xeroderma pigmentosum

xeroderma pig·men·to·sum -.pig-mən-'tō-səm, -.men- n a genetic condition inherited as a recessive autosomal trait that is caused by a defect in mechanisms that repair DNA mutations (as those caused by ultraviolet light) and is characterized by the development of pigment abnormalities and multiple skin cancers in body areas exposed to the sun abbr. XP

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a rare, autosomal recessive, pigmentary and atrophic condition characterized by extreme cutaneous photosensitivity to ultraviolet radiation, as a result of defects in mechanisms of repair of ultraviolet-damaged DNA. It begins in childhood with senile changes in sun-exposed skin, including excessive freckling, telangiectases, keratoses, papillomas, and increased risk of all major types of skin cancer; there are also ocular disorders, including photophobia, lacrimation, keratitis, opacities, and tumors of the lid and cornea. Some patients have mental retardation, areflexia, or other neurological disorders. Multiple complementation groups exist, representing various mutations interfering with different proteins in the global genome repair subpathway of nucleotide excision repair; a variant form (xeroderma pigmentosum variant) is instead defective in a DNA polymerase important in postreplication repair of damaged DNA.

Xeroderma pigmentosum, showing atrophic changes and pigment disturbances.