In T-cell acute lymphoblastic leukemia (T-ALL), the deletion of a CTCF binding site destroys the three-dimensional (3D) genome structure around the TAL1 and LMO2 gene loci, resulting in gene activation through enhancers which are normally located in the neighboring topologically associated domains (TADs) (28). The gene discussed is LMO2; the disease is T-cell acute lymphoblastic leukemia.