Congenital erythropoietic porphyria (CEP), also called Günther’s disease after the doctor who first described it, is the rarest of the porphyrias. It is estimated that about 1 in every 2-3 million people are affected by CEP, which affects males and females equally, and occurs in all skin types.
The word ‘congenital’ means a condition that exists at birth and often before birth, or that develops during the first month of life; ‘erythropoietic’ means associated with red blood cells and their formation.
The porphyrias are a group of inherited disorders in which there is abnormally increased production of substances in the body called porphyrins. Porphyrins are very important as they form haemoglobin that carries oxygen around the body in the red blood cells. The production of haemoglobin involves a chain of reactions in which one porphyrin is converted to another. If there is a block in the chain of reactions, there will be a build-up in the body of a specific porphyrin depending on where the block occurs. Porphyrins in high concentration are damaging to tissues. The problems caused by the different porphyrias relate to the particular porphyrin that accumulates. In the case of CEP, there is a build up of one of these porphyrins called porphyrinogen in the bone marrow, blood and urine and this leads to the symptoms and signs of CEP.
What causes CEP?
An enzyme is a protein that helps to convert one chemical substance into another. In CEP, there is a shortage of one particular enzyme (uroporphyrinogen III synthase), which normally helps to convert porphyrinogen into uroporphyrinogen III that is essential to form haemoglobin in red blood cells. As a result of this enzyme deficiency, porphyrinogen levels build up in the blood. As blood passes through the skin, the porphyrinogen absorbs the energy from sunlight and this sets off a chemical reaction that can damage surrounding tissues. The light that porphyrinogen absorbs is different from that which causes ordinary sunburn. Usually sunburn is caused by the shorter wavelengths of ultraviolet light (UVB), but in CEP the skin is more sensitive to visible light and to longer ultraviolet wavelengths (UVA).
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