Xeroderma Pigmentosum (XP) is a rare genetic disorder that may cause extreme sensitivity to the sun's ultraviolet rays. Unless patients with XP are protected from sunlight, their skin and eyes may be severely damaged. This damage may lead to cancers of the skin and eye. XP has been identified in people of every genetic group all over the world. There are about 100 confirmed cases in the UK.
Ultraviolet light damages the DNA in cells and disrupts normal cell functioning. DNA (deoxyribonucleic acid) within our genes contains all the coded information needed to direct cell functions.
Two factors combine to cause the abnormalities in XP. Firstly, a person inherits traits from each parent which, when combined, lead to an unusual sensitivity to damaging effects of ultraviolet light. Secondly, exposure to the sun, which contains ultraviolet light, leads to changes in the skin and eyes.
Damaged DNA is repaired by the DNA repair system. But the DNA repair systems of eople with XP do not function properly. As a result, un-repaired DNA damage builds and causes cancerous cell changes or cell death.
Many people with XP get unusually severe sunburn after a short period of sun exposure. The sunburn may last much longer than expected, perhaps for several weeks. This type of sunburn will usually occur during a child's first exposure, and it may be a clue to the diagnosis of XP. However, some people with XP do not burn more easily and the disease will be undetected until unusual skin changes appear over time.
Most patients with XP develop freckles at an early age. Continued sun exposure will lead to further changes in the skin, including irregular dark spots, thin skin, excessive dryness, rough-surfaced growths and skin cancers. These skin changes will resemble those of elderly people who have spent many years in the sun. In people with XP, the changes caused by sun damage often begin in infancy and almost always before the age of 20.
The eyes of a person with XP are often painfully sensitive to the sun and may easily become irritated, bloodshot and clouded. Non-cancerous and cancerous growths on the eyes may occur.
There is no cure for XP, but much can be done to prevent and treat some of the problems it causes:
Protection from ultraviolet light, by a combination of physical and chemical means. These include sun avoidance, shade, clothing (including hats), optical filtration and sunscreens.
Frequent skin and eye examinations.
Prompt removal of cancerous tissue.
Neurological examination in some cases.
Text extracted from: 'Understanding Xeroderma Pigmentosum' published by US Department of Health & Human Services (by permission).
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