G9a encoded by EHMT2 (euchromatic histone lysine N-methyltransferase 2) is a mammalian histone methyltransferase responsible for histone H3-lysine 9 methylation (H3K9) that contributes to the epigenetic silencing of tumor suppressor genes [37, 38]. The gene discussed is PRDM9; the disease is neoplasm.