It has been suggested that XRCC1 gene polymorphisms are modulating factors for PC risk, particularly in smokers.17–21 A synergistic effect between these gene polymorphisms and tobacco smoking in relation to PC risk has been suspected.14 Oxidative DNA damage produced by smoking is expected to be repaired by the BER system, which includes the XRCC1 gene.33 In this study, we observed a significant main effect of rs25487 in XRCC1 but found no statistically significant interaction between XRCC1 loci and smoking. The gene discussed is XRCC1; the disease is pachyonychia congenita.