Erythropoietic protoporphyria & X-linked dominant protoporphyria

Erythropoietic protoporphyria & X-linked dominant protoporphyria

What are erythropoietic protoporphyrias?

The word ‘erythropoietic’ means associated with red blood cells (‘erythro-’) and their formation (‘-poietic’). The porphyrias are a group of uncommon disorders caused by something going wrong with the production of chemicals known as porphyrins. These chemicals are the building blocks of haem, which, when combined with a protein (globin), forms haemoglobin, the material in red blood cells that carries oxygen round the body. In the case of EPP and XLDPP, there is a build-up of one of these porphyrins (protoporphyrin IX) in the blood, especially in the red blood cells. This leads to a sensitivity to sunlight.

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What does it look like?

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Main body location

All over / widespread

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Can it appear anywhere?

Yes

What causes EPP and XLDPP?

An enzyme is a protein that helps to convert one chemical substance into another. In EPP, there is a shortage of one particular enzyme, ferrochelatase, which normally helps to convert protoporphyrin into haem by adding iron to it. As a result of this enzyme deficiency, protoporphyrin levels build up in the blood.  In XLDPP, a problem in the ALA-synthase gene causes an increase in activity of this enzyme which causes the protoporphyrin to build up in the blood.

As blood passes through the superficial blood vessels under the skin, the protoporphyrin absorbs the energy from sunlight and this sets off a chemical reaction that can slightly damage surrounding tissues. The nerve endings in the skin interpret this as itching or burning pain, and if the blood vessels are affected, they can leak fluid, causing swelling.

The light that protoporphyrin absorbs is different from that which causes sunburn. Sunburn is caused by the shorter wavelengths of ultraviolet light (UVB), but in EPP the skin is more sensitive to longer ultraviolet wavelengths (UVA) and to visible light.

Are EPP and XLDPP hereditary?

Yes, but there is not always a family history of the condition. Everyone has two copies of the ferrochelatase gene in each cell in their body (one coming from their mother and one from their father). In most families, EPP occurs when an affected individual inherits a gene for a severely underactive ferrochelatase enzyme from one parent, and a less severely affected gene from the other parent. The less severely affected gene is quite common, being present in around 10% of the general population, but it never causes EPP by itself. The overall chance of a patient affected by EPP having an affected child is low. The chance of a patient affected by XLDPP having an affected child is high. On average, 50% of the children of a patient affected by XLDPP will also have XLDPP. This is the main difference between EPP and XLDPP for patients. In other ways, the two conditions cause exactly the same problems for patients.

What are the symptoms of EPP and XLDPP?

The symptoms of EPP and XLDPP are identical and typically start with abnormal sensitivity to sunlight. Exposure to sunlight causes tingling, itching, or burning, which may be associated with redness and swelling. These symptoms usually occur within a few minutes of skin exposure to sunlight, and often take hours or days to resolve. During this time, the skin may feel more sensitive than usual to extremes of temperature. The light producing these changes need not be direct – light reflected off water and sand, or passing through window glass, including car windscreens, can also cause the symptoms.

EPP usually starts in childhood and affects males and females equally. XLDPP also starts in early childhood.  Infants may cry or scream after being taken out into the sunlight; and older children may complain of burning and try to wave their hands in the air or put them into cold water to try to relieve the pain. A very small number of people who have been affected by EPP or XLDPP for many years may develop liver damage. Fortunately, this is rare.

What does EPP and XLDPP look like?

Despite severe discomfort, there may be nothing abnormal to see on the skin.  Sometimes there can be swelling of the skin, initially like a nettle rash. With time, some people develop thickening of the skin over their knuckles, and small scars on sun-exposed skin such as that on the cheeks, nose, and backs of the hands. However, these skin changes show wide variations between different individuals.

How are EPP and XLDPP diagnosed?

The diagnosis is usually suspected from the history of the patient’s symptoms and can be confirmed by a blood test. This measures the amount of protoporphyrin in the blood (plasma protoporphyrin) and in the red blood cells (erythrocyte free protoporphyrin). This test will also usually allow XLDPP and EPP to be distinguished.  Some doctors will also ask for a stool sample to measure the level of protoporphyrin in the faeces. No urine tests are relevant to this condition except to exclude other types of porphyria.

Although it is unlikely that you will develop liver problems as a complication of EPP and XLDPP (this happens in less than 5% of patients), your doctor may monitor the way your liver is working by yearly blood tests. If there is any evidence of deterioration in liver function, there are certain interventions that may help to halt or reverse this. You may also be referred to a liver specialist. There is also an increased risk of developing gallstones in EPP and XLDPP.

As EPP and XLDPP affect the production of haemoglobin, it is not uncommon for people affected by EPP to be slightly anaemic. Your doctor will probably also measure your blood count to make sure that you are not becoming too anaemic.

Can EPP or XLDPP be cured?

At present there is no cure for EPP or XLDPP.

How can EPP and XLDPP be managed?

The aim of most treatments is to give your skin extra protection from sunlight, so that you tolerate sunlight better.

Self-care (What can I do?)

It is sensible to avoid unnecessary exposure to sunlight. Other helpful measures include the wearing of protective clothing and the use of sunscreens:

Medical treatments for EPP and XLDPP include the use of:

Osteoporosis in EPP

Patients with EPP are at risk of thinning of the bones (‘osteoporosis’) developing, not just in older patients but sometimes in patients as young as those in their thirties. This is important because it can lead to some bones breaking fairly easily,

There are two reasons for this. One is a lack of weight bearing exercise because of the difficulty going outside. The second is that most patients with EPP have a low level of vitamin D, because sunshine causes vitamin D to form in the skin. You should make sure that you do enough weight bearing exercise, even in the spring and summer (either outside when it is dark or inside on an exercise machine). The exercise should be weight-bearing i.e. involves walking or running.

You should have your vitamin D level in your blood checked at least once a year. Most patients need vitamin D3 supplements in the long term to keep the vitamin D level high enough. The usual dose that is needed is 1000 Units/day of vitamin D3. Vitamin D3 supplements are widely available from health food shops and chemists.

This information is provided by the British Association of Dermatologists.


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