What is Xeroderma Pigmentosum?: "Xeroderma Pigmentosum
A rare genetic defect in ultraviolet radiation induced DNA repair mechanisms; characterized by severe sensitivity to all sources of UV radiation (especially sunlight).
XP is categorized in at least eight complementation groups according to the capacity of the body to repair DNA. These groups (i.e., genetic subtypes) are labeled A through G, plus the XP variant: XPV. Groups A, C, D, and Variant make up over 90% of XP cases. Group A, for example, has the lowest level of DNA repair and the most neurological manifestations. "