In hematologic malignancies, IDH1/2 and TET2 mutations occur in 10–30% of MDS or AML patients and are found to be mutually exclusive, where either can impart an overlapping DNA hypermethylation phenotype (Figueroa et al., 2010a; Akalin et al., 2012; Yamazaki et al., 2015). The gene discussed is TET2; the disease is myelodysplastic syndrome.