Loss-of-function mutations in epigenetic activators such as MLL4 COMPASS (13), the SWI/SNF complex (63), and CREBBP (64), along with hyperactivations of epigenetic repressors such as EZH2 (65) and HDAC3 (66) are frequently observed in B cell lymphoma, often resulting in the silencing of MHC-II cluster genes. The gene discussed is KMT2D; the disease is B-cell non-Hodgkin lymphoma.