause symptoms, including fluorescent and halogen lights. Protect the skin from exposure to operating lamps during a surgical procedure.
- Sunscreens may be helpful, especially formulations containing zinc oxide or titanium dioxide that reflect visible light.
- Oral beta-carotene (a food precursor of vitamin A found naturally in tomatoes and carrots) is thought to help reduce photosensitivity in some people. The dose for children is 30 to 150mg per day (1 to 5, 30-mg capsules) and for adults it is 30 to 300mg (1 to 10, 30-mg capsules).
- Cysteine 500mg twice daily reduces photosensitivity
- Colestyramine reduces photosensitivity and hepatic protoporphyrin content.
- Narrowband UVB phototherapy increases melanin content and induces skin thickening so may reduce sun sensitivity.
- Afamelanotide, an α-melanocyte stimulating hormone given by subcutaneous implantation, has been reported to provide good clinical effectiveness and safety in EPP. It is approved under exceptional circumstances by the European Medicines Agency for treatment of EPP (October 2014).
Patients with EPP that also have liver disease require specialist medical treatment and possibly liver transplantation.
Another more serious condition, congenital erythropoietic porphyria, is now curable by stem cell transfusion, paving hope for the future, but there is not yet a cure available for EPP.