XRCC1 and Xeroderma pigmentosum complementation group D: The polymorphisms of genes encoding antioxidant enzymes, such as glutathione S transferase (GST)[5, 8, 9], genes encoding DNA repair enzymes, such as xeroderma pigmentosum complementation group D (XPD) and X-ray cross-complementing group 1 (XRCC1)[7, 10, 11] have been confirmed as associated with ARC susceptibility.