Several heritable premature aging syndromes have been linked to mutations in genes encoding DNA repair proteins such as Werner syndrome (WS), Cockayne syndrome (CS), Bloom syndrome (BS), ataxia-telangiectasia (A-T), xeroderma pigmentosum (XP) and Rothmund–Thomson syndrome (RTS), suggesting that the maintenance of genome integrity has a central role in human aging (Navarro et al. 2006; Pereira et al. 2008). Here, PROS1 is linked to xeroderma pigmentosum.