Eukaryotic DNA methylation, an integral component of the epigenetic machinery, prevents genomic instability by regulating the expression of oncogenes and tumor suppressor genes. The importance of dysregulated DNA methylation in diverse blood cancers including Acute Myeloid Leukemia (AML) pathogenesis is highlighted by the strong correlation between mutations in the de novo DNA methyltransferase gene, DNMT3A, and adult patients with poor prognoses. We show that clinically observed DNMT3A mutations result in dramatic changes in enzyme activity, including mutations that lead to 6‐fold hypermethylation and 3‐fold hypomethylation on the p15 human promoter. Our results provide insights into the clinically observed heterogeneity of p15 methylation in AML. Cytogenetically normal AML (CN‐AML) constitutes 40–50% of all AML cases, is the most epigenetically diverse AML subtype and has pronounced changes in DNA methylation in non‐CpG regions. We identified a subset of mutations in DNMT3A that lead to a 2–8 fold enhancement in the enzyme's ability to perform non‐CpG methylation. Many of the mutations studied map to regions on the protein that are well known to interact with partner proteins, which themselves contribute to AML, such as the DNA base excision repair (BER) enzyme Thymine DNA glycosylase (TDG). Here we show that DNMT3A mutations cause significant and diverse changes in the ability of these regulatory partner proteins to affect DNMT3A function. Our results present a link between DNMT3A mutations and the disruption of the epigenetic landscape in AML. This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.