The formation of 5-hmC, the first step in DNA 5-methyl cytosine demethylation, was impaired in higher-risk MDS and AML-MR, suggestive of a possible mechanistic role of low TET2 expression and also of the continuum of higher-risk MDS and AML in context of loss of TET2 function. Here, TET2 is linked to myelodysplastic syndrome.