While fatal in up to 20% of cases, ~80 of infants with TMD fully recover from the diseases within 4 months. However, ~10% of individuals with a history of symptomatic or silent TMD develop DS-AMKL within 4 years. During this interval, these individuals may acquire somatic mutations in those of their megakaryoblasts that bear the original truncating GATA1 mutation. These newly acquired mutations appear to result from the interactions of GATAT1 truncating mutations with excessive copies of chromosome 21 genes. The genes with these mutations include TP53, FLT3, ERG, DYRK1A, CHAF1B, HLCS, RUNX1, MIR125B2 (which is the gene for microRNA MiR125B2CTCF, STAG2, RAD21, SMC3, SMC1A, NIPBL, SUZ12, PRC2, JAK1, JAK2, JAK3, MPL, KRAS, NRAS, and SH2B3. At least one but probably several of these mutations, whether occurring in individuals with silent or symptomatic TMD, are presumed responsible for or to contribute to the development of DS-AMKL.Rare cases of transient myeloproliferative disease and DS-AMKL occur in individuals who do not have Down syndrome. These individuals usually have a history of TMD and invariably have megakaryoblasts which bear extra copies of key chromosome 21 genes, truncating mutations in GATA1, and somatic mutations in one or more of the genes listed in the previous section. These individuals have extra copies of only a portion of the genes on chromosome 21.
Non-DS-AMKL has many clinical and laboratory features similar to and must be distinguished from Acute panmyelosis with myelofibrosis, a disorder characterized by bone marrow fibrosis, abnormal megakaryocytes, macrocytic erythropoiesis, defects in neutrophil production, reduced blood levels of most circulating cells (i.e. pancytopenia), and low levels of circulating blast cells. Analyses of circulating and bone marrow blast cells for features of AMKL (see Diagnosis section of DS-AMKL) and genetic aberrations is helpful in distinguishing the two diseases. Treatment
In a review of 153 patients treated for non-DS-AMKL between 1990 and 2014 with various intensive chemotherapy protocols that included cytarabine, an anthracycline (e.g. daunorubicin, doxorubicin), and in 25% of cases human stem cell transplantation, the probability of overall 4 year survival rate, probability of 4 year event-free survival, and probability of 4 year cumulative relapse rate were 56, 51, and 29%, respectively. A more recent treatment regimen that is similar to that used to treat DS-AMKL as described above (except it employs the high dose of cytarabine used to treat AML) gives better results and has been recommended for non-DS-AMKL. The response to this regimen approached that seen in non-DS-AMKL, i.e. its complete remission and estimated 10 year survival rates were both 76%. Similar to DS-AMKL treatment regimens, allogenic rather than autologous stem cell bone marrow transplantation should be considered in non-DS-AMKL cases that have relapsed following their first chemotherapy-induced complete remission.