Heterochromatin alterations have also been observed in other syndromes, such as an active heterochromatinization process mediated by SIRT1 in XP or CS cells after UV irradiation (Velez-Cruz et al., 2013), and the presence of unstable heterochromatin in FA cells (Edelman and Lin, 2001). Here, SIRT1 is linked to Cowden syndrome 1.