This duplication of only some chromosome 21 genes results from: a) Robertsonian translocations, wherein part of chromosome 21 is duplicated on another chromosome; b) partial trisomy 21, wherein only part of chromosome 21 is duplicated); c) an isochromosome, wherein chromosome 21 contains two long but no short arms); or d) duplications, wherein extra chromosome 21 genes are on this or other chromosomes. AMKL occurring in these individuals is classified as DS-AMKL. Presentation
DS-AMKL most often presents in children 1–2 years old but almost always less than 4 years old who have a history of TMD. Given this history, these children are usually followed-up medically with complete blood count tests. and therefore often present with elevated blood levels of abnormally appearing platelets and platelet precursor cells, particularly megakaryoblasts, and reduced blood levels of red blood cells. DS-AMKL usually progresses slowly with affected children gradually developing increasingly more severe changes in their blood counts as well as slowly developing symptoms of these developments such as fatigue and shortness of breath due to anemia. In cases of advanced disease, individuals with DS-AMKL may present with signs and symptoms that are more typical of acute myeloid leukemic diseases such as liver enlargement, spleen enlargement, leukemia cutis (i.e. skin nodules caused by leukemic infiltrates), or leukostasis (i.e. an emergency situation in which excessive elevations in circulating blast (i.e. early precursor) cells plug the microcirculation to cause life-threatening heart, lung, and neurological dysfunctions).
do not originate from the sperm cell line) and occur before or concomitantly with but not after the diagnosis AMKL is made. The three most common genetic aberrations in the bone marrow cells of these individuals (representing ~65% of all cases) were inversions in the p arm of chromosome 12, trisomy 8, and an extra X chromosome. In several of these cases, the genetic aberrations in the malignant platelet precursor cells were similar to those in the malignant mediastinal germ cells. These results and those of other analyses suggest that the two malignancies derive from a common founding clone of cells (i.e. a set of genetically identical cells).Overall, the most common genetic aberrations occurring in adult-AMKL are the previously described inv((3)(q21q26) inversion, translocation between the q arm of chromosome 9 at position 34 and the q arm of chromosome 22 at position 11, i.e. (t(9:22)(q34:q11), and various aberrations in chromosome 5 or chromosome 7. Aberrations in the latter two chromosomes are also commonly seen in an AML that is associated with myelodydplastic-related changes (i.e. predominance of immature blood cells in the bone marrow). The underlying malignancy-causing mechanism, if any, behind these genetic aberrations requires further study. Presentation
Adult-AMKL may occur in individuals who have a prior diagnosis of and/or present with chronic myelogenous leukemia, polycythemia vera, essential thrombocytosis, primary myelofibrosis, or mediastinal germ cell tumor. AMKL associated with mediastinal germ cell tumors typically occurs in younger adults, i.e. ages 13–36 (average age 24).