Although one study reported a decrease in DNA methylation activity of >50% with the DNMT3A R882 mutant [64] in an in vitro methyltransferase assay, AML patient samples with DNMT3a mutations were not found to have altered total 5-methylcytosine content or altered patterns of methylation [63] (Figure 1). The gene discussed is DNMT3A; the disease is acute myeloid leukemia.