XRCC1 and Crouzon syndrome-acanthosis nigricans syndrome: rs1108775 and rs1799782 of the XRCC1 gene were associated with reduced chances of developing CAN both before and after adjustment (OR 0.24, CI (0.09–0.68), p = 0.007, and OR 0.43, CI (0.22–0.84), p = 0.02, respectively).