Highlights d Genetic and functional analyses of myeloid preleukemia and leukemia in Down syndrome d Non-GATA1 preleukemic mutations are often not required for preleukemia d Previously undescribed transforming hotspot mutation in CSF2RB identified d Loss of function of 18 genes validated in transformation of preleukemia to leukemia

Quek and colleagues identify human leukemic stem cells (LSCs) present in CD34− AML. In-depth characterization of the functional and clonal aspects of CD34− LSCs indicates that most are similar to myeloid precursors.