ERCC5 and xeroderma pigmentosum: NER is a crucial DNA repair mechanism by which cells remove DNA lesions caused by UV radiation and some chemical agents.5 It is reported that a defective NER pathway can lead to xeroderma pigmentosum (XP) in human, which is mainly characterized by extreme UV-sensitivity and a high genetic predisposition to sunlight-induced skin cancers following a recessive model.6 Several XP complementation groups, XPA to XPG, have been identified, which represent the rate-limiting proteins in the NER mechanism.7