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At a glance

This is a rare genetically transmitted disorder characterized by an onset during childhood, between the age of 3 and 6. Affected individuals present with acute photosensitivity of the skin, where within few minutes of exposure to the sun, a severe pruritus, erythema, swelling, and pain are manifested. Longer periods of sun exposure can produce similar skin reaction as second-degree burn. After repetitive sun exposure, lichenification, hypopigmentation, hyperpigmentation, and scarring of the skin is usually observed. The severity of the symptoms and the pain (which can be very intense) can vary considerably amongst patients. It is the result of accumulation of protoporphyrins (porphyrin-heme) in erythrocytes, plasma, skin, and liver due to a reduction in the enzymatic activity of ferrochelatase.

Synonyms

Congenital Erythropoietic Protoporphyria; Erythrohepatic Protoporphyria; Heme Synthetase Deficiency; Protoporphyria.

History

Erythropoietic protoporphyria was first described in 1953 by Wilhem Kosenow, a German Physician, and Alfred E. Treibs (1899-1983), a German Organic Chemist who won the Nobel Prize of Chemistry for his discovery of porphyrin. I. Magnus and colleagues provided a complete description of the disease in a publication in 1961 while working at the St-John’s Institute of Dermatology in London, England.

Incidence

This medical condition is known to be prevalent around the world. The prevalence is estimated between 1:75,000 and 1:200,000 in the general population. It is possible that this evaluation will increase with the better understanding of the disease and diagnosis. It is estimated that 5,000 to 10,000 individuals are affected with erythropoietic protoporphyria (EPP) worldwide. It is considered the most common form of porphyria in children. The prevalence in Sweden is reported at 1:180,000.

Genetic inheritance

Mode of inheritance in erythropoietic protoporphyria (EPP) is complex and can be either autosomal dominant with low clinical penetrance, as is in most cases, or autosomal recessive. The gene for human ferrochelatase (FECH) has been mapped to 18q21.3. A clinically similar form of porphyria was identified in 2008 as an X-Linked dominant inheritance.

Pathophysiology

The basic defect affects the mitochondrial enzyme ferrochelatase. Deficiency of FECH results in increased release of protoporphyrin, which binds to albumin in plasma and subsequently undergoes hepatic extraction. The nature of the defect on the molecular level is uncertain. Protoporphyrin diffuses from the erythrocytes into the plasma to be bound to albumin and the heme-binding protein hemopexin. Protoporphyrin deposits in the skin are responsible for the extreme photosensitivity. The excess porphyrin comes from both erythropoietic and hepatic tissues. Ultraviolet light (wavelengths < 400 nm) photoactivates protoporphyrins in the plasma and erythrocytes when blood circulates in the dermal vessel, leading to cause tissue damage by release of free oxygen radicals, and therefore photosensitivity.

Diagnosis

Fluorescence of a significant proportion of red blood cells is detectable by ultraviolet microscopy because of the presence of free erythrocyte protoporphyrin. A reduction in the activity of the enzyme ferrochelatase (also called heme synthase, a mitochondrial enzyme responsible for the final step in the ...

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