The mouse Retroviral Tagged Cancer Gene Database (RTCGD) (http://rtcgd.abcc.ncifcrf.gov) lists four AKXD murine leukemias with insertional mutations at Lmo2[9], in addition to the AKXD leukemia analyzed previously which contains insertional mutations at Lmo2 and Il2rg. All of the Lmo2 insertions are located 5′ of coding exons 4–6 and are in the same general location as the insertions identified at LMO2 in SCID-X1 patient leukemias and the chromosomal breakpoints at LMO2 identified in sporadic human T-ALL [3],[12] (Figure 1A). This evidence concerns the gene LMO2 and leukemia.