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Xeroderma pigmentosum, or XP, is a genetic disorder of DNA repair in which the body's normal ability to fix mutations caused by ultraviolet (UV) light is disabled. This leads to multiple basaliomas and other skin malignancies at a young age. In severe cases, it is necessary to avoid sunlight.
Causes
Damage to DNA in epidermal cells occurs during exposure to UV light. High energy UV light causes 'nicks' in the DNA structure by disrupting base pairing. Cellular enzymes repair the damaged segment and replace the resulting gap in the DNA with the correct base pairs from the opposing strand ("nucleotide excision repair"). Enzymes called DNA polymerase and ligase complete this function. The most common defect in xeroderma pigmentosum is a genetic defect whereby nucleotide excision repair enzymes are defective and no longer recognize correct base pairing. Over a period of time, these mismatches build up in affected tissues. Eventually, there are enough mistakes in the DNA to remove normal proto oncogene function (such as p53), and cancer results.
Treatment
The most important part of managing the condition is reducing exposure to the sun.
The number of keratoses can be reduced with Isotretinoin ([1]) (though there are significant side-effects.) Existing keratoses can be treated using cryotherapy or fluorouracil. ([2]).
In popular culture
A notable fictional character who sufferers XP is Christopher Snow featured in the novels Fear Nothing and Seize the Night by Dean R. Koontz.
The television miniseries Ultraviolet includes a character, Oliver, who has XP.
During the second season of ABC's Extreme Makeover: Home Edition, the Pope family was selected for an Extreme Makeover as their daughter, Shelly, suffers from XP. Later, ABC and the Popes teamed Walt Disney World to give XP children a special treat - Walt Disney World made a special night-time opening (midnight to 4 AM) so XP children could spend time at the popular park. Footage from this event aired as part of an Extreme Makeover holiday special on December 11, 2005.
In the 2001 film The Others, the two main child characters have XP.
The following information is referenced from en.wikipedia.org/wiki/Xeroderma_pigmentosum
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