For instance, mice carrying hypomorphic Sfpi1 enhancer allele that reduces Pu.1 expression to 20% of normal levels develop acute myeloid leukemia (AML), while a 50% or even a 100% loss of Pu.1 expression only induc accumulation of abnormal myeloid precursors [6]. Here, SPI1 is linked to acute myeloid leukemia.