APEX1 and Down syndrome: For instance, apurinic/apyrimidinic endonuclease 1 (APE1) (Frossi et al. 2002), Cockayne syndrome A and B proteins (ERCC6 and ERCC8) (Kamenisch et al. 2010; Stevnsner et al. 2008), and Rad51 (Sage and Knight 2013) are cytosolic under basal conditions but translocate to the mt following oxidative stress.