, 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
Basalioma s and other skin
Malignancies at a young age. In severe cases, it is necessary to avoid sunlight.
There are eight types of xeroderma pigmentosum:
- Dominant Type ()
- Type A, I, XPA, Classical Form ()
- Type B, II, XPB ()
- Type C, III, XPC ()
- Type D, IV, XPD ()
- Type E, V, XPE ()
- Type F, VI, XPF ()
- Type G, VII, XPG ()
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 Pair s from the opposing strand ("nucleotide excision repair").
Enzyme s 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.
The most important part of managing the condition is reducing exposure to the sun.
The number of .) Existing
Keratoses can be treated using
Cryotherapy or
Fluorouracil . (
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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 '''', 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 .
- XP Society
- XP Family Support Group
- Emedicine
- [http://www.shadeshort.com Web Site of a Short Film about an Xeroderma pigmentosum (XP) Patient. Film is directed by Kimberly Williams Paisley]
- [http://www.lamberspublications.com/downloads/Two%20Families%20Fight%20Against%20Rare%20Disease.pdf Article About the Xeroderma pigmentosum (XP) Society by William Lambers (pdf format)]
