The classification of B-cell precursor (BCP)-ALL and T-cell ALL (T-ALL) has been refined based on gene expression-based subgroups, and recent studies have further identified several novel rearrangements including DUX4-rearranged [6], iAMP21 and MEF2D-rearranged [7,8], ZNF384-rearranged [9], and ETV6-RUNX1-like B-ALL [8]. The gene discussed is MEF2D; the disease is acute lymphoblastic leukemia.