MAPK activity is present in several tens of human proteins, and we have identified the member MAP3K10 as the critically repressed gene in the block of MK differentiation in the development of leukemia with MK features in that it appears down-regulated 300-fold in TMD cells and 500-fold in both DS and non-DS AMKL compared with normal MK samples (Tables 3 and 7). This evidence concerns the gene MAP3K10 and leukemia.