CHEK2 and Nail dystrophy: Interestingly, cell division in the presence of persistent DNA damage in long-lived Trf1Δ/ΔK5Cre Chk2−/− mice resulted in development of epithelial pathologies, which recapitulate some of the skin abnormalities characteristic of the human telomere syndromes, such as occurrence of nail dystrophy and fibropapilomas (Fig. 2G,H).