Among the numerous proteins and pathways known to regulate the dynamic behavior of mitochondria,27 Drp1 is the major mediator of mitochondrial fission, whereas mitofusin 1 (MFN1), mitofusin 2 (MFN2) and optic atrophy 1 (OPA1) participate in mitochondrial fusion.28 In an effort to account for the observed differences in mitochondrial length, we explored the expression of these key mediators in primary T-ALL cells. Here, MFN1 is linked to acute lymphoblastic leukemia.