Children with Down syndrome (DS) due to trisomy 21 (T21) are at an increased risk of developing the neonatal preleukaemic disorder transient abnormal myelopoiesis (TAM), which may transform into childhood acute myeloid leukaemia (ML-DS). Leukaemic cells in TAM and ML-DS have acquired mutations in the GATA1 gene. Although it is clear that acquired mutations in GATA1 are necessary for the development of TAM and ML-DS, questions remain concerning the mechanisms of disease.