We report the identification of a polymorphism in canine FANCG (Fanconi’s Anemia Complementation Group G, ~7 MB from the MTAP-CDKN2A locus, and explore its association with the development of HS or to earlier age of onset of HS, and functional studies examining the effect of this variant on DNA repair. The gene discussed is FANCG; the disease is histiocytic sarcoma.