In 2003, missense mutations in PTPN11 were discovered as somatic events occurring in juvenile myelomonocytic leukemia (JMML), as well as in childhood myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML) [15], marking a milestone in the development of the understanding of the underlying mechanisms of these hematological malignancies. This evidence concerns the gene PTPN11 and myelodysplastic syndrome.