XPA and xeroderma pigmentosum: Mutations in eight different genes have already been identified in XP patients, from which seven (XPA-XPG) are associated with a defect in nucleotide excision repair and one (XP-V) which codes a defective DNA polimerase n. 16, 17 Therefore, photo-protection is the only imperative measure to avoid the development of sunburn and skin cancers.