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Xeroderma pigmentosum, or XP, is an autosomal recessive genetic disorder of DNA repair in which the body's normal ability to repair damage caused by ultraviolet (UV) light is deficient. This leads to multiple basaliomas and other skin malignancies at a young age. In severe cases, it is necessary to avoid sunlight completely.
Additional recommended knowledge
Damage to DNA in epidermal cells occurs during exposure to UV light. The absorption of the high energy light leads to the formation of pyrimidine dimers, namely CPDs (Cyclobutane-Pyrimidine-Dimers) and 6-4PP (pyrimidine-6-4-pyrimidone photoproducts). The normal repair process is called nucleotide excision repair. The damage is excised by endonucleases, then the gap is filled by a DNA polymerase and sealed by a ligase. The most common defect in xeroderma pigmentosum is a genetic defect whereby nucleotide excision repair (NER) enzymes are mutated, leading to a reduction in or elimination of NER.
Unrepaired damage can lead to mutations, altering the information of the DNA. If mutations affect important genes, like tumour suppressor genes (e.g. p53) or proto oncogenes then this may lead to cancer. Since in XP patients the frequencies of mutations is much elevated, these patients have a predisposition for cancer.
There are 7 complementation groups, plus one variant form:
Some of the most common symptoms of XP are:
Treatment 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.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Xeroderma_pigmentosum". A list of authors is available in Wikipedia.|