XRCC1 and xeroderma pigmentosum-Cockayne syndrome complex: Xeroderma pigmentosum group D (XPD/ERCC2) polymorphism can alter the secondary structure of mRNA [14]; and SNP in the X-ray repair cross complementing group 1 (XRCC1) gene 5′ untranslated region (UTR) greatly enhance trans-activator Sp1 binding element, therefore decreasing promoter activity and decreasing protein expression [15].