MEF2D (myocyte enhancer factor 2D) rearrangements, occurring in 4% of children (median: 14–15 years) and up to 10% of adults with B-ALL, associate with a peculiar immunophenotype (CD10−, CD38+) and a poor prognosis, but increased HDAC9 expression suggests potential histone deacetylase inhibitor therapy [100,101]. Here, MEF2D is linked to acute lymphoblastic leukemia.