Gene Alterations In Acute Megakaryoblastic Leukemia (AMKL): a Comparison of AMKL with and without Down Syndrome

Childhood AMKL has heterogeneous clinical presentations with two major subcategories: AMKL in patients with Down syndrome (DS-AMKL) and AMKL in patients without DS (non-DS-AMKL). Related to DS-AMKL is the transient abnormal myelopoiesis (TAM), observed in neonates with DS, is considered to be a self-limited leukemia in most cases; only 20% of TAM patients develop AMKL within 4 years. The pathogenetic relationship is further illustrated by the presence of somatic mutations of GATA1 gene in children with both TAM and DS-AMKL. However, progression from TAM to AMKL may require acquisition of additional genetic alterations. Furthermore, little is known about the kinds of genetic alterations involved in the pathogenesis of non-DS-AMKL.

To investigate the mechanism of leukemogenesis, we comprehensively analyzed the molecular lesions in childhood AMKL (DS-AMKL, N=24; non-DS-AMKL, N=13; TAM, N=17) using single nucleotide polymorphism array (SNP-array) and mutation analysis of 9 genes, including GATA1, JAK3, JAK2, p53, FLT3, N-RAS, KIT, MPL and ASXL1. The diagnosis of TAM and AMKL was based on morphology, histopathology, the expression of megakaryocyte-specific antigens (CD41, CD42 or CD61) and/or the French-American-British (FAB) classification. The diagnosis of DS was confirmed by conventional cytogenetic analysis. Bone marrow or blood samples were obtained from the patients with TAM and AMKL at diagnosis after obtaining informed consent for banking and molecular analyses from the children's parents. Mutational screen was performed using Sanger sequencing of PCR amplified DNA. A high-density Affymetrix 6.0 SNP-array was used for karyotyping and copy number changes.

SNP array analysis revealed somatic gains other than trisomy 21 in 11/11 of DS-AMKL and in 7/12 of non-DS-AMKL, respectively including recurrent duplication of 1q in 4/11 patients with DS-AMKL (Table 1). Deletions were found in 8/11 and 5/12 of DS-AMKL and non-DS-AMKL, respectively. They included del(13p) in 2/11 patients with DS-AMKL and 1/12 with non-DS-AMKL, and del(17p) in 1/11 patients with DS-AMKL and 1/12 with non-DS-AMKL. A hemizygous p53 mutation was found in the DS-AMKL patient with del(17p). Uniparental disomy was found in 2 patients with DS-AMKL. The frequencies of the gene mutations in the DS-AMKL, non-DS-AMKL and TAM patients were distributed as follows: GATA1 (24/24, 1/13, 17/17, respectively), JAK3 (3/24, 1/13, 1/17, respectively), JAK2V617F (1/24, 0/13, 0/17, respectively), p53 (3/24, 0/13, 1/17, respectively), and ASXL1 (0/24, 1/13, 0/17, respectively) (Table 1). Mutations in the other genes were not detected. Two patients with DS-AMKL who had bone marrow samples at the TAM stage did not have additional gene mutations other than GATA1 mutations. Four gene mutations (GATA1, JAK3, JAK2, p53) were found in 1 patient with DS-AMKL, who did not respond to conventional chemotherapy and died of disease progression. The ASXL1 gene mutation was found in 1 patient with non-DS-AMKL who had additional chromosome abnormality t(1;22)(p13;q13) in his leukemic cells.

Considering the different patterns of molecular lesions, DS-AMKL needs to be classified into a different category than non-DS-AMKL.

No relevant conflicts of interest to declare.