XRCC3 and chronic obstructive pulmonary disease: In our study an influence of XRCC1 (Arg399Gln), OGG1 (Ser326Cys), XRCC3 (Thr241Met), and XRCC4 (Ile401Thr) genetic polymorphisms on DNA repair was found in COPD patients compared to controls, as shown by residual damage (Table 3).