The blast cells of DS AMKL patients almost universally harbor a somatic mutation in exon 2 of the transcription factor GATA1 gene (localized to Xp11.23), resulting in the introduction of premature stop codons and the synthesis of a shorter GATA1 protein (designated GATA1s, 40-kDa) initiated from a downstream initiation site and distinguishable from the wild-type GATA1 (50-kDa) [9]. Here, GATA1 is linked to acute megakaryoblastic leukemia.