Importantly, mice transplanted with Rab27bfl/fl LSKs expressing NRASQ61R mostly developed MML, while those transplanted with Rab27b-deficient LSKs expressing NRASQ61R had reduced incidence of MML, instead the moribund mice died of T cell–acute lymphoblastic leukemia (T-ALL), as evidenced by analysis of the bone marrow and spleen (Table 1 and Supplemental Figure 8A). The gene discussed is RAB27B; the disease is acute lymphoblastic leukemia.