The XP (Xeroderma Pigmentosum) family is made up of seven genes, XPA-XPG, involved in nucleotide excision repair (ER). Mutations can result in XP, an autosomal recessive genetic disorder characterized by extreme sensitivity to ultraviolet light and a predisposition to skin cancer. XP variant (XPV) is a form of XP caused by mutation in the DNA polymerase eta (POLH) gene.