This complex is critical for maintaining repressive heterochromatin at many repeat-rich regions, including telomeres (Lovejoy et al., 2012), pericentric repeats (Elsässer et al., 2015), and endogenous retroviruses (Elsässer et al., 2015), and mutations in the ATRX gene are linked to a developmental disorder and several cancer types (Lovejoy et al., 2012). Here, ATRX is linked to cancer.