Upon 2 Gy IR irradiation, the majority of cells from patients with Hutchinson-Gilford (HGPS) syndrome, Werner syndrome (WS), and Rothmund Thomson syndrome (RTS) underwent Cdt1-switching, whereas the majority from patients with Bloom syndrome (BS), Cockayne syndrome (CS), and Xeroderma Pigmentosum (XP) as well as normal HCA2 did not (Fig. 4A). Here, CDT1 is linked to Cowden syndrome 1.