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Xeroderma pigmentosum

Xeroderma pigmentosum is a genetic disorder of DNA repair in which the body's normal ability to fix mutations caused by UV light is disabled. This leads to multiple basaliomas and other skin malignancies at a young age. Therefore in very severe cases it is necessary to avoid all sunlight. more...

X-linked adrenal...
X-linked ichthyosis
X-linked severe combined...
Xeroderma pigmentosum
XX male syndrome
XY Female


There are eight types.

  • Dominant Type (OMIM 194400)
  • Type A, I, XPA, Classical Form (OMIM 278700)
  • Type B, II, XPB (OMIM 133510)
  • Type C, III, XPC (OMIM 278720)
  • Type D, IV, XPD (OMIM 278730)
  • Type E, V, XPE (OMIM 278740)
  • Type F, VI, XPF (OMIM 278760)
  • Type G, VII, XPG (OMIM 278780)


Damage to DNA is a frequent occurrence, and the body has mechanisms to fix it by cutting out the damaged segment and replacing the resulting gap in the DNA with the correct base pairs from the opposing strand ("nucleotide excision repair"). The enzymes DNA polymerase and ligase fulfil this role. The most common defect in xeroderma pigmentosum is an inherited defect that alters the nucleotide excision repair enzymes, and hinders their functionality. Therefore, DNA damage is not readily fixed.


The most important part of managing the condition is reducing exposure to the sun.

The number of keratoses can be reduced with Isotretinoin () (though there are significant side-effects.) Existing keratoses can be treated using cryotherapy or fluorouracil. ().

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 film The Others features characters who suffer from XP.

Late in 2005, ABC's Extreme Makeover: Home Edition gave kids with XP a once in a lifetime opportunity, a night at Disney World. Disney World opened for a night just for kids with XP. Footage from this event aired as part of an Extreme Makeover holiday special on December 11, 2005.


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Gene finding gives clues to DNA repair - defective DNA-repair genes that cause xeroderma pigmentosum identified
From Science News, 5/15/93 by Daniel Pendick

In the mid-1960s, as a postdoctoral student, James E. Cleaver thought a lot about the genetics of radiation sensitivity in cells. One day, he read a newspaper report about xeroderma pigmentosum (XP), a rare disease that renders people ultrasensitive to sunlight. Are people with XP, Cleaver wondered, somehow unable to repair the genetic damage caused by exposure to the sun's ultraviolet rays?

"It was the kind of [hypothesis] that if I was right, I had a living out of it, and if I was wrong, nobody would have noticed," recalls Cleaver, now a geneticist at the University of California, San Francisco. He proposed the connection between XP and faulty DNA repair and proved it. Now, 25 years after Cleaver's initial report, two teams of scientists have independently flushed out the defective gene that causes a particularly severe form of the disease, XP-G. The researchers report their work in the May 13 NATURE.

Defects in this gene, and in seven others linked to different forms of XP, interfere with normal DNA repair. Usually, these genes serve as a blueprint for enzymes that recognize and cut out sections of cells' damaged DNA. Other cell mechanisms clear away the wreckage and replace the damaged sections of genetic code.

People with XP suffer various symptoms, depending on which defective gene they carry. In people with XP-A, for example, DNA repair is almost completely knocked out, causing brain deterioration and many skin tumors. In contrast, people with less severe forms of the disease can avoid many of its serious symptoms by simply avoiding exposure to sunlight. About one person in 100,000 has the disease, says Richard D. Wood, a biochemist at Clare Hall Laboratories in South Mimms, England.

DNA repair, the researchers emphasize, has proved one of the most fundamental aspects of cell life. It counteracts the constant assault on cells by chemicals, radiation, and other environmental causes of genetic damage. Unfortunately for people with XP, "mutations in these [repair] genes can cause important developmental defects, such as mental retardation, immune-system diseases, and sensitivity to cancer-producing compounds," explains Stanford University molecular biologist Philip C. Hanawalt.

In one of the new studies, Wood and graduate student Anne O'Donovan found that extracts from normal cells, containing functioning repair enzymes, turned DNA repair back on in XP-G cell extracts. The scientists then isolated the particular enzyme that reversed the defect and mapped its gene to chromosome 13.

A team of researchers at the University Medical Center in Geneva, Switzerland, came upon the XP-G gene while studying an entirely different disease, systemic lupus erythematosus (SLE). Searching for a protein linked to SLE, these researchers by chance discovered a gene capable of restoring normal DNA repair function to XP-G cells, report Daniel Scherly and colleagues.

These two reports herald the final stage of a 25-year effort to identify and copy, or clone, the defective DNA-repair genes that cause XP, Wood explains. To date, five genes have been isolated. By next year, Wood predicts, investigators will find the remaining three. At that point, research will shift toward puzzling out the function of each repair gene.

Cancer treatment could benefit from increased intimacy with DNA-repair biology, says Wood. Typically, cancer drugs kill tumor cells by attacking their DNA. If researchers could find a way to selectively shut down tumor cells' repair machinery, cancer drugs could kill tumor cells much faster than they kill normal cells, he says.

COPYRIGHT 1993 Science Service, Inc.
COPYRIGHT 2004 Gale Group

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