The gain of function mutations in PTPN11 are associated with 35% of human JMML, a disorder with excessive proliferation of myelomonocytic cells, and have been reported in a low percentage of myelodysplastic syndrome (MDS) and AML cases, and a few cases of solid tumors [16,17,18]. The gene discussed is PTPN11; the disease is myelodysplastic syndrome.