XPA and xeroderma pigmentosum: New insight into this question has recently been provided by a study characterizing mutation patterns in skin cancers arising in patients with Xeroderma Pigmentosum (XP).[34] XP patients are extremely sensitive to the damaging effects of UV exposure and especially prone to skin cancers due to an inherited genetic deficiency in one of eight XP genes.[27, 42, 43] Seven of these (XPA to XPG) encode proteins involved in NER, rendering the cells in XP patients unable to efficiently repair UV photoproducts.